Scientists have known for some time that an electrical charge could be harvested from the metabolic processes of bacteria living in soil but the effort required to achieve this was time consuming for a very low power output. But a team of Harvard scientists has used the idea to design an inexpensive battery, a microbial fuel cell, which can produce enough current to power LED lights and charge cellphone batteries in rural Africa.
The device is simple to create, consisting of a graphite cloth (the anode) placed in the bottom of a container, covered with soil and a length of chicken wire (the cathode). A conductive wire connects the anode and the cathode to create a circuit, with an LED connected to the circuit. As the microbes eat the waste in the soil, they produce electrons which move through the bacteria network, moving from the graphite-cloth anode through the conductive wire to get to the chicken-wire cathode. As this current flows through the circuit, an LED lights up.
The scientists, calling themselves Lebone, estimate that a fuel cell measuring 1 square meter would produce 1 volt, which could charge a cell phone and 5 square meters could power a lamp or a fan. This would be useful in rural Africa where people often walk several miles to charge a phone or for students to do homework by an electric light at night.
In June 2009 Lebone carried out a trial in Namibia where they used 100 MFCs made from small canvas bags that were linked for increased voltage. The bags were filled with dirt and buried, and then watered to keep the microbes active. The buried cells could produce power for months. Over the next three years Lebone plans to roll out their energy/lighting system in villages in Namibia and have been awarded a $200,000 grant from the World Bank to support an 18 month trial.
Top image source: Geogrowers
For more attend: Energy Harvesting & Storage USA 2009