The development of solar energy is based on a use of solar radiation for generation energy. Solar energy is the kinetic energy of the radiation (mainly light) formed by reactions in the solar interior. As its stocks are almost inexhaustible (astronomers counted that the Sun will “burn” some more millions of years), solar energy belongs to a renewable source of energy. In natural ecosystems, only a small part of the solar energy is absorbed by chlorophyll that contains in the leaves of plants and is used for photosynthesis, namely for the formation of organic matter from carbon dioxide and water. Thus, it is collected and stocks up in the form of potential energy of organic substances. Thanks to these expansions, all the energy needs of all the other components of the ecosystem are satisfied.
It is estimated that even a small percentage of solar energy can meet the needs of transport, industry and our daily life needs, not only now but also in the foreseeable future. Moreover, despite the fact whether it will be used or not, the energy balance of the Earth and the state of the biosphere will not be affected. First, scientists directed their efforts to obtain water using solar energy. The principle of operation of the solar distiller is very simple. A transparent cover closes the vessel with the water sated with salts. Water is heated by sunlight, gradually evaporates, and the vapor condenses on the cooler cover. The purified water flows down from the cover into the other vessel.
The amount of solar radiation at the Earth's surface depends on many factors: the latitude and longitude of the area, its geographic and climatic characteristics, atmospheric conditions, the height of the sun above the horizon, and the placement of the receiver of solar radiation on the Earth etc. The source of solar energy is the thermonuclear reaction. Approximately 6 * 1011 kg of hydrogen is converting into helium every second at the Sun.
“The mass defect at the same time is 4000 kg, which according to Einstein relation E = mc2 leads to the allocation of 4 * 1020 joules of energy. Most of this energy is emitted in the form of electromagnetic radiation in the range of 0,2-3 microns. Since the total mass of the Sun ~ 2 * 1030 kg, it should remain in fairly stable condition more than 10 billion years with a constant release of energy” (“Solar Cells”).
Light emission can be used when it reaches the earth. This is the direct use of solar energy. It provides the water cycle, air circulation and accumulation of organic matter in the biosphere. It means that using this energy, we are engaged in the indirect use of solar energy. The sun emits an enormous amount of energy – about 1,1x1020 kWh per second. Kilowatt*hour – is the amount of energy required for the usage of the incandescent bulb of 100 watts for 10 hours. The outer layers of Earth's atmosphere intercept about one millionth part of the energy emitted by the Sun, or about 1,500 quadrillions (1,5 x 1018) kW*h per year. However, only 47% of the total energy, or approximately 700 quadrillions (7 x 1017) kW*h, reach the Earth's surface. The remaining 30% of solar energy are reflected back into space; around 23% evaporate water, 1% of the energy falls on the waves and currents, and 0.01% - on the process of photosynthesis in nature.
Thus, by using highly efficient methods of energy conversion, the Sun can provide the rapidly growing energy needs of the humanity. Solar electricity has long been used around the world. Today the main task of the scientists is to improve the already existing technology and increase their efficiency. Solar power plants convert the energy of solar radiation into electricity. There are two types of solar power plants:
1) Photovoltaic solar power plants - convert solar energy directly into electric energy using a photovoltaic generator.
2) Thermodynamic solar power plants - convert solar energy into heat, and then into electrical energy. The capacity of thermodynamic solar power plants is higher than the power of photovoltaic power plants.
The application of solar collectors underlies in numerous solar power systems. The collector absorbs solar light energy and converts it into heat, which is transferred to the heat carrier (liquid or air) and then is used for heating buildings, water heating, electricity generation, agricultural drying, or cooking. Solar collectors can be used in all processes virtually where heat is used. A typical solar collector accumulates solar energy in modules of tubes and metal plates, mounted on the roof of the buildings, painted black for maximum absorption of radiation. They are enclosed in a glass or plastic body and are inclined to the south to capture maximum sunlight. Thus, the collector is a miniature greenhouse, which stores heat under the glass panel. As solar radiation is distributed over the surface, the collector must have a large area (“Physics of Solar Energy”).
The main element of photovoltaic power plants is solar panels. Solar panels - is a set of interconnected elements that can convert solar radiation into electricity. These photovoltaic generators are composed of semiconductor elements. The panels consist of thin films of silicon or other semiconductor materials and can convert solar energy into direct electric current. Photoelectric converters are very reliable in work, stable, and their service life is virtually unlimited. They can convert both direct and diffused sunlight. Lightweight, easy maintenance and a modular type of design allow creating installations of any power. The main disadvantages of solar panels are their high price and low efficiency.
