The Sun produces a lot of free energy. In countries near the equator so that the Sun is high overhead for a good part of the day, the Sun's radiation can be used in many ways.
It can be used to heat water in a pan or kettle or to heat domestic water for heating or bathing. Most impressively though it can be used in a solar furnace.
Solar furnaces can produce megawatts of power – enough to power a steel or aluminium making factory. They can also be made to track the Sun and focus the Suns rays to a point, achieving temperatures of tens of thousands of degrees.
Because metal – especially aluminium refining – is energy intensive, it is economical to power aluminium smelters with solar furnaces of this type, especially in an era of rising fuel prices.