Keeping your phone fully charged by placing it on a windowsill beats having to spend your own money to charge it. Yet as appealing as the concept sounds, the solar-powered gadget market is off to a slow start. That is, unless you’re in Kenya. This month, Safaricom launched an inexpensive cell phone (in dollar terms) from China’s ZTE Corporation with an integrated solar panel and interest in the device is high. Despite the technical shortcomings, this signals to handset makers that they may find success in regions of the world with erratic or underdeveloped power grids before they can tailor the technology for eco-conscious tech junkies in these parts.