Researchers at Wageningen University have developed a fuel cell that runs off electrons present in the soil around living plants' roots. During photosynthesis, organic material is produced that the plant can't use, which is then secreted through the roots. Bacteria in the soil break down this organic material, which releases electrons. All that's needed is an electrode to capture those electrons and you've got electricity.
This is not a new discovery, of course. Plants have been used to power LED lamps, clocks and even as an interactive computer tool. What the Plant-Microbial Fuel Cell does is improves upon these ideas in size and efficiency.The university says, "Plant-Microbial Fuel Cells can be used on various scales. Initially on flat roofs or in remote areas in developing countries and later, when larger effective surface areas become feasible, central grids can be realised in areas of marshland. The researcher thinks that green energy-producing roofs will become a reality within a few years and production on a larger scale will follow suit soon after 2015."
Right now the technology is only able to produce about 0.4 W per square meter of plant growth, but the researchers think that soon they'll boost the output up to 3.2 W per square meter, which would allow a 100-square-meter green roof to power a household with an average energy consumption of 2,800 kWh per year.
The plants that can be used include any common grasses as well as rice in warmer climates. The major benefit to the Plant-Microbial Fuel Cell over other renewable energy technologies is that it doesn't compete for land use like solar panels, wind farms and biofuel production do since the electricity production is largely happening underground.
The researchers have created a company called Plant-e that plans to have a product on the market by next year that could be used to power things like LED lights, laptops and cell phones. On a larger scale, the company has installed the first proof-of-concept electricity-generating green roof at the Netherlands Institute of Ecology building.
Below is a video about the technology, made by Plant-e.