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1 Chapter 1 : Qualifying Solar Thermal in the APS blog.quintoapp.com In this paper a survey of the various types of solar thermal collectors and applications is presented. Initially, an analysis of the environmental problems related to the use of conventional sources of energy is presented and the benefits offered by renewable energy systems are outlined. In the non-concentrating type, the collector area i. In these types the whole solar panel absorbs light. Concentrating collectors have a bigger interceptor than absorber. Flat plate collectors[ edit ] Flat plate thermal system for water heating deployed on a flat roof Flat-plate collectors are the most common solar thermal technology. They consist of an 1 enclosure containing 2 a dark colored absorber plate with fluid circulation passageways, and 3 a transparent cover to allow transmission of solar energy into the enclosure. The sides and back of the enclosure are typically insulated to reduce heat loss to the outside air. The circulation fluid in tropical and sub-tropical climates is typically water. In climates where freezing is likely, a heat-transfer fluid similar to an automotive antifreeze solution may be used instead of water, or in a mixture with water. If a heat transfer fluid is used, a heat exchanger is typically employed to transfer heat from the solar collector fluid to a hot water storage tank. The most common absorber design consists of copper tubing attached to thermally conductive copper or aluminum fins. A dark coating is applied to the sun-facing side of the absorber assembly to increase it absorption of solar energy. A common absorber coating is flat black enamel paint. In higher performance solar collector designs, the transparent cover is tempered glass with reduced iron oxide content the green color visible when viewing a pane of window glass from the side. The glass may also have a stippling pattern an anti-reflective coating to trap more solar energy by reducing reflection. The absorber coating is typically a selective coating. Selective coatings have special optical properties to improve efficiency by reducing the emittance of infrared energy from the absorber. Some manufacturers have introduced inexpensive flat plate solar collectors that employ polycarbonate transparent covers and polypropylene absorber assemblies. Most air heat fabricators and some water heat manufacturers have a completely flooded absorber consisting of two sheets of metal which the fluid passes between. Because the heat exchange area is greater, they may be marginally more efficient than traditional absorbers. Absorber piping configurations include: Because the energy is absorbed in the boundary layer, heat conversion may be more efficient than for collectors where absorbed heat is conducted through a material before the heat is accumulated in a circulating liquid. These may be wholly polymer, or they may include metal plates in front of freeze-tolerant water channels made of silicone rubber. Polymers are flexible and therefore freeze-tolerant and can employ plain water instead of antifreeze, so that they may be plumbed directly into existing water tanks instead of needing heat exchangers that lower efficiency. By dispensing with a heat exchanger, temperatures need not be quite so high for the circulation system to be switched on, so such direct circulation panels, whether polymer or otherwise, can be more efficient, particularly at low light levels. For this reason polypropylene is not often used in glazed selectively coated solar collectors. In areas where freezing is a possibility, freeze-tolerance the capability to freeze repeatedly without cracking can be achieved by the use of flexible polymers. Silicone rubber pipes have been used for this purpose in UK since Conventional metal collectors are vulnerable to damage from freezing, so if they are water filled they must be carefully plumbed so they completely drain using gravity before freezing is expected, so that they do not crack. Many metal collectors are installed as part of a sealed heat exchanger system. Rather than having potable water flow directly through the collectors, a mixture of water and antifreeze such as propylene glycol is used. A heat exchange fluid protects against freeze damage down to a locally determined risk temperature that depends on the proportion of propylene glycol in the mixture. A pool or unglazed collector is a simple form of flat-plate collector without a transparent cover. Typically polypropylene or EPDM rubber or silicone rubber is used as an absorber. Used for pool heating it can work quite well when the desired output temperature is near the ambient temperature that is, when it is warm outside. As the ambient temperature gets cooler, these collectors become less effective. Most flat plate collectors have a life expectancy of over 25 years. Evacuated tube collectors[ edit ] Evacuated tube collector An array of evacuated tubes collectors on a roof Most vacuum tube collectors are used in middle Europe use Page 1

2 heat pipes for their core instead of passing liquid directly through them. Direct flow is more popular in China. Evacuated heat pipe tubes EHPTs are composed of multiple evacuated glass tubes each containing an absorber plate fused to a heat pipe. The manifold is wrapped in insulation and covered by a protective sheet metal or plastic case. The vacuum inside of the evacuated tube collectors have been proven to last more than 25 years, the reflective coating for the design is encapsulated in the vacuum inside of the tube, which will not degrade until the vacuum is lost. This advantage is largely lost in warmer climates, except in those cases where very hot water is desirable, e. The high temperatures that can occur may require special design to prevent overheating. Glass-glass evacuated tube Some evacuated tubes glass-metal are made with one layer of glass that fuses to the heat pipe at the upper end and encloses the heat pipe and absorber in the vacuum. Others glass-glass are made with a double layer of glass fused together at one or both ends with a vacuum between the layers like a vacuum bottle or flask, with the absorber and heat pipe contained at normal atmospheric pressure. Glass-glass tubes have a highly reliable vacuum seal, but the two layers of glass reduce the light that reaches the absorber. Moisture may enter the non-evacuated area of the tube and cause absorber corrosion. Glass-metal tubes allow more light to reach the absorber, and protect the absorber and heat pipe from corrosion even if they are made from dissimilar materials see galvanic corrosion. The gaps between the tubes may allow for snow to fall through the collector, minimizing the loss of production in some snowy conditions, though the lack of radiated heat from the tubes can also prevent effective shedding of accumulated snow. Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed. October Learn how and when to remove this template message A longstanding argument exists between proponents of these two technologies. Some of this can be related to the physical structure of evacuated tube collectors which have a discontinuous absorbance area. An array of evacuated tubes on a roof has open space between the collector tubes, and vacuum between the two concentric glass tubes of each collector. Collector tubes cover only a fraction of a unit area on a roof. If evacuated tubes are compared with flat-plate collectors on the basis of area of roof occupied, a different conclusion might be reached than if the areas of absorber were compared. In addition, the ISO standard [10] is ambiguous in describing the way in which the efficiency of solar thermal collectors should be measured, since these could be measured either in terms of gross area or in terms of absorber area. Unfortunately, power output is not given for thermal collectors as it is for PV panels. This makes it difficult for purchasers and engineers to make informed decisions. A comparison of the energy output kw. Firstly, as Tm-Ta increases the flat plate collector loses efficiency more rapidly than the evac tube collector. This means the flat plate collector is less efficient in producing water higher than 25 degrees C above ambient i. Although many factors obstruct the extrapolation from two collectors to two different technologies, above, the basic relationships between their efficiencies remain valid[ dubious â discuss ]. A field trial [11] illustrating the differences discussed in the figure on the left. A flat plate collector and a similar-sized evacuated tube collector were installed adjacently on a roof, each with a pump, controller and storage tank. Several variables were logged during a day with intermittent rain and cloud. The top maroon line indicates the temperature of the evac tube collector for which cycling of the pump is much slower and even stopping for some 30 minutes during the cool parts of the day irradiation low, indicating a slow rate of heat collection. The temperature of the flat plate collector fell significantly during the day bottom purple line, but started cycling again later in the day when irradiation increased. The temperature in the water storage tank of the evac tube system dark blue graph increased by 8 degrees C during the day while that of the flat plate system light blue graph only remained constant. They are inappropriate for high temperature applications such as process steam production. Based on absorber plate area, most evacuated tube systems are more efficient per square meter than equivalent flat plate systems. This makes them suitable where roof space is limiting, for example where the number of occupants of a building is higher than the number of square metres of suitable and available roof space. In general, per installed square metre, evacuated tubes deliver marginally more energy when the ambient temperature is low e. However, even in areas without much sunshine and solar heat, some low cost flat plate collectors can be more cost efficient than evacuated tube collectors. Although several European companies manufacture evacuated tube collectors, the evacuated tube market is dominated by manufacturers in the East. Several Chinese companies have track records of 15â 30 Page 2

3 years. There is no unambiguous evidence that the two designs differ in long term reliability. However, evacuated tube technology is younger and especially for newer variants with sealed heat pipes still need to demonstrate competitive lifetimes. The modularity of evacuated tubes can be advantageous in terms of extensibility and maintenance, for example if the vacuum in one tube diminishes. In most climates, flat-plate collectors will generally be more cost-effective than evacuated tubes. When employed in arrays and considered instead on a per square metre basis, the efficient but costly evacuated tube collectors can have a net benefit in winter and summer. They are well-suited to cold ambient temperatures and work well in situations of consistently low sunshine, providing heat more consistently than flat plate collectors per square metre. Heating of water by a medium to low amount i. Tm-Ta is much more efficiently performed by flat plate collectors. Domestic hot water frequently falls into this medium category. Glazed or unglazed flat collectors are the preferred devices for heating swimming pool water. EHPTs work as a thermal one-way valve due to their heat pipes. This gives them an inherent maximum operating temperature that acts as a safety feature. They have less aerodynamic drag, which may allow them to be placed onto the roof without being tied down. They can collect thermal radiation from the bottom in addition to the top. Tubes can be replaced individually without stopping the entire system. There is no condensation or corrosion within the tubes. One hurdle to wider adoption of evacuated tube collectors in some markets is their inability to pass internal thermal shock tests where ISO section 9 class b is a requirement for durability certification. There is also the question of vacuum leakage. Flat panels have been around much longer and are less expensive. They may be easier to clean. Other properties, such as appearance and ease of installation are more subjective. Applications[ edit ] The main use of this technology is in residential buildings where the demand for hot water has a large impact on energy bills. This generally means a situation with a large family, or a situation in which the hot water demand is excessive due to frequent laundry washing. Page 3

