A crazy guy tried a quite interesting potato-powered server experiment more than two years ago. He powered a very-low power server with five potatoes! After a while the experiment was terminated because potatoes rot
The CPU is a Microchip PIC16F876 running with a 76.8 KHz clock and a nominal 1.5V supply voltage (somewhat outside the manufacturer's specifications). At this speed and voltage, it draws 20 microWatts (0.00002 Watts), or roughly 100,000th to 1 millionth the power of any Intel 386 board I know of. It connects via SLIP at 4800 baud.