what exactly is fossil fuel? It is fossilized sunlight.
The ancient sun warmed the earth. The plants absorbed it and produced cellulose. When those leaves died they fell and piled up for millions of years. Covered by natural winds they compressed into carbon. COAL! When burned they release the trapped sunlight in the carbon. So when you turn on the lights you are using ancient sunlight. The original Solar Power.
Fossilized sunlight (energy) is a good way to put it. Don’t forget it energy content is also augmented by the energy of the geologic forces that formed these resources.