4 Chapter 2 : Solar thermal collectors and applications Soteris Kalogirou - blog.quintoapp.com In this paper a survey of the various types of solar thermal collectors and applications is presented. Initially, an analysis of the environmental problems related to the use of conventional. Such temperatures are too low for efficient conversion to electricity. The efficiency of heat engines increases with the temperature of the heat source. As the temperature increases, different forms of conversion become practical. Higher temperatures are problematic because different materials and techniques are needed. High temperatures also make heat storage more efficient, because more watt-hours are stored per unit of fluid. Commercial concentrating solar thermal power CSP plants were first developed in the s. The principal advantage of CSP is the ability to efficiently add thermal storage, allowing the dispatching of electricity over up to a hour period. With current technology, storage of heat is much cheaper and more efficient than storage of electricity. In this way, the CSP plant can produce electricity day and night. Reliability can further be improved by installing a back-up combustion system. The back-up system can use most of the CSP plant, which decreases the cost of the back-up system. CSP facilities utilize high electrical conductivity materials, such as copper, in field power cables, grounding networks, and motors for tracking and pumping fluids, as well as in the main generator and high voltage transformers. Copper in concentrating solar thermal power facilities. With reliability, unused desert, no pollution, and no fuel costs, the obstacles for large deployment for CSP are cost, aesthetics, land use and similar factors for the necessary connecting high tension lines. Although only a small percentage of the desert is necessary to meet global electricity demand, still a large area must be covered with mirrors or lenses to obtain a significant amount of energy. An important way to decrease cost is the use of a simple design. When considering land use impacts associated with the exploration and extraction through to transportation and conversion of fossil fuels, which are used for most of our electrical power, utility-scale solar power compares as one of the most land-efficient energy resources available: In the Bureau of Land Management approved nine large-scale solar projects, with a total generating capacity of 3, megawatts, representing approximately 40, acres. In contrast, in, the Bureau of Land Management processed more than 5, applications gas and oil leases, and issued 1, leases, for a total of 3. For low concentration systems and low temperatures tracking can be avoided or limited to a few positions per year if nonimaging optics are used. Therefore, it seems unavoidable that there needs to be a tracking system that follows the position of the sun for solar photovoltaic a solar tracker is only optional. The tracking system increases the cost and complexity. With this in mind, different designs can be distinguished in how they concentrate the light and track the position of the sun. Parabolic trough designs[ edit ] Main article: Parabolic trough Sketch of a parabolic trough design. A change of position of the sun parallel to the receiver does not require adjustment of the mirrors. Parabolic trough power plants use a curved, mirrored trough which reflects the direct solar radiation onto a glass tube containing a fluid also called a receiver, absorber or collector running the length of the trough, positioned at the focal point of the reflectors. The trough is parabolic along one axis and linear in the orthogonal axis. For change of 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 does not require adjustment of the mirrors, since the light is simply concentrated elsewhere on the receiver. Thus the trough design does not require tracking on a second axis. The receiver may be enclosed in a glass vacuum chamber. The vacuum significantly reduces convective heat loss. A fluid also called heat transfer fluid passes through the receiver and becomes very hot. Common fluids are synthetic oil, molten salt and pressurized steam. The fluid containing the heat is transported to a heat engine where about a third of the heat is converted to electricity. Full-scale parabolic trough systems consist of many such troughs laid out in parallel over a large area of land. Since a solar thermal system using this principle has been in full operation in California in the United States. Note however, that those plants have heat storage which requires a larger field of solar collectors relative to the size of the steam turbine-generator to store heat and send heat to the steam turbine at the same time. Heat storage enables better utilization of the steam turbine. Parabolic trough Inside an enclosed trough system The enclosed trough architecture encapsulates the Page 4

5 solar thermal system within a greenhouse-like glasshouse. The glasshouse creates a protected environment to withstand the elements that can negatively impact reliability and efficiency of the solar thermal system. A single-axis tracking system positions the mirrors to track the sun and focus its light onto a network of stationary steel pipes, also suspended from the glasshouse structure. Sheltering the mirrors from the wind allows them to achieve higher temperature rates and prevents dust from building up as a result from exposure to humidity. The Clark Mountain Range can be seen in the distance. A tower resides in the center of the heliostat field. The heliostats focus concentrated sunlight on a receiver which sits on top of the tower. The steam drives a standard turbine to generate electricity. This process, also known as the "Rankine cycle" is similar to a standard coal-fired power plant, except it is fueled by clean and free solar energy. The advantage of this design above the parabolic trough design is the higher temperature. Thermal energy at higher temperatures can be converted to electricity more efficiently and can be more cheaply stored for later use. Furthermore, there is less need to flatten the ground area. In principle a power tower can be built on the side of a hill. Mirrors can be flat and plumbing is concentrated in the tower. The disadvantage is that each mirror must have its own dual-axis control, while in the parabolic trough design single axis tracking can be shared for a large array of mirrors. The capacity factor for power towers was estimated to