It looks like Nokia won't be getting into the solar powered cell phone business any time soon. The mobile phone manufacturer just completed a research project in which they've been testing the feasibility of harvesting solar energy to power a mobile phone, and overall they found that solar powered phones are indeed possible, but are very challenging and are currently impractical.
The test involved five prototype feature phones equipped with built-in solar chargers that were then dispersed to various regions around the world to test under different climate conditions.
Two phones were tested in the Arctic Circle, one in southern Sweden, one in Kenya, and one on a sailboat in the Baltic Sea. Location ended up playing a major role in performance. Researchers found that the phone had better performance in areas closer to the equator with more direct sunlight. Even still, the power generated from the built-in solar charge was only able to supply enough energy for the device to be on standby with very limited talk time.
Other issues included the phones' small sizes, which meant they had to use small solar panels. The angle of how light entered the panels was also found to be important, as well the amount of light that could pass through the phones' waterproof casings to even get to the solar panels. Because the phones need to constantly be exposed to light, they also could be carried around in pockets or purses like most people normally would.
In other words, Nokia will not be making solar powered phones until it becomes more feasible and technology advances significantly.