Solar Energy Systems and Global Energy Crisis (Analysis Essay)
Currently, the question of the energy future of the world is one of the most considered and urgent problems of the humanity. It would seem that the solution to this problem is obvious: more power plants should produce more power. However, usage and maintenance of existing and built-to-be power plants need more fuel, which is derived from the natural resources of oil, gas, and coal that are not infinite. Nowadays, scientists and engineers around the world are searching for new sources of energy that could not only maintain and replace exhaustible natural resources, but also improve the ecological picture of the planet. Energy has numerous branches, depending on the main source type: nuclear, coal, gas, hydropower, and alternative, which is based on the use of renewable energy sources. Alternative energy includes wind, geothermal, biomass, tidal wave and solar energy. Comparing all these energy industries on the basis of environmental and economic criteria and indicators of safety, it is possible to conclude that solar power is the most promising. Current paper examines the problem of modern humanity that is the crisis of energy resources. In this regard, using new sources like alternative energy becomes necessary. Main attention is given to the areas of solar energy’s application as a clean and renewable source of energy. Besides, the paper describes existing inventions, their design and function.
Solar Power Systems and Devices
The most appropriate type of energy for the majority of autonomous objects is the energy of the sun. At the moment, solar energy is almost the only one, the reserves of which are completely inexhaustible. The amount of energy received by the Earth from the sun in one hour is equal to the total energy consumed by people in a year and at the same time this type of energy has almost no economic constraints (Tsao, Lewis. and Crabtree). It is quite natural that the development of solar energy and the attempts of its practical use, especially in the US and Western Europe, are extremely intense in the whole range of possible applications, ranging from micro electric for a few tens of watts for a variety of independent members to solar power plants for the industrial use, including applications such as spacecraft and solar powered cars.
The amount of solar energy reaching the Earth is greater than the energy of the world’s reserves of coal, gas, oil, and other energy resources. Usage of only 0.0125% of solar power could provide all the needs of today’s global energy (Kravchenko). Advantages of the technologies using solar energy are seen by the fact that solar installations do not provide heat added into the surface layers of the atmosphere where the greenhouse effect is not generated and there is no air pollution. However, there is a lack of solar energy. In particular, it is dependent on the state of the atmosphere, time of a day, and season. Use of solar energy mainly goes in two ways: in the form of thermal energy through the use of various thermal systems or by photochemical reactions. The most widely used technology in the world to use solar energy is hot water supply and heating. For this purpose, low-temperature energy is sufficient. Plants and solar heating systems are divided into passive and active (Fricke).
In passive systems, absorption and storage of solar energy are provided directly by the elements of building constructions with little use of additional devices or without them. Throughout the history, the humanity has learnt how to use the sun’s heat during the construction of houses. In many countries, buildings are characterized by thick walls, accumulation of energy, and orientation of windows on the sunny side. Even at the current time, there are new methods developed, which improve such system. The wall facing the south is black, before a wall there is a glazed surface, and there is air between them, which is heated and then circulated in the building by convection. A water wall can be used instead of the stone one formed by water-filled containers from fiberglass.
Active systems are based on the use of solar thermal collectors that convert solar energy into heat. Usually, a solar collector consists of energy absorbing plate glass and tubes disposed between the plate and the glass. Heated liquid circulates through pipes by a pump. Solar collectors can be used in a variety of low-temperature processes. For example, those can be used in the food industry for pasteurization of products, cleaning of cans, bottles, laundry in laundries, drying of agricultural produce, and so on.
Reflecting solar collectors that concentrate the heat and light of the sun by chasing the sun’s movements are used for getting higher temperature or for implementing any mechanical work. Such collectors have either mirrors or lenses. Mirrors can be parabolic, spherical, or paraboloid. The concentrated sunlight falls on the central heat sink and heats the liquid, which is then pumped. This system includes the storage tank for the heated fluid.
The main problem of the widespread usage of solar thermal systems is related to their economic efficiency and competitiveness as compared to traditional systems. The cost of energy generated by solar installations is higher than the cost of the energy obtained when using traditional fuels. However, the use of solar is more cost-effective for areas remote from centralized power supply (Corkish, Green, Watt and Wenham).
A more efficient way of using solar energy is its direct conversion into electrical energy using solar cells. Photovoltaic cells are light-sensitive plates made of semiconductor material: selenium, silicon, gallium arsenide, silicon, diselenide, etc. (Corkish, Green, Watt and Wenham). Photovoltaic is produced when light particles (photons) create an electric current that is absorbed by the semiconductor. Solar panels can be of different capacities, from portable units in a few watts to power wattage, covering millions of square meters. In order not to depend on seasonal and diurnal solar cycle and atmospheric conditions, there are technical energy storage methods such as electrochemical storage batteries and mechanical accumulation (using rotating flywheels) in the form of hydrogen. It is also possible to mix cells with other energy sources such as the most likely combination with wind turbines, as well as systems with fossil fuels.
