Solar energy ( STE ) is a form of energy and technology to harness solar energy to generate thermal energy or electrical energy for use in industry, and in residential and commercial sectors.
Video Solar thermal energy
Ikhtisar
Solar thermal collectors are classified by the United States Energy Information Administration as low, medium, or high temperature collectors. Low temperature collectors are generally glazeless and are used to heat a swimming pool or to heat air vents. Moderate temperature collectors are also usually flat plates but are used to heat water or air for residential and commercial use. The high temperature collector focuses sunlight using a mirror or lens and is commonly used to meet the thermal needs of up to 300 degrees C/20 bar pressure in the industry, and for the production of electric power. The two categories include Concentrated Thermal Solar (CST) to meet the requirements of heat in the industry, and Concentrated Solar (CSP) when the heat collected is used for power generation. CST and CSP can not be replaced in terms of applications. The largest facilities are located in the American Desert of Mojave California and Nevada. This plant uses a variety of different technologies. The biggest examples include, Ivanpah Solar Power Facility (377 MW), installation of Solar Energy Generating Systems (354 MW), and Crescent Dunes (110 MW). Spain is a major developer of solar thermal power plants. The largest examples include, Solnova Solar Power Station (150 MW), Andasol solar power plant (150 MW), and Solar Power Extresol (100 MW).
Maps Solar thermal energy
History
Augustin Mouchot demonstrates a solar collector with an ice cream making machine at the 1878 Universal Exposition in Paris. The first installation of solar thermal energy equipment took place in the Sahara approximately in 1910 by Frank Shuman when the steam engine was run with steam produced by sunlight. Since liquid fuel engines were developed and found to be more comfortable, the Sahara project was abandoned, only to be revisited decades later.
Low-temperature solar heating and cooling system
Systems for utilizing low-temperature solar thermal energy include tools for heat collection; usually heat storage, either short-term or interseasonal; and distribution within the structure or network of district heating. In some cases, more than one function is attached to a single feature of the system (eg some types of solar collectors also store heat). Some systems are passive, others are active (require other external energy to function).
Warming is the most obvious application, but solar cooling can be achieved to build or cool the district network by using heat absorption or the adsorption chiller (heat pump). There is a productive coincidence that the greater the driving heat of the insulation, the greater the cooling output. In 1878, Auguste Mouchout pioneered the cooling of the sun by making ice using a solar steam engine attached to a cooling device.
In the United States, heating, ventilation and air conditioning systems (HVAC) account for more than 25% (4.75 EJ) of energy used in commercial buildings (50% in northern cities) and nearly half (10.1 EJ) of the energy used. in residential buildings. Solar heating, cooling, and ventilation technology can be used to offset some of this energy. The most popular solar heating technology for heating buildings is the building of an integrated solar solar air collection system that connects to HVAC building equipment. According to the Solar Energy Industry Association more than 500,000m 2 (5,000,000 square feet) of these panels operate in North America by 2015.
In Europe, since the mid-1990s about 125 large district solar-thermal heating plants have been built, each with more than 500 m 2 (5400Ã, ft 2 ) from the solar collector. The largest is about 10,000m 2 , with a capacity of 7 MW-thermal and solar heat costs about 4 Eurocents/kWh without subsidies. 40 of them have nominal capacity of 1 MW-thermal or more. The Sun District Heating Program (SDH) has the participation of 14 European Countries and the European Commission, and works towards technical and market development, and holds annual conferences.
Low temperature collector
Glazed solar collectors are designed primarily for heating the room. They recirculate the air of the building through a solar air panel where the air is heated and then redirected back to the building. This solar space heating system requires at least two penetrations into the building and only performs when the air in the solar collector is warmer than the temperature of the building space. Most glass collectors are used in the housing sector.
The non-glaze solar collector is primarily used for preheating air-ventilation make-up in commercial, industrial and institutional buildings with high ventilation loads. They change the walls of buildings or parts of walls into low-capacity, high-performance, non-luminous solar collectors. Also called, "solar panels are lit" or "solar walls", they use metal coatings perforated metal metal perforated which also serves as the surface of the building's exterior walls. Heat to air transfer occurs on the absorbent surface, through a metal absorber and behind the absorber. The boundary layer of the hot air of the sun is drawn into the nearest perforation before heat can come out by convection into the outside air. The hot air is then taken from behind the absorbent plate into the building ventilation system.
The Trombe wall is a passive solar heater and a ventilation system consisting of air channels flanked between windows and thermal mass facing to the sun. During the ventilation cycle, sunlight stores heat in thermal mass and warms the airways that cause circulation through the vents at the top and bottom of the wall. During the heating cycle, Trombe's walls emit stored heat.
