Microbial fuel cells, which use electrodes in dirt to power a small motor, have long been more or less a laboratory curiosity. Because they generate such a small amount of power, developing them to charge devices would not be practical in places where electricity is readily available. However, Lebônê Solutions, a startup based in Cambridge, MA, aims to use microbial fuel cells to provide power to Africans who are off the grid. In some parts of Africa, a small amount of energy is enough for a few hours of lamp light in the evening, or for powering the ubiquitous cell phones–something that some residents will walk five hours to a generator to do, says Aviva Presser, a cofounder of Lebônê. The company is made up largely of Harvard University alumni and current Harvard students originally from African countries.
With funding from the Harvard Institute for Global Health, the team has recently completed a pilot study in Tanzania, where members brought six basic microbial fuel cells and taught residents how to use them. The team organized village meetings where team member and Tanzanian native Stephen Lwendo explained how to make the fuel cells.
The team found residents receptive to the idea of easy-to-grow power and keen to use the fuel cells to charge cell phones, run radios, and provide more light. “In Africa, people want to power [small] DC devices,” as opposed to large AC devices like a refrigerator, says Lebônê cofounder Hugo Van Vuuren, a Harvard graduate and a South African native. The team hopes to develop the technology to make it competitive with other renewable energies in countries across Africa. Microbial fuel cells could have a distinct advantage because they are initially cheaper to build than a windmill and easier to set up than solar panels. What’s more, they could last up to 10 years, says Lebônê cofounder David Sengeh.
Instead of using hydrogen as a fuel, as do conventional fuel cells, microbial fuel cells use naturally occurring microbes to generate power. Bacteria live in the anode, where they eat glucose, sewage, or other waste water, and turn that into electrons and protons. The bacteria transfer electrons to the circuit, which provides small amounts of power.
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.