Photovoltaic systems (solar panels) require minimal maintenance and they do not use water. Thus, they are well-suited for remote and desert regions. This method of converting solar energy is durable and environmentally friendly. It can also be used to improve environmental conditions at the place of use and in the future to regulate environmental conditions in large areas.
Basic needs in solar cells include: lighting, functioning of electronics (radio, TV, refrigerator), and pumps for lifting water in remote rural areas. It also helps to provide energy supply to environmentally friendly public recreation areas and treatment, as well as for radio and telecommunication systems, lighthouses, buoys. Installations of solar energy are not only environmentally friendly, but also have a positive impact on other areas of life. For example, the use of solar panels in hot desert regions such as a sun umbrella provide favorable conditions for growing underneath melons and citrus fruit, for which intense sunlight is not advisable. Another example is the use of solar panels or solar collectors as building elements for facades (Chiras).
Production of Solar Equipment
In many countries, there is a constant increase in the production of solar collectors. Their current global installed capacity is estimated at 15 GW (Sterner). The total area of solar collectors in the world, according to incomplete data, exceeds 21 million of square meters, while annual production of solar collectors exceeds 1.7 million of square meters. At this point, leading countries are (in millions of square meters): Japan – 7, USA – 4, Israel – 2.8, and Greece – 2. Photoelectric conversion of solar energy is one of the fastest growing trends in the domain of renewable energy. Currently, the total installed capacity of solar photovoltaic systems is over 938 MW. The annual growth rate has been 30% during the last 5 years. At this point, leading countries are: Japan – 80 MW, the United States – 60 MW, and Germany – 50 MW (Kalogirou).
The extent of the use of photovoltaic solar cells are limited to the higher cost of electricity generated as compared to the energy produced by the use of traditional energy sources. The unit cost of power flat solar modules on the world market is 4 – 5 $/W and the cost of photovoltaic installations is 7 – 10 $/Wt (Wolfe). The cost of electricity generated by the modules ranges from 0.2 to 0.3 / $/kWh, which is significantly higher than the cost of electricity from conventional sources. However, worldwide there are large areas with centralized energy supply experiencing an acute shortage of energy, thus resulting in significant losses, including material and financial ones. There are regions remote from centralized power like individual settlements, villages, and operating points. The use of renewable energy sources, including solar energy, would solve social and economic problems of these regions and remote locations. Therefore, the question of economic opportunity and efficiency must be addressed taking into account socio-economic conditions, including energy deficiency, the cost of fuel, as well as geographical and climatic conditions.
Scientists estimate that a small percentage of solar energy is sufficient to provide transport and industrial and domestic needs both now and in the future. The energy balance of the Earth and the state of the biosphere are not to be affected irrespective of whether or not the energy is used. However, one cannot overlook one major drawback. Solar radiation falling on the Earth’s surface does not have a fixed place of concentration. Thus, it is necessary to catch and turn this energy into a form that could be possibly used for human needs. In addition, there is a need in some way to stock solar energy to maintain the power supply at night and on cloudy days. At present, this problem is easily solved. The main thing is a correct usage of this resource to reduce its cost to a minimum. Moreover, taking into account day-by-day improvement of technology that becomes more expensive and, most importantly, traditional exhaustible resources, solar energy will find more fields of application. Thus, below are the main of them.
The task of solar collectors is accumulation of solar energy as efficiently as possible. Several well-known principles have been used in the design of the solar collector. For example, the heater is based on the property of solar rays, which freely pass through the transparent medium into the closed space and, being converted into thermal energy, are no longer able to come back through the transparent roof installation. The hydraulic system works by the principle of thermosiphon effect. That is known by the property of the liquid being heated to climb up, displacing the colder water and forcing the latter to move to a place of heat. It should also be noted that the development of solar energy has considered the effect of the accumulation and preservation of heat. Accumulated solar energy converts into heat energy that persists for a long time. There are different types of solar collectors differentiated by the external form of surfaces or by principles of absorbing surfaces and accumulating methods.
A flat solar collector is the most common type of solar collectors used for domestic water heating and heating systems. This solar collector has a glazing panel encasing the absorber plate. Absorber plate is made of metal with a good heat capacity (Kalogirou). The most frequently used metal is copper as it conducts heat better and is less susceptible to corrosion than aluminum. The plate is treated with a special highly selective absorber coating, which keeps better absorption of sunlight. This coating consists of a very strong thin amorphous semiconductor layer deposited on the metal base and has a high absorptivity in the visible region of the spectrum and low emissivity in the long wavelength infrared region. Heat loss reduces due to the glazing since frosted glazing glass with a low iron content that transmits only light is typically used in flat solar collectors. The bottom and side walls of the solar collector are coated with a heat insulating material, which further reduces heat loss.
