Laptops and Solar Power in the Field

by Alan on May 25, 2012

I live and do research in the Bolivian Amazon where there is a brutal mix of intense sun, heat, humidity, dust and rain mixed with a consistent lack of reliable electricity and potable running water.  I’ve been here for a year now and have learned many lessons along-the-way about how to do shoe-leather ethnographic research in these harsh conditions while still having some of the modern kit—many would say necessities—for collecting and analyzing data.  For me this includes a laptop for nightly transcription/entry, editing, fleshing out and—if there’s time—coding of my field notes and audio interviews. Yes, this can all be done without a laptop but it goes much smoother with one and keeps me from putting off analysis and processing until I’m “back from the field,” the death knell of iterative research.

But laptops need power, and a safe, cool, dry, relatively clean environment to operate in. My solution came in two parts.  First, protection and care of my laptop is provided by a Pelican 1620 everything-proof case and a reusable Eva-Dry 500 mini-dehumidifier.  The only other choice in this regard is to buy a ruggedized laptop like the Panasonic Toughbook line, but these computers are all Window’s machines and typically cost anywhere from $3,000 and up—and they’re still not submersible which likely means you need a protective case anyway. The second part of my solution is solar power.  To read more about how I tackled this daunting challenge (including an exhaustive list of my equipment) check out the rest of the post after the break.

Portability and Durability

So what does it take to make solar work in the field? My first concern was portability and durability.  This meant that I did not want to have 40-60lb glass-encased panels to lug around in dug-out canoes. With this in mind I purchased my first panel, a PowerFilm R-28 rollable 28W thin-film photovoltaic that weighs about 2lbs, when I started research in lowland Bolivia over two years ago.  My lastest panel, a UNI-SOLAR PVL-68 68W thin-flim panel that weighs 8lbs, was purchased just a couple of months ago through a new research grant.  You might think the new panel was likely about twice the price of the first but due to dramatic changes in the thin-film photovoltaic market over the last two years, the opposite is true.  What has been bad for American industry (it was China bullying into the markets with huge subsidies to its manufacturers that in fact caused the Obama administration’s stimulus-darling Solyndra to go out of business) has benefitted solar consumers. I was able to purchase a UNI-SOLAR 68W rollable solar panel for $157, almost half what a new PowerFilm 28W rollable panel still costs ($300 new on Amazon) but with over twice the power output.

Total Cost in Time and Money

The current price of solar is the good news but when it comes to doing solar right in the field the best advice I can give is to call an expert or friend who has actually done this sucessfully and be prepared to spend between $1,000-$2,000.  Failing that, be ready (and eager) to do this yourself by learning everything you can about amperage/current, voltage, shorts, appropriate wire gauges, fuses, inverters, converters, controllers, lead-acid, li-poly and ni-mh battery technology, meters, etc.  Anyone who tells you this is easy is either ignorant or lying to you.  My current 124W setup cost about $2,100 total including lights, fans, converters, chargers, cables, etc. (see my equipment list below for all the gory details) and three li-poly batteries but due to the price drops I described above  and if you stick with just one 100 amp lead-acid instead of li-poly, you could build a more powerful system right now (136W) for $850 less ($300 on a battery instead of $600 and $200 on two 68W panels) especially if you catch this sale at simpleray.com.

Alternatives?

You could always opt to buy a pre-packaged system but I cannot vouch for the whether it is even possible to transport such a system by commercial airline to a field site. If you can manage that then I can suggest a couple of options. Powerenz Inc. out of Kennesaw, GA sells the LFP40 Waterproof System for $3,250 which includes a 75 watt solar panel and a 40 amp Lithium Iron Phosphate battery that can be discharged to 30% (which means an effective energy storage of [(40A*13V=520)*(.70)=364 watt-hours). And EcoGeekLiving is selling a different version of the Powerenz product with a slightly smalled panel (64W) for $2,900. A word of warning, though, both of these products while ‘waterproof’ during temporary use are not meant to be left outside permanently, but instead stored inside and used as-needed.  Rollable panels (e.g. by Powerfilm or UNI-SOLAR) do not suffer this limitation and can be semi-permanently mounted/installed and left out with no adverse impact to the panels.

Power

But how much power do you need? Well, this depends.  If you’re doing what I do, which includes lots of daily fieldnotes and recorded interviews followed by nightly word processing/editing/coding, then you’re going to want enough power available—rain or shine—everyday to be able to work for about 5 hours on a laptop, run 6w lights for about four hours, run 6w fans for 5-12 hours, recharge ni-mh batteries on occasion, recharge a smart phone everyday, run a portable projector for movie night once a week, and occasionally recharge camera batteries or a mini-dehumidifier. So all-of-a-sudden the size of you laptop battery doesn’t matter as much as the efficiency of your computer’s power usage.  I have a MacBook Air so it is actually quite good in this regard so that if I have my screen brightness set to 50% and am not on wi-fi or bluetooth or blasting music I get 6-7 hours of battery life on one charge of its 50WH battery-or about 7 watts/hr. This is not typical of your average 13-15inch laptop, though most have improved dramatically.  Still, expect that an economically-priced Dell 15in laptop like the Inspiron i15RN-2354BK will get about 4.5 hours of life on its 48WH battery for a power usage rate of 11watts/hr.

In total, then, you’ll want enough charging power and reserve power to supply power even if it is completely cloudy and raining for 4-5 days straight.  Luckily, cloudy and rainy means you use fans less—unless, of course, you need to wash and dry clothes when there has been non-stop rain which requires fans unless you want everything to wreak after staying damp for several days. I estimate 50WH/day are needed for computer work, 100WH/day for fans, 25WH/day for lights, 25WH avg. for misc other. That’s 200 WH/day total.  So your reserve power supply for four cloudy days should, ideally, be 800WH.  With a lead-acid battery at 12V that means (800/13) 61.5 amps of available power (@ 13V in a fully charged lead-acid battery) .  But lead-acid batteries don’t work like li-poly laptop batteries so you need to get that 61.5 amps from your batteries while leaving 40% of their power unused so that you don’t ruin their life-span. In the end, you should be looking for a 100 amp sealed lead-acid battery, or a smaller lead-acid battery and additional (more expensive) li-poly batteries. Due to the weight and airplane-unfriendly nature of lead-acid batteries, you’ll have to look for one as close to your field site as possible. Friends living in big cities with access to bus courier services are a big help here. Unfortunately, batteries of this size and specification will cost more in the field than in the U.S.—likely around $200-300 depending on how big you want it. Full disclosure—I’m about 17 amps short of my 61.5 amp recommendation when you include 60% of my 33 amp lead-acid battery (257WH) and 320WH worth of li-poly batteries.

Conclusion

Can you do it? Yes, of course.  Is it more hassle and money than you expected? Probably so. Check out my equipment list below and good luck!—or as they say here in Bolivia “exito” (success).  If you have any questions/comments/suggestions, please leave a note below.

 

{ 2 comments… read them below or add one }

Andrew Tarter May 26, 2012 at 10:37 am

Alan, this is awesome, and most helpful, especially as I consider similar issues before heading to the field. Thank you!

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surveillance systems January 8, 2013 at 2:17 am

From my consideration this post is really awesome. I'm assigned for a field job and planning to use solar power for electricity supply. This post helped me quite a lot to know more about solar power in the field. Thanks.

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