According to the Guinness Book of World Records, the city of Yuma in Arizona is the sunniest place on earth. Of the possible 4,456 hours of daylight each year, the sun shines in Yuma for roughly 4,174 hours, or about 94% of the time. But if you’re not one of the city’s 77,000 inhabitants, what’s the best part of the world to have a solar powered mobile phone? After our four-month field study, we have a better idea of the answer to this and many other questions.
How well do solar powered phones work in Africa?
Near to the equator Amos, our Kenyan tester, was able to harvest charge for nearly 12 hours a day with Lokki, our solar powered mobile phone prototype. His best charging current was 32mA. If we assume the peak theoretical harvesting time is * peak*2/π, Amos’s theoretical maximum harvesting is 230mAh. However, his actual best was 134mAh, or 60% yielded capacity of the theoretical maximum. Nonetheless, in 59 days, Amos gained 20 hours talk time or sufficient standby for 41 days. If you ignore the variations in weather, at the equator these values should stay the same throughout the year.