be Since then a number of plants have been proposed, several have been built in a number of countries Spain, Germany, U. A solar power tower is expected to come online in South Africa in The entire unit acts as a solar tracker. It focuses all the sunlight that strikes the dish up onto a single point above the dish, where a receiver captures the heat and transforms it into a useful form. Typically the dish is coupled with a Stirling engine in a Dish-Stirling System, but also sometimes a steam engine is used. On top of the receiver a small parabolic mirror can be attached for further focusing the light. These systems aim to offer lower overall costs by sharing a receiver between several mirrors as compared with trough and dish concepts, while still using the simple line-focus geometry with one axis for tracking. This is similar to the trough design and different from central towers and dishes with dual-axis. The receiver is stationary and so fluid couplings are not required as in troughs and dishes. The mirrors also do not need to support the receiver, so they are structurally simpler. When suitable aiming strategies are used mirrors aimed at different receivers at different times of day, this can allow a denser packing of mirrors on available land area. The LFR differs from that of the parabolic trough in that the absorber is fixed in space above the mirror field. Also, the reflector is composed of many low row segments, which focus collectively on an elevated long tower receiver running parallel to the reflector rotational axis. Enclosed parabolic trough[ edit ] The enclosed parabolic trough solar thermal system encapsulates the components within an off-the-shelf greenhouse type of glasshouse. The glasshouse protects the components from the elements that can negatively impact system reliability and efficiency. This protection importantly includes nightly glass-roof washing with optimized water-efficient off-the-shelf automated washing systems. A single-axis tracking system positions the mirrors to retrieve the optimal amount of sunlight. The mirrors concentrate the sunlight and focus it on a network of stationary steel pipes, also suspended from the glasshouse structure. The steam is available for process heat. Sheltering the mirrors from the wind allows them to achieve higher temperature rates and prevents dust from building up on the mirrors as a result from exposure to humidity. Page 5

6 Chapter 3 : Solar Thermal Collectors Market Size Industry Report, Solar thermal collectors and applications 1. Solar thermal collectors and applications Soteris A. Kalogirou* Department of Mechanical Engineering, Higher Technical Institute, P.O. Box, Nicosia, Cyprus Received 18 June ; accepted 10 February Abstract In this paper a survey of the various types of solar thermal collectors and applications is presented. The different types of solar thermal panel collectors What are the different types of solar thermal hot water technologies? Evacuated tube solar thermal systems The evacuated tube solar thermal system is one of the most popular solar thermal systems in operation. An evacuated solar system is the most efficient and a common means of solar thermal energy generation with a rate of efficiency of 70 per cent. As an example, if the collector generates kilowatt hours of energy in a year then kilowatt hours would be utilised in the system for heating water. The rate of efficiency is achieved because of the way in which the evacuated tube systems are constructed, meaning they have excellent insulation and are virtually unaffected by air temperatures. The collector itself is made up of rows of insulated glass tubes that contain copper pipes at their core. Water is heated in the collector and is then sent through the pipes to the water tank. This type of collector is the most efficient, but also the most expensive. There are two main types of tubes that are used inside the collector which are glass-glass and glass-metal. The glass-glass version uses two layers of glass fused together at both ends. The double glass tubes have a very reliable vacuum but reduce the amount of light that reaches the absorber inside. The double glass system may also experience more absorber corrosion due to moisture or condensation forming in the non-evacuated area of the tube. The second kind of tube is a glass-metal combination. The glass-metal combination allows more light to reach the absorber and reduces the chances of moisture corroding the absorber. The cylindrical shape of evacuated tubes means that they are able to collect sunlight throughout the day and at all times in the year. Evacuated tube collectors are also easier to install as they are light, compact and can be carried onto the roof individually. The system is an efficient and durable system with the vacuum inside the collector tubes having been proven to last for over twenty years. The reflective coating on the inside of the tube will also not degrade unless the vacuum is lost. Flat plate solar thermal systems are another common type of solar collector which have been in use since the s. The main components of a flat plate panel are a dark coloured flat plate absorber with an insulated cover, a heat transferring liquid containing antifreeze to transfer heat from the absorber to the water tank, and an insulated backing. The flat plate feature of the solar panel increases the surface area for heat absorption. The heat transfer liquid is circulated through copper or silicon tubes contained within the flat surface plate. Some panels are manufactured with a flooded absorber that involves having two sheets of metal and allowing the liquid to flow between them. Using a flooded absorber increases surface area and gives a marginal boost in efficiency. The absorber plates themselves are usually made from copper or aluminium and are painted with a selective heat coating which is much better at absorbing and retaining heat than ordinary paints. The flat plate panel design utilises many different absorber configurations with the main design being the harp configuration. The harp design is usually used in low pressure thermosyphon systems or pumped systems. Other configurations include the serpentine which uses a continuous S shaped absorber and is used in compact hot water only systems which do not utilise space heating. There are also the flooded absorber