Solar power is pretty inefficient, taking a long time to charge up and only doing so in bright, direct sunlight. But new technology is working against these issues, including the new Solar Egg from XPAL.
The Solar Egg is designed to charge in "medium levels of natural light," meaning it works even when not lying flat on a totally sunny day at noon. In fact, it supposedly gets a 90% charge in four house of mild sunlight. Charge that can then be used to juice up your phone or PMP. Look for it to start shipping next month for a TBD price.