The Small Computing on Solar (SCOS) Handbook — 2018 Edition

Garagassi Point, Astrolab Bay, near Madang Town, Papua New Guinea (click to zoom)

Picture:  The site where "first contact" in 1870 occurred in Papua New Guinea.  Mikloucho Maclay, the Russian Anthropologist, lived near the point to the left and also left a diary translated from the Russian language into English.  There is still no electrical power in this part of the world.  -Brian Chapaitis, CC-BY-SA

Tools for National Language Workers

News: 

• Added the new Lenovo IdeaPad 320 model with 15 inch anti-glare screen, and still maintaining a low power consumption in the Notebook section.  There's no longer a need to be cramped under an 11 inch screen, and the Intel N-series "turbo" mode is plenty fast when needed for Paratext work.
•  

Please send your comments to:  [email protected]   Direct edits to this Wiki are welcome by others.  Please don't hold back on any ideas or knowledge you might have, and please do contribute to these pages.  The greater solar community thanks you.  This site wants to become a "live document" -- so edits and additions are welcome.  At any point in time, please print a section of the document and carry away for your purposes. See options on upper right "down wedge" icon.  However to print the entire Handbook in all it's glorious detail, then see the "Print this Manual" item now in the sidebar to the right.

Brian Chapaitis; Paul Zwierzynsk; Hannes Hirzel; Kim Blewett; others
Summer Institute of Linguistics
Papua New Guinea Branch
January 2018

Summary:

For the first time in recent memory, advances in solar technology and computer notebook technology have converged such that the goal of language work performed by Mother Tongue Language Workers (MTLW) can be realized in a relatively cost-effective manner by themselves and for themselves — with minimal oversight.  This work primarily concerns itself with hardware issues, on modern platforms where useful language software tools can work, created by SIL and other agencies.  It is meant as a “handbook” or a guide to collect in one place all the relevant technical issues and potential hardware suppliers useful to SIL administrators who want to set up somewhat independent, long term, national coworker projects with limited or minimal mentor/ advisor contact.  In short, it is an effort to outline the application of technologies for a sustainable MTLW programme and represents the present “state of the art.”.  This is a constantly moving target since technology changes so rapidly.  This document supercedes an original work created in 2010.  Since we are now electronically publishing this on a wiki site, the authors welcome contributions from others to make the content more accurate and more up-to-date in a rapidly changing technology environment.

Note:  It is possible now to print the entire Handbook to .PDF format.  Look for instructions in far right column under "Search Wiki".  Some readers to not see this column because they are in in "full screen" mode.  To exit this mode click the double-arrow icon in the far upper right corner of this page. An excellent free add-on for Firefox and Chrome would be "Print Edit", but there are others.

Introduction

The year 2016 was an amazing year for low-power consuming notebooks and laptops.  Intel pushed hard on it's process technology called "Bay Trail" and that produced a new family of processors that showed up in various manufacturer's lineups in this year.  The power-saving effects were astounding.  Processor speeds also improved steadily since 2010 and nowadays an inexpensive notebook is more than able to perform well with Word Processors, Spreadsheets, Paratext (SIL/UBS), Email, and Web Browsing activities.  These are today's computers commonly found in stores like amazon.com in the $250 to $400 range, with screen sizes from 11 inches to 15 inches.

At the same time huge advances occurred in new thin-film and poly-crystalline solar technologies within this same year.  It is not uncommon to find old monocrystaline solar panels in the $0.60 per watt range.  Portable and very light weight, thin-film technologies are also available in the US$ 3 per watt level.  This might still seem to be expensive, but when one considers that a modern notebook only requires a mere 30 watts to be sustained in the field in rainy weather, then even the relatively more expensive thin-film technologies are now much more affordable.  One new application is socio-linguistic survey work, where excursions in the remotest part of the world necessitate portable and light-weight solar equipment.  Yet powerful computers are still involved for data collection and possible field analysis.

This paper represents the state of the art for the merging of these two powerful trends in the industry for new Third-World applications.  We are actively developing significant “laymen” tools that, once placed on sustainable hardware, would empower national citizens to consider doing portions of the language development task.  And this includes, the Bible Translation task.

Summary: SCOS Goals and Objectives

“Define a complete system of solar powered hardware; an overall tool, suitable for third-world national coworkers to consider doing language development work for themselves and by themselves.  To build reliable, self-contained, and low maintenance hardware systems, where there is no readily available mains power.”

"To educate laypersons, in support of others, as to basic solar principles and adequately maintain future solar systems in the field."

“SCOS defines a sustainable equipment platform by which suitable national language software tools can be implemented in the field”

Beyond the scope of this “handbook” is the requirement of suitable national training programmes for a successful implementation within a Branch or Entity within SIL. That exercise is the subject of another paper and also would be integral to a far larger, comprehensive, entity strategic plan.

Note:  No technology, not even the use of mobile phones to call out to people, will work without adequate training.  Technology by itself, never works.  It is the same with even the simplest of solar systems.

Table of Contents

• 1 Choosing a low powered notebook : Notebooks
• 2 Using tablets with solar : Tablets
• 3 Solar Panels
• 4 Controller Battery
• 5 Battery Technologies
• 6 Solar Controllers
• 7 DC-DC (Auto) Adapters
• 8 Fuses
• 9 Wiring Principles
• 10 Tools
• 11 Basic Electricity
• 12 Advanced Topics

Click on Section Above for more Details on that Topic.

The Village System

These are the major components of a village system that desires to be energy efficient.  Note that there is no inverter here, but rather the DC-to-DC auto adapter in the sub-systems that make for a more energy efficient operation.  In a cost sensitive situation (local level churches and communities in the third-world) every joule of energy conserved is important per unit cost.  Such communities struggle with resources; practical costs are very important.

Block Diagram of a Complete Solar System

Description of Components

Note:  Although the manufacturers of the solar controllers mentioned here, say the order of connection of parts does not matter — the general wisdom says that under full sunlight, the converted energy of the sun's radiation should have a good place to go.  Therefore always connect the battery first, or disconnect the battery last during assembly/ disasembly of the parts.

Click on Topic Below for more Details.

Notebook / Laptop:

A new class of notebook computer that can run a major Operating System like Linux or Windows OS.  These range in size from the Lenovo 11 inch models such as the Lenovo 11e all the way to the Asus Vivabook line at 14 inches wide.  11 inch is about optimal.  Popular makes of notebooks come from Asus, Acer, Dell, Lenovo, Samsung, HP, and others. Asus is considered the most reliable by far, only to be rivaled by Apple Computer.)  (see more details)

Tablet:

2016 started to see many common 8 inch and 10 inch tablet offerings available for approximately $150.  Some were classic Android OS, however, a new breed of Intel tablet hit the marketplace opening possibilities for a future with ultra low-power consuming devices.  A product of Intel's "Bay Trail" efforts.  The term "Tablets" in this paper include a BlueTooth keyboard added.  For data entry chores one would not normally be expected to use the on-board touch-screen interface on most tablets, although in a pinch this would work.  Unlike notebooks, tablets do not require an external battery pack to run well all day, and can rely upon their internal batteries, reducing per seat costs further.  The required solar panels are quite small, even to sustain these 2.5 watt devices in rainy weather conditions.  In the so called, "direct connect" scenario, a solar panel is directly connected to a mobile phone or tablet, usually by a standard USB port, but implied is a 5 volt regulator device, still necessary to condition the solar panel power output.  (see more details)

Solar Panel:

A flat panel device, sometimes called a photo-voltaic panel, that converts incident solar radiation into electrical energy. Manufacturers include Solartec, Global Solar, Bioenno, and SunPower mentioned in this wiki.  This report focuses on small 12 volt micro-solar systems, and doesn't address the issues of major, Western-style residential systems, where names like Canadian Solar and First Solar would be common place and systems would be 48 volts or higher. SCOS is about small, inexpensive, 12 volt systems.  (see more details)

Combo Units: Controller with Battery

Recent advancements, mainly in the adoption of LFP batteries, has allowed smaller, complete units to be created that combine both the solar controller, fuses, batteries, and monitoring displays, all in one box. This simplifies the overall assembly of the system and doesn't tax the user's understanding of the system, simplfying installation in the field. Standard modular plug-type connectors are used to connect cables and no screw-drivers are required. This is easily the future of micro-solar systems, which is the subject of this report.  If you want "simple" and "reliable" then this is the topic you want to read about.  (see more details)

Battery:

An electro-chemical energy storage device. Many battery chemistries exist including Lithium Ion used in mobile phones, and laptops and Nickel-Metal Hydride, often used in LED flashlights and hand-transceivers. All can be re-charged. Lead-Acid is a relatively old technology, and well understood. It is sometimes favored in solar applications primarily due to common local availability and (assumed) low cost, compared with the other, newer technologies which often have to be imported. Certain Lithium chemistries are totally safe and will not overheat, such as the safest form: Lithium Ferrous Phosphate (LiFePO4). As the report hopes to illustrate, LFP technologies can actually be less expensive technology to deploy than Lead-Acid over the lifetime of the language project.  And LFP so far, is more robust and far less fragile, while being far more compact and light weight to transport (see more details).

Solar Charge Controller:

Due to rapid changes in solar radiation possible (think: a cloud drifts by), the solar panel voltage fluctuates dramatically. The purpose of the controller is to condition the power coming from the solar panel and make this power acceptable for storage batteries to store electrical power, and without premature damage to the batteries, shortening their useful life. Some people like to connect solar panels directly to batteries, without a controller and then permanently damage the batteries.  (see more details)

Automotive DC to DC Adapter:

Actually a voltage conditioner and regulator, notebooks would normally use these to condition the transients found in automotive 12 volt electrical systems, saving the internal notebook power supply from undue stress. In solar notebook applications these devices allow the up-conversion of 12 volts to the more common 19 v and 20 v power required by most notebook computers. These adapters are very energy efficient and superior for use over an AC inverter using the normal "power brick" supplied by the manufacturer for typical mains power use in a town or city. Typically these DC-DC adapters are not expensive, however, care must be taken to purchase one with the correct DC plug arrangement for the given notebook. Reliable automotive DC adapters can be purchased for as little as $15 in some situations.  (see more details)

Fusible Link:

A circuit component, that is designed to break, or burn, or time-delay-off, when a relatively high current is applied and thus save further damage from equipment attached to a power source. Examples are an automotive in-line fuse (which must be replaced when used once) and a mechanical circuit breaker which can be reset by the user. For national coworker settings the better systems have fuses that "reset" themselves and are hidden from the end user, thus saving the user from painful mistakes (such as electrical arcing leading to a house fire), while not troubling the user with the education required to maintain these devices. In time, these special fuses reset themselves, much like a circuit breaker.  (see more details)

Wiring Principles:

Choosing the appropriate wire diameter has a big effect on performance, however, too large a wire diameter greatly increases the cost of a system, especially if the solar array is very distant from the home office where work is accomplished on the computer. Long distance here means 50 meters or greater, but effects can be seen for a run as short as 10 meters.  (see more details)

Tools:

If you are maintaining a solar system you might be interested in a few basic tools to help beyond a mere hand-held DVM (Digital Voltage Multi-Meter).  In this section there will discussion of useful measuring instruments for various experiments in the lab, and would be very useful in rural settings if one were assigned to manage and repair very remote micro-solar systems (even very large ones, too).

Basic Electricity:

Many of us learned all the necessary solar principles for electricity in our secondary education, but since there was no practical application at the time, we have forgotten the basics. This section is to refresh our memories on basic concepts of electricity. This has a bearing on the language worker, when alone, and he/she is faced with figuring out what is wrong with a broken solar system, while attempting to repair it, "on their own", and without neighborly assistance.  (see more details)

Advanced Topics (Technicians Only):

This is the technicians corner and most readers should stay away from this part (their eyes will glaze over most likely) and they will become frustrated while not being able to follow the discussion. Issues with setting up a controller for the appropriate Low Voltage Disconnect (LVD) and other topics will be discussed in this section, and it's mostly for technicians who like to set up systems for others or build custom solar systems, from common parts.  (see more details)

Purchase Summary:

1)  Do your homework here and decide first how much CPU power to you really need in a computer. Most likely not much. Paratext and Word Processors do not tax small modern computer systems purchased in 2016.

2)  Purchase pretty much any notebook computer that uses the "Bay Trail" technology to manufacture the CPU inside the computer. Linux users will want to carefully note the processor model for now.

3)  Determine the average wattage of the machine in normal use.  For an 8 hr workday, and while working in rainy and overcast weather, multiply this value in watts by 5, and determine the minimum size solar panel you require.  For example, for a 6 watt notebook, you would require a 6x5 = 30 watt solar panel.  For some older (circa 2014) laptop computers running at 15 watts of power, plan on purchasing a 15x5= 75 watt solar panel.  It makes a huge difference what the notebook/ laptop computer you have to start with.  If your present laptop runs at 25 watts, you want to decommission that computer.

4)  If you are planning for 4 hrs of work time at nights, each and every workday, because the user works gardens in the day, or has some other job, then consider the size of battery you need.  Energy capacity is measured in Wh, so to run a 5 watt computer for 4 hrs at night, you want to purchase a battery pack at 4hrs x 5 watts = 20 Wh.  Due to "depth of discharge" issues (see section on this) you want twice that size larger in your LFP battery, so consider 40Wh minimum.  Note that the GTIS Half-Pint solar system (as an example- see section) is 72 Wh !!  Very nice.  You want the extra margin, believe us, for other reasons in the village.  Purchase this part.

