The sun is the source of almost all energy on Earth. We take energy from the sun Directly using solar powers. Earth's winds are a result of the changes in temperatures caused by the sun, so wind turbines are also powered by the sun. Fossil fuels (oil, coal) come from plants and animals that died millions of years ago; plants need sunlight to grow and animals eat plants, so fossil fuels are powered by sunlight. Hydroelectric power plants are powered by water running down hill, and it is the sun which moves water back up the hill by producing rain clouds.
The only forms of energy production which could work without the sun are nuclear, and geothermal.
Solar energy is the energy derived from the sun. It is a renewable and inexhaustible source of energy. It is in the form of heat and light. It is used to generate heat, electricity and de saline the sea water. The sun gives about 100000 trillion kilowatts of energy per year. The simplest definition of an energy source is that it is a source from which you can obtain heat, light and power. The sun provides you with all the three sources.
It is not just a source of energy but also the most important and also the most abundant. Without it we wouldn't be able to live as everything is somehow connected, in some way or the other, to the sun. Solar energy differs in latitude; that is the amount of energy received on the planet fluctuates from latitude to latitude.
The sun is an energy source because God invented a yellow circle and polished it to make it shiny. Then, he put it in a microwave to heat it up and transmitted energy so that humans could live with light. If you don't believe me, then screw off.