In the vacuum solar collector with direct heat transfer water, vacuum tubes are arranged at a certain angle and connected to the storage tank (Kalogirou). From it, water from a loop heat exchanger flows directly to tubes, heats up, and comes back. Advantages of this system concern a direct transfer of heat to water without other elements. Thermosiphon systems work on the principle of natural convection phenomena when warm water aspires upwards. In thermosiphon systems, the tank should be located above the collector. When water in tubes of the solar collector heats up, it becomes lighter and naturally rises to the top of the tank. Cooler water in the tank flows down into the tube; thus, it is circulated throughout the system. In smaller systems, the tank is integrated with solar collectors and is not designed for rail pressure. Therefore, thermosiphon systems need to use either water supply from upstream capacity or through reduction of pressure reducers. This type of solar collector has a minimum flow resistance. The system is required to be non-pressurized (open expansion tank) for tubes to avoid pressure. The drawback of such system is a slightly larger volume of water loop heat exchanger. There could also be a case of leaking water if the tube of solar collector is broken. However, the main advantage is low cost with all the benefits of a solar collector with vacuum tubes.
The first prototype of a solar vehicle appeared in 1955 in Chicago thanks to William Cobb (Freestone). The model had a design with a length slightly larger than a foot and consisted of thirteen selenium solar cells on the roof and a small electric motor. It was the first attempt at creating silent and environmentally friendly transport. In the late 80-ies of the 20th century, the idea spread around the world. The idea is certainly unique, but also quite expensive. To make a solar power car able to compete with the motor car, one must use the most lightweight and durable construction materials, as well as a high-performance drive system, the latest achievements in the field of electronics, electrical engineering, and aerodynamics.
Mobile station photoelectric is an autonomous energy source that can be used both in an open remote place and for the stationary use. However, of course, the main purpose of the station is the battery charging. The principle of operation of mobile photovoltaic plant is direct conversion of sunlight into electricity through solar cells. The station consists of modular solar panels, collapsible structures, and inter-module cable. Solar cells used in the modules are protected with light-resistant film on the front side and on the back side they have a rigid substrate. All this helps to protect them from mechanical damage and environmental influences. Solar modules are suitable for storage and transport as they are created in a convenient folding design. Concerning power characteristics of such installation, the cable can switch in parallel all the modules for charging a nominal voltage of 12 V, while series-parallel to the voltage of 24 V. In order to achieve voltage of 48 V, one must connect all modules with their own current leading in a daisy chain (Kalogirou).
Portable solar power system is intended primarily for energy supply to DC house and special equipment with power up to 60 W and is based on solar photovoltaic modules. The structure of the portable system includes: a solar battery, a sealed rechargeable battery with charge controller-level, a warning device, a network adapter, and a lamp with a fluorescent lamp.
Features of the system are the following:
- Accumulation of energy from different sources, including thermoelectric solar batteries and charger power;
- Ease of use and assembly of the technology implemented through the use of electrical connectors;
- Light weight and undeniable compactness that are important for the mobility of the system.
Solar kitchen is household solar plants intended for cooking. The main element is a solar concentrator that focuses the sun’s rays on the surface of the radiation detector – dishes in which food is prepared. Often, solar concentrators used for solar dishes have a low accuracy of the focusing solar radiation; however, it is enough for everyday usage’s convenience. Rotation after the apparent motion of the sun is carried out by hand and efficiency of the plant reaches 55-60% (Hesselbach and Herrmann). Benefits of solar kitchen are its compactness for the use in open space conditions, indispensability of the absence of gas, and, of course, budget of the installation.
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Lamps with solar batteries: today, there cannot be a huge surprise in case someone uses photovoltaic systems for night illumination of streets, highways, and other areas. These systems are autonomous power supply, which are based on solar module that allows making the lighting less expensive. The principle of operation of such systems is reliable and simple. During the daylight hours, the photovoltaic cell recharges batteries, turning solar energy into electricity. At night, the light automatically comes on and stays on until dawn. Intensity of solar radiation does not affect charging abilities of the battery; it can be recharged even in cloudy weather, not to mention the winter season.
The structure of the photovoltaic system includes:
- PV module that converts sunlight into electricity;
- Battery that accumulates energy. Sealed and maintenance-free batteries are commonly used, the service life of which does not exceed 10 years;
- Controller, which optimizes the level of charge/discharge of the battery and automatically switches on the light at night and turns off the light in the daytime;
- An inverter, which converts direct current into alternating;
- Lighting unit, including the ceiling and the lamp.
Of course, all electronic devices equipped with a photovoltaic system are protected against short circuit, overload, and overheating, while providing reliability and efficiency of the system.
In conclusion, the main thing is that solar energy is one of the most renewable and readily available sources of energy. The fact that sunlight and heat are available for free in large quantities and do not belong to anyone makes them one of the most important alternative energy sources. Currently, the potential of solar energy is extremely high in addition to a large number of positive aspects in favor of the use of this resource in comparison with conventional energy. However, as mentioned in the beginning, there is one major drawback. Despite the fact that the amount of solar energy is enough to supply all the energy needs of the world, unfortunately these huge potentials will hardly be ever implemented on a large scale. This is impossible because of the low intensity of the solar lighting. Moreover, the use of a large number of collectors involves considerable material costs. Perhaps, the situation will change for the better in case cheaper materials for collectors are created and applied.