Almost everything a person does in their day-to-day life requires energy. Much of the energy that is used by people comes from a range of different stores. Systems that can store large amounts of energy are called energy sources.
Energy sources are physical things, but energy is not. The major energy sources available for use are fossil fuels (coal, gas and oil), nuclear power, biofuel, wind power, hydroelectricity, tidal power, and solar power.
Within communities, energy is used in a range of different ways:
Hundreds of years ago, human beings used wood as their main source of energy for fire, as this was readily available. Today, the energy needs of the human race are very different to what they used to be, due to the modernisation of technology and machinery. This means that the way energy is harnessed has also changed.
Over the last century, fossil fuels have been the main source of energy in most developed countries. However, because of the recognised impact on the environment of burning fossil fuels, this method of generating energy is slowly reducing. Scientists and governments are working to develop the use of renewable energy sources, such as wind power, solar power, and hydroelectricity. Much work has also been done over recent decades to make machines, technology, and people's own homes more efficient.
The demand for energy also varies with the time of year and the time of day. For example, during early evenings there is a lot of demand for heating, lighting and cooking. This demand falls overnight while people sleep. During winter, more heating and lighting is required than in summertime.