If you have an old photovoltaic system you can also add new cells to your existing ones so you do not just have to replace an older system. They also require no destruction of the environment and do not pollute. An interesting experiment with photovoltaics was conducted at the 1996 Olympic Games as the swimming pool was heated by power derived from photovoltaics. Flow of electricity from PV cell to the consumer Fuel Cells are a third form of micropower that is showing increasing promise for the consumer market. The fuel cell has been around as long as the Sirling engine being discovered in 1839 by Sir William Grove .
Most fuel cells burn hydrogen but can use a variety of ther fuels such as methanol.
The hydrogen-oxygen reaction will only produce water leaving no pollutants however the hydrogen is usually derived from natural gas. The fuel cell resembles a battery in that it has a positive and negitive electrode. The hydrogen molecule is split by the negative electrode which causes electrons to flow out of the cell causing the current that provides electricity. There are many different kinds of fuel cells however Phosphoric Acid Fuel Cells seem to be the most common. Fuel cells have been used to power the space shuttle and Apollo programs.