Thermal solar energy
The solar thermal energy or thermal solar energy consists of the use of the Sun's energy to produce heat that can be used to cook food or for the production of hot water for domestic water consumption, whether domestic hot water, heating or for the production of mechanical energy and, from it, electrical energy. Additionally, it can be used to feed an absorption refrigeration machine, which uses heat instead of electricity to produce cold, with which the air in the premises can be conditioned.
Solar thermal energy collectors are classified as low, medium and high temperature collectors. Low temperature collectors are generally flat plates used to heat water. Medium temperature collectors are also usually flat plates used to heat water or air for residential or commercial uses. High temperature collectors concentrate sunlight using mirrors or lenses and are generally used for the production of electrical energy. Solar thermal energy is different from and much more efficient than photovoltaic solar energy, which converts solar energy directly into electricity. While generating facilities provide only 600 megawatts of solar thermal power globally as of October 2009, other plants are under construction for another 400 megawatts and other concentrating solar power projects totaling 14 gigawatts are under development.
Domestic hot water (ACS)
Regarding the generation of hot water for sanitary uses (also called «hand water»), there are two types of installations commonly called heaters: open circuit and closed circuit. In the former, drinking water passes directly through the solar collectors; This system reduces costs and is more efficient (energy speaking), but it presents problems in areas with temperatures below the freezing point of the water, as well as in areas with a high concentration of mineral salts that end up clogging the panel ducts. Two systems are distinguished in closed circuit installations: thermosiphon flow and forced flow. Solar thermal panels have a very low environmental impact.
Solar heating and cooling
Solar thermal energy can be used to support the conventional heating system (gas or electric boiler) through solar thermal collectors and storage tanks ("boiler"), support that, usually, It consists of between 10% and 40% of the energy demand for heating, depending on the level of insulation of the building. To do this, the installation or boiler must have a plate heat exchanger (which will allow the solar heating system to be connected to the boiler) and a regulator (which gives priority to the use of hot water to be used in hand water).
On the other hand, it is also possible to use solar air collectors to heat and ventilate a home, offices and commercial premises. These solar air heating and ventilation systems are expanding their use, due to the advantages of low cost, saving heating energy and improving indoor air quality.
Solar heating of swimming pools
Another of the important uses of Solar Thermal Energy is the heating of swimming pools or swimming pools. For this purpose, uncovered solar collectors («unglazed solar collectors») are used, usually made of polypropylene, EPDM or polyethylene. Its operation is very simple, since it takes water from the same filter pump, takes it to a group of collectors normally placed on a nearby roof, heats the water and returns it to the pool, as can be seen in this video. Through these equipment, the use of swimming pools can be extended from spring to autumn in temperate climates, and throughout the year in hot climates. Its installation is very economical compared to the use of gas or electric boilers and, in addition, it does not consume energy. Its use is widespread in countries such as the United States, Canada, Australia, Brazil, Mexico and South Africa.
Installation components
A solar thermal installation is made up of solar collectors, a primary and secondary circuit, heat exchanger, accumulator, expansion vessel and pipes. If the system works by thermosiphon, it will be the difference in density due to temperature change that will move the liquid; if the system is forced, then we will need in addition: pumps and a main control panel.
Solar collectors
Solar collectors are the elements that capture solar radiation and convert it into thermal energy, that is, heat. Flat plate solar collectors, vacuum tube collectors and unprotected or uninsulated absorber collectors are known as solar collectors. Flat collection systems (or flat plate) with a glass cover are the most common in the production of DHW domestic hot water. The glass lets the sun's rays through, these heat metal tubes that transmit the heat to the liquid inside. The tubes are dark in color, since dark surfaces heat up more.
The glass that covers the collector not only protects the installation, but also allows heat to be conserved, producing a greenhouse effect that improves the performance of the collector.
They are made up of a closed aluminum casing resistant to marine environments, an eloxat aluminum frame, a silicone-free perimeter gasket, environmentally friendly rock wool thermal insulation, a highly transparent solar glass cover, and finally by ultrasonic welded tubes.
Solar collectors are made up of the following elements:
- Cover: It is transparent, may be present or not. It is usually glass although they are also used as plastic, since it is less expensive and manageable, but it should be a special plastic. Its function is to minimize convection and radiation losses, and therefore it must have a solar transmittal as high as possible.
- Air channel: It is a space (empty or not) that separates the cover from the absorbing plate. Its thickness will be calculated taking into account to balance the convection losses and the high temperatures that can be produced if it is too narrow.
- Absorbent Plate: The absorbing plate is the element that absorbs solar energy and transmits it to the liquid that circulates through the pipes. The main characteristic of the plate is that it has to have a large solar absorption and a reduced thermal emission. Since common materials do not meet this requirement, combined materials are used to obtain the best absorption/emission ratio.
- Tubes or ducts: Tubes are touching (sometimes welded) the absorbing plate to make the energy exchange as large as possible. Through the tubes circulate the liquid that will heat and go to the accumulation tank.
- Insulating layer: The purpose of the insulating layer is to coat the system to avoid and minimize losses. In order for the isolation to be the best possible, the insulating material must have a low thermal conductivity.
Flat plate solar collectors
The soul of the system is a vertical fence made of metal tubes, to simplify, that conduct the cold water in parallel, connected from below by a horizontal tube in the cold water intake, and above by another similar one to the return.
The grill is embedded in a cover, like the one described above, usually with double glass on the top and insulation on the back.
In some models, the vertical tubes are welded to a metal plate to take advantage of the insolation between tube and tube.
Evacuated tube solar collectors "all glass", without copper tube
In this system, the metal tubes of the previous system are replaced by glass tubes, introduced, one by one, into another glass tube between which a vacuum is created as insulation. These equipments may have a higher performance than flat plate ones at high hot water temperatures or very cold climates but have lower performances at temperatures close to typical domestic consumption (45 °C) or temperate or hot climates.[citation required]
Manufacturing costs are much less than flat plates. Since they are made 100% of borosilicate glass, on the other hand, flat collectors are made of copper, which is why they are more expensive to manufacture.
Also an additional advantage of glass tubes is their greater versatility of placement, both from a practical and aesthetic point of view. Being cylindrical, they tolerate variations of up to 25º on the ideal inclination without loss of performance. For this reason it is possible to adapt them to the vast majority of existing buildings. Another interesting aspect is that they need a smaller solar collection area due to their higher efficiency. In addition, due to their cylindrical shape, they are also much more efficient, since they receive the sun's rays perpendicularly throughout the day. On the contrary, flat collectors are only effective when they are perpendicular to the sun.
Evacuated tube solar collectors with “heat pipes” by phase change, with copper tube
This system takes advantage of the phase change from vapor to liquid within each tube, to deliver energy to a second circuit of transport liquid.
