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Plant Microbial Fuel Cells let you enjoy both plants and solar energy at the same time!
Plants use light to produce sugars, and some of those sugars get deposited into the soil via the plants' roots. There, the plant sugars nourish soil bacteria, and with some clever use of electrodes, you can steal a little of the metabolic energy from those bacteria.
Essentially, you're using a living plant as a solar cell. It doesn't give you very much electricity but it's cool. 