5)  Consider avoiding Lead-Acid type batteries, particularly car automotive type batteries. The above formula does not work for them and you need a much larger capacity battery to do the same work. Plus the lead-acid battery does not have the lifetime cycles of an LFP chemistry battery. You will pay more for the necessary larger battery size, and the battery will expire in around two years anyway, at least under solar applications. Each day is a heavy discharge, and you don't necessarily top up the next day. For a deeper discussion of this see the Battery sub-section, if you have time.

On the Threshold of a Dream

We are on that threshold where appropriate and robust technology may launch us into a new era of involvement by third-world national coworkers that would not otherwise be able to participate in the work of vernacular Language Development. The dream is to provide the tools (and training) necessary to encourage native speakers of a given vernacular, to take pride in their own language and culture; to begin to document their mother tongue for themselves and to consider the translation task as well. Given the harsh realities of our limited number of outside visitors to complete the task, it is time for the citizens of the third-world to enter into this exciting work as well, perserving their language and culture for future generations.  By adopting new methods, it may be possible for national citizens and the local level community churches, to be encouraged to join us in the work with their own equipment and resources.

About One Author

Additional References and Comments:

Notebooks/ Laptops

December 2019 update

Notebook processors change continually, with pendulum swings from "lower power consumption" to "higher speed and capacity." However, the mid-higher-functioning processors of 2019 have power requirements similar to the low-end processors that were recommended for low-power language work in 2014-16. This is good, since language software has become more processor-hungry as well.

What to consider when choosing a laptop for use in low-power situations:

• Processor: I compared several laptops in a quick speed test—(I timed opening Paratext 9 with the same complex screen arrangement on each), and I measured power consumption also.
  • For "advanced" translation or language work, using Paratext 9-Fieldworks-Logos, I recommend at least 8GB RAM and an i3 or i5 8th-gen laptop processor; or a Ryzen 3 or 5. My Lenovo E495 (AMD Ryzen 5 3500U) and a similar Lenovo with Intel i5-8250U perform very similarly. These two processors used at least 30% less power than the older Lenoxo X131E machines that were recommended for several years.
  • For more basic translation or language work a Lenovo 14W with 4GB RAM and AMD A6-9220C processor performed a bit more slowly in my test. Or an older N43xx processors are even slower but adequate, and they use about 30% less power than the "5" processors above. Paratext 8 and 9 seem very slow, but read on for a tip.
  • Important note about Paratext 8 and 9: Turning off all internet access speeds up Paratext significantly! Internet is required to register new users and projects or change project properties, and for send/receive operations. It can be turned off for everyday editing and checking operations.
• Screen size still affects total power consumption:  but price seems to be inversely proportional to screen size this year, except for some 11-in laptops with older N4xxx processors. With 14-15" screens available at lower prices than smaller ones, and with more translation resources available through Paratext 9, I feel that 14-inch (diagonal) screens are the sweet spot for laptops designed for language work.

Changes: 

Guidelines for 2017-2018

The 2017 model year saw a bumper crop of suitable machines to purchase that were "low power consuming".  Why?  Because many of the models were based on Intel's new (2015) "Bay Trail" technology which had smaller geometries that translated into several processor types that were even less power hungry than ever before.  Then by 2016, companies like Lenovo, Dell and Asus started placing them inside their boxes for sale.

Year 2016 popular models, like the Lenovo x140e were pushing 8-9 watts for comparison purposes here.  These models are no longer for sale anyway.  In the labs we easily sustained this type with a 55 watt solar panel, and sometimes we ran such computers for 16 hour work-days.  The target for SCOS is a sustained 8 working hours.

Basically if you want astounding and awe-inspiring "low power" performance, then look for these processor models inside the box: Intel N3700, N3050, N3150  (2015)   These will be running at around 5 watts.

If you want good low power that still is amazing compared to last year's (say as found in the defunct Lenovo x140e): Intel N2940, N3540, N3530  (2014)  These notebooks/ laptops will be running around 7.0 watts.

And if you want "flea power" and yet still have processor speed, go for the fabulous Intel M-5Y10c or M3-6Y30 processors, which we can now recommend.  Evidently these have two speed modes, both 0.8 and 2.0 Ghz and in a recent field test by Kim Blewett comparing Lenovo 11e models but with different processor types, she reports that the M-5Y10c was significantly faster while doing a standard test under FLEx (SIL Linguistic Software), than other processors in the same 11e type machine.  That is remarkable really, and welcome.  

Also, for Linux users there are no reported issues under Ubuntu 16.04 and derivative OSs, as there has been reported by the N2940 box. This M-5Y10c processor should run well on a amazingly small 20 watt solar panel. Overall notebook power:  ~3.6 watts  (Lab observed; Intel TDP is 4.5 watts)   Go for a mere 20 watt solar panel on this one.  If significant village social pressures to "leech" power, then go for 30 watts.

Amazon Store:   Lenovo with M-5Y10C processor

By 2017 there was consider interest in "tablets as computers" which meant even lower power for fan-less slate-type devices that may or may not have an external keyboard.  The Asus Transformer Book below, is an example.

Now the caveats:  You should purchase a box with 4GB RAM.... so you are going to find other models for sale ($150-200) that are only 2GB RAM and much less expensive to purchase.  Some boxes have the memory soldered on the motherboard and you cannot expand the memory.  Others have modular memory modules that might allow expansion to 8 GB.  FLEx users (SIL Linguistic software) are going to want that for heavy linguistic work.  If you are thinking Paratext (UBS/SIL) and Word Processing applications then go for 4 GB minimum.

We are no longer limited to 11 inch screen sizes.  We  suspect that a 14 inch model with any processor above, is not going to be significantly higher power than any 11 inch model.   Screen size is almost a "religious" like experience for some users.   Note the Asus 14 inch Vivobook, far below.  We tested one such unit in the labs and were able to confirm it's low-power consumption.  In 2017 Lenovo sold a 15 inch notebook with the N3060 processor, listed below.

CPU Summary:

Note:  Processors manufacturered in 2015 arrive in notebooks for sale in the year 2016;  2016 processors in 2017

Special Note to Paratext Users:  Don't ignore the M series of Intel processors here.  When heavy processing like a Paratext Interlinear is required, turbo mode kicks in and actually beats the times of more expensive processors.  Meanwhile for normal operations the box runs cool, without a fan, and waits for keypresses and for the user to think.  That's most of the time.  Same for the 2016 processors with their "turbo" mode.
 

2018: Breaking the 15 inch Barrier
The Lenovo IdeaPad 320 15 inch Notebook

Click to Enlarge Image

If the goal is to empower third-world, local-level church workers, well trained in Bible Translation skills, software, and back-translation methodologies, then you want to look below.  Those smaller units are sometimes less expensive, and more affordable... at least for national ownership.

However, many expatriate workers are also looking for low-power solutions now for their work.  These users are particularly interested in FLEx applications and also Paratext with many, many child windows open on a single desktop.  They immediate ask for a 14 inch or 15 inch notebook display size.

Enter the year 2018, where we finally see such a box and with an ultra-low power consuming Intel processor.  Note that "low power" consumption does not necessarily equate to "slow" anymore due to the N-series and the brilliant "turbo" mode.  This indeed kicks in under Paratext while doing any CPU intensive work, such as building a new Interlinear of present vernacular text.

CPU: This box has the newer Intel N3350 processor (Amazon.com) and N4200 processor (Lenovo.com) and runs around 5 watts using Paratext/ Word Processing.  Approximate size of solar panel required:  30 watts (Calculated;  not yet observed)  An independent observer reported a true usable power in the field, of around 6.5 watts, which could be due to the larger, 15 inch screen.  We have yet to test one of these in the labs, however, even at 6.5 watts, a 30 watt solar panel from GTIS and a Half-Pint (72 Wh) 12v system will be sufficient.  Note: do not order the Intel iCore variant if you want "low power consumption" on solar power.  There is also the highly prized Anti-Glare Display (1366x768) which third-world village level workers (particularly expats) would "die for".

Price: $269-$300

See:  Lenovo Store    Special Note:  Do not opt for the iCore processor option if you want ultra-low power consumption

And:  Amazon Store    Special Note:  4GB Ram, however a 1TB HD included

2017: The Asus T100HA "Transformer Book"

Click to Enlarge Image

This amazing transformer book class machine is typical of many models produced by ASUS company.  The one tested in the labs is officially called the T100HA-C4-GR and is special in that it has a very low power processor running about 2 watts (!) and is charged via a standard USB 5v charging cable.  Suddenly a host of inexpensive, fold out solar panels with USB regulators can be used with varying amounts of success, so be warned.  We will recommend here as the best so far found in the labs: the Dragon-X 20 watt solar panel.  All such equipment can be purchased on amazon.com

The T100HA-C4-GR is special in the ASUS standard offerings in that a full 4 GB of main memory was on board, which many feel is the optimum point for Paratext sotware users.  We have not tried running Paratext in 2 GB of main memory which many, many Windows class tablet/ keyboard systems utilize.  It is strongly encouraged to look for a 4 GB tablet/ transformer unit for your work.

There is considerable discussion and notes for the solar panel requirements for such a "direct connect" venture, so we will merely state that it is probably a good idea to puruse the solar section in this handbook before purchasing the solar panel part.  Basically, not all solar panels with USB regulators are made alike and you have to try them out, before purchasing to make sure that they work with your particular device to charge, whether it be a smart-phone, iPhone, tablet, or transformer type machine.  Details are in the solar panel section.  The short explanation is that USB technology has a special "PD power specification" that goes beyond simply stating USB v 2.0 and USB 3.0 devices.  The USB power standards are there;  it's just that power delivery can be complicated within the normal specification.

Field User Scenario:  We are saying that we expect the user to work in the field for a typical 8 hour day, where some of the hours could be at night time.  With the typical run time of this machine around 12 full hours, we can easily reach this goal with the internal 30 Wh battery inside the box.  This then leads to the question of when to recharge in the typical daily work cycle.  Obviously it's advantageous to recharge when the sun is most shining, from 10 a.m. to 2 a.m.  The water-proof, 20 Watt Dragon-X fold out panel will easily "turn-on" in cloudly conditions, but due to the USB Power Distribution issues (see solar panel section) at a slower rate than the standard ASUS power brick.  The output charge current of the panel is more like 1.1 amps instead of 2.0 amps, but at least it is steady even in overcast conditions.

Click to Enlarge Image

But the general rule of thumb here is "2 for 1" usage to recharge rate.  So for example if you used the machine for 4 hours of work last time, then expect the recharge time with the machine lid closed, to be 2 hours to regain the energy used.  The four hour period from 10 a.m. to 2 a.m. wouid then translate out to 8 hours of "work energy" for the user.

Now if this is all too constraining for the user then facilitator/ advisor for such projects could include a smallish "power bank" as an option, to augment the charge cycle.  All that is required is a 12,000 mAh or greater power bank and there are dozens of suppliers of such devices on the market right now.  In the selection of a suitable power bank, better, but not necessary, is one that delivers a full 2.0 amp charge output to charge an external device, so look for that characteristic in the specs.  So for the added cost of a small power bank, the user could then work during the day-time independent of the solar panel charging the power brick by day.  At night, while the user finished work and went to sleep the transformer book, could be recharged from the energy stored in the power brick.  This process is repeated the next day.  Note that one does not need a long USB cable in either scenarios above.

BUT we must hasten to add here that the power brick scenario is not necessary.  One can save the additional cost of the power brick.  The power brick is totally optional.  One can indeed "direct connect" the solar panel to the transformer book, and recharge the device directly, but obviously you must do this procedurally during the day, even in cloudy weather (which still works).

Weatherproof:  Many of the solar panels sold are constructed with a water-proof, PET material, and probably do well in the rain.  However, the better panels place the electronics behind one fold out section, covering and shielding that part from weather, and often there is a pocket to place your phone or power bank behind.  The ASUS transformer book device, will need a roof eave, or plastic tent supplied by the user for this to work out.  Or one can place underneath the solar panel, itself.  It is not recommended to leave the Asus transformer device outside unattended, or unprotected from the elements.  Actually this goes for most devices, including phones.

Intel x5-Z8500 quad-core processor.  Approx. 2 watts   Tested in field with Paratext

Amazon.com   ASUS Transformer Book   ~US$ 300

Amazon.com   Dragon-X 20 W Fold-Out Solar Panel   US$ 50  or  SoKoo 22 W panel

Amazon.com   Anker 2 Meter, USB cable   US$ 10

Amazon.com   Optional ToHLo 20K Power Bank   US$ 26  or  RAVpower 16K Power Bank with Light  US$ 30

2016: Lenovo Netbooks Preferred

Where do I Purchase a Notebook?

11 Inch Lenovo 11e                                     

Lenovo 11e Model

11 Inch Dell Inspiron 3000 series

Asus 14 inch Vivobook

12.5 Inch Lenovo x260

Back to the Lenovo line.  This one is for the "power users" who want a faster processor and also have the extra money to spend for it.  It still manages to weigh in with an acceptable wattage for solar. Any field testing and power data was provided by Nate Marti.  This is probably the machine one would want if they were an avid FLEx user (SIL software) and doing a lot of processor intensive tasks, and the x260 starts with 8 GB RAM standard.  Upgrade to 16 GB possible.

