Energy harvesting is otherwise known as power harvesting or energy scavenging. It is the use of ambient energy to power small electronic or electrical devices. That means solar cells on satellites, heat powered sensors buried in engines, vibration harvesting for helicopter electronics and the wind- up radio or lantern. However, there are also several more esoteric options.
Energy harvesting has reached a tipping point. This is because the necessary lower power electronics and more efficient energy gathering and storage are now sufficiently affordable, reliable and longer lived for a huge number of applications to be practicable. From wind-up laptops for Africa to the wireless light switch working from the power of your finger, these things are either available or imminently available. And photovoltaics, long used in aerospace, has come down-market, even to road furniture but it has much further to go even to disposable solar film and even solar paint. The first solar powered watches and phones have appeared. Some new photovoltaic technologies are printed reel to reel at low cost, the resulting film working off heat as well as light. For example, Sony is commercialising flexible solar cells for indoor use.