systems and boundary absorbers which use multiple layers of absorber sheet where the heat is then collected in the boundary layer of the sheets. Polymer flat plate collectors are an alternative to metal plate collectors. Metal plates are more prone to freezing whereas the polymer plates themselves are freeze tolerant so can dispense with antifreeze and simply use water as a heat transferring liquid. Any antifreeze that is added to the heat transfer liquid will reduce its heat carrying capacity at a marginal rate. A benefit of polymer plates is that they can be plumbed straight into an existing water tank removing the need for a heat exchanger which increases efficiency. Some polymer panels are painted with matte black paint rather than a selective heat coating. This is done to prevent overheating although high temperature silicone is now normally used to prevent overheating. This design of solar panel is, overall, slightly less compact and less efficient when compared with an evacuated tube system, however this is reflected in a cheaper price. This design of solar can work well in all climates and can have a Page 6

7 life expectancy of over 25 years. Thermodynamic panels Thermodynamic solar panels are a new development in solar thermal technology. They are closely related to air source heat pumps in their design but are deployed on the roof or walls like regular solar thermal panels and do not have to be south facing. The concept behind thermodynamic solar technology is that it acts like a reverse freezer and they differ from conventional solar thermal in that they do not use solar radiation to heat up heat transferring liquids. The panels have a refrigerant passing through them which will absorb heat. The heat that passes through the panel will then in turn become a gas. The gas is then compressed which raises its temperature and it will then be passed on to a heat exchanging coil that is located within a hot water cylinder. The heated water in the cylinder is heated to 55 degrees and can then be used around the property. The system has a built in immersion which occasionally raises the temperature to 60 degrees to eliminate the risk of legionella. A system that uses thermodynamic panels will in theory be able to generate energy all year round due to it not being reliant on having optimal climate conditions to reach its maximum output potential. A thermodynamic panel can work in temperatures as low as -5 degrees Celsius although there are not as yet any official performance figures for systems operating in the UK. The main manufactures of thermodynamic systems are in Spain and Portugal and these systems were not designed for the UK initially. More companies are now developing more UK specific models and bringing them to market. As an example of performance, a four person family would need to utilise one panel and a litre cylinder. This is sure to change however, and it is probable that thermodynamic panels will be eligible for the RHI in the future. The government says that it is currently gathering information on standards and performance. Solar thermal air collectors Solar air heaters are mostly used for space heating and can be both glazed and unglazed. They are among the most efficient and economical solar thermal technologies available and are mostly used in the commercial sector. The top sheet of a glazed system has a transparent top layer and an insulated surrounding frame and back panel to prevent heat loss to the surrounding air. An unglazed system uses an absorber plate which air passes over while heat is taken from the absorber. A spherical or bowl mirror gets around the problem of tracking the sun in order to focus the light in one spot. A fixed mirror is at a disadvantage with regard to energy output as it cannot track the sun in order to focus the sunlight, however a fixed bowl will save the energy output that is associated with having to move a giant mirror to track the sun. Domestic Solar Hot Water Systems Low temperature solar thermal technologies, especially those that do not generate electricity, rely on the scientific principles behind the Greenhouse Effect to generate heat. Electromagnetic radiation from the sun, including visible and infrared wavelengths, penetrates into the collector that is absorbed by the surfaces inside the collector. Once the radiation is absorbed by the surfaces within the collector, the temperature rises. This increase in temperature can be used to heat water. The energy from the sun can provide hot water for many domestic and industrial applications, displacing the need to burn fossil fuels. Two main components of SWH systems are collectors and storage tanks. There are many different types of configurations and collectors. The most commonly used type of collector is the flat plate. Flat Plate Collectors These collectors consist of airtight boxes with a glass, or other transparent materia,l cover. There are several designs on the arrangement of the internal tubing of flat plate collectors as shown in Figure 1. Traditional collectors, like the Serpatine and Parallel tube examples above, consist of a number of copper tubes, known as risers that are orientated vertically with respect to the collector and placed in thermal contact with a black coloured, metal absorbing plate. The use of selective surfaces on absorbers improves the efficiency of solar water heaters significantly due to a very high absorbance percentage of incoming energy that a material can absorb and low emittance percentage of energy that a material radiates away of electromagnetic radiation. At the top and bottom of the metal absorbing plate, thicker copper pipes, known as headers, assist in the removal of heated water and the arrival of colder water to be heated. Insulation is placed between the absorbing plate and the external wall to prevent heat losses. Whilst the principles of operation for flat plate collectors are fairly consistent, significant improvements in the design of systems, particularly absorber plates have occurred. Flooded plate collectors are similar to their tubed cousins, except that two metal absorbing plates are sandwiched together, allowing the water to flow through the whole plate. The increased thermal contact results in significant improvements in the efficiency of the system. In recent years, much research has been conducted on selective surfaces, which has seen significant improvements in Page 7