The solar rooftop pool is a unique solar heater and cooling system developed by Harold Hay in the 1960s. The base system consists of a bladder mounted on the roof with a movable insulation cover. This system can control the heat exchange between interior and exterior environments by closing and exposing the bladder between day and night. When heating is a concern the bladder is revealed during the daytime that allows sunlight to warm the bladder of the water and store heat for night use. When cooling is a concern the bladder closed draws heat from the building's interiors during the day and is revealed at night to radiate heat into the colder atmosphere. Skytherm House in Atascadero, California uses a prototype roof pool for heating and cooling.
Solar heating with airborne solar collectors is more popular in the United States and Canada than heating with solar liquor collectors since most buildings already have ventilation systems for heating and cooling. The two main types of solar air panels are glass and not sparkling.
Of the 21,000,000 square feet (2,000,000 m 2 ) of the solar thermal collectors produced in the United States in 2007, 16,000,000 square feet (1,500,000 m 2 ) is the lowest range of temperature. Low temperature collectors are generally installed to heat the pool, although they can also be used for heating the room. Collectors can use air or water as a medium to transfer heat to their destination.
Thermal storage in low temperature solar systems
Interseasonal storage. The solar heat (or heat from other sources) can be effectively stored between the opposite seasons in aquifers, underground geologic strata, large specially constructed holes, and large tanks isolated and covered with earth.
Short-term storage. Thermal mass materials store solar energy during the day and release this energy during cold periods. Common thermal mass materials include rocks, concrete, and water. The proportion and placement of thermal mass must consider several factors such as climate, sunlight, and shadow conditions. When properly inserted, thermal mass can passively maintain a comfortable temperature while reducing energy consumption.
Solar-driven cooling
Worldwide, in 2011 there were about 750 cooling systems with solar-driven heat pumps, and the annual market growth was 40 to 70% over the previous seven years. This is a niche market because the economy is challenging, with the number of hours of annual cooling a limiting factor. Individually, the annual cooling hour is approximately 1000 in the Mediterranean, 2500 in Southeast Asia, and only 50 to 200 in Central Europe. However, the cost of system development fell by about 50% between 2007 and 2011. The working group of International Heating and Refrigeration Energy (IEA-SHC) task group is working on the further development of the technologies involved.
Ventilation of solar thermal power
The solar chimney (or thermal chimney) is a passive solar vent system consisting of a hollow thermal mass connecting the inside and outside of the building. As the chimney warms up, the air inside is heated and causes an upward flow of air that pushes air through the building. This system has been used since Roman times and remains common in the Middle East.
Heat process
Solar heating systems are designed to provide large amounts of hot water or heating for nonresidential buildings.
The evaporation pool is a shallow pond that concentrates dissolved solids through evaporation. The use of evaporation ponds to get salt from seawater is one of the oldest applications of solar energy. Modern uses include saltwater solutions used in leach mining and removal of dissolved solids from waste streams. Overall, the evaporation pool is one of the largest commercial applications of solar energy currently in use.
The non-luminous transponder collector is a downward-facing wall used for preheat air heating. The liberated collector can also be installed on the roof for year-round use and can raise the air temperature to 22 Â ° C and provide 45-60 Â ° C. outlet temperatures. The short payback period of the recorded collector (3 to 12 years) making them a more cost-effective alternative to glass collection systems. By 2015, more than 4000 systems with a combined collector area of ​​500,000m 2 have been installed worldwide. Representatives include the 860m 2 collector in Costa Rica used for drying coffee beans and a 1300m 2 collector in Coimbatore, India used to dry marigolds.
A food processing facility in Modesto, California uses a parabolic trough to produce the steam used in the manufacturing process. Collector area 5,000m 2 is expected to provide 15 TJ per year.