The elements are closed tubes, usually copper, that contain the liquid that, when heated by the sun, boils and turns into vapor that rises to the top where there is a wider head (condensation zone), which on the outside it is in contact with the transporting liquid, which, being colder than the vapor in the tube, captures the heat and causes the vapor to condense and fall into the lower part of the tube to start the cycle again.
The liquid in the tube can be water, to which the pressure has been reduced to a partial vacuum, it will have a low boiling point, which allows it to work even with insolation from infrared rays in the presence of clouds.
The heat pipe (or copper pipe) can be wrapped with a jacket of special materials to minimize irradiation losses.
The heat pipe is closed inside another glass tube between which a vacuum is made as insulation. Strong glass tubes are often used to reduce damage in the event of small hailstorms.
They are up to 163% more efficient than coiled flat plates and equally cheaper to manufacture than flat plates, as the price of glass is lower than the copper of the coil contained in the flat plate.
Primary circuit
The primary circuit, is a closed circuit, it transports the heat from the collector to the accumulator (system that stores heat). The heated liquid (water or a mixture of substances that can transport heat) carries the heat to the accumulator. Once cooled, it returns to the collector to heat up again, and so on.
Heat exchanger
The heat exchanger heats drinking water through the heat captured from solar radiation. It is located in the primary circuit, at its end. It has the shape of a serpentine, since, thus, it is possible to increase the contact surface and, therefore, the efficiency.
The water that enters the storage tank—as long as it is colder than the coil—will heat up. This water, heated during sunny hours, will be available for later consumption.
Accumulator
The accumulator is a tank where useful heated water for consumption accumulates. It has an inlet for cold water and an outlet for hot. The cold enters below the accumulator where it meets the exchanger. As it heats up, it moves upwards, which is where the hot water for consumption will come from.
Internally, it has a system to prevent the corrosive effect of stored hot water on materials. Outside. it has a layer of insulating material that prevents heat loss and is covered by a material that protects the insulation from possible humidity and blows.
Secondary Circuit
The secondary or consumption circuit (open circuit) enters cold supply water and the other end of the heated water is consumed (shower, sink, etc). The cold water goes through the accumulator, first, where it heats the water until it reaches a certain temperature. Outdoor hot water pipes must be covered by insulation.
If the consumption includes heating, the heat emitting system (radiators (60 °C), fan-coil (45 °C), underfloor heating (30 °C), radiant baseboard, radiant wall, etc.) that is The most convenient to use is the low temperature one (<=50 °C). In this way, the solar heating system has a higher performance.
However, systems that are not low temperature can be installed, in order to use conventional radiators.
Bombs
The pumps, in the event that the installation is of forced circulation, are of the recirculation type (there are usually two per circuit), one working half the day, and the couple half the remaining time. The installation consists of the clocks that keep the operation of the system, they make the exchange of the pumps, so that one works the first 12 hours and the other the remaining 12 hours. If there are two pumps in operation, there is the advantage that, in the event that one stops working, there is the substitute, so that, thus, the process cannot be interrupted due to the failure of one of these. The other reason to consider is that, thanks to this exchange, the pump does not suffer as much, rather it is left to rest, cool down, and when it is in good condition again (after twelve hours), it is put back on. on going. This means that the pumps can extend the operating time without having to do any type of prior maintenance.
In total and as defined above, there are usually four pumps: two on each circuit. Two in the primary circuit. that pump the water from the collectors; and the other two, in the secondary circuit, which pump the water from the accumulators, in the case of a forced circulation type installation.
Expansion vessel
The expansion vessel absorbs volume variations of the heat transfer fluid, which circulates through the collector ducts, maintaining the appropriate pressure and avoiding fluid mass losses. It is a container with a gas chamber separated from that of liquids and with an initial pressure depending on the height of the installation.
The most commonly used is with an expansion vessel closed with a membrane, without mass transfer outside the circuit.
Pipes
The installation pipes are covered with a thermal insulator to prevent heat loss to the environment. In the past, copper pipes were used. Then, PEX-AL-PEX pipes were used, consisting of three layers: plastic-aluminum-plastic, much cheaper and with a longer useful life than traditional copper pipes. Over the years of use of the equipment and due to the accumulation of solar radiation, it was found that the PEX crystallized, being destroyed by pressure. Currently, BPDN stainless steel pipes insulated with elastomeric foam and surrounded by EPDM mica that gives thermal insulation and provides durability by protecting against radiation and failures due to rupture of joints and welds are used for closed circuits.
Control Panel
There is also a main control panel in the installation, where the temperatures are displayed at all times (a thermal regulator), so that the operation of the system can be controlled at any time. The watches in charge of exchanging bombs also appear.
During the summer, the plates can be covered to prevent them from being damaged by high temperatures, or they can be used to produce solar cooling (cold air conditioning).
Teams
Especially popular are compact domestic equipment, typically made up of a tank with a capacity of about 150 liters and a collector of about 2 m². These devices, available in both open and closed circuits, can supply 90% of the annual hot water needs for a family of four, depending on radiation and usage. These systems prevent the emission of up to 4.5 tons of harmful gases into the atmosphere. The approximate energy return time (time needed to save the energy used to manufacture the appliance) is approximately one and a half years. The useful life of some equipment can exceed 25 years with minimal maintenance, depending on factors such as water quality.
These teams can be distinguished between:
Forced Circulation Equipment: Basically composed of collectors, a solar accumulator, a hydraulic group, a regulation and an expansion vessel.
Thermosiphon Equipment: The main characteristic of which is that the accumulator is located on the roof, above the collector.
Equipment with Drain-Back System: A compact and safe system, very appropriate for single-family homes.
It is common to find installations in which the accumulator contains an electrical support resistance, which acts in the event that the system is not capable of reaching the temperature of use (normally 40 °C); In Spain, this option has been prohibited after the approval of the CTE (Technical Building Code), since the heat from the resistance can, if the panel is colder than the integrated accumulator, heat the panel and lose heat, and therefore therefore energy through it. In some countries, equipment that uses gas as support is commercialized.
The constructive characteristics of the collectors respond to the minimization of energy losses once the fluid that passes through the tubes has been heated, for which reason there are insulations for conduction (vacuum or others) and low-temperature reradiation.
In addition to its use as sanitary hot water, heating and cooling (by means of an absorption machine), the use of thermal solar panels (generally made of cheap materials such as polypropylene) has proliferated for heating outdoor residential swimming pools, in countries where the legislation prevents the use of other types of energy for this purpose.