The Tablet Corner

August 2016

Someday computing in the field will look like this:

Tablets, whether Android OS or Windows OS are clearly the future of Bible Translation and Language Development, at least if the intent is to mobilize the local indigenous church to share in the work.  What other strategy will ultimately win the world in our lifetime?  Already we are seeing the results of Scripture App Builder (SIL software) producing electronic readable versions of vernacular text with spoken audio, on both mobile phones and tablets.  In PNG Reading App Builder (SIL Software) and "Education for Life" systems are preparing the way to teach vernacular and English language skills.  This alone addresses a major vernacular distribution problem that before was limited by paper and mitigates the logistics of getting paper printed and transported.  Especially if the tools are on popular and readily available mobile smart phones. More and more software will be available on tablets.  As of this writing there is even a movement to have a Paratext (SIL/UBS software) like functionality present in the tablet space. 

It is true that not all regions of the world have enough mobile phone penetration... but that is progressing forward over time.  Even in PNG there are remote regions without mobile phone coverage, but even in these area people might purchase a mobile phone as an inexpensive "reader" of materials, and people do purchase for this reason.

So, in light of tablets and mobile phones getting stronger and stronger use, and more usable software is becoming available the ultimate question is:  "How to do sustain power to these devices?"  Most of PNG, as an example does not have mains power available.  Up to 90% of the country and the population.  They want to recharge their devices, and inexpensively.  Enter solar power (renewable energy) as the solution.

The Tablet Power Block Diagram:

Tablets are "5 volt" devices, whereas the typical notebook is a 19 volt device.  This has a profound technical bearing on a 12 volt solar system.  I only have to really supply reliable regulated 5 volt power to a tablet and keyboard combo, instead of a "step up" in voltage for the typical notebook/ laptop.  It is much easier in low-light situations to "turn on" my charging system when I am trying for 5 volts systems than reach high for a 19 volt system.  That is primarily why we need those external battery packs.  The external batteries act as a buffer or conditioner for power, that helps in the controller/ charger process.  And of course they store extra energy.  But extra energy is not really necessary for tablets which often have longish run times even with the diminutive batteries inside the tablet.

This means we have a change to eliminate the external battery/ solar controller combo and head to a more simple 5 volt regulator in our circuit.  See this diagram.

Data Entry?  Tablet Keyboards Included

(Click for Zoom; Click again for Ultra-Zoom)      

When we talk about data entry software, like Paratext (SIL/UBS) or basic email or Word Processing tasks then we must include "tablet keyboards" in the discussion.  For some, this is an automatic "given" but for others this has to be further explained when one talks about "tablets" in general use and work.  Bluetooth and wired keyboards of all shapes and sizes can be purchased for around $30 to $100 depending upon other features.  Some from Logitech have tiny solar cells embedded and can run forever under office lighting.  For these, you would never have to replace the AAA batteries, because they don't exist.  Even those with replaceable AAA batteries run for months at a time before replacement is necessary.  Shown here is a Samsung Android tablet with Logitech keyboard, with stand.

But Why Not Just Use a Notebook Instead?

Cost.  Sustainability.  The cost of the computer and the cost of the sustaining solar system to run the computer, is greatly reduced.  The Goal:  Affordable systems that the local level churches and communities can afford themselves, and create a "sustainable" environment.  In some countries this level of hardware is already for sale in the cities within that country.  In terms of longevity and "buy in" for the language project this "sustainability" argument is not to be ignored, at least for our work in the next 1000 langauges.  We should not be embracing strategies that perpetuate a dependence upon Western aid and support structures. (End of sermon, )  The biggest thing we lack is great software and royalty free resources in this space.... but people are working on that even now.

So What Does This Really Look Like?

     (Click for Zoom; Click again for Ultra-Zoom)

Picture: A 20 watt flexible, thin-film GP-Solar, solar panel powers a Samsung Galaxy Tab 4, 8 inch Android tablet.  This tablet could draw 5 watts when its battery is discharged, and by the standard "4 x rule" one would normally want a 20 watt solar panel if you want this all to work in rainy, and overcast conditions.  In bright sunlight you could easily get by with 10 watts of panel, but that's not a guaranteed reality in the Highlands of PNG.

Voltage Regulators (central block in diagram above) come in all shapes and sizes.  This one is nice because he had solid screw terminals to attach wires, but the basic principle is often built-in already with various fold-out solar panels with USB charge ports as found all over Amazon.com stores.  Here is a lab design in PNG:

Note the Tobsun sealed potted module here that can handle an enormous 10A if necessary, which is over-kill in this application.  Look for the three parts in this photo that correspond to the block diagram above. $11 on Amazon.com. The 5A unit is $1 less.

 See:  Amazon Store   If you need such a thing, there is also a 12 volt variant on Amazon.com instead of a 5 volt regulator.

So what are the problems with this setup?  It has been reported by others (GTIS: Charging Directly from a Solar Panel ), that strange things can happen when we mix and match parts in this environment.  Different things happen, with different regulators, solar panels, and tablets and phones when you connect the parts together.  Problem scenarios include:  The system starts to charge (indicated on the tablet screen) in full sunlight, but then a cumulus cloud rolls by placing one in the shade.  When the sunlight returns later, the charge circuit within the tablet refuses to re-engage and start a charging cycle again.  It just gives up and the user has to coax the system back into charge mode, usually by plugging and un-plugging the USB cable.  Not a good solution if you have something else you would rather be doing for two hours.

But if you substitute a different panel (usually a slightly bigger one) or you substitute a different tablet, you will get a different result.  Some tablets and their internal chargers are just plain different... they are not all designed the same way.

So for the rest of us, this means we still have to experiment a bit to get that optimum "universal" set of parts that will be the least troublesome for all users and all tablets out there in life.  This could be a tall order.  The biggest lesson, as of this writing, is "Try before you Buy" as you complete a setup for others.  You need to do some testing, but in this space we will try to list all the latest news on what works and what doesn't.

The next experiment, yet to be tried as of this writing, is to substitute the GTIS 15 watt, Solartec panel instead of the 20 watt GP Solar panel above.  These GTIS panels are in aluminum frames and heavier to transport, but at $18 each (SIL Member Price) there are amazingly inexpensive.  See: GTIS PowerMon Store

The other experiment to try is various fold-out 15 watt solar panels (see below), where the advantage is extreme portability and lower weight over the Solartec conventional panel.  However, the canvass/nylon fold-out panels are considerably more expensive to purchase, relatively speaking, and the Solartec panels might be more durable in settings where they don't move around a lot and are mounted on roofs for years at a time.

Highly Portable, 15-20 watt, Tablet Solar Chargers

There is big interest in Tablets over Mobile Phones for language work, because most of our software will look similar in the larger screen format offered by the 8 to 10 inch tablets.  Android is in focus now, but soon Windows OS based tablets will be affordable and our most popular language software applications are going to be there.  One would expect a Bluetooth keyboard added for serious data entry.

Recent tests of the Anker "PowerPort Solar Lite" product (Model A2422) in the field produced some pretty nice results sustaining a Samsung 8 inch Android tablet, model "Galaxy 8 Tab 4" (~$250).  The Anker fold out screen has two major panels and a rugged polyester canvas construction material.  It is reasonably weather-proof, but not "water proof".  Don't leave this one in the rain while out in the garden.  It has recently dropped price on Amazon.com to $42 versus around $65 before.  Of the making of fold-out panels there is no end, but Anker is a good, solid name with a good reputation on their product line.  Sure enough in the lab, this panels performed well in high and medium sunlight, using its 15 watts max output to good advantage. 

Tests included covering and uncovering the panel and seeing whether the Samsung Tablet would "restart" its charging process.  It did.  However, the threshold for charging at 15 watts of panel for a 4.5 watt (while charging) 8 inch tablet was at 1/2 Sol, or 1/2 the normal brightness of full sunlight, at least as found in the Highlands of PNG.  So, this means that certain rainy weather conditions will not allow the Samsung Tablet to recharge.  My suspicion is that when we move to a 20 watt folding panel, we will get the desired performance of re-charging the tablets at 1/3 Sol which would cover most every day in PNG.  We will be testing such panels in the future.

Unlike with the small, low-power consuming notebooks (see that section) where you must have an external battery pack involved (so far), the charging circuit of the typical tablet, simply does not "turn on" well in low-light conditions.  It means that a larger panel is required if one has the goal of charging the tablet on rainy days, as well as fair weather days, and everything in between.  The modern solar controller plus external battery in the other notebook solar system designs, allows for charging to start at much lower sunlight times, like early dawn and dusk times.  That's simply not going to happen with the typical tablet arrangement.

Note that the Anker A2422 panel has dual USB ports, a charge activity light, and claims an top output of 2.1 Amps at 5 volts for the USB ports.  Many other panels are going to limit their performance to a mere 1.2 Amps or worse to 0.5 Amps like the old USB 2.0 computer ports of olden days.  So, these are the kinds of specs to look for if you are looking for a subsitute panel to this Anker panel.   The normal charge rate for the 8" Samsung table is 0.9 amps while screen on, and recharging the internal battery, or approximately 4.5 watts.

Highly Portable, 7 watt, Mobile Phone Solar Chargers

Mobile Phones are even easier to charge up in the field on solar.  Here is a typical 7 watt fold out panels and it is recharging a 2.5 watt Asus Zenfone 4 with dual SIM cards.  The screen here was "full bright" for the picture and note that the charge LED is glowing.  The boxed area is the place on this fold-out panel were the 5 volt regulator is included.  Simple plug in your USD cable and go.  Note that this is inside my house, and the outside sunshine is overcast at the time of the picture.  That is the recharge performance we seek.  Time to recharge a "flat" mobile smart-phone battery would be 2.5 hours and at 3 watts.

Note that 7 watts to charge a 3 watt phone is pretty amazing.  This says something about the on-board regulator here, the superior "low-light" performance of thin-film solar panels, and the overall brightness of my "overcast" condition.  Shade performance actually matches full-sunlight performance, indicating a true current regulation at a measured 550 ma.  In other words, it doesn't matter if I am in the sun or in the shade, if I am charging, I'm cranking out .55 A to the phone and it takes an appropriate but longer time to recharge.  However, back in the lab, with a 2 amp USB port to play with, the bench charger delivers what the phone wants which is more like 990 ma. (1 Amp)  Therefore on the bench, the mobile phone will recharge that much faster, as in less than an hour.  But for field settings, taking 2.5 hours to recharge in the shade is actually pretty nice.

All this sort of defies the normal "4x rule" for panels powering devices.  More like "2x" here.  Basically if the sunlight is cut down by this factor of full sunshine, we are still in business for today's work.  We don't have to stop our routines to keep going.

Picture:  This 7 watt fold-out panel, is similar to the PowerAdd panel which we have tested as well.  This panel is of an unknown make and was purchased direct from China, sent to PNG.  The only mark on it says: "Witi".  The PowerAdd panel is very similar in size and performance.   $20  7 watt  See:  Amazon Store   The highlighted box is the housing for the on-board regulator, and USB port on the side.

During a recent trip to a tropical climate town, in PNG, the PowerAdd panel failed a few significant tests.  It is not recommended at this time for purchase.  1) In bright sunlight, the regulator strangely "clamped down" to a mere 50 mA at 5 volts, while charging a mobile smart-phone.  2) Stranger still, the mobile app Ampere indicated a nice positive charge of 350 mA (@ 200 mA consumption; total: 550 mA) while the panel was placed in the shade, but failed to actually recharge the phone.  3) In contrast, a portable USB battery bank, with 1000 mA high-current USB port, allowed the moble phone to recharge at 950 mA, under the same conditions.  Conclusions:  Be sure to test any USB charging panels in a variety of real-life conditions, and look for panels with regulators that allow delivery of currents beyond 500 mA output.

There are no good recommendations on the best 7 watt fold-out panels at this this time.  The SCOS Handbook welcomes additional reports by users in the field at this time (Aug-16)

For more folding panel ideas just search "7 watt fold out solar panel" in Amazon.com search.  See $20 7 watt MQB See:  Amazon Store  and see: $25 8 watt Eco-Worthy  Amazon Store   but really there are a dozen other companies out there.

Note:  The construction varies quite a bit on this panels in terms of their canvas, or nylon shells and whether they will handle scratches well, flex forever without breaking internal wires, and hold up under abuse (front face of active solar elements).  It would be great if readers could add any experiences they may have had, good or bad in this space, to help others on purchasing decisions.  Also all the 7 watt Amazon.com panels say they are for various mobile phone models.  They do not say they can power common tablets.  This is not surprising at the 7 watt level.  And the lab agrees.  We are moving to 15 watt or more, fold-out panels to test for normal 8-10 inch, Android Tablets.

Battery Banks with Small Integrated Solar Panels

These are great as energy storage devices, and yes, many will recharge a mobile phone quickly and maybe two times with a full charge.  Fine, except their solar panels are way, way too small to recharge the battery bank and then continue to charge mobile phones each and every day, even in full sunshine.  Worse on rainy day weeks. So, if you re-charge a phone, and deplete the capacity of the battery by half, expect four full charge days, before you regain the energy you used to re-charge the phone.  It's not the storage that is wanting;  it's the capacity of the tiny solar panel that let you down.  Note the relative size of the 7 watt solar panels above for a mobile phone for comparison purposes.

