Four flat plate solar collectors (low-temperature solar thermal energy de invernadero con colectores solares planos y concentradores cilíndrico- parabólicos. particularmente del tipo para concentradores solares lineales parabólicos y F24S20/20 Solar heat collectors for receiving concentrated solar energy, e.g. Más destiladores solares serán construidos en otras islas durante el año próximo . en el destilador Colectores solares parabólicos fueron usados con tal fin.
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Comparison of thermal solar collector technologies and their applications.
This paper presents the operation of different thermal solar collector technologies and their main characteristics. It starts by providing a brief description of the importance of using solar collectors as an alternative to reduce the environmental impact caused by the production of non-renewable sources like coal and oil.
Subsequently, it focuses on each solar concentrator technology and finishes with a theoretical analysis hub application in different industrial processes. Global energy consumption grows rapidly due to factors like population increase and technological development, increasing energy production requirements in its different forms, with electric energy and thermal energy having the highest demand.
To meet these requirements, it is indispensable to use fossil fuels like coal, oil, and natural gas, but these generate negative effects because of the emission of residues and contaminating gases onto the environment, as well because of their high costs.
Solar collectors offer a sustainable energy solution given that they permit capturing and using thermal energy from the sun, thus, using the great energy potential it offers us. This technology provides viable and sustainable options over time, which undoubtedly will be of great importance in the near future, which is why there is a need to identify and implement new energy sources capable of providing energy sustainability in the mid- or long-term .
Additionally, it helps to reduce the environmental impact caused by increased greenhouse gases like carbon dioxide CO 2sulfur dioxide SO 2 and nitrogen oxide NOxwhich are triggering climate change. The sun, as main source of light and heat for the earth, is considered an inexhaustible resource of energy, of easy access, free, clean, and renewable; from which it is possible to obtain direct benefits through systems capable of transforming the direct solar radiation into other types of useful energy to then be used in industrial processes or in small applications for the home.
These are devices that permit focusing radiation from the sun on a reduced area focusto concentrate thermal energy and light to easily use it with devices like Stirling motors, heating systems, solar kitchens, vapor turbines, or photovoltaic cells among other devices that operate with thermal energy or with the visible radiation from the sun.
These devices permit direct use of the energy obtained or its transformation into another type of useful energy   . The concentrator is a device constructed with a high-reflectance material, which permits focusing radiation components released for the sun visible radiation, infrared and ultraviolet rays to avail of and use the energy contained in these signals.
All the concentrators have the same operating principle, but present differences regarding geometry, amount of energy concentrated, and how the energy is used. In most cases, the thermal energy obtained is used to generate vapor with water or alcohol and propel vapor turbines with which energy is produced; there is also the option of storing saline solutions or synthetic oils at high temperatures to later use this energy when there is no direct radiation or at night.
Structurally, solar concentrators comprise three necessary elements for their functioning, which are mentioned ahead:. Solar collectors can be classified depending on their geometric configuration or on the temperature obtained by the working fluid after gaining heat. According to their geometric configuration they can be flat solar collectors and concentrating solar collectors. According to the temperature, they are classified according to the range of temperatures reached by the working fluid, which in turn depends on the type of application for which the device is required.
Table 1 indicates how these are classified according to the temperature reached:. Usually, very low and low temperature collectors are used for heating devices like water heaters and solar kitchens.
Collectors of medium, high, and very high temperature are used to generate electric energy and for activities that require high temperatures like incineration of hazardous wastes. Parabolic cylindrical shaped collectors permit capturing direct radiation from the sun along a semi-cylindrical or parabolic structure placed horizontally, which has a sensor receptor tube located on the focal line of the parable along the structure Figure 1  .
Within this sensor tube circulates the fluid that absorbs the thermal energy obtained heating until reaching the desired temperature. Temperature in the fluid increases as it goes through the pipes. Usually, it is used in electric power generation facilities with large power capacity.
The type of working fluid used in this type of collector is usually demineralized water or ethylene glycol. The hot fluid is taken to a heat exchanger where thermal energy is used to generate water vapor, which propels a vapor turbine connected to an electric generator.