Amortization
In many countries there are subsidies for the domestic use of solar energy, in which cases a domestic installation can pay for itself in about five or six years. On September 29, 2006, the Technical Building Code entered into force in Spain, which establishes the obligation to implement sanitary hot water systems (ACS) with solar energy in all new buildings, with the aim of complying with the protocol of Kyoto, but that forgets the heating, which is included in the solar ordinances of the municipalities.
Low temperature collectors
The flat solar collector is the most representative device of photothermal solar technology. Its main application is in heating water for bathrooms and swimming pools, although it is also used to dry agricultural products by heating air and to distill water mainly in rural communities.
It is basically made up of:
- Anodized aluminium frame
- Tempered glass cover, low iron content
- Pipe absorber. Roofed with copper fins
- Power and water discharge heads
- Insulating, usually polystyrene, or unicel
- Colector box, galvanized.
For most solar collectors there are characteristic dimensions. In general terms, the basic unit consists of a flat collector with a surface area of 1.8 to 2.1 m², connected to a storage hot water tank with a capacity of 150 to 200 liters; To this system, frequently, some thermostatic control devices are added, in order to avoid freezing and heat loss during the night. The domestic units work through the thermosiphon mechanism, that is, through the circulation that is established in the system due to the difference in temperature of the stratified layers of liquid in the storage tank. For industrial installations, various modules connected in series-parallel arrangements are used, depending on the case, and pumps are used to establish forced circulation.
Process heat
Solar process heating systems are designed to provide large amounts of hot water or space heating for non-residential buildings.
Evaporation pools are shallow pools that concentrate dissolved solids through evaporation. The use of evaporation pools to obtain salt from salt water is one of the oldest applications of solar energy. Modern uses include concentration of brine solutions used in mining by leaching and removal of dissolved solids from waste streams. Collectively, evaporative pools represent one of the largest commercial applications of solar energy currently in use.
Unglazed Transpired Collectors (UTC") are perforated walls facing the sun used to preheat ventilation air. UTC can increase air temperatures up to 22°C and are capable of delivering outlet temperatures between 45-60°C. The short payback period of transpired collectors (3 to 12 years) makes them a more cost-effective alternative to glazed collection systems. As of 2009, over 1,500 systems have been installed worldwide with a total collector area of 300,000 m². Typical examples include a 860 m² collector in Costa Rica, used to dry coffee beans, and a 1,300 m² collector in Coimbatore, India, used to dry marigolds.
A food processing facility located in Modesto, California uses parabolic troughs to produce steam in the manufacturing process. The 5,000 m² collector area is expected to provide 15 TJ per year.
Medium temperature collectors
Medium temperature installations can use various designs, the most common designs are: glycol pressurized, back drain, batch systems and newer freeze tolerant low pressure systems using photovoltaic pumped water containing polymer pipes. European and international standards are being revised to include innovations in the design and operation of medium temperature collectors. Operational innovations include the operation of "permanently wet collectors". This technique reduces or even eliminates the occurrence of high temperature non-flow stresses known as stagnation, which reduce the expected life of these collectors.
Sun drying
Solar thermal energy can be useful for drying lumber for construction and fuel wood such as wood chips for combustion. It is also used to dry foods such as fruits, grains, and fish. Crop drying by means of solar thermal energy is environmentally friendly as well as economical while improving the quality of the result. Solar drying technologies are varied. The simplest use a mesh stretched out in the sun, while the industrial type use glazed air collectors that conduct hot air to a drying chamber. Solar thermal energy is also useful in the drying process of products such as wood chips and other forms of biomass by raising the temperature while allowing air to pass through and wicking away moisture.
Cooking using thermal solar energy
Solar cookers use sunlight for cooking, drying, and pasteurization. Solar cooking reduces fuel consumption, whether fossil fuels or firewood, and improves air quality by reducing or removing the source of smoke.
The simplest form of solar cooking is the cookbox which was first built by Horace-Bénédict de Saussure in 1767. A basic cookbox consists of an insulated container with a transparent lid. These cookers can be used effectively with partly cloudy skies and typically reach temperatures between 50-100 °C.
Concentrating solar cookers use reflectors to concentrate solar energy onto a cooking container. The most common reflector geometries are flat, disk and parabolic trough plates. These designs cook faster and at higher temperatures (up to 350°C) but require direct sunlight to function properly.
The Solar Cooker in Auroville, India uses a unique concentration technology known as the solar bowl. Unlike conventional fixed receiver or tracking reflector systems, the Solar Bowl uses a fixed spherical reflector with a receiver that tracks the light source as the sun crosses the sky. The receiver of the solar bowl reaches temperatures of 150 °C that is used to produce steam that helps cook 2000 daily rations.
Many other solar cookers in India use another unique concentration technology known as the Scheffler reflector. This technology was first developed by Wolfgang Scheffler in 1986. A Scheffler reflector is a parabolic dish that uses a single tracking axis to track the sun's daily course. These reflectors have a flexible reflective surface that is capable of changing its curvature to adjust for seasonal variations in the angle of incidence of sunlight. Scheffler reflectors have the advantage of having a fixed focal point which improves the ease of firing and are capable of reaching temperatures between 450 to 650 °C. In 1999 in Abu Road, Rajasthan, India the system of The largest Scheffler reflectors in the world, this is capable of cooking up to 35,000 daily servings. At the beginning of 2008, over 2,000 large kitchens have been manufactured, using the Scheffler design, worldwide.
Distillation
Solar stills can be used to process drinking water in areas where clean water is not common. Solar energy heats the water in the container, then the water evaporates and condenses on the bottom of the glass cover.
High temperature collectors
Temperatures below 95 degrees Celsius are sufficient for space heating, in which case non-concentrating flat collectors are generally used. Due to the relatively high heat losses through the glass, flat plate collectors fail to reach much above 200 °C even when the transfer fluid is stagnant. Such temperatures are too low to be used for efficient conversion to electricity.
The efficiency of heat engines increases with the temperature of the heat source. To achieve this in thermal power plants, solar radiation is concentrated by means of mirrors or lenses to achieve high temperatures using a technology called Concentrated Solar Power (CSP).. The practical effect of the higher efficiencies is to reduce the size of the plant's collectors and the use of land per unit of energy generated, reducing the environmental impact of a power plant as well as its cost.
As the temperature rises, different forms of conversion become practical. Up to 600 °C, steam turbines, the standard technology, have an efficiency of up to 41%. Above 600 °C, gas turbines can be more efficient. Higher temperatures are problematic and different materials and techniques are needed. One approach for very high temperatures is to use liquid fluoride salts operating at temperatures between 700 °C to 800 °C, using multi-stage turbine systems to achieve thermal efficiencies of 50% or more. Higher operating temperatures they allow the plant to use high-temperature dry heat exchangers for its thermal exhaust, reducing plant water use, which is critical for practical desert-based plants. Higher temperatures also make heat storage more efficient, since more watt-hours are stored per unit of fluid.
