12V systems are currently the cheapest and most practical as far as storage is concerned - an associate of mine was telling me that from wholesale sources car batteries can be obtained for ten or fifteen dollars. Electricity can be generated from windmills, sunlight, or even human power and can be used to charge a battery using very simply electronics. Converting 12V DC to 120AC is more difficult, but commercial units are available. The downside is that eventually any kind of battery is going to wear out and won't recharge any more.
Offered by Michael.