8 the efficiency of solar water heaters. Today, a majority of absorber plates are composed of solar selective surfaces, made of materials that strongly absorb electromagnetic radiation i. Batch systems consist of black storage tanks contained within an insulated box that has a transparent cover. Cold water is added to the hot water stored in the tanks whenever hot water is removed. Modern batch systems are used as preheating systems, where the water is then heated further by conventional gas, electric or wood systems. To retain the heat within the water, the system requires insulated covering to be placed over the glazing at night to prevent the heat being lost to the environment. Figure 2 shows a typical Breadbox water heater. Therefore, an ideal selective surface the dark coloured material that lines the inside of the collector for solar collectors should strongly absorb electromagnetic radiation light in the visible range and only weakly emit radiation back in the infrared range of the spectrum, so that the maximum amount of energy from the incoming sunlight is used to heat water. Several coating methods for selective surfaces are used in the manufacture of solar collector absorber plates: Chemical Vapour deposited Oxide Chemical coatings are usually sprayed onto the absorber plate metal, with or without the use of electricity. These coatings do not alter the re-radiative properties of the plate metal, only enhance the absorption of the solar radiation. The thickness of the chemical coating is proportional to the selectivity of the surface. That is, the coating thickness influences not only the absorptivity of the surface, but also the emissivity how easily the surface emits the longer wavelength IR radiation. Despite the low relative cost and ease of application, chemical coatings are often undesirable because of the temperatures reached inside collectors, which can cause a degradation in the chemical coatings. For example, black paint applied to the plate is considered to be a chemical coating. At high temperatures, the paint is likely to melt or burn off the surface, releasing volatile organic compounds into the environment. Electroplated coatings are the most widely used coatings in the solar collector industry. These coatings are applied to the absorber plate metal using traditional electroplating technology. Prolonged exposure to elevated temperatures around oc and humidity can cause slow degradation in the selective coating as oxidation and crystal lattice reconstruction occurs. Black Chrome, a common electroplated coating used in the manufacture of solar collectors is relatively stable, particularly in humid, tropical conditions. Vapour deposited coatings are not traditionally used in flat plate collectors, as there are a number of significant engineering problems which are yet to be overcome. However, they are used extensively in evacuated collectors, which utilise a partial vacuum, such as the receivers in high temperature solar thermal systems. Oxide coatings were the first type of coating used in solar collectors. Metals used in early solar collectors, such as copper and iron underwent natural oxidation, which have desirable absorptivity. Page 8

9 Chapter 4 : Solar Collectors â Solar thermal for buildings applications Solar-thermal collectors heating liquid. Solar collectors are either non-concentrating or concentrating. In the non-concentrating type, the collector area (i.e., the area that intercepts the solar radiation) is the same as the absorber area (i.e., the area absorbing the radiation). Solar thermal for buildings applications Solar Collectors The means for using this solar energy comes via a solar collector. A solar collector captures solar radiation. Depending on the application different solar collectors are used. Basic terms Glazed â Solar collectors collect heat but absorbing heat through radiation. Transmission fluid â A fluid that is heated in the tubes of the collectors and then circulates throughout the system to transmit heat. Typically air, water, or antifreeze is used. Low Temperature Collector â A collector that operates at less than degrees Fahrenheit. These are typically used for space heating and for heating pools Medium Temperature Collector â A collector that operates between and degrees Fahrenheit. These can also be used for space heating but also for air conditioning. High Temperature Collector â A collector that operates over degrees Fahrenheit. This is used for electricity generation, and is also called Concentrated Solar Electricity generation. It is a commonly used technology in the application of solar water heating. The flat plate collector contains a dark, flat plate absorber to absorb incoming solar radiation. The absorber itself is consists of a sheet mixed with thermally stable polymers, aluminum, steel or copper, and coated with a matte black or selective coating. Evacuated Tube Collector Evacuated tubes, or vacuum tubes work on the basic principle that heated fluid will rise. The collector has several glazed tubes that are exposed to the outside. They are not covered by anything like the flat plate collector. The tubes themselves are dark in color to attract radiation. The tubes are sealed on the bottom and open on the top. When heated, the transmission fluid rises to the top. It can then circulate throughout the system heat the target and then it will return to the tubes. When it returns it will be cold, and so it will sink to the bottom of the tube to be heated again. The air is heated and directly pumped throughout a building. These are very simple and are not typically glazed. Page 9

