Fossil fuels are a source of non-rewewable energy. These hydrocarbon-rich resources were typically formed ages ago when rapid burial of organic materials (brought on by mudslides, etc) was forced under the surface of the earth before being oxidized.
Over time, temperature and pressure have forced this organic mass into a useable natural resources which power much of the world's energy needs. When fossil fuels are burned, energy is generated, and this energy is usually used to generate steam, which in turn turns a turbine, which generates usable electricity. Fossil fuels are current cheaper and more reliable than solar power, but unlike solar panels, which are clean and utilize virtually limitless renewable energy, the burning of fossil fuels pollutes the atmosphere, degrades local environments, cause health and smog problems, and fossil fuels are in limited supply. Fossil Fuel reserves are expected to run dry (meaning that so little will be left that extraction will no longer be sustainable or profitable) some time in the next century. Solar panels are a viable solution to meet the world's energy needs during, and after, the impending energy crises brought on by the depletion of oil, coal, and natural gas.