Since a concentrated solar power (CSP) plant first generates heat, it can store that heat before converting it into electricity. With current technology, heat storage is much cheaper than electricity storage. In this way, a CSP plant can produce electricity during the day and at night. If the CSP plant location has predictable solar radiation, then the plant becomes a reliable power generation plant. Reliability can be further improved by installing a backup system that uses an internal combustion system. This backup system can use most of the CSP plant facilities, which lowers the cost of the backup system.
With reliability issues overcome, with empty deserts, no pollution problems and no costs associated with the use of fossil fuels, the main obstacles to the large-scale deployment of CSP plants are costs, aesthetic pollution, land use and similar factors for high voltage power transmission lines. Although only a small percentage of the deserts are needed to supply global electricity requirements, this is still a large area covered with mirrors or lenses that are needed to obtain a significant amount of energy.
Parabolic trough systems use parabolic reflectors in a trough configuration to focus direct solar radiation onto a long tube that runs the length of their focus and leads to the working fluid, which can reach temperatures up to 500 °C
Photothermal electricity generation is currently one of the most extensive applications of solar energy in the world. There are more than 2.5 million m² of solar concentrators installed in 9 Solar Energy Generation System (SEGS) plants of Israel Light Company, representing 354 MW and more than 85% of the electricity produced with solar energy. The company Luz left the market in 1991 because of the reduction that occurred in parallel in the costs of conventional energy and in the subsidies for renewable energy in the United States. Its plants use synthetic oil as a heat transfer medium in the concentrator field; As a primary circuit, the heat collected by the oil is later exchanged with water where steam generation takes place, which in turn expands to complete a Rankine cycle. During periods of low insolation, or to level the offer, they are assisted with natural gas.
Currently, the combined cycle has been introduced to improve the thermodynamic efficiency of these systems and the possibility of directly generating steam in the concentrator field is being studied. This is expected to bring generation prices to competitive levels with conventional thermoelectric plants.
There are other systems, not yet commercial, such as central tower systems that use heliostats (highly reflective mirrors) to focus sunlight, with the help of a computer and a servomechanism, on a central receiver. Parabolic dish systems use these reflectors to focus sunlight onto a receiver mounted above the dish, at its focal point.
During the day and year, the sun changes its position relative to a point on the planet's surface. For low temperature systems sun tracking can be avoided (or limited to a few positions per year) by using non-visual optics. However, for higher temperatures, if the mirrors or lenses do not move, the focus of these changes, causing the acceptance angles to be inefficient, although this is partly offset by the use of non-visual optics. Therefore it is necessary to implement a system to follow the position of the sun, the disadvantage of this is that it increases the cost and complexity of the plant. Different designs have been devised to solve this problem and that can be distinguished in how they concentrate sunlight and follow the position of the sun.
Parabolic trough designs
Parabolic trough power plants use a curved cylindrical mirror to reflect direct solar radiation onto a glass tube containing a fluid (also called a receiver, absorber, or collector) located along the length of the cylinder, positioned at the point focal length of the reflectors. The cylinder is parabolic along an axis and linear in the orthogonal axis. The change during the day of the position of the sun perpendicular to the receiver is followed by tilting the cylinder from east to west in such a way that the direct radiation remains focused on the receiver. However, seasonal changes in the angle of incidence of sunlight parallel to the cylinder do not require adjustment of the mirrors, since the solar radiation is simply concentrated elsewhere in the receiver, thus the design does not require tracking in a second axis.
The receiver may be enclosed in a glass vacuum chamber. The vacuum significantly reduces convective heat loss.
A fluid, also called a heat transfer fluid, passes through the receiver and is heated very strongly. The most common fluids are synthetic oil, molten salt, and pressurized steam. The fluid containing the heat is transported to a heat engine where approximately one third of the heat is transformed into electricity.
Andasol 1 in Guadix, Spain uses the parabolic trough design, which consists of long parallel rows of modular solar collectors. These follow the Sun from east to west rotating on its axis, high-precision reflector panels concentrate solar radiation onto an absorber pipe located along the focal axis of the collector line. A heat transfer medium, a synthetic oil, such as in automobile engines, is circulated through absorber pipes at a temperature of up to 400°C and generates steam under pressure to drive a steam turbine generator. in a conventional power block.
Full-scale parabolic trough systems consist of many such troughs arranged in parallel over a large area of land. Since 1985 SEGS (Solar Energy Generating Systems, SEGS), a solar thermal system using this design, has been operating at full capacity in California, United States.
The Solar Energy Generating System (SEGS) is a set of nine plants with a total capacity of 350 MW. It is currently the largest operational solar system (both of the thermal type or not). The Nevada Solar One plant has a capacity of 64 MW. The Andasol 1 and 2 plants in Spain are under construction, each plant has a capacity of 50 MW, however, these plants are of a design that has a heat storage system that requires land with larger solar collectors in relation to the size of the generator and steam turbine to store the heat and send it to the steam turbines at the same time. Heat storage allows better utilization of steam turbines. With daytime and partially nighttime operation, the Andasol 1 steam turbine with a peak capacity of 50 MW produces more energy than Nevada Solar One with a peak capacity of 64 MW, due to the heat storage system and collector field largest that owns the Andasol 1 plant.
An additional 553 MW had been proposed to be installed at the Mojave Solar Park, California but this project was canceled in 2011. A 59 MW heat storage hybrid plant has also been proposed near Barstow, California. Near Kuraymat in Egypt, approximately 40 MW of steam is generated as input for a gas plant. 25 MW of steam is also generated as input for a gas plant in Hassi R'mel, Algeria. The government India has started developing an initiative called the Jawaharlal Nehru National Solar Mission (also known as the National Solar Mission) to solve India's energy supply problem.
Designs with towers
Power towers (also known as 'centre tower' solar plants or 'heliostat' plants) capture and focus the sun's thermal energy with thousands of mirrors that follow the sun (called heliostats) located on land adjacent to the tower. A tower is located in the center of the terrain occupied by the heliostats. The heliostats focus the sunlight onto a receiver that is located at the top of the tower. In the receiver, concentrated solar radiation heats a molten salt to about 538 °C. Subsequently, the molten salt is sent to a thermal storage tank where it accumulates, with a thermal efficiency of 98%, and is finally pumped to a steam generator. The steam drives a turbine which generates electricity. This process, which is also known as the Rankine cycle, is similar to that used by a plant that uses fossil fuels (coal, natural gas, oil, etc.), except that the energy source in this case is clean solar radiation.
