Energy comes in many forms. Energy is never created or destroyed, but it can change form and quality. We most commonly think of energy in the forms of electricity and heat. Electricity can be easily converted to heat, as in a hair dryer or oven. Electricity can also provide cooling, as in refrigeration or air conditioning. Conversely, heat can be converted to electricity through steam cycles, as in power plants, or gas turbines, or automotive engines. Creating the heat requires fuel, as in coal, oil, natural gas, wood, or sunlight.
Unlike the fossil fuel options of coal, oil, and gas (which are depleted as the fuel is converted to electricity and heat); renewable energy options take a naturally occurring resource such as sunlight, water (with the assistance of gravity), the movement of wind, the burning of biomass, or the heat of the earth in the form of geothermal energy to provide our electric and thermal needs on a sustainable basis.
As fossil resources continue to decline and the price continues to rise due to depletion, the world is increasingly looking toward the renewable energy options to provide our heat, run our appliances, and provide our transportation needs.