We have been testing the possibility of powering mikroMMB boards with Solar energy. Having 4 solar panels connected in parallel, each giving 4,5V with maximum of 80mA, we have achieved some great results.
Here's the video that demonstrates "Paint" example running on a 100W standard yellow light bulb.
It can be a great benefit to have some kind of autonomous power supply, when no other energy is available nearby. Picture yourself having MP3 player on a beach on a sunny day, that can be powered with solar energy. Or having a solar powered GPS device with TFT display when you are lost somewhere in the mountains.