The advantage of this design compared to the parabolic trough design is that it manages to reach higher temperatures. Thermal energy at higher temperatures can be converted to electricity more efficiently and is cheaper to store for later use. Additionally, the adjacent terrain need not be as flat. In principle a power tower could be built on the side of a hill. The mirrors can be flat and the pipes are concentrated in the tower. The disadvantage is that each mirror must have its own control on two axes, whereas in the parabolic trough design the tracking control of one axis can be shared by a larger set of mirrors.
NREL conducted a cost/performance comparison between power tower and parabolic trough designs, estimating that by 2020 electricity could be produced for a cost of 5.47 cents per kWh for power tower designs and a cost of 6.21 cents per kWh for parabolic trough designs. The plant factor for power pylons was estimated at 72.9% and for parabolic trough designs it was 56.2%. The development of cheap, durable and mass-produced components for power plant heliostats is expected to would lower these costs.
Examples of plants built
In June 2008, eSolar, a Pasadena, California-based company founded by Idealab CEO Bill Gross with financing provided by Google, announced a Power Purchase Agreement (PPA) with utility Southern California Edison to produce 245 megawatts of power. Also, in February 2009, eSolar announced that it had licensed its technology to two development partners, Princeton, New Jersey-based NRG Energy Inc. and India-based ACME group. In the agreement with NRG, the companies announced plans to jointly build 500-megawatt concentrating solar thermal plants throughout the United States. The goal for Grupo ACME was nearly double this figure; ACME planned to start building its first eSolar power generating plants in 2009 and within the next 10 years to complete 1 Gigawatt.
eSolar's proprietary sun-tracking software coordinates the movement of 24,000 1-square-meter mirrors per tower using optical sensors to adjust and calibrate the mirrors in real time. This allows for the use of a high-density reflective material that enables the development of Concentrating Solar Thermal Power (CSP) plants with 46-megawatt units on plots of approximately (MW) π square miles, making resulting in a land to power ratio of 16,000 m² per 1 megawatt.
BrightSource Energy signed a series of Power Purchase Agreements with Pacific Gas and Electric Company in March 2008 for up to 900 MW of electricity, the largest solar commitment ever made by a utility. BrightSource is currently developing several solar generation plants in southern California, planning to start construction on the first one in 2009.
In June 2008 BrightSource Energy inaugurated its 4-6 MW Solar Energy Development Center (SEDC) in the Negev Desert, Israel. The site, located in the Industrial Park de Rotem, has 1,600 heliostats that follow the sun and reflect solar radiation onto a 60-meter-high tower. The concentrated energy is then used to heat a boiler, located at the top of the tower, to a temperature of 550 degrees Celsius, generating superheated steam.
There is a tower operating in PS10 in Spain with a capacity of 11 MW.
A 15 MW plant called Solar Tres with heat storage is under construction in Spain. In South Africa, a 100 MW solar plant equipped with between 4,000 and 5,000 heliostats, each with an area of 140 m², is planned. A plant located in Australia called Cloncurry Solar Farm (using purified graphite as heat storage located directly on the tower).
Morocco is building five thermal solar plants around Ouarzazate. The plants will produce approximately 2,000 MW by the year 2012. About ten thousand hectares of land will be used for all the plants.
The 10 MW Solar Uno project was decommissioned (later developed into the Solar Dos project) and also the 2 MW Thémis solar plant.
Disc Layouts
A dish Stirling system uses a large parabolic reflector dish (similar to the shape of a satellite television dish). It focuses all of the solar radiation hitting the disk onto a single point at the top of the disk, where a receiver captures the heat and transforms it into something usable. Typically the dish is coupled to a Stirling engine, known as a Disk-Stirling System, but sometimes a steam engine is used. These engines create rotational kinetic energy that can be converted to electricity using an electrical generator.
The advantage of a disk system is that it can reach much higher temperatures due to a higher concentration of light (similar to tower designs). Higher temperatures allow for better conversion to electricity, and disk systems are very efficient in this regard. However, there are also some disadvantages. Converting heat to electricity requires moving parts and that results in increased maintenance requirements. In general, a centralized approach to this conversion process is better than a decentralized one in disk layout. Second, the motor, which is heavy, is part of the structure that moves, which requires a rigid structure and a strong tracking system. Additionally, parabolic mirrors are used instead of planar mirrors which means that tracking must be done in two axes.
Examples of plants built
In 2005 Southern California Edison announced an agreement to purchase Stirling motors for solar power from Stirling Energy Systems over a twenty-year period and in sufficient quantities (20,000 units) to generate 500 MW of electricity. In January 2010, Stirling Energy Systems and Tessera Solar commissioned the first 1.5 MW demonstration solar plant ("Maricopa Solar") using Stirling technology in Peoria, Arizona. In early 2011, Stirling Energy's development subsidiary, Tessera Solar, sold its large projects, the 709 MW Imperial project and the 850 MW Calico project to AES Solar and K. Road, respectively, and in the fall of 2011 Stirling Energy Systems filed for Chapter 7 bankruptcy due to competition from low-cost photovoltaic technology.
Fresnel Reflectors
A solar power plant with linear Fresnel reflectors uses a series of long, narrow, low curvature (or even flat) mirrors to focus light onto one or more linear receivers located on the mirrors. At the top of the receiver a small parabolic mirror can be positioned to support the focus on the receiver. The idea of these systems is to offer low total costs by sharing a receiver between several mirrors (when compared to cylindrical and disk concepts), while using the simple geometry of linear focus with a follow axis. This is similar to the cylinder design (and different from the mid-tower and dual-shaft disc designs). The receiver is stationary and therefore does not require fluid couplings (as is the case with cylinder and disc designs). Also the mirrors don't need to support the receiver, so they are structurally simpler. When proper aiming strategies are used (mirrors aimed at different receivers at different times of day), a higher density of mirrors can be allowed on the available terrain.
A concept has also been developed with the idea of Fresnel reflectors with point focus called the Multi-Tower Solar Array (MTSA), but it has not yet been built a prototype. In this concept, the mirrors of alternate positions point to different towers as their targets, thus minimizing the blocking between mirrors and allowing a denser grouping of these. In the tower the solar radiation would be received by a curved beam splitter, made of coated quartz, this splitter would separate the green and red portion of the visible spectrum and the near-infrared portion and would send them to a photovoltaic receiver, since these parts of the electromagnetic spectrum are the most efficient to be used with the photovoltaic generation of electricity. The rest of the wavelengths would be sent to the thermal receiver and turbine, a process that uses the energy of the radiation and not the wavelengths. This concept won funding from the Australian Research Council to build a single tower prototype in Australia that can generate approximately 150 kW(e) and will use a combined microturbine and photovoltaic receiver.
