Sunlight is actually the Earth's primary source of energy.
It makes possible the photosynthesis process of plants, algae and bacterias that maintains the atmosphere's level of oxygen thus making life possible as we know it. The amount of energy generated only by photosynthesis on Earth's organisms is about six times larger than the whole human power consumption.
Currently mankind's energy production is mostly derived from fossil fuels, such as coil, oil and gas. An interesting fact is that most of that energy is really Sun's energy stored. So one way or another it is the Sun's energy that we are using, why not do it in most efficient, clean and directway?