It is used for electric power generation and for devices requiring high temperatures like furnaces to incinerate hazardous wastes. The system is basically comprised of a collector, a heat exchanger receptorand a solar tracking system that aims the collector directly at the sun during the day.
Este uses la thermal energy to propel el motor y el electric generator, integrated as a single device, as seen in Figure 2. In other versions, energy is used to generate water vapor that is used to propel a vapor turbine and a generator.
Generation systems based on this technology are currently constructed for powers from 3 to 25 kW for each collector, and it is possible to integrate several units to achieve medium power MW and high power GW projects, according to requirements or needs and the availability of the solar resource.
This comprises a group of heliostats flat reflectors aligned in circular manner. A tower is located in the center of the circumference, which captures the radiation reflected by the heliostats. The thermal energy captured is stored by using a salt-based fluid or with synthetic oils capable of withstanding very high temperatures. The fluid can be stored in a thermal condenser for later use or it can be brought directly to a heat exchanger where vapor is produced to propel a turbine and a generator as done with parabolic cylindrical collectors.
The thermal condenser is a storage device where the fluid at high temperatures is deposited and which significantly reduces energy losses, given that it minimizes heat exchange with the environment because of the thermal isolation with which it was designed   . One of the advantages offered by this system against the rest is that it permits storing part of the energy obtained during the day for later use, during night hours or during days with low levels of solar radiation Figure 3.
This technology is being implemented to construct large power capacity thermo solar plants in which a support system is also required.
Central tower systems have a great potential to reduce electricity costs in the concentradore compared to the technology of parabolic cylindrical collectors, given that they permit integration of thermal cycles. This system is made up of a set of almost-flat reflectors, which concentrate solar radiation in high inverted receptors.
Unlike cylindrical collectors, this system uses a single receptor that captures the radiation reflected by several flat reflectors.
This system permits increasing efficiency and reducing installation costs compared to cylindrical collectors Figure 4. Table 2 presents the advantages and disadvantages of thermo solar technologies, bearing in mind relevant aspects like their operating temperature, efficiency, materials for their construction, storage capacity, among others.
Thermal solar collectors are used in a vast number of applications, given the benefits they bring to the environment and reduced energy consumption in numerous industrial processes and homes. The following present the main applications of these thermo solar elements. Drying of agricultural and industrial products requires constant hot air to eliminate humidity. Via dish-type solar collectors, heat is produced that is circulated through the crops, fruits, or products, eliminating water on them.
This system offers advantages with respect to others, given that the product remains free of dirt, dust, and its flavor and texture are maintained. In addition to the aforementioned, energy consumption is reduced to a minimum. In agriculture, it is used to dry fruits, vegetables, species, and flowers. In industry, it is used to dry tea, coffee, rubber, cotton, thread, leather, and textiles. The environmental heating system is used in low-temperature zones with very good solar radiation.
In these systems, solar collectors are employed to heat a thermal fluid, which transfers its heat through a heat exchanger. This air is circulated through open spaces, with which a constant temperature is maintained, reducing electric energy consumption. Figure 5 shows the waste water evaporation system installed in India, which permits incineration of hazardous waste liquids from pharmaceutical industries, hospitals, and processing plants  .
These industries use fields of collectors to heat water and produce vapor used in paper drying Figure 7. In these industries for example manufacture of cosmetic products numerous processes exist requiring heating. For this, boilers are used to produce vapor yielded through heat exchangers to reservoirs to heat water or intermediate products; in other cases, vapor is used directly.
Plataforma Solar de Almería
In all cases, the vapor generated by the solar collectors can be used to heat the boilers Figure 8. Many places exist like the Middle East concentradords Africa that do not have enough water suitable for human consumption, even though they coastal zones with access to the sea. Some of these places have high levels of direct radiation and this has permitted the implementation of desalinating systems with solar technology to produce drinking water by desalinating sea water.
Using solar concentradoges to desalinate water requires large areas of land and it is not as efficient when compared to conventional systems non-solarbut its low cost and ease of concfntradores make it one of the most promising technologies among the applications using direct radiation from the sun  . Water desalination is achieved through successive stages.
The water vapor generated is taken to a cooling system condenser to condense it, thus, obtaining distilled water that is then stored in an adequate container.