Examples of plants built
Recent prototypes of this type of system have been built in Australia (of the Compact Linear Fresnel Reflector type) and by Solarmundo in Belgium.
The Solarmundo research and development project, with its pilot plant in Liège, was closed after successfully testing the concept of linear Fresnel technology. Subsequently, the company Solar Power Group GmbH, based in Munich, Germany, was founded by some of the members of the Solarmundo team. A prototype based on Fresnel mirrors with direct steam generation was built by SPG in conjunction with the German Aerospace Center (DLR).
Based on the Australian prototype, a 177 MW plant located near San Luis Obispo in California has been proposed and would be built by the company Ausra., but Ausra sold this project to First Solar, eventually First Solar (a manufacturer of thin-film photovoltaic solar cells) will not build the Carrizo project, this resulted in the cancellation of Ausra's contract to provide 177 MW to P.G.& E. Small capacity power plants are a huge economic challenge for parabolic trough and dish designs, few companies build such small projects. SHP Europe, a former subsidiary of Ausra, has plans to build a 6.5 MW combined cycle plant in Portugal. The German company SK Energy GmbH has plans to build several small 1-3 MW power plants in southern Europe (especially Spain) using Fresnel mirror and steam engine technology.
In May 2008, the German company Solar Power Group GmbH and the Spanish company Laer S.L. They agreed on the joint execution of a thermal solar power plant in the center of Spain. This will be the first solar thermal power plant in Spain based on Fresnel collector technology from the Solar Power Group company. The planned size of the plant will be 10 MW with a backup unit based on fossil fuel. Construction is scheduled to begin in 2009. The project is located in Gotarrendura, a small town that pioneered the use of renewable energy, approximately 100 km northwest of Madrid, Spain.
Since March 2009, the Puerto Errado 1 (PE 1) solar power plant operated by the German company Novatec Solar is operating commercially in southern Spain. The solar plant is based on Fresnel linear collector technology and has an electrical capacity of 1.4 MW. In addition to a conventional potential block, the plant includes a solar boiler with a mirror surface of around 18,000 m². The steam is generated by concentrating direct solar radiation on a linear receiver that is located 7.4 meters above the ground surface. An absorber tube is located in the line of focus of the mirror field, in which the water is directly evaporated into saturated steam at a temperature of 270 °C and at a pressure of 55 bar by concentrated solar energy. Since September 2011, due to a new receiver design developed by Novatec Solar, steam can now be generated at a temperature of 500 °C.
The 30 MW Puerto Errado 2 (PE 2) solar power plant is an enlarged version of PE 1, it is also based on Fresnel collector technology developed by the German company Novatec Solar. It covers a mirror surface of 302,000 m² and has been in operation since August 2012. The plant is located in the Murcia region.
Linear Fresnel Reflector Technologies
Other single-axis tracking technologies include the relatively new Linear Fresnel Reflector (LFR) and Compact-LFR (CLFR). The LFR differs from the parabolic trough in that the absorber is fixed in space above the field of mirrors. Also, the reflector is composed of many low row segments, which are collectively focused on a long raised receiving tower that runs parallel to the reflectors' axis of rotation.
This system offers a low cost solution since the row of the absorber is shared with several rows of mirrors. However, a fundamental difficulty with LFR technology is avoiding obscuring incident solar radiation and blocking reflected solar radiation from adjacent reflectors. Blocking and obscuration can be reduced by using taller towers or by increasing the size of the absorber, which allows increasing the spacing between reflectors furthest from the absorber. Both solutions have extra costs associated, since a larger area of land is required.
The CLFR offers an alternative solution to the TFR problem. The classic LFR has only one linear absorber installed on a single linear tower. This precludes any choice in the direction of the orientation of a specific reflector. Since this technology would be introduced in a large field, one can assume that there will be many linear absorbers in the system. Therefore, if the absorbers are close enough, the individual reflectors will have the option of directing the reflected solar radiation towards at least two absorbers. This additional factor allows for the potential for high-density arrangements, since patterns of staggered reflector tilts can be made in such a way that high-density installed reflectors do not block or shadow each other.
CLFR solar power plants offer cost reductions in all elements of the solar array. These cost reductions encourage the advancement of this technology. Cost-reducing features of this system compared to parabolic trough technology include minimized structural costs, minimized parasitic pumping losses, and reduced maintenance. The decreased structural costs are attributed to the use of flat or resiliently curved glass reflectors instead of costly recessed glass reflectors mounted close to the ground. Also, the heat transfer loop is separate from the reflector field, avoiding the cost of high-pressure flexible tubing required for cylindrical systems. The decreased parasitic pumping losses are due to the use of water for the passive direct boiling heat transfer fluid. The use of evacuated glass tubes ensures low radiation losses and they are cheap. Existing studies for CLFR plants have shown an efficiency between the radiation beam received and the electricity generated of 19% on an annual basis as a preheat.
Fresnel Lenses
Prototype Fresnel lens concentrators for thermal energy recovery have been built by International Automated Systems. No thermal systems using Fresnel lenses are known to be in full-scale operation, although some are already available. products that incorporate Fresnel lenses in conjunction with photovoltaic cells.
The advantage of this design is that lenses are cheaper than mirrors. Additionally, if a flexible material is chosen, then a less rigid support structure is required to resist the load generated by the wind. In the Desert Blooms project you can see a new concept of technology for lightweight and 'non-disruptive' which uses asymmetrical Fresnel lenses that occupy minimal land surface area and which allows for larger amounts of concentrated solar power per concentrator, although a prototype has not yet been built.
Closed parabolic trough
The closed parabolic trough solar thermal system encapsulates the components inside a greenhouse-like glass enclosure. The enclosure protects components from the elements that can negatively impact system reliability and efficiency. Lightweight curved solar reflector mirrors are suspended from the ceiling of the glass enclosure supported by cables. A single-axis tracking system positions the mirrors to retrieve the optimal amount of solar radiation. The mirrors concentrate solar radiation and focus it onto a network of stationary steel pipes, also suspended from the structure of the glass enclosure. Water is pumped through the pipes and boiled to generate steam using the concentrated solar radiation. The steam is then used as process heat. Protecting the mirrors from the wind allows higher temperatures to be achieved and prevents dust from accumulating on the mirrors as a result of being exposed to ambient humidity.
Solar ovens
Solar ovens are precision-constructed parabolic reflectors or lenses to focus solar radiation onto small surfaces so they can heat "whites" at high temperature levels. The temperature that can be obtained with a solar furnace is determined by the second law of thermodynamics and is equivalent to the surface temperature of the sun, that is 6000 °C, and by consideration of the optical properties of a furnace system that limit the maximum available temperature. Solar ovens have been used for experimental studies that have reached up to 3,500°C and temperatures in excess of 4,000°C have been reported. Samples can be heated in controlled atmospheres and in the absence of electrical or other fields if desired.
