Solar energy is defined as radiation produced by nuclear fusion reactions, deep in the Sun’s core. The sun provides almost all the heat and light Earth receives and therefore sustains every living being.
Photons allow solar energy to travel through space to earth. On the side of Earth facing the sun, our atmosphere receives 1,400 megawatts of solar power every minute (solarenergy,2003). Only half of that amount, however, reaches Earth’s surface. The atmosphere and clouds absorb or scatter the other half of the incoming sunlight. The amount of light that reaches any particular point on the ground depends on the time of day, the day of the year, the amount of cloud cover, and the latitude at that point. 
 
 

History

Around one hundred years ago efforts to design and construct devices for supplying renewable energy came about. Contrary to the general opinion of the day, a number of engineers questioned the practice of an industrial economy based on nonrenewable energy and worried about what the world's nations would do after exhausting the fuel supply.
 
 

Development

People have devised two main types of artificial collectors to directly capture and utilize solar energy. Flat plate collectors and concentrating collectors both require large surface areas exposed to the Sun since so little of the Sun’s energy reaches Earth’s surface(solarenergy,2003). 
Flat plate collectors are pretty much flat, thin boxes with a clear cover that are put on rooftops facing the Sun. The Sun heats a black metal plate inside the box that then heats fluid running through tubes within the collector. The energy transferred to the carrier fluid, divided by the total solar energy that falls on the collector, is called the collector efficiency. Flat plate collectors are typically capable of heating carrier fluids up to 180°F (Britannica, 2003). 
For appliances such as air conditioning, central power generation, and many industrial heat requirements, flat plate collectors cannot provide carrier fluids at high enough temperatures to be effective. They may be used as “first-stage” heat devices. Instead, more complex and expensive collectors can be used, such as concentrating collectors. These devices reflect the Sun’s rays from a large area and focus it onto a small, black receiving area. The light intensity is concentrated to produce temperatures of several hundred or even several thousand degrees Celsius. 
 
 

Today and The Future

Because of the irregular nature of solar radiation as an energy source, excess solar energy produced during sunny periods must be stored. Insulated tanks commonly store this energy in hot water. Batteries also, store excess electric energy produced from wind. One possibility for the future is the use of excess solar-generated electric energy as a supplemental source for existing power networks. However, uncertain economics and reliability make this plan difficult to put into practice(Brown,1998).