As the great site lightingafrica.org points out, many developing countries are suffering from a lack of mains electricity, often linked to lower rainfall that affects hydroelectric power plants. In Hall 7 in Mobile World Congress, Barcelona, there were various companies with solar power solutions, many of them in a much further stage of development than I've seen recently. Suntrica are based in Finland and have specialised in building cheap solar panels that can be incorporated into clothing. Like their competitors, the solar panels first charge an internal battery, and this in turn is used to charge the external device.