Solar energy: The sun plays an exceptional role in the life of the earth. The whole organic world of our planet owes its existence to the Sun. The sun is not only a source of light and heat but also the initial source of many other types of energy (energy of oil, coal, water, wind).
Since the advent of the world people began to use the sun’s energy. According to archaeological data, it is known that for housing we gave preference to a quiet, closed from cold winds and open sunny areas.
Perhaps the first known solar system can be considered a statue of Amenhotep III, dating back to the 15th century BC. e. Inside the statue was a system of air and water chambers, which under the sun’s rays set in motion a hidden musical instrument. In ancient Greece they worshiped Helios. The name of this god today formed the basis of many terms related to solar energy.
The problem of providing electric energy to many sectors of the world economy, the ever-growing needs of the world’s population is now becoming increasingly urgent.
Use of solar energy
Solar radiation can be converted into useful energy using the so-called active and passive solar systems. Passive systems are obtained through the design of buildings and the selection of building materials in such a way as to maximize the use of solar energy. Active solar systems include solar collectors. The development of photovoltaic systems is also underway – these are systems that convert solar radiation directly into electricity.
Energy is the driving force of any production. The fact that a large amount of relatively cheap energy was available to a person contributed significantly to the industrialization and development of society.
Passive use of solar energy
Passive solar buildings are those which the project developed, taking into account local climatic conditions, and where applicable, appropriate technologies and materials for heating, cooling and lighting of buildings due to the energy of the Sun. These include traditional building techniques and materials such as insulation, solid floors, South-facing window. Such premises can be built, in some cases, at no additional cost. In other cases, encountered in the construction of additional expenditures can be offset by lower energy costs. Passive solar buildings are environmentally friendly, they promote energy independence and a balanced energy future.
Active use of solar energy
The active use of solar energy is done by solar collectors and solar systems.
Solar collectors and their types
At the heart of many solar energy systems is the use of solar collectors. The collector absorbs the light energy of the Sun and converts it into heat, which is transferred to the heat carrier (liquid or air) and then used to heat buildings, heat water, produce electricity, dry agricultural produce or cook food. Solar collectors can be used in almost all processes that use heat.
Production technology of solar collectors reached almost the current level in 1908 when William Bailey of the American “Carnegie Steel Company” invented a collector with an insulated body and copper tubes. This collector is much like modern thermosiphon system. By the end of the first world war Bailey sold 4000 collectors, and a businessman from Florida, who bought his patent, by 1941, had sold almost 60000 collectors.
A typical solar collector collects solar energy in the installed on the roof of the building modules of tubes and metal plates, painted black for maximum absorption of radiation. They are enclosed in a glass or plastic case and are tilted to the south to capture maximum sunlight. Thus, the collector is a miniature greenhouse that collects heat under a glass panel. Since solar radiation is distributed over the surface, the collector should have a large area.
There are solar collectors of various sizes and designs depending on their application. They can provide household hot water for washing, washing and cooking, or can be used to pre-heat water for existing water heaters. Currently, the market offers many different models of collectors.
The simplest type of solar collector is a “capacitive” or “thermosiphon collector”, which received this name because the collector is also a heat storage tank in which a “disposable” portion of water is heated and stored. Such collectors are used to pre-heat water, which is then heated to the desired temperature in traditional installations, for example, in gas columns. In household conditions, pre-heated water enters the storage tank. Due to this, the energy consumption for its subsequent heating is reduced. Such a collector is an inexpensive alternative to an active solar water heating system that does not use moving parts (pumps), requiring minimal maintenance, with zero operating costs.
Flat collectors are the most common type of solar collectors used in domestic water heating and heating systems. Typically, this collector is a thermally insulated metal box with a glass or plastic lid, in which is placed a black-colored plate of the absorber (absorber). Glazing can be transparent or matte. Flat collectors typically use frosted, light-transmitting, low-iron glass (it transmits a significant portion of the sunlight entering the collector). Sunlight falls on the heat-receiving plate, and thanks to the glazing, heat loss are reduced. The bottom and sidewalls of the collector are covered with an insulating material, which further reduces heat loss.
