The sun has always been an energy source. Plants use the sun's light to make food.
Animals eat plants for food.
And as we found out earlier, decaying plants and animals millions of years ago produced the coal, oil and natural gas that we use today. So, fossil fuels actually got their start as sunlight many millions of years ago. The sun can also be used to heat water for hot water in our homes and businesses. In the 1890s solar water heaters were first used in California. They proved to be a big improvement over wood and coal-burning stoves.