By evaporating the water separation of salt is achieved and water suitable for human consumption is obtained Figure 9. Projects with different capacities exist; some in which solar kitchens are developed for household uses and others developed for large projects for community use   . The solar kitchen shown in Figure 10 is located en Rajasthan, India and has 14 dish-type parabolic collectors, with 10 m 2 of reflecting surface. This solar vapor cooking system was designed to generate kg of water vapor per day; sufficient to cook meals for 10, people.
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Additionally, the system has an oil boiler that guarantees its operation under all conditions . At xolares above sea level, and when solar radiation peaks are reached on certain days, the system can provide approximately 38, meals.
Development of thremo solar energy in the whole world depends on direct solar radiation, availability of land, and auxiliary services like water, gas, and electric networks. Figure 11 illustrates the map of direct solar radiation in the world; cobcentradores that Argeria, Australia, China, Egypt, Greece, India, Israel, Italy, Mexico, Morocco, Spain, and the United States are suitable places for the development of thermo-solar technologies. Figure 12 shows that the concentradorez of thermo-solar technology is located mainly in the United States and Spain.
It is worth mentioning that other countries like Algeria 25 MWThailand 9. Figure 14 presents the places and types of technology of the thermo-solar plants under construction, highlighting the plants located in California, concejtradores Studies conducted by GreenPace have evaluated the increase expected in installed power with thermo-solar technology for different penetration scenarios for the following years untilassuming that government policies will be in place to promote progress and use of this technology in every country.
The global power installed, projected under different scenarios forcould be 18, MW in a low reference scenario;MW in a moderate scenario; and 1, MW in an advanced scenario, bringing as a consequence a notable reduction in CO 2 emissions for the environment, which could diminish emission to 5-billion tons annually within an advanced scenario by . Under these conditions, it is expected that the regions with the highest strengthening of the technology will be Europe, the United States, the Middle East, and China.
Figure 15 shows the Shams 1 concenhradores cylindrical concentraxores, which has MW capacity and permits providing energy to some 20, homes. The rows of collectors of Shams 1 generate energy that avoids the emissions oftons of CO 2 per year, which is equivalent to removing 15, automobiles from circulation . Development of thermo solar energy depends on direct solar radiation, sun shine, availability of surface area, and auxiliary services like water, gas, and electric networks.
Thermo solar technologies are still a favorable option to combat the use of nonrenewable energy sources, like coal and petroleum derivates, contributing to CO parabolucos reduction in the environment and associated costs. Although thermo solar systems have a vast number of applications in the industrial sector, electric energy production has most-influenced sector by these concenrradores of technologies.
A Meyers, Academic Press,pp. Services on Demand Article. English pdf Article in xml format Article references How to cite this article Automatic translation Send this article by e-mail. Direct solar radiation, energy, solar collectors, steam, temperature. Introduction Global energy consumption grows rapidly due to factors like population increase and technological development, increasing energy production requirements in its different forms, with electric energy and thermal energy having the highest demand.
Thermal solar concentrators These are concentrdores that permit focusing radiation from the sun on a reduced area focus solafes, to concentrate thermal energy and light to easily use it with devices like Stirling motors, heating systems, solar kitchens, vapor turbines, or photovoltaic cells among concentradres devices that operate with thermal energy or with the visible radiation from the sun.
These devices permit direct use of the energy obtained or its transformation into another type of useful energy    The concentrator is cconcentradores device constructed with a high-reflectance material, which permits focusing radiation components released for the sun visible radiation, infrared and ultraviolet rays to avail of and use the energy contained in these signals.
Structurally, solar concentrators comprise three necessary elements for their functioning, which are mentioned concentradoree System element that concentrates the radiation that will then be transformed into another type of useful energy.
It is found on the device focus when working with spherical or cylindrical geometries. Concentrator or optical device: Classification de thermal solar concentrators Solar collectors can be classified depending on their geometric configuration or on the temperature obtained by the working fluid after gaining heat. Table 1 indicates how these are classified according to the temperature reached: Parabolic cylindrical solar collector Parabolic cylindrical shaped collectors permit capturing direct radiation from the sun along a semi-cylindrical or parabolic structure placed horizontally, which parablicos a sensor receptor tube located on the focal line of the parable along the structure Figure 1  .