Temperature collector
This collector can be used to produce about 50% and more hot water required for residential and commercial use in the United States. In the United States, a typical $ 4000- $ 6000 retail system ($ 1400 to $ 2200 wholesale for materials) and 30% of eligible systems for additional federal state credit credit credits exist in about half of the state. Labor for a simple open-loop system in southern climates can take 3-5 hours for installation and 4-6 hours in the North. The northern system needs more collector areas and more complex pipes to protect the collector from freezing. With this incentive, the payback period for ordinary households is four to nine years, depending on the country. Similar subsidies exist in parts of Europe. A crew of one solar plumber and two assistants with minimal training can install the system per day. The thermosiphon installation has a negligible maintenance cost (rising costs if antifreeze and electric power are used for circulation) and in the US reduces the cost of household operations by $ 6 per person per month. Solar water heating can reduce CO 2 emissions from four families by 1 ton/year (if replacing natural gas) or 3 ton/year (if replacing electricity). Medium temperature installations can use one of several designs: the common design is pressurized glycol, drain back, batch system and newer lower pressure tolerance system using water-filled polymer pipes with photovoltaic pumping. European and International Standards are being reviewed to accommodate innovations in the design and operation of medium temperature collectors. Operational innovation includes the operation of "permanently dampened collectors". This innovation reduces or even eliminates the occurrence of high temperature pressure without a flow called stagnation that will reduce the life expectation of the collectors.
Sun drying
Solar thermal energy can be useful for wood drying for construction and wood fuel such as wood chips for burning. Solar is also used for food products such as fruits, grains, and fish. Drying plants by the way of the sun is environmentally friendly as well as cost effective while improving quality. The less money needed to make a product, the less that can be sold, the buyer and the seller delight. Technology in solar drying includes air collectors of ultra cheap pumped airbags based on black fabric. Solar thermal energy is helpful in the process of drying products such as wood chips and other forms of biomass by raising the temperature while allowing air to pass through and get rid of moisture.
Cooking
The solar stove uses sunlight for cooking, drying and pasteurization. Diesel cooking balances fuel costs, reduces fuel or fuelwood demand, and improves air quality by reducing or eliminating sources of smoke.
The simplest type of solar stove is a box cooker first made by Horace de Saussure in 1767. The base box consists of an insulated vessel with a transparent cap. This cooker can be used effectively with partially cloudy skies and will usually reach 50-100 ° C.
Concentrate solar cookers using reflectors to concentrate solar energy into a cooking container. The most common reflector geometries are flat plates, discs and parabolic trough types. This design cooks faster and at higher temperatures (up to 350 Â ° C) but requires direct light to function properly.
Solar Kitchen in Auroville, India uses a unique concentrate technology known as a solar bowl. Contrary to the conventional tracking reflector/fixed receiver system, the solar bowl uses a fixed ball reflector with a receiver that tracks the focus of light as the Sun moves across the sky. The recipient of the solar bowl reaches a temperature of 150 Â ° C which is used to produce steam that helps cook 2,000 times a day.
Many other solar kitchens in India use another unique concentration technology known as the Scheffler reflector. This technology was first developed by Wolfgang Scheffler in 1986. The Scheffler Reflector is a parabolic dish that uses single axis tracking to follow the daily course of the Sun. This reflector has a flexible reflective surface capable of changing its curvature to adjust to seasonal variations in the angle of sunlight. The Scheffler Reflector has the advantage of having a fixed focal point that enhances the ease of cooking and is capable of reaching temperatures of 450-650 ° C. Built in 1999 by Brahma Kumaris, the world's largest Scheffler reflector system in Abu Road, Rajasthan India is capable of cooking up to 35,000 meals a day. As early as 2008, over 2,000 large cooks from Scheffler's design have been built around the world.
Distillation
Solar stills can be used to make drinking water in areas where clean water is not common. Solar distillation is required in this situation to provide water purified to people. Solar energy heats the water in silence. The water then evaporates and condenses on the underside of the cover glass.
High temperature collector
Where temperatures below about 95Ã, Â ° C are sufficient, due to space heating, flat plate collectors of an unconcentrated type are commonly used. Due to the relatively high heat loss through glass, the flat plate collector will not reach temperatures well above 200 ° C even when the heat transfer fluid is stagnant. Such temperatures are too low for efficient conversion to electricity.
The efficiency of the heat engine increases with the temperature of the heat source. To achieve this in solar thermal energy generation, solar radiation is concentrated by a mirror or lens to obtain a higher temperature - a technique called Solar Power Concentrated (CSP). The practical effect of high efficiency is to reduce the size of factory collectors and the total land use per unit of power generated, reducing the environmental impact of power generation as well as the cost.
As temperatures increase, various forms of conversion become practical. Up to 600 Â ° C, steam turbines, standard technology, has an efficiency of up to 41%. Above 600 Â ° C, gas turbines can be more efficient. Higher temperatures become a problem as various materials and techniques are needed. One proposal for very high temperatures is to use liquid fluoride salts that operate between 700 ° C to 800 ° C, using a multi-stage turbine system to achieve 50% or more thermal efficiency. Higher operating temperatures allow the plant to use higher temperature dry heat exchangers for its heat dissipation, reducing the use of plant water - essential in deserts where large solar plants are practical. High temperatures also make heat storage more efficient, as more watt-hours are stored per unit of fluid.
