There are two types of solar energy normally collected: thermal and photovoltaic. Thermal energy is collected by allowing the sun to heat up a working fluid (like water) and you can store this hot water in an insulated hot water tank for use later in the day or night. Photovoltaic panels made from silicon convert the Sun's energy into electricity which has to be used right away or be stored. The most common method for storing electricty is batteries. However, batteries, like the lead-acid batteries in cars, are not very efficient and can be environmental hazards if not properly handled.

A better solution for storage is to not store it at all, but sell it to your neighbor! I have solar panels on my roof, and during the day when they are producing energy/leectricity that i don't use, the excess is put back into the electrical grid (so called "grid tie system'). In effect, my electricity meter runs backward so I am selling electricity to the electric company. At night when I need electricity, the meter runs forward and I buy back some of the electricity. This works out really well for me in that I don't have to buy and maintain many lead-acid batteries at home, I use the grid as my battery. It also works out well for the electric company in that they have an extra source of electricty during the sunny parts of the day when everyone is using their air conditioners and demand is high. They don't have to build new power plants to cover this demand.