A group of volunteer engineers are finishing the design for a home-brewed wind turbine that will bring electricity to off-the-grid Guatemalan villages by this summer.

After the U.S. engineers finish the design, local workers in the town of Quetzaltenango will manufacture the small-scale turbine. It will produce 10-15 watts of electricity, enough to charge a 12-volt battery that can power simple devices like LED lights.

"They're replacing kerosene lamps, if anything at all," said Matt McLean, a mechanical engineer by day and leader of the wind-turbine project by night. "The biggest driver is just keeping the cost way down. We're shooting for under $100, which is a challenge, but we're in that range."

The effort comes amidst recent efforts to bring new light and power to small towns in the developing world. An estimated 1.6 billion people worldwide are without electricity, and many of them are forced to light their homes with kerosene. Using one of these lamps is like smoking two packs of cigarettes a day, says the World Bank, and the lamps present a significant fire risk. That's why many startup companies, such as d.Light, are trying to bring cheaper LED lights to homes, but they still need a solution for producing power locally.

That's where organizations like Engineers Without Borders come in. Founded in 2002 by Bernard Amadie, a professor at the University of Colorado-Boulder, it has grown to more than 10,000 members in over 250 chapters. According to Cathy Leslie, the executive director of the U.S. organization, 340 projects are underway.

The turbine was created by the Appropriate Technology Design Team of EWB's San Francisco chapter. Team members like Malcolm Knapp and Heather Fleming spend their nights and weekends inside D2M's design shop trying to perfect low-tech gadgets for people 2,500 miles away. D2M, which is Knapp and Fleming's employer, donates the lab space for after-hours use by the EWB team.

Unlike the large-scale assemblies found in wind farms, the roughly two-foot-wide and three-foot-tall turbine has a vertical axis. McLean said that orientation worked better in the choppy conditions likely to meet the turbine out in the field, where it'll be bolted on to buildings, towers or even trees.

The turbine, which Fleming refers to as a "she," is undergoing its final tweaks. Next Sunday, the prototype will undergo its next-to-last build before Fleming and another volunteer head down to the Guatemalan manufacturing facility, XelaTeco, with the building plans in hand.

The engineering team had to make their design simple enough that it could be assembled from cheap and widely available components. As a result, their plans call for building the turbine out of hard plastic (or canvas) bolted on to a steel-tube structure. The rotor, which creates mechanical energy from the movement of the blades, runs into an alternator (actually a cheap DC motor running in reverse), which converts the mechanical energy into electricity.

"We've had to simplify the way we were thinking and get rid of the idea that everything had to be as efficient as possible," McLean said.

For instance, one key obstacle was creating a good bearing system to reduce friction within the turbine. Steel bearings proved unavailable to the Guatemalan manufacturer. Instead, the designers were forced to dig deep into their bag of tricks, eventually pulling out Teflon tape.

"It's normally used for sealing pipes," said McLean. "But it's a very low cost way of reducing friction."

XelaTeco, for its part, received seed funding from the Appropriate Infrastructure Development Group, a nonprofit dedicated to incubating for-profit businesses in developing countries. AIDG's goal is not just to bring cheap wind-powered generators to Guatemalan villages, but also to build self-sustaining businesses that are well integrated with the local economy.

"For us, this is hopefully the start of a lot more projects like this in other areas as we start more businesses," said Peter Haas, executive director of the AIDG.