The commercial thermal energy heat (CSP) concentrate plant was first developed in the 1980s. The largest solar thermal power plant in the world today is a 370 MW MW Ivanpah Solar Power Facility, commissioned in 2014, and 354 MW SEGS CSP installations, both located in the Mojave Desert of California, where several other solar projects have been realized as well. With the exception of Shams solar power plant, built in 2013 near Abu Dhabi, United Arab Emirates, all other 100 MW or larger CSP power plants are located in the United States or in Spain.
The main advantage of CSP is the ability to add heat storage efficiently, allowing power delivery over 24 hours. Because peak electrical demand usually occurs between about 4 and 8 pm, many CSP power plants use 3 to 5 hours of thermal storage. With today's technology, heat storage is much cheaper and more efficient than electrical storage. In this way, the CSP factory can generate electricity day and night. If the CSP site has predictable solar radiation, then the CSP plant becomes a reliable power plant. Reliability can be further enhanced by installing a back-up burning system. The back-up system can use most of the CSP plant, which lowers the cost of back-up systems.
CSP facilities utilize high electrical conductivity materials, such as copper, power cables in the field, grounding networks, and motors to track and pump liquids, as well as in main generators and high-voltage transformers. (See: Copper in concentrating solar thermal facilities.)
With reliability, unused deserts, no pollution, and no fuel costs, barriers to large deployments for CSP are cost, aesthetic, land use and similar factors to connect the required high voltage lines. Although only a small part of the desert is required to meet global electricity demand, still a large area must be covered with a mirror or lens to gain large amounts of energy. An important way to reduce costs is the use of simple designs.
When considering the impact of land use associated with exploration and extraction through the transportation and conversion of fossil fuels, which are used for most of our electric power, utility-scale solar power compares as one of the most energy efficient land resources available:
The federal government has dedicated nearly 2,000 times more land for oil and gas leasing than the development of the sun. In 2010, the Bureau of Land Management approved nine large-scale solar projects, with a total power plant capacity of 3,682 megawatts, representing approximately 40,000 hectares. In contrast, in 2010, the Bureau of Land Management processed more than 5,200 gas and oil lease applications, and issued 1,308 leases, totaling 3.2 million hectares. Currently, 38.2 million acres of land public land and an additional 36.9 million acres of offshore exploration in the Gulf of Mexico are under rental for oil, gas exploration and production.
System design
At noon the sun has a different position. For low concentration systems (and low temperatures) tracking can be avoided (or limited to a few positions per year) if nonimaging optics are used. However, for higher concentrations, if the mirror or lens does not move, then the focus of the mirror or lens changes (but also in these cases the nonimaging optics provide the widest reception angle for a certain concentration). Therefore, it seems unavoidable that there should be a tracking system that follows the sun's position (for solar photovoltaic solar trackers only optional). Tracking systems increase cost and complexity. With this in mind, different designs can be distinguished in the way they concentrate light and track the position of the sun.
Design of parabolic trough
Parabolic trough power plants use a curved trough, a mirror reflecting direct solar radiation to a liquid filled glass tube (also called a receiver, absorber or collector) running the length of the trough, positioned at the reflector focal point. This trough is parabolic in shape along one axis and linear on the orthogonal axis. For changes in the daily position of the sun perpendicular to the receiver, the trough tilts east to west so that the direct radiation remains focused on the receiver. However, seasonal changes in the angle of sunlight parallel to the trough do not require mirror adjustment, since light is only concentrated elsewhere on the receiver. Thus the trough design does not require tracking on the second axis. The receiver may be enclosed in a vacuum of glass. Vacuum significantly reduces convective heat loss.
A liquid (also called heat transfer fluid) passes through the receiver and becomes very hot. Common liquids are synthetic oils, molten salts and pressurized steam. Heat-containing liquids are transported to a hot engine where about a third of the heat is converted into electricity.
The full-scale parabolic trough system consists of many such troughs arranged in parallel over a large area. Since 1985 the solar thermal system using this principle has been fully operational in California in the United States. This is called the Solar Energy System (SEGS) system. Other CSP designs do not have such long experience and therefore nowadays it can be said that the parabolic trough design is the most thoroughly proven CSP technology.