However, straight "battery banks" are quite useful devices and many can be connected directly to a USB solar panel for charging.  These will work well and recharge once a day in normal use, if the solar panel is comparable to the work involved by the devices in use during the day.  So, small Lithium battery based battery banks do have their place, just not the fancy ones with tiny integrated solar panels on one back-side.  That feature is a waste of money.  Purchase a larger external solar panel instead.

Summary:

Hopefully we have shown here some viable solutions to powering and working well with a tablet computer.  A small solar panel, without the need for an external battery and fancy solar contorller, with the comensurate reduction in expenses, can be deployed.   A bluetooth keyboard should be added for data entry purposes, and that might even include a mobile phone setup, but obviously an 8 inch tablet is nicer.  All of this equipment is within the reach of local level language communities to purchase and to use their own equipment.  This same equipment should be introduced with adequate training and can easily be incorporated in our present National Training courses (PNG Context).  Training costs are reduced in this scenario as well, since everyone already knows pretty much how to re-charge mobile phones and tablets in a town environment where power is available.  On the brighter days, the user can help relatives and friends recharge their phones, and perform a community service, while working on a language project and doesn't have to worry about having enough power to do everything (a problem with higher power laptops, where the person with the resources might be considered "stingy" in not sharing those same resources).

Solar Panels:

June 2017

2017: Fold-Out Portable USB (5 volt) Panels

Click to Enlarge Image

With the advent of the highly portable, relatively inexpensive, Asus Transformer Book (T100HA) and similar notebook computers (see Notebook Section), we suddenly have a host of fold-out portable panel solutions that back-packer and outdoor camping types like to use to re-charge their tablets and mobile phones.  As we will see that not all panels are made alike and worse one must carefully match the panel with the device or devices you wish to charge, if you want optimum performance.  But this section is an attempt to share the research we have already done in the field.... so you don't have to.

The best tested panel in the lab to date has been the relatively inexpensive 20 watt fold-out panel by X-Dragon.  It is superior to many in that it has great low-light performance, and it doesn't seem to suffer from any kind of "return to maximum" charge problems, as found with some other panels when clouds come and go.  This phenomina is not fully understood, but some products "down-shift" when the incident sunlight falls momentarily and then power to the device fails to return to maximum output later.  This means your device might continue to recharge still... but at a much slower rate than expected.  You might be disappointed at the end of the day, to find your phone or tablet or transformer book, not fully recharged.

USB Ports are Not all the Same:

You might be thinking.  Yes, I know all about USB v2.0 has maximum output capability of 1.1 amps and the new USB 3.0 spec can be up to 2.4 amps, but life is never so easy really.  There is a new specification out called the USB Power Distribution spec and it outlines the various modes that allows for USB charging all the way to 100 watts!  That's enough to cause fires, shock hands, and burn up devices if improperly wired, but that's progress.  But the striking news is that the new PD spec is not just for USB 3.0 devices but can be applied to new USB 2.0 devices.  That's exactly what we see with the Asus T100HA model (see Notebook section) where the standard tiny power brick (the module you plug into the wall socket) can up-shift to the next highest charge rate of 9 volts out, and 2 amps.  So it might look like a standard micro-usb port on that box, but it's not really. That's why recharging (so far) is faster using the AC power brick, in comparison to using these fold out USB solar panels (at 5 volts)...  but maybe someday we will find such a panel that accomodates some of the USB PD charging modes.  We are still searching.

Also specified is a data communication protocol for power transfer between the source and target devices.

For more on this PD topic see here:  USB Power Distribution Specification

But for the purposes of our work on the field, any combination that allows for two hours of use on the device, and requires a one hour recharge rate, is considered acceptable.  This is the unofficial "2 for 1" rule and is the situation we now have with the Asus Transformer Books and the X-Dragon (and other) type panels.  For today, this panel at least, is highly recommended.

Amazon:  X-Dragon 20 Watt fold-out panel   US$ 50   (Tested)
Amazon:  Sokoo 22 Watt   US$ 50   (Consider)
Amazon:  Anker 20 Watt    US$ 60   (Consider)

Typical of these panels, the X-Dragon comes with three solar sections under a clear transparent window and water-tight PET nylon cloth-like coverings.  The sealed electronics and connectors are hidden behind one panel flap and as such would protect the ports and cable connections from rain.  There is even a pocket back there to protect small devices such as a phone, or USB power bank (a battery storage device), but for larger tablets and transformer books, one should just place underneath the entire panel assembly.  These panels claim to be water-proof, but I would consider them water-resistant.  You don't really want to throw these into a lake and fish them out and expect them to work immediately after that.

How about the 15 watt variants of these panels by the same manufacturers?  Not recommended.  If you live in sub-Sahara Africa where the sun shines almost every day of the year, with blue sky weather, then you might consider even a 10 watt panel... but for the rest of us, you want a panel that simply works during the early dawn hours of the day, or very late afternoon sun, or when it's heavy overcast.  In PNG one could have heavy overcast for an entire week.  You want a panel that simply "always works" especially if the user is less tech savvy, but well trained in the Bible Translation and Language Develiopment tasks.  You want something simple for when there is no advisor around to work out any problems.

The Power Bank Option

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The “Direct Connect” solar approach does have at least one caveat as represented by the Asus Transformer Book (see Notebooks section). Recharging procedures change somewhat. The Asus Transformer Book style notebooks can run easily around 12 hours, but the average work-day is designed to be 8 hours only.  This means that daily there should be a recharge during the daylight hours, and preferably between 10:00 a.m. and 2:00 p.m.  So far, the fold-out style panels only supply about 1.1 Amps and therefore a fast recharge is not possible.  Nonetheless a good rule of thumb is about 2 hours of work, for 1 hour of recharge (even in overcast conditions).  So to sustain 8 hours of work, expect a 4 hour recharge period using these panels.

However, a good option to consider is an auxiliary USB “power bank"; a small Li-Ion rechargeable battery pack with USB ports.  With the extra investment of a power bank unit, the user can now leisurely connect solar panel to small power bank and recharge anytime in the day, while working on the computer anytime day or night.  The noon-time period is not wasted for work, if so desired.  Then before sleeping at night (a period where no work is performed obviously) the user can easily recharge the Asus transformer book back to full charge for the next day.  So, although “direct connect” is possible, it is probably a good idea to add the cost of a small power bank. It’s just a versatile setup, and remember that the longest USB cables only run about 2 meters in length anyway, so we are not in the original scenario of "solar panel on the roof, and 10 meters of cord down into the village office".  USB cords do not run 10 meters.

For this scenario, we would recommend a power bank of twice the recommended energy storage of the Transformer Book, so for 30 Wh, then we want a 60 Wh power bank, more or less.  So a quick check of amazon.com here:  ($25-$30)

Amazon.com  Anker PowerCore 10000 would be fine. Simple power indicator LEDs.

Amazon.com  ToHLo 20000mAh unit is more precise with it's digital energy display.

Amazon.com  RAVPower 16750mAh with higher current output.

We consider RAV of the quality of Anker unit which has bar power display, and the potential for a true 2 Amp recharge rate.  It also has flashlight LED.  But the Asus T100HA may not allow for a faster recharge and self-limit to 1.1 Amp anyway.

But we don't really need all the "bells and whistles here"  If the user were simply going to sleep at night, closing the computer for the day, and then recharging the Asus while they slept.... the least expensive Power Bank would do the trick.  Fancy options like a flashlight just means that it's going to be borrowed, battery drained, and not returned right away by a neighbor.  Better to not tempt anyone with extra functional usability.

2016: You live in the Third-World? Where to Purchase for the "Big" panels.

This section is for the "time-challenged" workers among us, who are typically supporting others in a third-world context.  These are the ones who say:  "I don't care about the details... just tell me what to purchase and where to purchase."  Obviously the recommendation we give here, will not be the only option and lots of excellent stores can be found on-line via Amazon.com and eBay.com.  But the problem, invariably is how to ship the parts and complete solar systems to where you are on the planet.

Primary Recommendation:  GTIS Powermon store:  Home Page

Specifically for Solar Panels:  GTIS Solar Panels

This can be your "one stop" shop, since they sell parts and complete kits specially designed to support computer systems in the field.  The Purchasing and Shipping department is a certified DHL world-wide shipping agent, and therefore if DHL is available in your country, they can ship to you, directly by air freight.  If you want to do surface transport (slower and less expensive) that is an option too.  You simply have to declare "how" you want your parts shipped and by what method.  So the major advantage here is that GTIS Powermon store is highly experienced in shipping parts anywhere in the world.

The least expensive solar panels, by watt are the Solartec line as seen here:  GTIS PowerMon Store

These aluminum frame 15 watt panels are a steal at US$18 (SIL Discount) and are of a granularity that is perfect for various applications.  You want to power a tablet?  Fine, start with one Solartec 15 watt panel.   You want to power all day and 4 hours into the night, a modern year 2016 Notebook?  Fine, start with 2x the Solartec 15 watt panel.  You want to power an old style notebook, say a 9 watt Lenovo x140e model?  Fine, work with 3x Solartec 15 watt panels.   You have a very old (2014) Dell 6420 model to power running at maybe 12 watts?   Fine, you purchase 4x Solartec 15 watt panels (60 watts total).  You won't do better, pricewise anywhere else, but you can substitute more flexible options that are handy (see next section) but are more expensive per watt.

The very handy, portable, lightweight, but more expensive Bioenno Panel is perfect for ease of transport, say in a major hiking situation and you are powering a 2016 "Bay Trail" notebook (see Notebook section).

This is built upon the latest thin-film technolgies and folds up nicely.  You could purchase two of these for the near 60 watt scenario above.  See:  GTIS PowerMon Store

Note that in this picture is the handy, extremely light-weight, "Half-Pint" battery bank with controller, but please see the appropriate section for more details on that very useful LFP battey pack.

Different Solar Technologies

Thin Film Flexible Technology

CIGS Solar Panels

Controller / Battery Combined Units

June 2016

These are the kind of units/ systems that people really want, combining the function of the latest LFP technology and a solar controller in one small, self-contained box with simple connectors.  Perfect for more tamper proof operations in village settings.  Internal thermal fuses that reset themselves are also inside such boxes, and another level of complexity or point of failure is hidden from the end user.

Overview:

If we look at the original solar system block diagram, we can see the part that is combined in the special units under discussion here.  Note the simplified wiring setup now required into and out of the "red" marked zone here.  There is a solar panel module that is simply plugged into the "Combo" box here, and there is the 11-14 volt conditioned voltage output, that heads to the Auto-adapter unit which is next in line to the notebook itself.  These boxes typically have a standard female car-adapter port, similar to what's found in any automobile and people are very familiar with plugging tools that require electricity in such a recepticle.  It's quite commonly understood what to do.  So, you plug in your auto-adapter charger for the computer, and your done.

Note too, that safety devices like fuses and breakers are inside the box.  Some use a time-out thermal fuse that the user doesn't have to really think about.  When a short or overload occurs by mistake, the system protects itself and shuts down.  The user has to wait a while for things to reset, but doesn't have to do anything except disconnect whatever it was that created the fault in the first place.  It's not normal to shut down, so the user has to figure that part out.... but the box made it's own decision to protect itself and that makes training the user, that much easier.

Purchase Summary:

Someone says:  "Just tell me what to purchase"

First, you must know the power consumption of the computer you hope to power, in watts, in it's normal "steady state" mode of operation.  This would mean activities such as Word Processing and Email as a guide, and if you need it Wifi services turned "on".  If you do not know this figure in wattage, then you cannot proceed.

Remember that the user working spec is 8 working hours a day, including 4 hours of night-time work, under typical rainy weather or overcast conditions for week long intervals.  The idea is that the language worker never has to really think about power at all and can just concentrate on their work.  If you are working in sub-Sahara Africa, then obviously you can go with less hardware.  These recommendations work for rainy, tropical Papua New Guinea.

The GTIS (JAARS Inc.) store is:  GTIS PowerMon Store

There is an on-line "cart" to fill up, and SIL members get a 20% discount on parts.

All parts including the LFP batteries can be air-freighted by DHL to anywhere in the world via Purchasing and Shipping department.

The "Half-Pint" System

If you are in a hurry to set up, and if you are using a modern "Bay Trail" notebook as commonly sold in 2016, THEN proceed immediately to purchase the GTIS "Half-Pint" system.  ($188; SIL Discount) See:  GTIS PowerMon Store

     (Click to Zoom; Click again for Ultra-Zoom)

We have no idea why GTIS came up with this name, but they did, and one name is as good as the next.  This is an amazingly light weight box, and easily held in one hand.  It's about as light as a rugby-ball, and can be hefted about as far (don't try this!).  It comes with a cute carrying pouch with strap, and with space enough for the universal Vanson auto-adapter with multiple connectors for many popular makes and models of notebooks/ laptops.  This box is a "4 amp" box, limiting it's use to charging small, truly low-power consuming netbooks in the 4-7 watt range. 4 amps is a limitation of both the load, or the netbook as well as the solar panel.  Thus the suggest maximum solar panel wattage is capped at 45 watts.  (3x Solartec 15 watt panels, or equivalent)

This box listed at 72 Wh of energy storage, and combined with a mere 30 watts solar panel, will sustain a modern 2016 notebook running Paratext (SIL/UBS software) for 8 working hours a day, including 4 working hours at night, even during a week of rainy, overcast weather.  Every day will be a "work day" with this setup.

