The total amount of solar energy incident on Earth far exceeds the world's current and projected energy needs. If harnessed properly, this highly diffused source has the potential to meet all future energy needs. In the 21st century, solar energy is expected to become increasingly attractive as a renewable energy source due to its inexhaustible supply and non-polluting nature, in stark contrast to the finite fossil fuels coal, oil, and natural gas.
The Sun is an extremely powerful source of energy, and the sunlight is by far the largest source of energy the Earth receives, but its intensity at the Earth's surface is quite low. This is essentially due to the enormous radial spread of radiation from the distant Sun. A relatively minor additional loss is due to Earth's atmosphere and clouds, which absorb or scatter up to 54 percent of incoming sunlight. Sunlight reaching the ground consists of nearly 50 percent visible light, 45 percent infrared radiation, and smaller amounts of ultraviolet radiation and other forms of electromagnetic radiation.
The potential of solar energy is enormous since the Earth receives every day in the form of solar energy about 200,000 times the total daily electricity generation capacity of the world. Unfortunately, although solar power itself is free, the high cost of its collection, conversion, and storage still limit its exploitation in many places. Solar radiation can be converted into thermal energy or electrical energy, although the former is easier to achieve.
Among the most common devices used to capture solar energy and convert it into thermal energy are flat plate collectors, which are used for solar heating applications. Because the intensity of solar radiation on the Earth's surface is so low, these collectors must have a large area. Even in sunny areas in temperate regions of the world, for example, a collector must have an area of about 40 square meters (430 square feet) to gather enough energy to meet a person's energy needs.
The most commonly used flat plate collectors consist of a blackened metal plate, covered with one or two sheets of glass, which is heated by sunlight falling on it. This heat is then transferred to air or water, called carrier fluids, which pass through the back of the plate. The heat can be used directly or it can be transferred to another medium for storage. Flat plate collectors are commonly used for solar water heaters and home heating. Heat storage for use at night or on cloudy days is commonly accomplished by using insulated tanks to store heated water during sunny periods. Such a system can supply a home with hot water drawn from the storage tank or, with the hot water flowing through the pipes in the floors and ceilings, it can provide heating. Flat plate collectors generally heat carrier fluids to temperatures ranging from 66 to 93 ° C (150 to 200 ° F). The efficiency of these collectors (that is, the proportion of the received energy that they convert into usable energy) varies between 20 and 80 percent, depending on the collector design.
Another method of converting thermal energy is found in solar ponds, which are bodies of saltwater designed to collect and store solar energy. The heat extracted from these ponds enables the production of chemicals, food, textiles, and other industrial products and can also be used to heat greenhouses, swimming pools, and livestock buildings. Solar ponds are sometimes used to produce electricity through the use of the Rankine organic cycle motor, a relatively efficient and inexpensive means of converting solar savings Lee county. which is especially useful in remote locations. Solar ponds are quite expensive to install and maintain and are generally limited to warm rural areas.
On a smaller scale, the sun's energy can also be harnessed to cook food in specially designed solar ovens. Solar ovens typically focus sunlight from a wide area to a central point, where a black-surfaced container converts sunlight into heat. The ovens are usually portable and do not require any other fuel input.
Solar radiation can be converted directly into electricity by solar cells (photovoltaic cells). In such cells, a small electrical voltage is generated when light strikes the junction between a metal and a semiconductor (such as silicon) or the junction between two different semiconductors. The power generated by a single photovoltaic cell is typically only two watts. However, by connecting large numbers of individual cells, as in solar panel arrays, hundreds or even thousands of kilowatts of electrical energy can be generated in a solar power plant or large home array. The energy efficiency of most photovoltaic cells today is only 15 to 20 percent, and since the intensity of solar radiation is low, to begin with, large and expensive arrays of such cells are required to produce even moderate amounts. of energy.