The sun’s energy has been used for centuries to: Dry clothes and Dry meats. Plants use solar energy to make food through a process called “photosynthesis”. Therefore, fossil fuels are solar energy stored for billions of years. The sun is the source of the life on our planet Earth and, directly or indirectly, is the fuel for most renewable systems. Photovoltaic and solar thermal systems, as well as solar thermal power stations, convert solar irradiation directly into use-able energy.