The digital display is energized by the black momentary push-button as seen in the picture.  This is handy to quickly see the state of charge (voltage at battery terminals; 11.0 to 13.9 volts) and would be advantageous for diagnostic purposes, say over the radio or via mobile phone (or email) to technicians if there are any problems in deployment in remote settings.

There is a prototype unit, under development that foregoes this display unit and has a LED Bar-Graph indicator, for users who are confused by the digital nomenclature indicating "state of charge".  For some of our language workers, this is indeed the case.  But "bar-graphs" commonly found on mobile phones are easily understood already.  If this is your need, then presently one must special order this type of unit from GTIS.  This prototype will also have some sort of LVD function, or low-voltage alarm.  

Note:  a normal "Half-Pint" system does not have an LVD function and the user therefore must be trained to avoid abuse of this system. We are working to change this situation as of this writing. On a positive note, field testing of low-voltage or severe discharge abuse has shown the normal "Half-Pint" to recover brilliantly from severe discharge states..... so that is a very positive outcome of using LFP technologies. But true "damage" is hard to determine in terms of overall cycle time (longevity) performance when we are talking about a system that normally runs beyond 10 years of service.

Possible Extra Items:

For Lenovo models you need an addtional "square" adapter purchased.  This gets added to the Vanson Adapter set that normally comes from GTIS with their systems.  See:  Amazon Store

We anticipate that such a simple and inexpensive part ($5) will already be listed in the GTIS catalog on-line in the future.  Again, ask for this from GTIS.  They may have them in stock. One disadvantage to the popular universal Vanson auto-adapters is their manual voltage control slide switch.  These must be glued in place to prevent casual users and friends in the village from "playing" with the switch and then potentially damaging your notebook computer later. It might be preferred to never allow this situation to happen.  See below.

Instead, you might want to forego the popular Vanson Unit and simply purchase an Auto-adapter specific for your machine.  For Lenovo see:  Amazon Store

Here is a complete Lenovo style DC auto-adapter, listed at $22 or so.

Note:  This DC-DC auto-adapter is preferred over using an AC inverter, which wastes precious joules of energy in the conversion from DC to AC electricity and then back to DC once more. See the Auto DC-to-DC Adapter section for more details on this topic.

The Villager-III

     (Click to Zoom; Click again for Ultra-Zoom)

The Villager-III units are another "combination" box, like the "Half-Pint" above, but larger.   It is the box you want to purchase if you have a larger, power consuming box, such as an anceint (2014) Dell Latitude E6420 model running perhaps at 12 watts.  The very good news is that this box can handle up to 12 amps of current, so it can handle very old computers if necessary and with relatively large solar arrays, up to 144 watts of solar panel.  (Yes, "large" is a relative term here)

See:  GTIS PowerMon Store

Picture:  A complete "kit" with flexible Sunpower 100 w panel. Note too the 10 meters of UV resistant power cable for a roof installation of the panel.

Note the aluminum metal box chasis and the dual, covered, 12 v automotive output ports and digital display.  The total capacity in the LFP battery packs, installed is 216 Wh, which is slightly less than the old Villager-N units that are no longer in production, but with the superior amperage of the Villager-III (12 amps) versus the max of 5 amps before... the Villager-III is clearly a better built box and no exposed battery terminals to "hang onto" with an alien apparatus. And, best of all, unlike the older Villager-N box, there are no air-freight transport restrictions.  The Villager-III can be flown anywhere in the world, without restrictions, so long as it is sent as cargo in the hold.  This is a major deal.  The extreme light weight over a Lead-Acid solution, also lends itself well to air transport.

The Villager-III does have an adjustable LVD (Low-Voltage-Disconnect) feature, therefore preventing an undesirable deep discharge of the battery.  There's even an indicator light if the depth has been exceeded by the user.  It is recommended to leave this at the GTIS factory settings, internal to the box.  Normally the user does not set this.  The solar controller inside the box is the popular Xantrex C-12 PC Board.  See the Solar Controllers section.

Inside the Villager-III the LFP battery packs sport Anderson Power Pole connectors.  This is great for easily swapping out units for maintenance, but more importantly, they discourage unwarranted connection of other loads should the user open the box for power modifications in the village.  There are no "terminals" to easily hang onto with extraneous other devices to power.  This is important for unsupervised language projects.

The Villager-III (Dual Packs)

In some situations, the user might want to special order a slightly modified Villager-III box.  Inside is normally 3x of a 72 Wh LFP battery pack, and for a large, older notebook where the goal is 4 hours of run time at night, then one would want the standard Villager-III.

However, some machines sold in 2015, such as the popular Lenovo x131e and the Lenovo xx140e models would be served well by only 2x LFP battery packs installed in the Villager-III box.  GTIS says this would save approx. $80 in the purchase price.  How do you calculate your need?  When should you ask for the dual pack option?

For four hours of night-time use, let's say you are using a laptop running at about 9-10 watts.  You are planning to work for 4 hours each night, but realistically there's about 2 extra night-time hours at dawn or dusk where the solar panels have not really turned on to deliver any usable power.  So really 6 hours of "night-time" here.  Energy consumed:  6 x 10 watts or 60 Wh (watt hours).  

Inside the Half-Pint and Villager-III solar units are either 1, 2 or 3  72 Wh battery packs.  These are completely sealed units with Anderson style power-pole connectors.

The Villager III with 2 battery packs would have 2x 72 Wh of energy, but remember that you can only really use 80% of the capacity here, so practically speaking you have, 2 x 72 Wh x 0.80 = 115 Wh of energy.  Wow!   That's a lot of extra energy storage.  But remember that for the LFP batteries (see the Battery Technology section) to achieve 5000 or so cycles (well beyond 10 years of lifetime), one must discharge to around 50% or so of the full capacity of the battery.  Well, consuming 60 Wh or energy each day, from 115 Wh of usable storage, is close enough for a 50% depth of discharge, each and every day. Congratuations!   You have saved $80 and yet have a system that could last you, over 15 years of service!  Wonderful!  This would be for older netbooks like the Lenovo x131e models.

However, for older Dells and Lenovos and Toshiba laptops of the past, say those purchased back in 2012-2014, they could be running 15-20 watts while in use.  You MUST specify the standard Villager-III unit, in that scenario.

Don't even think to try to get this kind of lifetime performance with a Lead-Acid battery, even the "deep discharge" more expensive variety.  They will be replaced in 2 years.

Important Point:

If it is not clear from this paper already.  The choice of computer you are planning to use has a severe impact on the size and cost of your solar system for stand-alone, rural use.  It's quite possible that in a truly remote solar site, that it is worth the cost to ditch the old laptop you have in hand today, and start over with a more modern low-power computer, and then save a bundle of money with a tiny solar system that would be required.  It's one of those situations where one can be a "penny-wise but pound foolish" by insisting on using the older computer at thand, and trying to go forward with your project.  The modern netbooks we are talking about today weigh in at $300 cost or so, but the savings in solar equipment costs could exceed $1000 or more!  It all depends, of course, on "how old" your present laptop might be that you are trying to re-purpose here.

But do not think that all computers are the same, power wise.  They are very different. It pays to do your homework.

Battery Technologies

Summary:

If you have decided to use LFP batteries in your system.  Then simply read the LFP section below.  Congratulations because your world, at least related to support, is easy to understand.  Training issues are minimized.

If you have decided to go with Lead-Acid batteries in your system, then indeed read this section, because there are a host of complicated issues concerning the proper care and feeding of Lead-Acid batteries.  Not exceeding a maximum depth of discharge (ever) is a major issue.  Proper training is important with some controllers.

Lithium Ferrous Phosphate (LFP) Batteries

LFP Batteries are Not Really more Expensive

If you are reading this section and below it means you are interested in a Lead-Acid Battery deployment for your upcoming solar system.  There could be good reasons for this, but you will notice that this section is quite long.  Why?  Because Lead-Acid batteries have quite a few "issues" if you want them to give you good service, and the issues are rather complicated here to express.  If you want simplicity and a system that simple "just works" and for a very long time, say over 10 years of service.  Then read through the LFP section above, a second time.

Obviously training costs are going up, as you invest the time to teach the solar user all the technical issues of using Lead-Acid batteries.  In the PNG context, this cost is quite high, because the user typically doesn't understand these issues well enough, or there are significant village and family social pressures that lead to battery abuse, and then a failed solar system.

AGM or Absorbed Glass Mat Batteries

Advantages of AGM over Liquid "Flooded" Batteries

Consider Manufacturing Date Codes

Amp-Hour Capacity as Listed on Battery Labels.

Lead-Acid Battery Life Issues

Depth of Discharge affect Useable Capacity

Capacity Monitoring - Batteries Age over Time

Other Battery Chemistries

Solar Charge Controllers:

June 2016

Note:  This section is for those who want more details and perhaps would like to mix and match solar parts for some reason in their field situation. This section is for more more sophisticated designers of custom solar systems.  For most normal users, they would do better to simply read the Controller - Battery Combo Units section, and skip this part.  The Combo Units are highly recommended to those who are in a hurry to deploy a solar system on the field and want "simplicity" and "robustness" first and foremost in their decisions.

Due to rapid changes in solar radiation possible, the corresponding solar panel voltages fluctuate dramatically.  The purpose of the controller is to condition the power coming from the solar panel and make this power acceptable for various battery chemistries to store electrical power, and without premature damage to the batteries, shortening their useful life.

The best batteries suitable for the variances in solar power, today, are the LFP technologies.  Lead-Acid batteries, although extremely old tech and well known, are the worst possible chemistry for solar.  Nice for automobiles; fragile in a solar system.  Nickle-Metal Hydrid can also be used.  In all these cases, the Charge Controller is the "watch man" or sentinel who makes sure that the batteries are receiving a good charge under the given solar conditions.  Clouds come and go; rain storms hit; night time comes, and yet the controller does the right action to help the battery live a long and useful life.

All solar panels have a Maximum Power Point (MPP) and manufacturers proudly give specifications for this. It's the “knee in the power curve” where the total power is maximized at a certain specific voltage and certain specific current output in brilliant sunshine. This point changes with the different solar panel technologies. The Morningstar and the Xantrex controllers discussed here are trying to hold the solar panels at that optimum point for max power, and also regulate the charge current for what the battery really needs at the moment. The state of the battery is changing as it charges back up again, while the incident solar radiation is changing by the minute as well. Finally the netbook or “load” may or may not be in use. The controller then makes new and different decisions about the charge voltage and current applied. All this activity and decision making is to help your battery live a much longer and healthier life before replacement while performing its work function as well.

Best All Around Solar Controller:  Xantrex C-12

Many previous designs were centered around this excellent controller that is still in production after many years.  It is a printed circuit board (not in a sealed potted module) and therefore can be diagnosed and fixed by trained electronics technicians.  It is field repairable, which is handy.  It also tops out at 12 Amps, which covers a wide range of netbooks, laptops and old power-hungry laptops who can demand high current loads in use.  So a good universal performer for many different kinds of laptop computers, old and new.

Quick Info:  If you don't want more details, but want to purchase a complete system which is built around this controller than see:  GTIS PowerMon Store

This box, nicely sealed from the elements, has the C-12 Controller inside plus fuses, plus a built-in voltage meter, plus three 72 Wh LFP battery packs.  Fool-proof external connectors are mounted in the box.  This will also be described in the Controller - Battery Combo Units section

Further Details:

This is the standard Xantrex C-12 controller box which can also be directly purchased from the Internet stores.   There is a metal Nema enclosure, and a repairable circuit board inside.  Best of all, there are five individual pots or adjustment wheels to customize the charging cycle for your particular batteries.  If you have Lead-Acid batteries, you want different settings, than if you are deploying LFP type batteries, although the settings are close enough.  See advantages of various battery chemistries in the Battery Technology section.

Operating Principles

Beware of charge-recharge inefficiencies on your notebook batteries.  It might be helpful to note here, that while charging a typical netbook's internal batteries, that this appears to be a most power inefficient mode. Charging currents go quite high, from 2.5 to over 6 amps at times, and often the energy conversion efficiency drops dramatically.  If this scenario of charging/ recharging the netbook's internal batteries is required for daily use in the language program, then one would suggest increasing the solar panel size.  It is better to simply run off the external battery pack that you are providing, and leave the internal batteries at an indicated 100%.  You can, of course, use the notebook batteries as a "reserve" for when weather conditions are really, really abnormally bad that day. 

If under normal conditions your solar system appears to be more than adequate, and you are always running the notebook batteries at an indicated 100%, then we would suggest removing the internal battery pack (usually a clip unit that is easily removed) completely.  Place it on the shelf for emergencies later.  Why?   Because prolonged overcharging the internal battery pack over months without using the battery pack, reduces the lifetime of those internal batterys.  That's the reason why in the town situations with reliable mains power, we are still often replacing our internal battery packs after two years, even though we have hardly used them at all.  We are overcharging them and slowly releasing electrolyte to the atmosphere.

But in solar setups, like mains power setups, the power is reliable.  There is no real need to run the internal batteries all that much.  Use the once in a while, and keep then healthy and exercised slightly.

