The energy that we obtain instantly from the sun is called solar energy. The nuclear fusion reactions occurring inside the sun discharge enormous quantity of energy in the form of heat and light. The solar energy received by the near earth space is approximately1.4 kJ/s/m2 referred to as solar constant

The Earth obtains an amazing availability of solar energy. The sun, an average star, is a fusion reactor that has been burning over 4 billion years. It offers enough energy in one minute to supply the world's energy needs for one year. In one day, it provides more energy than our current population would consume in 27 years. In fact, "The amount of solar radiation striking the earth over a three-day period is equivalent to the energy stored in all fossil energy sources."