Just to back this point up, I have an atmel 328p (auduino duo) thats been running on single tiny solar panel, and 5 farads of super capacitor for about 4 years.

Just to back this point up, I have an atmel 328p (auduino duo) thats been running on single tiny solar panel, and 5 farads of super capacitor for about 4 years. It transmits a temperature reading every 30 seconds over rfm12b radio. (obviously the panel keeps the charge topped up, but it easily lasts through the night and a very cloudy day. It even works indoors. )