Low Voltage Disconnect Issues (LVD/ LVR)

The Low Voltage Disconnect (LVD) should be set in a manner that protects the netbook user from overusing the battery and potentially discharging the battery too far for a given daily charge/ recharge solar cycle. Equally important is the Low Voltage Reconnect (LVR) setting. Once the load is disconnected with a hard-worked battery, the user must be “blocked” from continuing to drain the battery, until a suitable battery state is reached.  For the fragile Lead-Acid battery we are suggesting here just below the standard “float” voltage or 13.6 volts, although the “Bulk” charge phase of the Xantex controller goes beyond this to 14.6 volts. Above the LVR point, the user could start working again or at least start charging the netbook's internal battery through the auto-adapter. See next section “Typical Charging Cycles”. Some consultants might consider a higher LVR setting. Obviously the user can still run, sometimes as long as 8 working hours, on the internal Li-Ion batteries of the netbook, but this is not recommended as "normal" practice due to inefficiencies in charging and recharging yet another battery in the system.

Note as stated already in the Battery Technologies section, the LiFePO4 (LFP) battery chemistry is a much more forgiving technology for solar use.  Typically the "Bulk" phase setting is set around 14.4 volts, and the "Float" setting is around 13.6 volts.  There is a sharp drop-off beyond the "knee" of the LFP discharge curve and so anything below 12.3 volts is recommended for the LVD seeting, say 11.5-12.0 volts.  But it could be lower than that, because the curve is so steep at that point.  The LVR is typically 0.8 volts above that, but around 12.5 would be good.

If all this sounds too complicated, please don't trouble yourself on these points.  Proceed to the Controller - Battery Combo Units section and simply purchase the Villager-III model, and leave all these settings the same as GTIS applied.

Morningstar SunSaver Model SS-10L

The SS-10L is a very popular solar controller, and sold on many solar oriented web sites and stores.  It has a very solid look and feel when held in one's hand.  This 10 Amp controller with LVD function, is a sealed “potted” module with mounting brackets and terminal posts, making repair service a bit more difficult. GTIS also has these units at 20 A (SS-20L) for sale at approximately US$ 80. See: GTIS PowerMon Store

See: Amazon Store but note that at 10 A (SS-10L) then the GTIS store is really the place to shop here.

Some very nice features are the smaller size and a solid “low voltage disconnect”, but unfortunately the built-in LVD setting at under 12.0 volts, is way too low for Lead-Acid purposes, but would be acceptable for LFP batteries.  See the Battery Technologies section.  The Xantrex C-12, 12 A controller is favored, because it is adjustable, but many would never change the adjustments to begin with. Never purchase the ordinary Morningstar SS-10 model as that does not have any LVD function at all.  A large advantage to the SS-10L is that it is very small, in comparison to the C-12, with its large PC Circuit Board.

(Click for zoom)     

However, there is a possible reason for the lower than expected LVD of the Morningstar Controller. In field testing many users are not using a proper gauge of wire, running from roof-top to controller, and especially from controller to battery. There can be a significant difference between the recorded voltage at the battery terminals and what is “sensed” by the controller, even for short wire run lengths. So for a desired LVD of 12.3 volts at the battery, the controller might have to wait for 12.0 volts at its sense terminals. The voltage drop is created by the high enough load currents and the typically small diameter wire that some people use.  This might explain the thinking of Morningstar, however their design is a compromise of possible conditions at best.  The C-12 Controller allows the savvy technician person to make fine adjustments for each unique installation in the field.

Picture:  EcoDirect.com  A very nice mounted Morningstar Controller, with three mounted 10A DC circuit-breakers and terminal block nearby. This company wanted fuse protection on the solar panel side, the battery side, and the load side of the controller circuit.  This is a great looking setup.  Also note the insulated cover plate over the normally exposed contacts of the Morningstar.  Falling metal objects are less likely to short out this arrangement.  For more about fuses and breakers, see the Fuses section.

Morningstar SunGuard SG-4 Controller

This discussion would not be complete if we didn't include the heart of the GTIS Half-Pint system here.  The SG-4 is for "light duty" solar applications, and is inexpensive at around $30. However, with the new 2016 netbooks on the scene, this controller is more than large enough to supply energy.  The new netbooks would draw a maximum of 2.5 watts, to put this in perspective.

The only problem with the SG-4 is the lack of any LVD cut-off.  It's up to the user to determine when to turn the solar system off, and stop supporting the netbook.  In the Half-Pint system box, there is space for an alarm circuit, which for an additional $5 or so, would be well worth the installation.  We are presently working on a good modification to the present Half-Pint at this time. See the Controller Battery section for more details on the GTIS "Half-Pint" system.

Automotive Adapters:

No Inverters Please!

Well you can use one of course, but it's wasteful of your preciously collected solar energy for the day.  If you purchase an inverter which takes the 12 Volts DC power from your battery and then converts to 110 VAC or even 220 VAC, and then plug in your standard manufacturer's "power brick" to charge you notebook, then there is another conversion energy loss getting back to 19 V DC power for the computer.  A waste of energy changing states and back again.

Now that many new notebooks themselves are running at a mere 5-6 watts or power or less....using a DC-DC converter for the given box is much more critical, otherwise you are wasting energy, necessitating larger solar panels and bigger batteries at increased costs.... to do the same work.

19 Volt Notebooks

Older 12 Volt "Netbooks"

Fusible Links:

Automotive Style In-Line Fuses

Circuit Breakers

Wiring principles, such as standard polarity conventions, and wiring sizes by gauge.  Some discussion of power losses due to low voltage, but very thin profile wires, which are less expensive, but waste a lot of energy.  Controllers have trouble sensing the correct terminal voltage of the batteries, if the charging wires are too thin as well, leading to charging errors and battery cutout errors.

Also we have now seen village allocations where the gauge of wire used from the roof top to the solar controller within the village house is way too “high” or “too small” in diameter. The user should start by thinking about 10 gauge wire as a minimum and definitely move to 8 gauge wire if available and affordable. Otherwise considerable power is wasted due to resistive losses in the length of wire required, typically 5-10 meters.

Wiring Principles

Wire Diameter Sizes

Useful Tools:

June 2017

Non-Invasive, Clamp-Style DC Ammeters

Ammeters are instructments that measure amperage or the rate of current flow in a circuit.  There are AC type and DC type ammeters, and you want those that can measure DC current in solar setups.  AC (Alternating Current) power is the kind you would find in a residence or a business office in the mains power supplied by a utility company.  DC (Direct Current) flows continuously in one direction and so, when purchasing a measuring device, be sure to look for a DC capability (which is harder to find, often).

Portable Clamp Style, Ammeters are usually multi-funciton devices and add standard DVM multi-meter capabilities as well.  They are easily spotted with their rather large "C-Clamp" looking sensor at the top of the device.  One pushes a small lever, and opens the clamp sensor, which is placed around a single wire in the circuit to be measured.  Depending upon the current flow in relation to clamp orientation you chose, the current will be indicated in either a positive (+) direction or the opposite, a negative (-) direction.  There will be indication for this on the digital display.  Units are typically in Amps.  The picture here is measuring 8.7 amps through the brown wire.

The advantage of the clamp style ammeter is that you don't have to modify your solar setup in any drastic way, other than to reach a single wire to wrap around with current flowing in one direction.  You cannot wrap around two wires, for example both wires coming and going from a battery because the two currents in the two wires will cancel each other out, if they are flowing in opposite directions.  You need to isolate one wire in your measurement.  Also, a DC ammeter cannot be used on an AC circuit since the current is alternating back and forth up to 50 or 60 times a second.

If one were to permanantly wire an ammeter into their solar setup then one can subsitute a much less expensive analog or digital meter, which are also readily found on amazon.com to purchase.  These meters must break the DC circuit at some point and be placed in a series configuration to re-connect the working circuit. They can monitor in real time, but are a more permanent installation.  Nice, but for a temporary monitor, the clamp meter is more useful for random measurements and used to diagnostically determine what might be wrong or right about an aging solar system in the field.  This is a great investment for the solar technician, helping others.

The Uni-T model UT-203 is highly recommended at US$ 30

amazon.com: UT-203

The YKS, USB Power Monitor

With the advent of more and more useful applications coming to Android mobile phones and tablets, including the new "Paratext Lite" application (coming soon for Android OS), we have been doing a lot more research with inexpensive fold-out solar panels and a "direct connect" charging scheme, via a typical USB cable.  These are 5 volt systems instead of the typical 19 volt DC systems we see with a more conventional notebook class computer.  For more details on these new developments see the Asus Transformer Book class of notebook computer in the computer section.

Click to Enlarge

But various solar panels, and various tablets/ mobile phones do not all behave alike, and so there needs to be careful testing.  It's important to be able to see the charge levels and rates of charging from the solar panel.  Therefore there are any number of in-line monitoring devices that can be found on amazon.com.  One simply connects the USB meter in-line with the charging cable and then takes some readings in real-time.  However, most of these devices on the market are inadequate because they have standard color OLED or electro-luminescent displays, that are totally unreadable in direct sunlight, outdoors.  And most of the time you are indeed outdoors with a portable solar panel in hand, and a relatively short USB charging cable.

Enter the brilliant YKS USB Power Monitor, pictured here.  it uses the "old style" mono-chrome LCD technology which has high contrast in normal ambient light outdoors.  Sort of like the e-Ink displays on certain Kindle tablet readers.  These are totally readable in bright sunlight and not an expensive device.

Click to Enlarge

The "smarts" of the device are also quite superior.  It will monitor voltage, current, power, time since you started charging, energy consumed in mAh (multiply by voltage for mWh), and finally total energy, if you managed to re-charge more than one device.  These modes are easily switched by a single push-button mode switch at any time in your measurements.  Finally, you can set up your experiment and walk away for a few hours, since the unit will also sense when the device is fully charged and then self-disconnect the circuit, ending all charging.  That not only protects the device from overcharging (which is a good standard practice anyway) but all the stats are there recorded for you to read later.  This means you can go do other work while you wait....  like write reports on the SCOS wiki page, or do emails.

This part now appears to be sold out, so substitute:

amazon: Centech Power Meter

Note: Centech has not been evaluated, but is LCD type display

July, 2017

Basic Electricity for Solar Understanding

Click image to enlarge pictures below

This is the place for a simplified discussion and any tutorial training on principles of electricity that are important for understanding solar systems.  Many people learned about electricity in their youth, but have long since forgotten the basics.  In the age of solar systems, suddenly there is a need for increased understanding, since there is now a practical application.  There is an attempt here to minimize the concepts and make it more helpful to non-native speakers of English.

The Concept of Energy

Energy is simply defined as the ability or the capacity to do work.  And there are many forms of energy including nuclear energy, wind energy, water (hydro) energy, and burning coal and fossil fuels.  However, we are more interested here in solar energy:  the energy freely given to the earth daily by our sun.  We often speak of "renewable" energy sources like wind and hydro, however they are basically transformations of solar energy at the origin.  The transport to the top of the mountain for water is actually by solar energy converted to "stored" energy as the water flows down the mountain.  The winds of the earth are created by unequal solar radiation upon the surface of the earth.

There is kinetic energy when things are in motion, or some activity while doing work at the moment, such as an electric light glowing. And there is potential energy, which is really stored energy.  Potential energy resides in an inactive bolder sitting on the top of a mountain, that then gets released when gravity takes over and it falls due to an earthquake.  There is potential or stored energy when we translate electric energy into the chemicals of a battery, where such electrical energy can easily be released later by an electric circuit.  The latter is what solar energy is all about:  Converting the energy from the sun into electricity, storing that energy for later use typically by employing batteries, and then the release of that energy back to electricity when we want to do useful work. We might want to illuminate a room with lights, boil water with a heating element, refrigerate an important vacine in a refrigerator, or run a notebook computer to engage in Bible Translation and other Language Development tasks.

Most of us live near rivers where energy in the form of flowing water is readily seen.  In the olden days often people often redirected water supplies to engage water-wheels that converted some of the freely flowing river water over a wheel that turned a rotating shaft to do useful work.  This might be grinding wheat into flour.  These places were called mills.  Once the free energy of the river was harnessed and transformed into a rotating shaft, this shaft could then be connected to machines to do other tasks.  So one can hopefully see that doing work requires energy;  energy is really doing work.

When it comes to solar systems, we usually talk about storing energy inside batteries to do useful things like power lights in our houses.  There is an analogy (a similar picture) here with the source of the river and its water energy stored, for example, in a reservoir at the top of some mountain, and then we pipe the water to a water-wheel.  In the electrical analogy with water, we have wires that direct electrical energy from a storage source, usually a battery, to something that does useful work, like a light-bulb.

Consider this simple picture of an electrical circuit to the lower-right.  The energy stored in the battery is directed to the light-bulb and if the circuit is "complete" where the energy travels in an unbroken circle, then the light, is "on" and glowing.  If there is a break in the circuit (circle of wires) then the light is turned "off" and no longer glowing.  One could break the circuit by cutting it with scissors, but then it would be hard to reconnect the circuit at a desireable time.  So we introduce a "switch" a device that is designed to break and re-connect the wires thousand of times without wearing out.

But the main points are that once solar energy is converted to stored electrical energy, then there are many useful things we can do with that energy and we can control it as we would like.

You  may be wondering about the "circle" here in the electrical circuit.  Isn't this different than the water analogy?   Well, yes, and no.  The water analogy does indeed fail us at times in understanding electrical circuits, but with hydro power (above) consider this.  The water from the river, once it has done it's work at the mill eventually flows to the ocean.  The sun and its solar radiation, cause the water to transform to vapor and form clouds while also causing the winds that blow the clouds and their water vapor to the mountains.  Then it rains, and fills lakes and streams that then create the river that flows past the mill house.  The "circle" is now complete.  In one sense there is a complete "water circuit" related to water and rivers doing work.  And if I could somehow block the water flow by using a dam of some kind, then the water would not flow, and the mill would cease its ability to do work.  In fact when the mill owner above wishes to stop the mill wheel from turning, they simply block the "sluice" or pipe that directs the water.  it could simply be a sliding door at the start of the pipe.  A kind of switch.

