Electricity is called a secondary energy source because it is generated from other sources (primary).    Examples of primary sources are coal and natural gas.    Electricity is easily transmitted over long distances through cables.    Electricity can be used in many ways. (Lighting, heaters, computers, TVs, motors...)    In a coal and gas fired power stations, fossil fuels release a lot of heat energy when they      are burned.    The heat released is used to heat water. The steam produced is used to drive turbines. The      turbines then drive generators which produce electricity.    Power stations that burn carbon fuels (coal and gas) produce carbon dioxide.    Fossil fuels are the main primary source for generating electricity.