To make the fuel cell, the team put graphite cloth–the anode–in the bottom of a bucket along with chicken wire–the cathode–and microbe-laden waste, either mud, cow manure, or residue from coffee crops. A layer of sand acts as an ion barrier while salt water helps the protons travel more easily. The team adds a power management board (the only device that the villagers will most likely have to import, says Presser) to regulate the power and send it to a battery. Such a fuel cell can run a cheap, efficient light-emitting diode (LED) for four to five hours per evening. “We’re hoping the entire system will be around $10 when we’re ready,” says Presser.
“The beauty of it is it’s a self-sustaining system,” says Derek Lovley, a professor at the University of Massachusetts Amherst, who is not involved in the work and who published initial studies on microbial fuel cells in 2002. Using LED lights is “a nice, practical application for this, if they can get it to be simple and inexpensive,” says Lovley. “This is actually, as far as I know, the only current practical application of [microbial] fuel cells.” Right now, most microbial fuel-cell work is research based, although there have been attempts to use microbes in fuel cells to treat waste water.
How much power the microbial fuel cell can generate depends on the area of the graphite sheets. About one square meter of fuel cell yields one watt, which could recharge a cell phone, according to Van Vuuren. Five square meters can power a portable stereo, fan, or small light.
For the next test, due to launch in December in Namibia and funded by the World Bank, the team plans to couple a new fuel-cell design with conventional high-efficiency LED lights. For that trial, Lebônê will make 100 fuel cells and ultimately hopes to reach up to 3,000.