Looking at energy and solar systems:  The solar panel is a device that converts the solar energy coming to earth into electrical energy.  The first solar panels were invented in the late 19th century, and have become better and better over the years, in terms of their abilitiy to capture more solar radiation (energy) and convert to larger amounts of electrical energy.  Even today, most of the sun's solar energy is not captured and warms the ground and panel instead.  Also related to solar systems is the concept of "energy storage" where the captured energy from the sun flows through wires and charges up a battery of some kind.  Later, when we most want to work, for example in the evening when there is no sunshine, we can apply the stored energy found in the batteries to do useful work later.

Power in Comparison with Energy (Work)

There is a difference between Power which is the ability or rate of doing work, instead of talking about Energy, which is the work performed itself, or the potential to do work, as in the case of a battery which might store energy.  When we fill up a battery with electrical energy, we can expect a certain amount of work to be performed later, by the same battery. The "work" we want performed could be to run a motor that pumps water that fills an irrigation ditch for our food crops.  Let's see if we can make any practical illustrations about this.

You have probably heard the term "horsepower" and indeed in the olden days, horses were commonly in use for performing work duties.  So the "power" of an average horse was eventually made standard as to how much work could be performed for a unit of time, say a second of labor, or a minute of labor.  So "One Horsepower" was equivalent to the amount of energy used by the horse over a period to time, to get a standard amount of work done.  Consider this picture.

Here we see one horse, lifting a weight a given distance for a minute or a second of work.  What happens if I hitch two horses in this diagram?  I could expect the weight to move twice as far in a second, or I can lift twice as much weight for the same distance as before.  Power defines how much work can be performed for a given amount of time.  This is often expressed in a formula: 

Work = Power x Time  or  W = P x T

So again, if I double the power, I can get twice as much work done, for the same amount of time.

So how does all this relate to solar systems?  Well probably you have looked as solar panels, and noted that they come in different sizes and also different prices.  Their ability to do work is also measured in Power units called watts.  In this case, and with electricity in general, we don't talk about horses as units, but rather we talk about Watts (W) in terms of the ability for the solar panel to do useful work.  Note that in the horse diagram above, the horsepower can also measured in Watts:  746 Watts to be exact.  For our village setting, work could mean capturing the sun's energy, and converting it to electricity and storing it inside a battery of a known capacity.  It could be that it takes one hour to fully charge a given battery with a solar panel of 50 watts, Then if we increase the size of the solar panel to 100 watts, then we would expect the battery to fill up with energy, in 1/2 the time as before.  In this case 30 minutes.  I get the same amount of work done (filling the battery) but in one-half the time.  This is similar to the one horse above having a partner (two horses) and then they lift the same weight the same distance, but in 1/2 the time as before.  One could easily replace the horse above with a motor that then lifted the weight; the motor would spin faster with the larger solar panel connected to it and get the same amount of work done, but in one half the time.

Concepts Unique to Electricity

So the reader now understands better the relationship and difference between energy and power, but often when encountering a solar system there are more new concepts to address such as voltage and current.  We face the challenge of understanding when say we see a "12 Volt" car battery, the ability to deliver "200 Amps current".  What are these units and how do I usefully interpret their meaning?

For electrical circuits, including those found in automobiles and houses, voltage and current are parts of the whole called "Power".  You already know about Power above as the "rate of doing work".  In other words how fast can I work.  For electricity power gets divided out into two related parts:  voltage and current.  In this section we hope to show the relationships of these two concepts and to power.

Electricity is all about the flow of electrons around a circuit.  The "push" behind the movement of these electrons is called "eletromotive force" or the Voltage.  The rate or the number of electrons moving around is the Current.  Current relates well to the water analogy (picture) above because water has a current as it flows down a mountain.  However, the "push" behind the water is a bit more abstract.  For that we need to get away from the river concept (we don't normally get to alter gravity), and move to pipes and pumps where the pump can be stronger or weaker.

So consider this diagram on the right and please ignore all the fancy notes.  If the pump (voltage) is twice and strong, then we could reasonably expect the current flow to be twice as fast.  We would say the pump or the battery is more "powerful" and we would be correct.  It would have twice the power or the ability to do work (see above) because we increased the "push" or the voltage by twice the amount as before.  So by raising the voltage, we have raised the power of the system.

Some readers will no doubt want a discussion on that part of the diagram that represents "resistance" or really the "load" of the circuit.  For the less advanced reader, just think that the "necked down" part of the pipe, or the "resistor" in the electrical circuit would be where the light bulb was in our other diagrams.  The "R" or "neck" represents the object doing work, like the motor, light, heating coil, fan, or the smart-phone battery we want to recharge.  We are purposefully avoiding the discussion on Ohm's Law here, but you can read about that if you want a more "advanced topic" below in the reference section. 

More importantly for solar applications:

Power = Voltage x Current  or  P = V x C

Which is to say that if you want to know the power of something, you need to know its voltage and current.  For electricity, power is measured in Watts (W). Voltage is measured in Volts (V) and Current is measured in Amperage or Amps (A) for short.

So for a solar panel marked as 100 Watts, and we know that it is a "12 volt" solar panel, then we can expect by the formula above that it would produce 100 watts divided by 12 volts = 8.33 amps.  This of course is what one would expect in full sunlight and no cloud cover in the sky.  The full power output of the 100 watt panel would be close to 100 watts of power.

We tried to make things simple above.  Some of the confusion in all this comes from people talkng about the measurement units, instead of the overall concept.  So Watts (a unit of power) is often expressed into the basic units of current and units of voltage as well.  Therefore the formula above is often merely expressed:

Watts = Volts x Amps  or  W = V x A  or  W = VA

This is all the same thing, but expressed in the units of measurement.

Making this practical:  You are in the village and system that was once working well, is not performing all that well today.  The solar batteries don't seem to be charging up as fast as they used to on a sunny day.  You take your "current meter" (see Tools section) and you wait for a full sunny day, and you measure the current coming down the wire from the roof-top solar panel to the solar controller and battery box (see other sections for explanations of a solar system).  But with the 12 volt, 100 watt solar panel you know about, you only measure 4 Amps, instead of 8 Amps of current.  The solar panel is not working as hard as it should be to deliver energy to the system.  What is wrong?  Probably the front solar panel glass is covered with dust and grime and debris from village life.  Someone should climb on top of the roof and possibly wash the solar panels.  Because you understood the formula above, you could determine that the panel was in trouble without having to actually climb up on the roof to investigate.  You could also determine that the problem was the solar panel, and not the batteries.  Sometimes it's the batteries that are at fault, but not in this case.

Basic Battery Knowledge

The major point for this section is that batteries store electrical energy in Watt-Hours, whereas we often want to talk about how "Powerful" the battery is.  It's not about Power with a battery; it's about how much energy is in there to do useful work.

Think of the battery in your solar setup.  It could be a Lead-Acid battery similar to what is found in an automobile or it could be a new Lithium Iron Phosphate battery (See Battery section).  They all have a similar purpose in that they are like a bucket or a reservoir, or a container that holds energy.  The unit of energy can be expressed in Joules, or in our case is often expressed at Watt-Hours (Wh) or energy.  So just as a container might hold 1000 liters of water, a battery might hold 1200 Wh of energy, such as this large Prismatic type battery shown here on the right.

So, let's go back to our light-bulb circuit above.  If the light-bulb glows and consumes 5 watts (It's the nice LED variety) and brightly illuminates your kitchen table, and if it runs for 4 hours... then the energy (work performed) that night was 5 watts, burning for 4 hours, or 5 x 4 = 20 Wh of energy consumed.  This amount of energy was transferred from the battery.

If you turn on another light for four hours, then add another 20 Wh of energy consumed.  But what about your Codan Radio that runs off your 12 volts solar system?  Each morning you talk to the capitol city in your country, which is very far away, but the radio consumes 200 watts!  However, you only have a conversation for 15 minutes.  That's 1/4 of an hours.  So the energy consumed from your battery, was 200 watts x 1/4 hr = 50 Wh.

So now a typical day you spent 20+20+50 Wh to do lights at night and a radio work by day.  That's 90 Wh or energy.  Do you have that amount in your solar system?  It depends upon the size of your batteries at this point.  If you have an old-style and fragile Lead-Acid battery (see Battery section) and it's a standard automotive 12 V, 100 Ah size, then you might think that a fully charged battery contains 12 x 100 = 1200 Wh (Remember W = V x A).  But you would only be partially correct.  Lead-Acid can only really release 30% of their stored energy, otherwise you hurt the battery and it must be replaced quickly.  So 30% of 1200 Wh, means you only really have 360 Wh of useable stored energy.

(Note:  LFP batteries might appear to be more expensive at first, but because they are lighter, last longer (10 years or more) and can use 80% of their available stored energy... they might actually be less expensive in the long run)

Back to our lights and Codan radio example, we have already used 90 Wh of energy in our daily allotment, and we only had a maximum of 360 Wh to use each day.  Now if we add a computer into the mix, we may be in trouble, depending upon whether you have an older-style computer, or the new kind as mentioned in this Handbook.  With one computer you might only be able to work 2 hrs a day;  with the other kind, 10 hrs each day.  it makes a huge difference.

Quick but Deeper Understanding (References)

It's hard to imagine someone setting up a solar system without some fundamental knowledge of the science of electricity.  However, the concepts above are meant to make things practical and simple.  if you want a deeper knowledge of electricity and circuits created to do real work, then these references will help with the basics... yet they are more than you need to know to maintain a working solar system.

For those of you who are fluent in English and come from a well-educated background then there are many on-line lesson plans, and most go far deeper into the details about working systems than one would really need for understanding a solar system.  But if you want a deep refresher course, one where the materials are in .PDF form and can be downloaded for your own purposes, then consider the Lessons in Electric Circuits, web-site by Tony R. Kuphaldt

Another great resource on the web appears to be the School for Champions - Basic Electricity, web-site by Ron Kurtus.  We prefer the diagrams at this one, plus there are some quizes on the material learned.

No doubt others can introduce further web-sites to look through in this space.  Feel free to contribute if you know of more appropropriate resources out there, but keep in my that we are interested in freely available materials that can be easily copied in terms of their license agreements, since anyone can print these SCOS Handbook pages at will.

Advanced Topics:

The technician's corner.  Most readers will not really want to read this part and might feel "embarrassed" that they don't know or understand the details given here.  Not to worry;  simply skip this part if you are a normal OWL and well, you rely on the technicians in your life to set up custom solar systems.  This section is for the ones who like to make and design there own solar systems with bits and parts from other suppliers, and connect the various sub-systems together.  If this doesn't sound like you, dear reader.... skip this section completely.

Setting Up Solar Controllers for Optimum Performance

Various recommened controller settings can be discussed here with battery issues based on chemistry and thoughts about optimum LVD settings and more.  Why you want to setup and test a specific way.  This topic is for those with a technical background, in support of others on the field.

Xantrex Model C-12

With a much larger physical dimensions (16.5 x 11 x 4 cm)⁴ and a discrete circuit board with easily serviceable electronic parts⁵ the more expensive Xantrex C-12 controller (approx US$ 80) has significant advantages in ease of service, should something fail in the system. However one of its greatest and most desirable features is a programmable LVD cut-out of the netbook “load” when the operating voltage of the AGM battery falls below a user setting. This means that we can set the LVD to anything we want, and would suggest no lower than 12.5 volts as the maximum “depth of discharge” point. 12.6 volts would be much better. Note in the drawing (right), the five user setting controls, specifically the Low Voltage Disconnect and the Low Voltage Re-Connect. Best of all, the control knobs themselves can be removed to further discourage changes later.

Convenient Digital Voltmeter (DVM) probe points are provided to make accurate threshold settings.

Unlike the Morningstar Controller, it is now possible to compensate for field conditions. In reality, many users are not using a proper gauge wire, running from roof-top to controller, and especially from controller to battery. There can be a significant difference between the recorded voltage at the battery terminals and what is “sensed” by the controller, even for short wire run lengths. As high as 3 tenths of a volt. So for a desired LVD of 12.5 volts at the battery, the controller might have to wait for 12.2 volts at its terminals. Finally, we can accurately set the solar controller to maximize run times for the netbook, while at the same time, using the minimum Depth of Discharge (DoD see section below) to greatly extend useful life of the relatively expensive batteries. Once proper settings are established by an expert (consultant), the control knobs can be removed and front panel sealed, reducing “tinkering” later.

Typical Charging Cycles

The Xantrex solar charge controller, like the older Trace Inverter chargers, follow a typical three phase charging method in three distinct phases: “Bulk, Absorption, Float”. The battery voltage will vary during the three stage charging process, as follows:

• g" target="_blank"> {cke_protected}{C}%3C!%2D%2D%3Cstrike%2D%2D%3E>>->>>>->>>>>- end tiki_plugin >>BULK— The first stage of 3-stage battery charging. During this stage the PV (solar) array is allowed to charge at its full output. Once the voltage of the battery reaches the BULK voltage setting, the controller goes to the next stage. Current is sent to batteries at the maximum safe rate they will accept until voltage rises to near (80-90%) full charge level. Voltages at this stage typically range from 10.5 volts to 15 volts. There is no “correct” voltage for bulk charging, but there may be limits on the maximum current that the battery and/or wiring can take.

