Now this is nifty.
We Make Money, Not Art interviews, Gilberto Esparza about his Plantas Nómadas (Nomadic Plants), an autonomous walking robot that is powered by a combination of solar cells and a microbial fuel cell. When the fuel cell output drops beneath some threshold, the bot seeks out a water source, extends a proboscis and refills the fuel cell. Additional water is used nourish a colony of on board plants.
Gilberto’s earlier work is equally interesting. Parasitos Urbanos (Urban Parasites) (flashless site) was a series of robots inductively powered from electrical transmission lines that would move through the urban environment mimicking sounds they encounter.