Solar energy is the result of radiation produced by nuclear fusion reactions. Humans are generally aware of the vitality of the sun in our daily lives, but most are not aware that the sun provides nearly all of the heat and light that the Earth receives. It is this heat and light that sustains the life of organisms.

     Photons carry energy to the Earth through space. When the Earth is facing the sun, just one square kilometer receives 1,400 megawatts of solar power every minute. This one piece of land carries the same amount of energy as the largest generating electricity plant in Nevada. 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. The solar intensity varies with the time of day, peaking at solar noon and declining to a minimum at sunset. The total radiation power (1.4 kilowatts per square meter, called the solar constant) varies only slightly, about 0.2 percent every 30 years. Any substantial change would alter or end life on Earth.

Indirect and Direct Collection of Solar Energy

Indirect

     Through various modes, people can indirectly take advantage of solar energy that has been naturally collected. For example, we can consider the windmill. Modern windmills are strong, light, weather-resistant, aerodynamically designed machines that produce electricity when attached to generators. Without the sun, these windmills would not work because the sun’s energy promotes ocean currents which change the atmosphere. Other indirect sources of energy from the sun are waterpower, thermodynamics, and photosynthesis.

Direct

     Generally, only there are only two types of artificial solar energy collectors: flat plate collectors and concentrating collectors. A universal downfall of artificial solar energy collectors is that they must spread across a large surface area in order to capture adequate energy. Even in areas of the United States that receive a lot of sunshine, a collector surface as big as a two-car garage floor is necessary to gather enough energy for just one person.

Flat Plate Collectors

     These collectors are flat, thin boxes with a transparent cover. Most people mount flat plate collectors on rooftops that face the Sun. The sun heats a blackened metal plate inside the box, called an absorber plate, that in turn heats fluid (air or water) 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.

     This collector is capable of heating carrier fluids up to 180 degrees Fahrenheit. Their energy efficiency in making use of available energy has a wide range, varying from 40 to 80 percent, depending on the type of collector.

Putting it into action

     These collectors are used for water and space heating. They are positioned different in different locations in order to provide maximum efficiency for the level of available solar energy.

Concentrating collectors

     Concentrating collectors are used for larger tasks such as industrial energy intake. These systems are much more complex and expensive than flat plate collectors. The light intensity is concentrated to produces temperatures of several hundred or even several thousands degrees Celsius.
     Concentrators make used of curved mirrors with aluminum or silver reflecting surfaces that coat the front or back surfaces of glass or plastic. This glass is generally very expensive, but researchers are developing alternative polymer films to replace the glass.

Putting It Into Action

     This method is the least expensive way to generate electrical power from the Sun. Large systems, such as the government, industry, and utilities have formed partnerships in producing this energy in order to make the process more cost efficient.

Passive Solar Heating

     Houses in certain colder hemispheres, such as Northern North America, make use of passive solar heating. This process is fairly simple. The consumer makes use of products that allow easy entry of light, such as large windows with great surface area. In addition, they use bricks and cement which absorb heat and make it difficult for the heat to escape from the house. This effect can lower the amount of electricity used to keep the house warm during winter.

Photovoltaic cells

     Photovoltaic cells are solar cells which are created from thin slices of crystalline silicon, gallium arsenide, or other semiconductor materials. These cells are connected to one another and layered for maximum efficiency.

Putting It into Action

     These cells are used widely across America. Most watches and calculators make use of some form of photovoltaic cells Complex systems can provide electricity for houses, but more importantly, photovoltaic cells are used to provide power to low maintenance items such as weather buoys, communication satellites, and equipment on spacecrafts.