SEGS is a collection of nine factories with a total capacity of 354 MW and has become the world's largest thermal power plant, both thermal and non-thermal, over the years. The new plant is Nevada Solar One plant with a capacity of 64 MW. The 150 MW Andasol solar power station in Spain with each site has a capacity of 50 MW. It should be noted however, that the plant has a heat storage requiring a larger solar collector field relative to the size of the steam turbine generator to store heat and send heat to the steam turbine at the same time. Thermal storage allows better utilization of steam turbines. With day and night operations of the Andasol 1 steam turbine at 50 MW peak capacity generates more energy than Nevada Solar One at a 64 MW peak capacity, due to the plant's former thermal energy storage system and the larger solar field. The 280 MW Solana plant begins operations in Arizona in 2013 with power storage for 6 hours. Hassi R'Mel integrated combined solar power plant cycles in Algeria and Martin Next Generation The Center for Solar Energy both use a parabolic trough in a combined cycle with natural gas.
Closed trough
The attached trough architecture encapsulates the solar thermal system in a greenhouse like a greenhouse. Greenhouses create a protected environment to withstand elements that can negatively impact the reliability and efficiency of the solar thermal system.
The curved reflective mirror of the sunlight is hung inside the greenhouse structure. A single-axis tracking system positioned a mirror to track the sun and focus its light onto stationary steel pipelines, also suspended from the greenhouse structure. Steam is produced directly, using quality water in the oil field, when water flows from the inlet to the entire pipe, without heat exchangers or intermediate work fluids.
The resulting vapor is then fed directly to the existing steam distribution network in the field, where steam continues to be injected deep into the oil reservoir. Protecting the mirrors from the wind allows them to reach higher temperatures and prevent dust from forming as a result of exposure to moisture. GlassPoint Solar, the company that created the Enclosed Trough design, claims that the technology can generate heat for the EOR of about $ 5 per million British thermal units in a sunny region, versus between $ 10 and $ 12 for other conventional thermal solar technologies.
The GlassPoint closed trough system has been used at the Miraah facility in Oman, and a recent project has been announced for the company to bring a closed trough technology to South Belridge Oil Field near Bakersfield, California.
Design tower power
The power tower (also known as 'central tower' power station or 'heliostat' power plant) captures and focuses solar thermal energy with thousands of tracking mirrors (called heliostats) in about two square miles of field. A tower is in the middle of a heliostat field. Heliostats focus concentrated sunlight on the receiver that is above the tower. In recipients of concentrated sunlight heats the molten salt to more than 1,000 Â ° F (538 Â ° C). The heated molten salt then flows into the thermal storage tank where it is stored, maintains 98% thermal efficiency, and is ultimately pumped to the steam generator. Steam drives a standard turbine to generate electricity. This process, also known as "Rankine cycle" is similar to a standard coal-fired power plant, unless it is triggered by clean and free solar energy.
The advantage of this design over the design of the parabolic trough is the higher temperature. Thermal energy at higher temperatures can be converted to electricity more efficiently and can be stored less costly for later use. In addition, there is less need to level the ground area. In principle, electric towers can be built on the hill side. Mirrors can be flat and pipes are concentrated in the tower. The disadvantage is that each mirror must have its own dual-axis control, while in a single-axis-track parabolic design can be shared for a large array of mirrors.
The cost/performance comparison between electric towers and parabolic concentrators is made by NREL which estimates that by 2020 electricity can be produced from electric towers of 5.47 Â ¢/kWh and for 6.21 Â ¢/kWh of parabolic troughs. The capacity factor for power towers is estimated at 72.9% and 56.2% for parabolic troughs. There is hope that the development of cheap, durable, and mass produced heliostate power generating components can lower this cost.
The first commercial tower power station is the PS10 in Spain with a capacity of 11 MW, completed in 2007. Since then a number of plants have been proposed, some have been built in a number of countries (Spain, Germany, US, Turkey, China). , India) but some of the proposed plants were canceled due to the falling solar photovoltaic price. A solar power tower is expected to be online in South Africa in 2014. The Ivanpah Solar Power Facility in California generates 392 MW of electricity from three towers, making it the largest solar power plant when it comes online by the end of 2013.
The dish design
CSP-Stirling is known to have the highest efficiency of all solar technologies (about 30%, compared with about 15% solar photovoltaic), and is expected to be able to generate the cheapest energy among all renewable energy sources in high-scale production and hot, semi-desert, etc. A Stirling system uses large, reflective, parabolic dishes (similar in shape to satellite television antennas). It focuses all the sunlight that touches the disk to a point above the disc, where the receiver captures heat and turns it into a useful form. Usually this dish is paired with a Stirling engine in a Dish-Stirling System, but sometimes there is also a steam engine in use. This creates a kinetic rotational energy that can be converted into electricity using an electric generator.