10 Chapter 5 : Solar thermal collector - Wikipedia Solar thermal collectors and applications Solar thermal collectors and applications Kalogirou, Soteris A. In this paper a survey of the various types of solar thermal collectors and applications is presented. Growing demand for solar thermal collectors from various commercial, residential and industrial applications is anticipated to provide positive scope for market growth over the forecast period. Asia Pacific was the largest market in in terms of revenue. Rapid industrialization across Asia Pacific is expected to drive the product demand. However, high cost of the product is expected to restrain the growth over the forecast period Development of new technologies to increase the efficiency of the product is anticipated to provide positive scope for the market growth. Various companies and educational institutes are investing in research and development to reduce the cost of the product and increase its output. Fossil fuels are witnessing depletion owing to large-scale use of resources such as crude oil and coal for the power generation. This in turn, leads to increased environmental pollution. The demand for electricity is also witnessing a growth owing to improved standard of living. Therefore, the growing demand for power and the depleting fossil fuels have triggered the need to find alternatives to the fossil fuels for power generation which is anticipated to drive product demand. In terms of industrial application, solar thermal collectors are not widely used due to a shortage of skilled workers and installers. However, due to increase in construction sector and high electricity rates, the demand for the product in domestic application is expected to increase. South Korea is expected to show high growth in the construction industry owing to private and public investments in commercial, industrial, and infrastructure projects. Growth of construction sector across Asia Pacific is anticipated to provide positive scope for market growth over the forecast period. The initiatives taken by the government to reserve the natural resources coupled with growing awareness among people is anticipated to drive the market growth. Solar thermal collectors are of two types concentrating and non-concentrating out of which non-concentrating was the largest segment accounting for The segment is expected to witness the fastest growth on account of increasing scope of the product in industrial application. Non-concentrating segment includes a flat plate, evacuated tube, unglazed water, and air collectors. Evacuated tube collector was the largest segment accounting for However, in Europe flat plate products were the largest sub-segment. Flat plate collectors are typically utilized for residential water heating, drying and for applications which required liquid temperature that is less than degrees centigrade. Increasing demand for the product in domestic purposes is likely to augment the flat plate collectors growth over the forecast period. Application Insights The applications of solar thermal collectors include commercial, residential and industrial. Increase in conventional energy costs as a result of growing resources demand is likely to provide positive scope for market growth over the forecast period Utilization of the product in commercial constructions such as shopping malls and hotels is anticipated to provide positive scope for market growth over the forecast period. However, availability of PV with more efficiency is expected to restrain demand for the product across various regions. Solar thermal collectors are used in water heating applications and other residential activities. Growing population along with other environmental challenges is overstraining the limited energy resources coupled with rising human needs is expected to increase the demand for solar thermal collector for residential application over the forecast period. The residential application has the market share of The recent developments in industrial heating and cooling application has fueled the market growth. Regional Insights The U. Heating of swimming pools and commercial application account for a major market in the U. Rising concern regarding depletion of natural resources is likely to augment solar thermal collector demand in the U. Increasing technology development in the region is likely to propel utilization of evacuated tube collectors in industrial application over the coming years. Presence of key market players in the U. Due to greater investment in the tourism sector by European government the solar thermal collector market is expected to witness growth over the forecast period. The European players are bringing different solutions for heating and cooling problems which will foster the growth of solar thermal collector market. Demand for the solar thermal collector is stagnant in European region as the conventional heating systems in households are not being replaced. The consumers are not aware Page 10

11 of the existence of solar thermal collectors and higher electricity rates and lower oil and gas prices have an adverse impact on investment. Competitive Insights The competitive rivalry in the market is expected to be moderate due to the presence of limited players. The market is anticipated to be fragmented as no particular company holds a major share. Threat of substitutes is expected to be high in the market due to the high cost of the product and easily available substitute products such as photovoltaics and concentrated photovoltaics. However, intensive research and development to increase efficiency can reduce the risk of substitute products. Page 11

12 Chapter 6 : Global Solar Thermal Collectors Market Research Report A solar thermal collector gathers the heat from the solar radiation and gives it to a fluid named as heat transport fluid. The heat is received from the collector by the fluid and delivers it to the thermal storage tank, boiler steam generator, heat exchanger etc. The heat is received from the collector by the fluid and delivers it to the thermal storage tank, boiler steam generator, heat exchanger etc. For few hours, the heat is stored by thermal storage system. The heat is released during cloudy hours and at night. Thermal-electric conversion system receives thermal energy and drives steam turbine generator or gas turbine generator. The electrical power is delivered to the electrical load or to the substation. There are many solar thermal energy system applications ranging from simple solar cooker of 1 kw rating to complex solar central receiver thermal power plant of MW rating. A solar thermal collector collects heat by absorbing sunlight. A collector is a device for capturing solar radiation. Solar radiation is energy in the form of electromagnetic radiation from the infrared long to the ultraviolet short wavelengths. Flat plate collectors are used for low temperature applications. For achieving higher temperature of transport fluid, the sun rays must be concentrated and focused. Terminologies