Solar Energy: An Alternative Energy Imagine a perfect source of energy. One with which no pollution what-so-ever is associated with. No poisonous gasses or destruction of rain forests. This abundant source of energy comes from the sun. Solar energy is the visible energy produced in the sun as a result of a constant nuclear fusion reaction that is taking place. The amount of energy at the solar constant, which is at outer edge of the earth's atmosphere, is two calories per minute per cm squared. A calorie is the amount of energy needed to raise one gram of water one degree Celsius. If we could