In 2005 Southern California Edison announced an agreement to purchase a solar-powered Stirling engine from Stirling Energy Systems over a period of twenty years and in quantities (20,000 units) sufficient to generate 500 megawatts of electricity. In January 2010, Stirling Energy Systems and Tessera Solar commissioned the first demonstration of a 1.5-megawatt ("Maricopa Solar") power plant using Stirling technology in Peoria, Arizona. In early 2011, Stirling Energy's development arm, Tessera Solar, sold two major projects, the Imperial 709 MW project and the Calico 850 MW project for AES Solar and K.Road, respectively. In 2012 the Maricopa plant was purchased and disassembled by United Sun Systems. United Sun Systems released a new generation system, based on a V-shaped Stirling engine and a 33 kW peak production. The new CSP-Stirling technology lowers LCOE to USD 0.02 on utility scale.
According to the developer, Rispasso Energy, a Swedish company, by 2015 the Dish Sterling system tested in the Kalahari Desert in South Africa shows a 34% efficiency.
Fresnel Technology
A Fresnel linear reflector power plant uses a series of long, narrow, shallow-curved (or even flat) mirrors to focus light onto one or more linear receivers placed above the mirror. Above the receiver, a small parabolic mirror can be mounted to focus the light further. The system aims to offer lower overall cost by sharing recipients between multiple mirrors (compared to trough and plate concepts), while still using simple focal-line geometry with one axis for tracking. This is similar to the trough design (and different from central towers and plates with double axes). The receiver of the stationary and so liquid clutch is not required (as in troughs and plates). The mirror also does not need to support the receiver, so it is structurally simpler. When appropriate targeting strategies are used (mirrors intended for different recipients at different times of the day), this may allow for the packaging of denser mirrors in the area of ​​available land.
Single rival axis tracking technology including linear Fresnel linear (LFR) and compact-LFR (CLFR) technology is relatively new. LFR differs from the parabolic trough where the absorber is fixed in the space above the mirror plane. Also, the reflector consists of many low-row segments, which are collectively focused on long elevated tower receivers running parallel to the reflector axis of rotation.
Fresnel lens concentrator prototypes have been produced for heat energy collection by the International Automated System. No full-scale thermal systems that use Fresnel lenses are known to operate, although products that incorporate Fresnel lenses together with photovoltaic cells are readily available.
MicroCSP
MicroCSP is used for community-sized power plants (1 MW to 50 MW), for industrial, agricultural, and process 'process heat' applications, and when large amounts of hot water are required, such as resort pools, water parks, large laundry facilities, sterilizers, , and other uses.
Closed parabolic trough
The attached parabolic solar system encloses components in a greenhouse-type greenhouse. Glasshouse protects components from elements that can negatively impact the reliability and efficiency of the system. These important safeguards include nighttime glass washings with an efficient, efficient water-efficient washing system. A lightly curved reflective solar mirror is hung from the greenhouse ceiling by a cable. A single-axis tracking system puts a mirror to take the optimal amount of sunlight. The mirror focuses the sunlight and focuses it on stationary steel pipes, also depending on the greenhouse structure. Water is pumped through pipes and boiled to produce steam when intense solar radiation is applied. Steam is available for process heat. Protecting the mirrors from the wind allows them to reach higher temperatures and prevent dust from forming in the mirror as a result of exposure to moisture.
Collection and heat exchange
Lebih banyak energi terkandung dalam frekuensi cahaya yang lebih tinggi berdasarkan rumus , di mana h adalah konstanta Planck dan adalah frekuensi. Pengumpul logam turun mengkonversi frekuensi cahaya yang lebih tinggi dengan memproduksi serangkaian pergeseran Compton ke kelimpahan cahaya frekuensi rendah. Kaca atau pelapis keramik dengan transmisi tinggi dalam penyerapan UV yang terlihat dan efektif dalam logam perangkap pemblokiran IR (penahan panas) menyerap cahaya frekuensi rendah dari kehilangan radiasi. Konveksi isolasi mencegah kerugian mekanis yang ditransfer melalui gas. Setelah dikumpulkan sebagai panas, efisiensi penahanan termos meningkat secara signifikan dengan peningkatan ukuran. Tidak seperti teknologi Photovoltaic yang sering terdegradasi di bawah cahaya pekat, Solar Thermal bergantung pada konsentrasi cahaya yang membutuhkan langit yang jernih untuk mencapai suhu yang sesuai.
