Nokia has finished a research project that's been testing the feasibility of harvesting solar energy to power a mobile phone. The test involved five prototype feature phones equipped with built-in solar chargers that were distributed to various regions around the world to test under different climate conditions. Overall, Nokia finds that solar-powered phones are possible but very challenging and, at its current state, impractical.
Two of the prototype solar-powered phones were tested in the Arctic Circle, while one was in southern Sweden, one in Kenya, and one on a sailboat in the Baltic Sea. And it turns out that location did play a major role, as the phone had better performance in areas closer to the equator where there was more direct sun. However, the power generated from the built-in solar charger was only able to supply enough energy for the device to be on standby with a very limited talk time.
Other limitations included the small size of the phones, which meant small solar panels. The angle of how light entered the solar panels was also important as was the amount of light that could pass through the phones' weatherproof casings to get to the solar panels. Also, since the phone constantly needs light to stay charged, the phones can't be carried around, as most folks do, in a pocket or purse.