Solar batteries are used for power supply of independent consumers of low power, for the power supply of the radio navigational and low-power radio-electronic equipment, the drive of experimental electric cars and planes. There is a hope that in the future they will be used for heating and power supplying of houses. There is a hope that in the future for them will find application in heating and electricity supply of the houses.
For the construction of thermodynamic solar power plants, scientists use the heat exchange elements with the selective light-absorbing coating. These elements are capable of absorbing up to 97% of a sunlight, which gets on them. These elements even due to usual solar lighting can heat up to 200 °C and even more. With their help, the water turns to steam in ordinary boilers that allow receiving an effective thermodynamic cycle in the steam turbine. The energy conversion efficiency of the solar steam turbine plant can reach 20% (“Photovoltaic effect”).
The design of an aerostat solar power station was developed based on this effect. The gasbag filled with water vapor is a power source for the solar power station. The outer part of the balloon is able to pass the sun's rays, and the inside is covered with a selective light-absorbing coating that allows heating the contents of the cylinder up to 150-180 ° C. The temperature of the received steam will be about 130-150 °C, and pressure will be the same as atmospheric. While spraying water inside the container with the superheated steam, scientists can obtain steam generation. The steam from a balloon is transferring to the steam turbine by the means of a flexible steam line, and at the exit steam turns into the water in the condenser. By means of the pump, water from this condenser is pumped back into a cylinder. Due to the steam that was accumulated during the day, this power station can work all the night long. Within days, the power of the turbo generator can be adjusted according to the needs of consumers (Chen, 27).
The main problem in obtaining solar energy in this way is a process of placement of solar power aerostat stations. Such power plants can be placed only above the ground, above the sea or in the mountains. In each case, there are pros and cons. In this case, it is necessary to consider every little detail; length of a steam line, the location of a turbo generator and balloons should not interfere with the movement of aircraft.
During the history of studying of this question, scientists tried a huge number of various options and ways of production and use of solar energy. Expensive and inefficient technologies gave way to attractive and low-cost developments that do not stop being improved for many years. The use of solar energy has its disadvantages they include the following:
Impermanence. Solar energy is an intermittent source of energy. Access to a sunlight is limited during certain periods (for example, in the morning and in the evening). It is almost impossible to predict cloudy days, and furthermore to predict the production of energy in these days. This is the main reason why solar power cannot be the main source of power for the consumers, without accumulation.
Expensive accumulation. Systems of storage of energy, such as batteries help to smooth schedules of generation and consumption of electricity. It considerably stabilizes solar power supply systems. However, accumulation is very expensive technology.
It takes a lot of space. The power density in Watts per square meter (W/m ²), is important in terms of, how much energy can be received from a certain area. The world indicator of average power density for sunlight is 170 W/m ². This is more than have the other renewable energy sources, but is not comparable, for example, with oil, gas and, especially, to nuclear power in any way.
The advantages of using of solar energy include the following:
Solar energy - a renewable resource, unlike non-renewable resources such as fossil fuels, coal, nuclear fuel etc.
The high potential. The potential of solar energy defies the imagination. One hundred and twenty thousand terawatts of solar radiation reach the Earth's surface it is twenty thousand times more than is necessary for the whole of humanity.
Stability. Sustainable energy sources can meet the needs of present and future generations without any damage.
Environmentally friendly. The use of solar energy usually does not cause environmental pollution. Solar energy gradually reduces our dependence on non-renewable energy sources. This is an important step in the fight against climate change on our planet.
Availability. Solar energy is available all over the world, not only in the southern countries, which are close to the equator. Germany is a bright example of the use of solar energy; the country is in the lead in terms of the total capacity of the constructed solar power plants.
Noiseless. Generation of electricity from the energy of the Sun does not require any moving parts. It is also a big plus compared to the wind generators.
No need for servicing. Solar energy systems are virtually maintenance and attention to themselves from outside. Solar modules in home solar power plants can be cleaned only1-2 times a year.
Wide range of applications. Solar energy can be used for various purposes and in various ways. For example, electricity can be generated at the places without electrical networks, for distillation of water in Africa and, of course, to generate electricity in the cosmos. Technology of thin-film cells and modules make it easy to install solar panels into the buildings.
Today the humankind are using only a small part of the solar energy due to the fact that the existing solar cells have relatively low efficiency and are very expensive to produce. Scientists all over the world are exploring the nature of the Sun; study its impact on the Earth, and working on the problem of the use of virtually inexhaustible solar energy. Today, solar panels have entered the everyday life of millions of people. They are ideal for travel and in options of mobile use.
Chen, C. Julian (2011). “Physics of Solar Energy”. Columbia University, Department of
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