related to solar thermal collector Concentration Ratio CR: Using heliostats with sun-tracking in 2 planes, a high CR is obtained which can be of the order of CR up to can be achieved by using parabolic trough collectors with sun tracking in one plane. Flat plate solar thermal collector: One of the widely used types of solar thermal collector is flat plat collector. Flat plate collector absorbs both beam and diffuse components of radiant energy. The absorber plate is a specially treated blackened metal surface. Sun rays striking the absorber plate are absorbed causing rise of temperature of transport fluid. Thermal insulation behind the absorber plate and transparent cover sheets glass or plastic prevent loss of heat to surroundings. Applications of flat plate solar thermal collector: Solar water heating systems for residence, hotels, industry. Desalination plant for obtaining drinking water from sea water. Solar cookers for domestic cooking. Losses in flat plate solar thermal collector: Shadows of some of the neighbor panel fall on the surface of the collector where the angle of elevation of the sun is less than sun-rise and sunset Shadow factor is less than 0. The effective hours of solar collectors are between 9AM and 5PM. Cosine loss factor For maximum power collection, the surface of collector should receive the sun rays perpendicularly. The collector glass surface and the reflector surface collect dust, dirt, moisture etc. With the passage of time, the reflector surface is corroded, deformed and its shine fade away. Hence, the efficiency of the collector is reduced significantly with passage of time rust Maintenance of flat plate solar thermal collector: Yearly overhaul change of seals, cleaning after dismantling Types of flat plat solar thermal collector Parabolic trough collector: Parabolic trough with line focusing reflecting surface provides concentration ratios from 30 to 50 as a result very high temperatures such as C can be attained. Light is spotted on the middle of the parabolic trough surface. Heat is absorbed by the pipe which is present alongside of the pipe the working fluid is circulated through the pipe. The beam radiation is reflected by paraboloid dish surface. The point focus is obtained with CR above and temperatures around OC. Page 12

13 Chapter 7 : Solar thermal energy blog.quintoapp.com is a platform for academics to share research papers. Among the different applications of solar thermal energy there is the possibility of generating electric power. The current technology allows to heat water with solar radiation to produce steam and subsequently obtain electrical energy. Although the principle of operation is very similar there are two main applications of solar thermal energy: Thermal single energy for use in homes and small installations Large thermal solar power plants. In these plants the heat is concentrated in a point to generate steam, with the steam a turbine is activated to generate electric power. Once the heat is generated, the operation of a solar thermal power plant is very similar to that of a thermal power plant or a nuclear power plant. The difference is that a thermal power plant the heat to generate the steam comes from the combustion of fossil fuels, usually coal, and in a nuclear power plant, the heat is obtained by fissuring the nucleus of uranium atoms. The collectors of solar thermal energy are responsible for capturing the thermal energy of solar radiation. These solar collectors are classified as low, medium and high temperature collectors depending on the way they work. They are used for the generation of electric power. Systems that form a solar thermal installation The basic scheme of a solar thermal installation is as follows: A solar thermal installation consists of several systems: Solar radiation collection system The solar radiation collection system consists of solar collectors connected to each other. Its mission is to capture solar energy to transform it into thermal energy, increasing the temperature of fluid circulating through the installation. There are a lot of systems for capturing solar radiation. The choice of one system or another will depend mainly on whether it is solar thermal installations of low, medium or high temperature. Among the different solar collection systems we highlight: It is used in low temperature thermal solar plants. Non-glazed solar thermal collectors. It is common, for example, to heat pool water. They are more economical than flat solar collectors. They consist of metal tubes that cover the metallic tube that contains the working fluid, leaving between them a chamber that acts as an insulator. They have a very high yield, but their cost is also high. Solar collectors with radiation concentration systems. They are used for installations that require higher temperatures. Parabolic or semi-cylindrical panels are used. Solar thermal collectors with tracking systems for the position of the Sun. Its position varies throughout the day to maintain a position perpendicular to the received solar radiation. Solar thermal energy accumulation system Consists of storing the heat energy in an accumulation tank for later use. The hot water obtained through the collection system is conducted to the place where it will be used. The stored hot water can be used directly, as is the case of heating the water of a swimming pool, in hot water or heating applications the demand. Because the moment of need for hot water does not always coincide with the time when there is enough radiation it will be necessary to make the most of the hours of Sun to accumulate thermal energy in the form of hot water. Chapter 8 : Basics of Solar thermal collector, its types maintenance and applications A solar collector, the special energy exchanger, converts solar irradiation energy either to the thermal energy of the working fluid in solar thermal applications, or to the electric energy directly in PV (Photovoltaic) applications. Chapter 9 : Solar Thermal Collectors - Industrial Solar - Renewables Onsite Industry Insights. The global solar thermal collectors market size was valued at USD billion in in terms of revenue. Growing demand for solar thermal collectors from various commercial, residential and industrial applications is anticipated to provide positive scope for market growth over the forecast period. Page 13