1.2 Solar systems
Solar Hot Water Systems
Hot water is the most common direct use of solar energy. A typical installation consists of one or more collectors in which the liquid is heated in the sun, as well as a tank for storing hot water heated by means of a heat-transfer fluid. Even in regions with relatively little solar radiation, such as northern Europe, the solar system can provide 50–70% of the demand for hot water. It is impossible to get more, except with the help of seasonal regulation. In southern Europe, the solar collector can provide 70–90% of the hot water consumed. Heating water using solar energy is a very practical and economical way. While photovoltaic systems achieve an efficiency of 10–15%, thermal solar systems show an efficiency of 50–90%. In combination with wood-burning stoves, the domestic need for hot water can be satisfied almost all year round without the use of fossil fuels.
Thermosiphon Solar Systems
Thermosiphon are called solar water heating systems with natural circulation (convection) of the coolant, which are used in warm winters (in the absence of frost). In general, these are not the most efficient of solar power systems, but they have many advantages in terms of housing construction. Thermosiphon coolant circulation occurs due to a change in the density of water with a change in its temperature. The thermosiphon system is divided into three main parts:
- flat collector (absorber);
- Hot water storage tank (boiler).
When the water in the collector (usually flat) is heated, it rises along the riser and enters the storage tank; in its place, cold water flows into the collector from the bottom of the storage tank. Therefore, it is necessary to position the collector below the storage tank and insulate the connecting pipes.
1.3 Solar thermal power plants
In addition to the direct use of solar heat, in regions with a high level of solar radiation, it can be used to produce steam that rotates the turbine and generates electricity. The production of solar thermal electricity on a large scale is quite competitive. The industrial application of this technology dates back to the 1980s; Since then, this industry has developed rapidly. Currently, US energy companies have already installed more than 400 megawatts of solar thermal power plants, which provide electricity to 350,000 people and replace the equivalent of 2.3 million barrels of oil per year. Nine power plants located in the Mojave Desert (in the US state of California) have 354 MW of installed capacity and have accumulated 100 years of experience in industrial operation. This technology is so advanced that, according to official data, it can compete with traditional power generation technologies in many parts of the United States. In other regions of the world, projects to use solar heat to generate electricity will also be launched soon. India, Egypt, Morocco and Mexico are developing relevant programs; grants are provided by the Global Environment Facility (GEF). In Greece, Spain and the USA, new projects are being developed by independent electricity producers.
Large mirrors – with a point or linear focus – concentrate the sun’s rays to such an extent that the water turns into steam while emitting enough energy to rotate the turbine. The company “Luz Corp”. established huge fields of such mirrors in the California desert. They produce 354 MW of electricity. These systems can turn solar energy into electricity with an efficiency of about 15%.
The following types of solar concentrators are available:
- Solar parabolic concentrators
- Dish Type Solar Installation
- Tower-type solar power plants with a central receiver.
Currently, only an insignificant part of solar energy is used due to the fact that existing solar cells have a relatively low efficiency and are very expensive to manufacture. However, one should not immediately abandon the practically inexhaustible source of clean energy: according to experts, solar energy could alone cover all imaginable human needs for energy for thousands of years in advance. It is also possible to increase the efficiency of solar installations by several times, and by placing them on the roofs of houses and next to them, we will provide housing heating, water heating and household appliances even in moderate latitudes, not to mention the tropics. For the needs of industry, requiring large energy expenditures, you can use kilometer-long vacant lots and deserts, completely laden with powerful solar installations. But the solar energy industry faces many difficulties with the construction, placement and operation of solar energy installations on thousands of square kilometers of the earth’s surface. Therefore, the total specific gravity of solar energy has been and will remain rather modest, at least in the foreseeable future.
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