The heat in the solar thermal system is guided by five basic principles: heat acquisition; heat transfer; heat storage; heat transport; and heat insulation. Here, heat is a measure of the amount of heat energy that an object contains and is determined by the temperature, mass, and heat of the object. Solar thermal power plants use heat exchangers designed for constant working conditions, to provide heat exchange. Copper heat exchangers are important in solar thermal heating and cooling systems due to high copper heat conductivity, resistance to atmospheric and water corrosion, sealing and solder incorporation, and mechanical strength. Copper is used both in receivers and in primary circuits (pipes and heat exchangers for water tanks) of solar hot water systems.
The heat obtained is the heat that accumulates from the sun in the system. Hot thermal sun trapped using greenhouse effect; The greenhouse effect in this case is the ability of the reflective surface to transmit shortwave radiation and reflect long wave radiation. Infrared heat and radiation (IR) are produced when short-wave radiation light touches the absorber plate, which is then trapped inside the collector. The liquid, usually water, in the absorber tube collects the trapped heat and transfers it to the heat storage cupboard.
Heat is transferred either by conduction or convection. When water is heated, kinetic energy is transferred through conduction to water molecules throughout the medium. These molecules disperse their heat energy by conduction and occupy more space than the cold slow moving molecules above them. The distribution of energy from the rising of hot water to the submerged cold water contributes to the convection process. Heat is transferred from the collector absorber plate in the fluid by conduction. The collector fluid is circulated through the carrier pipe to the heat transfer dome. In the vault, heat is transferred throughout the medium through convection.
Thermal storage enables solar thermal plants to generate electricity for hours without sunlight. Heat is transferred to a thermal storage medium inside an isolated reservoir for hours with sunlight, and is drawn to a power station during less sunlight hours. Thermal storage media will be discussed in the heat storage section. The heat transfer rate is related to conductive and intermediate convection and temperature difference. The body with a large temperature difference transferring heat faster than the body with a lower temperature difference.
Heat transport refers to the activity in which heat from a solar collector is transported to a heat storage cabinet. Heat insulation is particularly important in both heat transport tubes as well as storage dome. This prevents heat loss, which in turn is related to energy loss, or decreased system efficiency.
Heat storage for heating
A set of adult technologies called seasonal thermal energy storage (STES) is able to store heat for months, so that the sun's heat collected especially in the Summer can be used for year-round heating. The solar-supplied STES technology has advanced primarily in Denmark, Germany, and Canada, and applications include individual buildings and district heating networks. Drake Landing Solar Community in Alberta, Canada has a small district system and in 2012 reached a world record that provides 97% of the year-round space heating needs from the sun. STES thermal storage media includes deep aquifers; the original rocks surrounding the small diameter group, heat exchangers equipped with drill holes; large, shallow pits, lined with gravel and isolated upon; and large, isolated and buried surface water tanks.
Thermal storage to stabilize solar power plants
Thermal storage enables solar power to generate electricity during the night and on cloudy days. This allows the use of solar power for base load generation and peak power generation, with the potential to replace coal-fired power plants and natural gas. In addition, higher generator utilization reduces costs. Even short-term storage can help by smoothing the "duck curve" of rapid changes in the needs of the generation at sunset when the grid covers a large amount of solar capacity.
Heat is transferred to thermal storage media in an isolated reservoir during the day, and is drawn for power plants at night. Thermal storage media include pressurized steam, concrete, various phase change materials, and aqueous salts such as calcium, sodium, and potassium nitrate.
Steam accumulator
The PS10 solar tower stores heat in the tank as a pressurized vapor at 50 bar and 285 ° C. The steam condenses and flashes back into steam, when the pressure is lowered. Storage for one hour. It is recommended that longer storage is possible, but that has not been proven in existing power plants.
Storage of liquid salt
Various liquids have been tested for transporting solar heat, including water, air, oil, and sodium, but Rockwell International chooses the best liquid salt. Liquid salt is used in solar tower systems because of liquid at atmospheric pressure, providing a low cost medium for storing thermal energy, operating temperatures compatible with current steam turbines, and non-combustible and non-toxic. Liquid salt is used in chemical and metal industries to transport heat, so industry has experience with it.
The first commercial liquid salt mixture is a common form of saltpeter, 60% sodium nitrate and 40% potassium nitrate. Saltpeter melts at 220 ° C (430 ° F) and is stored liquid at 290 ° C (550 ° F) in an isolated storage tank. Calcium nitrate can reduce the melting point to 131 Â ° C, allowing more energy to be extracted before the salt freezes. There are now some stable technical calcium nitrate grades at more than 500 ° C.
