power company if they pay extra for it. In theory, what this means is that instead of using normal electricity which comes from many non-renewable sources, the provider of the electricity ensures that the equivalent electricity used in your home is fed to the grid via a renewable source, such as solar arrays or wind turbines. However, in the past there has been instances of fraud involved in such schemes. Fuel cells Fuel cells create energy through chemical reactions. A fuel cell is an electrochemical cell which captures the electrical energy of a chemical reaction between fuels. It is an electrochemical conversion device which converts the chemical energy of fuel (i.e. hydrogen and oxygen) into water; and which produces electricity and hot air in the same process. Fuel cells have no moving parts and do not involve combustion or noise pollution. A fuel cell is similar to a battery but does not need to be recharged; a battery gets recharged by using electricity which is then stored in a closed system, whereas a fuel cell uses an external supply of fuel which needs to be continuously replenished. Fuel cells are not commercially available yet, and remain very expensive. They are used as power sources in remote areas. NASA uses fuel cells on space shuttles; they are also used for military applications, and in large public parks. Fuel cells cannot store energy like batteries. Even if the energy delivered from fuel cells is stored, their electrical efficiency is not nearly as