The parabolic reflector has the property of concentrating in a focal point the rays that enter the reflector parallel to the axis. Since the sun spans an angle of approximately 32', the ray bundles are not parallel and the image at the focus of the receiver has a finite magnitude. As a rule of thumb, the diameter of the image is approximately the ratio of the focal length divided by 111. The focal length determines the size of the image, and the reflector aperture determines the amount of energy that passes through the focal area for a given velocity at incidence. of direct radiation. The ratio between the aperture and the focal length is thus a measure of the flow of energy available in the focal area and based on this flow a black body temperature can be calculated.
The usefulness of solar ovens increases with the use of heliostats, or moving flat mirrors, to bring solar radiation to the parabolic reflector. This allows the stationary assembly of a dish, normally in a vertical position, with which devices for controlled atmosphere and movement of samples, target supports, and others can be placed, without the need to move all the equipment. The reflection power of the heliostat varies from 85 to 95% depending on its construction, resulting in a flow loss of 5 to 15% for the oven, and the corresponding decrease at the temperatures that can be reached.
Solar ovens up to 3 meters in diameter are built with mirrors made from a single piece of aluminum, copper or other elements, and larger ovens with multiple curved reflectors have been built.
The reflector or target used in solar ovens can be of various shapes. Substances can be melted into themselves in blackbody cavities, enclosed in glass or other transparent material for controlled atmospheres, or introduced into a rotating "centrifugal" vessel. Measurement of target temperatures in solar ovens is made by melting substances of known melting point and by radiation or optical pyrometric means.
Solar furnaces are used in a variety of experimental studies, including melting refractory materials, conducting chemical reactions, and investigating phase relationships in high-melting point systems such as silica-alumina.
The stabilization of refractory zirconium oxide by adding small amounts of CaO in centrifugal vessels is one of many papers published by Trombe, who has also removed fluorine from mixed phosphates by heating in a furnace in the presence of silica and steam of water, according to the reaction:
[Ca3(PO4)2]3.CaF2 + xSiO2 + H2O ® 3 Ca2(PO4)2 + (SiO2)x.CaO + 2HF
Zirconium oxide has been prepared, with good yield, by heating zirconium silicate at 1400 °C with sodium carbonate, According to the equation:
ZrSiO4 + 2Na2CO3 ® Na4SiO4 + 2CO2 + ZrO2
Other proposed uses for solar furnaces include flash pyrolysis experiments in inorganic and organic chemistry research, and geochemical studies of rocks and minerals.
Accumulation and exchange of heat
There is more energy in the higher frequencies of the formula-based light E=h.. {displaystyle E=hnu }Where h It's Planck's constant and .. {displaystyle nu } It's the frequency. Metallic collectors decrease the higher frequencies of light producing a series of Compton changes in abundance of lower frequencies of light. Glass and ceramic coatings with high transmissivity in the visible and ultraviolet spectrum and with a metal trap with effective absorption in the infrared spectrum (heat block) absorb low-frequency light produced by radiation loss. The insulation of the convection prevents mechanical losses transferred through the gas. Once recovered as heat, thermal storage efficiency increases with size. Unlike the photovoltaic technologies that are often degraded by concentrated light, solar thermal technology depends on the concentration of light, which requires a clear sky to reach the temperatures needed to produce electricity.
Heat in a solar thermal system is controlled by five basic principles: heat gain, heat transfer, heat storage, heat transport, and thermal insulation. In this situation, heat is the measure of the amount of thermal energy contained in an object and is determined by the object's temperature, mass, and specific heat. Thermal solar power plants use heat exchangers that are designed for constant working conditions to provide heat exchange.
Heat gain is the heat accumulated by the sun in the system. Thermal solar heat is trapped using the greenhouse effect, this effect in this case is the ability of a reflective surface to transmit shortwave radiation and reflect longwave radiation. Heat and infrared radiation are produced when shortwave radiation strikes the absorber plate, which is then trapped inside the collector. A fluid, usually water, in the absorber passes through tubes and collects the trapped heat and transfers it to a heat storage tank.
Heat is transferred by either conduction or convection. When water is heated, kinetic energy is transferred by conduction to water molecules through the medium. These molecules disperse their thermal energy by conduction and take up more space than the slower moving cold molecules above them. The distribution of energy from the hot water rising to the cold water sinking contributes to the convection process. Heat is transferred in the fluid from the collector absorber plates by conduction. The collector fluid is circulated through the conveying pipes to the heat storage location. Inside the storage, heat is transferred through the medium by convection.
Storing heat allows solar thermal power plants to produce electricity during daylight hours without sunlight. Heat is transferred to a heat storage medium in an insulated tank during daylight hours and is recovered for electricity generation during non-daylight hours. The heat transfer rate is related to the conductivity and convection of the medium as well as to temperature differences. Bodies with large temperature differences transfer heat faster than bodies with lower temperature differences.
Heat transport refers to the activity in which heat from a solar collector is transported to the heat storage tank. Thermal insulation is vital both in the heat transport pipes and in the heat storage tank. It prevents heat loss, which is related to energy loss which in turn negatively affects the efficiency of the system.
Heat storage
Heat storage allows solar thermal plants to produce electricity at night and on cloudy days. This enables the use of solar energy for baseload generation as well as peak power generation, with the potential to replace fossil fuel-fired power plants. Additionally, the use of generators is higher, which reduces costs.
The heat is transferred to a thermal storage medium in an insulated tank during the day and withdrawn for electricity generation at night. Thermal storage media include pressurized steam, concrete, a variety of phase change materials, and molten salts such as calcium, sodium, and potassium nitrate.
Steam accumulator
The PS10 solar power plant stores heat in tanks as pressurized steam at 50 bar and 285 °C. The vapor condenses and instantly turns back to steam when the pressure is lowered. Storage can be done for up to an hour. It has been suggested that it can be stored longer but has not yet been tested in an existing plant.
Storage in molten salt
A variety of fluids have been tested to carry the sun's heat, including water, air, oil, and sodium, but in some cases molten salt has been selected as the best option. Molten salt is used in the systems of solar power towers as it is liquid at atmospheric pressure, providing a low cost means of storing thermal energy, its operating temperatures are compatible with that of current steam turbines, and it is non-flammable and non-toxic. Molten salt is used in the chemical and metal industries to transport heat, so there is a great deal of experience in its use.
