Cutting all the wires: Solar power in the field

by Matt Blair
Posted: 8/25/2004

For the past few years, HumaniNet has been working to find the most inexpensive, easy-to-use technology for humanitarian teams who need to communicate from anywhere, to anywhere. Satellite modems, like the RBGAN, have become a proven solution because they can be used in remote locations, independent of any local telecommunications infrastructure.

These remote locations are also frequently "off-grid", away from wired power grids, or energy infrastructure of any kind. Laptops, PDAs, cell and satellite phones all have batteries, and even the RBGAN can operate on its internal battery for short periods of time. But in a truly off-grid situation, how can you recharge? Once you've cut the communication wires, how can you cut the electrical wiring, and attain true independence of movement?

Using a generator or continuously running a vehicle engine is impractical because it provides far more power than most electronic communication devices need. At the same time, recharging many electronic devices can take hours, so charging them from a vehicle battery is not always advisable. Most car/truck batteries are designed to maintain a relatively high charge, and deep, frequent discharges will dramatically shorten the life of the battery, and/or diminish its performance.

For these reasons, we have had our eye on solar power, and believe it is an interesting option worth considering in many remote locations.

I recently attended a seminar and several exhibits at the American Solar Energy Society's SOLAR 2004 convention in Portland, Oregon. Most of the solar equipment on display was designed for fixed, long-term installation, but in talking with vendors, and through subsequent research, HumaniNet has discovered several systems which may be of use in the field. The following examples could be quickly deployed with minimal technical hassle and cost.

The Portable Energy System by Sunwize is designed specifically for laptops, satellite phones, cell phones, GPS units, and 'gadgets' of similar size and power requirements. It is slightly larger (10.5 by 15.5 inches, or 26.7 by 39.5 cm) than the average laptop computer, but less than 2 cm thick and weighs only 2.5 lbs (about 1.1 kg). Despite its low weight, this is a solid, well-reinforced panel. It provides power output up to 8.5 watts with a variety of DC outputs from 3-12 volts. There is also an add-on panel available, called the System Doubler, that can increase the power output.

If you need something less rigid, literally, take a look at the PowerFilm line by Iowa Thin Film Technologies. These flexible solar panels can actually be rolled up for storage and transport, and there are a variety of adapters available to charge batteries or provide a 'cigarette lighter' connection to your electronic devices. The panels are about a foot wide (about 30.5 cm) and vary in length from 21 to 73 inches (about 53 to 186 cm). The weight of the longest panel is 1.9 pounds (0.88 kg). When rolled, even the longest panel is about the size of a compact sleeping bag.

Iowa Thin Film's informative website provides details about using these panels to charge batteries and to directly power electronic devices. Each page provides a chart that translates the technical specifications into real-world charge times and "application run times" for several scenarios.

The same company has also integrated this flexible panel technology into a series of 'army tents' that provide shelter and power at the same time. The solar-equipped tents can generate between 200 watts and 1 kilowatt of power, which would be stored in a bank of batteries, and could then provide power for a variety of applications, including mobile communications.

If your ambitions for solar go beyond charging batteries or powering a single device, putting a system together can require detailed research into inverters, charge controllers, line conditioners, deep-cycle batteries, etc. The EN-R-Pak is an all-in-one 'compact power center' that eliminates a lot of that complexity. It includes a solar panel and a single battery unit (18 by 14.5 by 12 inches, or about 46 by 37 by 30 cm) that integrates a battery and everything else you need to provide up to 200w of 110v AC power or 15-amps of 12 volt DC in one single unit. When fully-charged, it can provide 40 watts of AC power for twenty hours of operation. The total weight of the panel and the battery unit is 115 lbs, or just over 52 kg.

During the solar conference, I also attended the "Basics of Using Solar Energy in a Disaster" seminar. A few key points of the presentation were:

Negotiating mutual aid agreements, "push-button" contracts, and MOUs with other organizations in advance, before deploying to the disaster area, is vital. This can include sharing of equipment, staff, logistics support, communications, and other resources.
Training, drills, exercises, and prior planning are essential to an effective response. Don't plan to figure out how to use solar in the field.
Carefully consider the lifecycle cost of solar versus gas/diesel generators during a disaster. While the initial cost of solar may be higher, what effect will the disaster have on the price of fuel needed to run the generators?

We hope this article will encourage more discussion of mobile power solutions among humanitarian teams. If you have any experiences with solar in the field, or would like to partner to explore solar projects, please let us know by sending email to info@humaninet.org.

For additional information on portable power, see the Power Options section of Vern Gillespie's Mobility Portal.

back to Power Solutions index page