This solar power system can generate power in cloudy weather or at night by using heat in a hot salt tank. The tanks are insulated, capable of storing heat for a week. The tank that drives the 100-megawatt turbine for four hours is about 9 m (30 ft) and 24 m (80 ft) in diameter.
Andasol power plant in Spain is the first commercial solar thermal power plant that uses liquid salt for heat storage and nighttime generators. It came in March 2009. On July 4, 2011, a company in Spain celebrated a historic moment for the solar industry: a solar power plant concentrated in Torresol 19.9 MW being the first to generate uninterrupted power for 24 hours, using a salt heat storage melt.
In 2016 SolarReserve proposes a 2 GW, $ 5 billion solar plant concentrated with storage in Nevada.
Phase change material for storage
Phase Change Material (PCM) offers an alternative solution in energy storage. Using a similar heat transfer infrastructure, PCM has the potential to provide more efficient storage facilities. PCM can be organic or inorganic. The advantages of organic PCMs include no corrosion, low or no cooling, and chemical and thermal stability. Disadvantages include the enthalpy of low phase change, low thermal conductivity, and flammability. Inorganic is advantageous with enthalpy of larger phase changes, but indicates a loss with undercooling, corrosion, phase separation, and lack of thermal stability. The enthalpy of greater phase change in inorganic PCM makes hydrate salt a strong candidate in the field of solar energy storage.
Water usage
Designs that require water for condensation or cooling may conflict with the location of solar thermal generators in desert areas with good solar radiation but limited water resources. The conflict is illustrated by the Solar Millennium plan, a German company, to build a factory in the Amargosa Valley of Nevada that would require 20% of the water available in the area. Some other plants projected by the same company and others in the California Mojave Desert may also be affected by difficulty in obtaining adequate and appropriate water rights. California's water law currently prohibits the use of drinking water for cooling.
Other designs require less water. The Ivanpah Solar Power Facility in south-east California conserves rare desert water by using air cooling to turn steam back into the water. Compared to conventional wet cooling, this results in a 90% reduction in water usage at the expense of some efficiency losses. Water is then returned to the boiler in an environmentally friendly closed process.
Conversion rate from solar energy to electrical energy
Of all these technologies, solar/dish stirling machines have the highest energy efficiency. A single parabolic-Stirling machine installed at Sandia National Laboratories National Solar Thermal Test Facility (NSTTF) generates as many as 25 kW of electricity, with a conversion efficiency of 31.25%.
The solar parabolic plant has been built with an efficiency of about 20%. Fresnel reflectors have slightly lower efficiency (but this is compensated by a more dense packing).
The gross conversion efficiency (taking into account that a solar plate or trough occupies only a fraction of the total area of ​​a power plant) is determined by the net generation capacity of solar energy falling on the total area of ​​a solar power plant. The 500-megawatt (MW) SCE/SES plant will extract approximately 2.75% of the radiation (1 kW/mÃ,²; see solar power for discussion) that falls on 4,500 hectares (18.2 km²). For 50Ã, MW Your Sol Power Plant is under construction in Spain (total area 1,300ÃÆ' â € "1,500 m = 1.95Ã, kmÃ,²) gross conversion efficiency out at 2.6%.
Furthermore, efficiency is not directly related to cost: at the total cost calculation, both efficiency and construction and maintenance costs must be taken into account.
Standard
- EN 12975 (efficiency test)
See also
Note
References
External links
- The time of solar power to shine on MSN Money
- The largest Solar Thermal in Saudi Arabia
- Renewable Technologies in Place on the United States Environmental Protection Agency website
- The updated solar energy website in Curlie (based on DMOZ)
- World Bank Strategy Review/GEF for Solar Power System Development of Solar Power Generation
- Solar thermal energy calculator
- Concentrating Solar Energy Technological overview by Gerry Wolff, TREC-UK coordinator
- NREL Concentrating the Solar Program Site
- A comprehensive review of technology and parabolic markets
- Nevada Gets US Solar Thermal Plant First
- Solar Thermal Solar Barometer and Concentrated - 2013 Pdf
- TechScope Solar Technological Technological Readiness Certification Report - UNEP
- Guidance for Solar Awareness and Cooling Enhancement Campaign - UNEP
- Guidelines for Standardization and Quality Assurance for Thermal Solar - UNEP
- Guidance for Heating and Cooling Policies of Solar Heating and Framing Provisions - UNEP
- Solar Water Heating, Strategic Planning Guide for Urbanities in Developing Countries - UNEP
Source of the article : Wikipedia
0 Comments