• ABSORPTION— The 2nd stage of 3-stage battery charging. During this stage the voltage of the battery is held at the BULK voltage setting until a timer accumulates 1 hour (C-12). Voltage remains constant and current gradually tapers off as internal resistance increases during charging. It is during this stage that the charger puts out maximum voltage. Voltages at this stage are typically around 14.2 to 15.5 volts.

• FLOAT— The 3rd stage of 3-stage battery charging. During this stage the voltage of the battery is held at the FLOAT voltage setting. Full current from the PV array can still be delivered to the loads during this stage during the day powering the netbook. After batteries reach full charge, charging voltage is reduced to a lower level (typically 12.8 to 13.2) to reduce gassing and prolong battery life. This is often referred to as a maintenance or trickle charge, since it's main purpose is to keep an already charged battery from discharging.⁶ {cke_protected}{C}%3C!%2D%2D%3Cstrike%2D%2D%3E>>->>>>->>>>>- end tiki_plugin >>

Both controllers here use PWM, or “pulse width modulation” where the controller or charger senses tiny voltage drops in the battery and sends very short charging cycles (pulses) to the battery. This may occur several hundred times per minute. It is called “pulse width” because the width of the pulses may vary from a few microseconds to several seconds.

If the voltage of the battery drops below the FLOAT setting for a cumulative period of one hour, a new BULK or ABSORPTION cycle will be triggered (C-12). This typically occurs during each night. If the battery is full at the start of the day, it will receive only an ABSORPTION charge for 1 hour and then be held at the FLOAT setting for the remaining period of the day unless the battery is discharged.⁷ {cke_protected}{C}%3C!%2D%2D%3Cstrike%2D%2D%3E>>->>>>->>>>>- end tiki_plugin >> Note that the voltage levels of both the Bulk Mode and the Float mode are settings one can control, unlike with the less expensive Morningstar SS-10L model.

Typical Battery Charging Voltages by Type

g" target="_blank"> {cke_protected}{C}%3C!%2D%2D%3Cstrike%2D%2D%3E>>->>>>->>>>>- end tiki_plugin >>There are many different chemistries and construction types for lead-acid batteries. For the best information on your particular battery, please consult the manual from your particular manufacturer. Be particularly careful with Gel Cell models, since they have the largest variance from “normal” and are often abused, fail, overheat or worse, if not charged properly.

Sadly the chart on the right doesn't included “flooded lead acid” batteries, or the kind one typically finds in automobiles that need refills with distilled water from time to time. As of this writing, we are not sure what the correct charge voltages are for such a battery. See chart at right.⁸ {cke_protected}{C}%3C!%2D%2D%3Cstrike%2D%2D%3E>>->>>>->>>>>- end tiki_plugin >> (Sb= Antimony; Ca= Calcium)

It is our opinion that SLA AGM batteries should not be equalized which means you should turn off the “auto-equalize” function on the Xantrex C-12 controller if you are using that style of battery. See “Battery Technologies” section.

1. Far more than you ever wanted to know about “insolation” can be found at http://en.wikipedia.org/wiki/Insolation

2. Solar Buzz. See http://www.solarbuzz.com/technologies.htm

3. See AltE store: http://www.altestore.com/store/Solar-Panels/1-to-50-Watt-Solar-Panels/Global-Solar-Energy-Global-Solar-30W-12V-Framed-Solar-Panel/p5573/ Download spec sheet here as well.

4. www.xantrex.com/web/id/405/docserve.aspx (Brochure)

5. www.mrsolar.com/pdf/xantrex/C12.pdf(Manual)

6. Elements of this text taken from the very nice solar reference: “WindSun Deep Cycle Battery FAQ”; See http://www.windsun.com/Batteries/Battery_FAQ.htm

7. From the Xantrex Manual: “C12 Charge/Load/Lighting Controller Owner’s Manual” – March 2005; 975-0130-01-01 Rev. D; www.xantrex.com

8. From the web site: http://www.batteryfaq.org See section 9: “How do I charge (or equalize) my battery?” which has considerable specific charging cycle graphs by lead-acid battery type.

{cke_protected}{C}%3C!%2D%2D%3Cstrike%2D%2D%3E-->->>>>->>>>>>- end tiki_plugin >

Lead-Acid (Pb) Battery Issues

AGM or Absorbed Glass Mat Batteries

A newer type of sealed battery uses “Absorbed Glass Mats”, or AGM between the plates. This is a very fine glass mat composed of Boron-Silicate fiber. These type of batteries have all the advantages of gelled, but can take much more abuse. Panasonic, Lifeline, PowerSonic, Yuasa and all the rest manufacture AGM batteries. These are also called “starved electrolyte”, as the mat is about 95% saturated rather than fully soaked. That also means that they will not leak acid even if broken - very important to the aviation industry, and therefore considered “non-hazardous” cargo. Therefore they are more easily transported.

AGM batteries have several advantages over both gelled and flooded (liquid filled), and were more expensive than gelled in the past. But recently prices have fallen such that now they are completely replacing gelled altogether, and rapidly closing in on “flooded” batteries.

Advantages of AGM

Since all the electrolyte (acid) is contained in the glass mats, they cannot spill, even if broken. This also means that since they are non-hazardous, the shipping costs are lower. In addition, since there is no liquid to freeze and expand, they are practically immune from freezing damage, which is admittedly more important in northern Canada, not sub-Sahara Africa.

Nearly all AGM batteries are “recombinant” - that is - the Oxygen and Hydrogen recombine INSIDE the battery. These use gas phase transfer of oxygen to the negative plates to recombine them back into water while charging and prevent the loss of water through electrolysis. The recombining is typically 99+% efficient, so almost no water is lost.

The charging voltage profiles are the same as for any standard battery - no need for any special adjustments or problems with incompatible chargers or charge controls as with the older Gel Cell type batteries. And, since the internal resistance is extremely low, there is almost no heating of the battery even under heavy charge and discharge currents. Amazingly the AGM batteries have no charge or discharge current limits (not sure that one should test this however).

AGM's have a very low self-discharge rates - from 1% to 3% per month is usual. This means that they can sit in storage for much longer periods without charging than standard batteries. AGM batteries can be almost fully recharged (95% or better) even after 30 days of being totally discharged (but please don't do this, nonetheless, as discussed more fully in this paper).

AGM's do not have any liquid to spill, and even under severe overcharge conditions hydrogen emission is far below the 4% max specified for aircraft and enclosed spaces. The plates in AGM's are tightly packed and rigidly mounted, and will withstand shock and vibration better than any standard battery.

Even with all the advantages listed above, there is still a place for the standard flooded deep cycle battery. AGM's will sometimes cost 2 to 3 times as much as flooded batteries of the same capacity, although recently we have seen a dramatic price reduction. In many installations, where the batteries are set in an area where you don't have to worry about fumes or leakage, a standard or industrial deep cycle is a better economic choice. AGM batteries main advantages are no maintenance, completely sealed against fumes, Hydrogen, or leakage, non-spilling even if they are broken, and can survive most freezes. Not everyone needs these features.

No Equalization Charging. Unlike the more “Flooded” type batteries, equalization charging to extend the life-time of the batteries that some charge controllers allow for “automatically” are not to be used. In fact, this will decrease the lifetime of AGM batteries due to electrolyte loss via the vented valves supplied. Once electrolyte is expelled it is lost forever. However, this is one less maintenance headache that the user has to concern themselves with. Plus there is no need to ever refill the batteries with distilled water, for the lifetime of the battery.

So when considering solar systems for our national colleagues to use, the combinations of increased safety, easier transport, no-refilling and no equalization charging are considered great advantages.

Consider Manufacturing Date Codes

Each manufacturer of lead-acid batteries has their own system of stamping on the unit the date of manufacture. This becomes important for AGM style batteries especially as their capacity generally degrades in time “just sitting around” on the shelf. This can be an important factor in a third-world setting, where the supplier in a port town, has had stock sitting around for a very long time, and the store- reseller has not taken the time to maintain a trickle charge of the batteries while waiting for sale.

If possible, contact the manufacturer of the given part directly on email and convince them (if possible) to tell you their system of date code stamping. Then you can easily verify the claim that the given stock you are about to purchase indeed has been manufactured recently.

Valve Regulated Batteries

All gelled (Gel Cell) are sealed and are “valve regulated”, which means that a tiny valve keeps a slight positive pressure. Nearly all AGM batteries are also sealed valve regulated (commonly referred to as “VRLA” - Valve Regulated Lead-Acid). Most valve regulated batteries are under some pressure - 1 to 4 psi at sea level.

Amp-Hour Capacity

“All deep cycle batteries are rated in amp-hours. An amp-hour is one amp for one hour, or 10 amps for 1/10 of an hour and so forth. It is amps x hours. If you have something that pulls 20 amps, and you use it for 20 minutes, then the amp-hours used would be 20 (amps) x .333 (hours), or 6.67 AH. The accepted AH rating time period for batteries used in solar electric and backup power systems (and for nearly all deep cycle batteries) is the “20 hour rate”. This means that it is discharged down to 10.5 volts over a 20 hour period while the total actual amp-hours it supplies is measured. Sometimes ratings at the 6 hour rate and 100 hour rate are also given for comparison and for different applications. The 6-hour rate is often used for industrial batteries, as that is a typical daily duty cycle. Sometimes the 100 hour rate is given just to make the battery look better than it really is, but it is also useful for figuring battery capacity for long-term backup amp-hour requirements.”10)

g">So what is our expected performance per average netbook? How long can we reasonable expect to supply power to a netbook while in use in the day? Consider this graph from Power-Sonic (right).11) Reading the chart to the right, let us consider a typical low power Asus 1101 HA netbook, that is running at 0.80 amps and while in use during the day. To reach the LVD point of 12.5 volts (see “depth of discharge”-next section) one would expect a “run time” of approximately 6 hrs. But this assumes that there is no supplemental solar energy also going to power the device even during heavily overcast days. Reality can yield much better performance than indicated in this pure load chart. With some of the new third generation solar panels, the “shade” performance is quite exceptional. It is not uncommon to see on an “overcast” day, enough solar energy to be completely sustaining a netbook, via the solar charge controller alone, while leaving a small “trickle charge” left over for charging the battery at the same time.

So, does one need to specify an 18 Ah battery, or a 35 Ah battery for everyday use? The answer depends upon the number of expected work hours for the end user, and also the number of expected “totally overcast” days, per average week. If the realities of village life means that one can only expect 4 hours of good day-time work, due to village level obligations to family members, then probably an 18 Ah battery would suffice. If the user is going to truly work 8 hrs a day, and perhaps 3 of those hours will be into the evening, then certainly consider purchasing a 35 Ah battery instead. If 12 volt house lights are in the equation, then go further, but also go for larger solar panels than 40 watts.

Remember that if one constrains the work to only during the day, it is possible with a 30 or 40 watt solar panel to completely remove the battery from this circuit entirely (in theory). The panel, even in overcast conditions, would charge the netbook's internal battery, and certain netbooks are capable of running 8-10 hours now on their internal Lithium Ion batteries. Such a “battery eliminator” circuit might be advantageous to fight off potential familial demands to use the battery elsewhere, a perennial problem in the field.

Lead-Acid Battery Life Issues

Depth of Discharge

A very important factor for battery lifetime is the average level of discharge over the lifetime of the project. Basically lead-acid batteries are designed to be fully charged at all times. While using the batteries, the overall level of discharge should be keep to a minimum, and still achieve daily work goals that are practical for the given work conditions. Consider this chart: 12)

g">

g">A consistent “depth of discharge” (DoD) of 50% (above) will yield a standard lifetime of 1000 charge/ discharge cycles per battery. If the user is constantly using the system each day, and recharging via solar, one would only expect their lead-acid batteries to live for approximately 3 years. This discharge level corresponds to 50% of the usable electrolyte solution and an operating voltage at the terminals of 12.5 volts.

However, if the user consistently discharges to the 30% level, or approximately 12.7 volts then the battery lifetime jumps to 2000 charge/ discharge cycles. Suddenly lifetime moves out to 6 years without the need for battery replacement.

Since the price of solar and netbooks is rapidly decreasing, but lead-acid batteries are not, this DoD issue needs to be monitored closely. Note too that “total lifetime kWh” peaks at the 30% discharge level.

Capacity Monitoring

g">The goal of the solar controller is to protect the lead-acid battery, while allowing useful work to be done as required from the battery. As we have seen, the total number of solar cycles for the lifetime of the battery is dependent upon the average LVD cut-off (there are other factors as well). “Capacity” or the ability to store a given amount of energy is 100% for a newly acquired battery, but diminishes over time. Capacity can be monitored in the evenings for a “no load” situation. Using a Digital Voltmeter (DVM) at the battery terminals, turn off all loads including the netbook, any lights and anything else attached to the battery (you can leave the solar controller connected), and then refer to this chart on the right to see your present battery status.13)

So if my battery was held at a float voltage of 13.7 volts during the day in good sunshine, but at dusk with no load, the voltage at the terminals was found to be 13.0 volts or less, then one can conclude that your battery is at 80% of its normal capacity. It has “aged” that much, where age is relative term here, and not based on the actual number of days of use. Note that temperature has an effect here too, but is beyond the scope of this particular paper. See reference for such details.