Except for nuclear and geothermal, all energy we use comes from the sun in one form or another. As sunlight reaches the Earth’s surface, it powers heat transfers that move air and ocean currents, used for wind and tidal power. The sun evaporates water, contributing to the hydrologic cycle that fills reservoirs for hydroelectricity.
Even fossil fuels—coal, oil, and gas—are forms of solar energy, created when, hundreds of millions of years ago, plants absorbed and converted sunlight through photosynthesis, then retained that energy when they died, decayed, and became compacted and buried deep in the Earth, along with the animals that ate them. Wood, peat, dung, and other plant-based fuels are a less concentrated form.
Most people think of solar energy in its direct form, harnessed in a variety of ways from the sun’s rays as they hit Earth. Technologies range from windows and water tanks placed strategically to make use of the sun’s energy, to photovoltaic cells (or solar panels), to large mirrors that concentrate solar heat to boil water and drive turbines.