The first commercial mixture of molten salt was a common form of nitro, 60 percent sodium nitrate and 40 percent potassium nitrate. Nitro melts at 220°C and remains liquid at 290°C in an insulated storage tank. Calcium nitrate can lower the melting point to 131°C, allowing more energy to be extracted before the salt freezes. There are now several technical grades of calcium nitrate that are stable over 500°C.
These solar power systems can generate electricity in cloudy weather or at night using heat stored in hot salt tanks. The tanks are equipped with insulation and are capable of storing heat for a week. Tanks that feed a 100 MW turbine for four hours should be 9m high by 24m in diameter.
The Andasol solar power plant located in Spain is the first commercial thermal solar power plant to use molten salt to store heat and generate electricity at night. This plant came into operation in March 2009. On July 4, 2011, a milestone in the history of the solar industry was achieved: the 19.9 MW Gemasolar solar plant was the first to generate electricity uninterruptedly for 24 hours straight using a molten salt heat storage.
Graphite heat storage
Direct
The proposed solar power plant located in Cloncurry, Australia will store heat in purified graphite. The plant uses a power tower design. The graphite is located at the top of the tower. The heat captured by the heliostats goes directly to storage. The heat used for power generation is recovered from the graphite. This simplifies the design.
Indirect
Molten salt coolants are used to carry heat from the reflectors to the heat storage tank. The heat carried by the salts is transferred to a secondary heat transfer fluid through a heat exchanger and then to the storage medium, or alternatively, the salts can be used to directly heat the graphite. Graphite is used since it has relatively low costs and is compatible with liquid fluoride salts. The high mass and volumetric heat capacity of graphite provide an efficient storage medium.
Use of phase change materials for storage
Phase change materials (PCM) offer an alternative solution in energy storage. Using a similar heat transfer infrastructure, PCMs have the potential to provide a more efficient means of storage. PCMs can be organic or inorganic materials. Advantages of organic PCMs include non-corrosiveness, low or no subcooling, and chemical or thermal stability. Disadvantages include a low enthalpy of phase change, low thermal conductivity, and flammability. The advantages of inorganic PCMs are a higher enthalpy of phase change, but they exhibit disadvantages in issues related to subcooling, corrosion, phase separation, and lack of thermal stability. The higher enthalpy of phase change in inorganic PCMs makes hydrated salts a strong candidate in the field of solar energy storage.
Water use
A design that requires water for condensation or cooling can be a problem in solar thermal power plants located in desert areas with good solar radiation but limited water resources. The conflict is clearly seen in the plans of the German company Solar Millennium to build in Nevada's Amargosa Valley which required 20% of the available water in the area. Certain other projects by the same and other companies in the Mojave Desert in California may also be affected by the difficulty in obtaining adequate or appropriate water rights. California Water Law currently prohibits the use of potable water for cooling.
Other water designs require less water. The proposed Ivanpah solar plant in southeast California will conserve scarce available water by using air cooling to convert steam to water. Compared to conventional wet cooling, this results in a 90% reduction in water use at the cost of less efficiency loss in the cooling process. The water is then returned to the boiler in a closed process that is environmentally friendly.
Conversion rates from solar energy to electrical energy
Of all these technologies the solar disk/Stirling engine has the highest energy efficiency. A single Stirling engine-solar disk installation located at the National Solar Thermal Test Facility (NSTTF) at Sandia National Laboratory produces as much as 25 kW of electricity, with a conversion efficiency of 31.25%.
Parabolic trough solar plants have been built with efficiencies of approximately 20%. Fresnel reflectors have an efficiency that is slightly lower, but this is offset by a denser distribution.
Gross conversion efficiencies (taking into account that solar disks or cylinders occupy only a fraction of the total area of a plant) are determined by the net generating capacity on solar energy that falls on the total area occupied by the solar plant. The 500 megawatt SCE/SES plant would extract approximately 2.75% of the radiation (1 kW/m²; see Solar Energy for a more detailed discussion) that falls on its 18.2 km². For the Andasol solar plant in 50 MW being built in Spain, with a total area of 1,300×1,500 m = 1.95 km², has a gross conversion efficiency of 2.6%.
In any case, efficiency is not related to cost. When calculating the total cost, both the efficiency and the cost of construction and maintenance should be considered.
Normalized cost
Since a solar plant does not use any type of fuel, the cost consists mainly of capital costs with minor operational and maintenance costs. If the useful life of the plant and the interest rate are known, the cost per kWh can be calculated. This is called the normalized cost of energy.
The first step in the calculation is to determine the investment in the production of 1 kWh in a year. For example, the data for the Andasol 1 project indicates that a total of 310 million euros were invested to produce 179 GWh in one year. Given that 179 GWh is 179 million kWh, the investment per kWh for a year of production is 310 / 179 = 1.73 euros. Another example is that of the Cloncurry solar power plant in Australia. It was planned to produce 30 million kWh in one year with an investment of AU$31 million. If actually achieved, the cost would be A$1.03 to produce 1 kWh per year. This would have been significantly cheaper than Andasol, which could be partly explained by the higher radiation received at Cloncurry relative to Spain. The investment per kWh per year should not be confused with the cost per kWh over the entire life cycle of a solar plant.
In most cases the capacity is indicated for a particular plant, for example: for Andasol 1 a capacity of 50 MW is indicated. This figure is not suitable for comparison purposes, since the capacity factor may be different. If a solar plant has heat storage, it can also produce electricity after sunset, but that will not change the capacity factor; it just shifts the generation. The average capacity factor for a solar plant, which is a function of tracking, shading and location, is approximately 20%, which means that a solar plant with a capacity of 50 MW will typically provide a generation of 50 MW annual electricity x 24 hours x 365 days x 20% = 87,600 MWh/year or 87.6 GWh/year.
Although the investment for one kWh per year of production is adequate to compare the price of different solar plants, this still does not yield the price per kWh. The form of financing has a great influence on the final price. If the technology is proven, an interest rate of 7% should be possible. However, investors in new technologies seek a much higher rate to compensate for the higher risks. This has a significant negative effect on the price per kWh. Regardless of the form of financing, there is always a linear relationship between the investment per kWh produced in a year and the price of 1 kWh, before adding operational and maintenance costs. In other words, if due to technology improvements the investment falls by 20%, the price per kWh also falls by 20%.
See also vc
- Aerotermia
- Hot solar water
- Geothermal heat pump
- District heating
- Solar thermal
- Geothermal air conditioning
- Solar kitchen
- Desertec
- Difusor
- Solar energy
- Photovoltaic solar energy
- Thermoelectric solar energy
- Steam generator
- Geosolar
- Thermal Facilities Regulations in the Buildings (Spain) (RITE)
- Drain-Back system
- Radiant floor
- Energy return time
- Energy transition
- Radiant cell