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Number of pages Your email address. I recommend this publication for the following reasons. Cite this book There are two ways to cite this book:. Edited Volume and chapters are indexed in Show more. Table of Contents Open access chapters. Available on. Delivered by. Request an Exam Copy. In non-concentrating collectors, the aperture area i. A common example of such a system is a metal plate that is painted a dark color to maximize the absorption of sunlight. The energy is then collected by cooling the plate with a working fluid , often water or glycol running in pipes attached to the plate.
Concentrating collectors have a much larger aperture than the absorber area. The aperture is typically in the form of a mirror that is focussed on the absorber, which in most cases are the pipes carrying the working fluid.
Non-concentrating collectors are typically used in residential, industrial and commercial buildings for space heating , while concentrating collectors in concentrated solar power plants generate electricity by heating a heat-transfer fluid to drive a turbine connected to an electrical generator.
Flat-plate and evacuated-tube solar collectors are mainly used to collect heat for space heating, domestic hot water, or cooling with an absorption chiller. In contrast to solar hot water panels, they use a circulating fluid to displace heat to a separated reservoir. The first solar thermal collector designed for building roofs was patented by William H.
Goettl and called the ” Solar heat collector and radiator for building roof “. Flat-plate collectors are the most common solar thermal technology in Europe. The sides and back of the enclosure are typically insulated to reduce heat loss to the ambient.
A heat transfer fluid is circulated through the absorber’s fluid passageways to remove heat from the solar collector. 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 joined to a high conductivity metal sheet copper or aluminum.
A dark coating is applied to the sun-facing side of the absorber assembly to increase its absorption of solar energy. A common absorber coating is black enamel paint. In higher performance solar collector designs, the transparent cover is tempered soda-lime glass having reduced iron oxide content same as for photovoltaic solar panels. The glass may also have a stippling pattern and one or two anti-reflective coatings to further enhance transparency. The absorber coating is typically a selective coating, where selective stands for having the special optical property to combine high absorption in the visible part of the electromagnetic spectrum coupled to low emittance in the infrared one.
This creates a selective surface , which reduces black body energy emission from the absorber and improves performance. Piping can be laser or ultrasound welded to the absorber sheet to reduce damage to the selective coating, which is typically applied prior to joining to large coils in a roll-to-roll process. A flat plate collector making use of a honeycomb structure to reduce heat loss also at the glass side too has also been made available commercially.
Most flat plate collectors have a life expectancy of over 25 years. Evacuated tube collectors are the most common solar thermal technology in the world. The vacuum that surrounds the absorber greatly reduces convection and conduction heat loss, therefore achieving greater energy conversion efficiency.
The absorber can be either metallic as in the case of flat plate collectors or being a second concentric glass tube “Sydney Tube”. Heat transfer fluid can flow in and out of each tube or being in contact with a heat pipe reaching inside the tube. For the latter, heat pipes transfer heat to the fluid in a heat exchanger called a “manifold” placed transversely with respect to the tubes. Glass-metal evacuated tubes are made with flat or curved metal absorber sheets same as those of flat plates.
These sheets are joined to pipes or heat pipes to make “fins” and placed inside a single borosilicate glass tube. An anti-reflective coating can be deposited on the inner and outer surfaces of such tubes to improve transparency.
Both selective and anti-reflective coating inner tube surface will not degrade until the vacuum is lost. This seal is cycled between ambient and fluid temperature each day of collector operation and might lead to failures in time.
Glass-glass evacuated tubes are made with two borosilicate glass tubes fused together at one or both ends similar a vacuum bottle or dewar flask. The absorber fin is placed inside the inner tube at atmospheric pressure. Glass-glass tubes have a very reliable seal, but the two layers of glass reduce the amount of sunlight that reaches the absorber. The selective coating can be deposited on the inner borosilicate tube high vacuum side to avoid this, but heat has then to flow through the poorly conducting glass thickness of the inner tube in this case.
Moreover, moisture may enter the non-evacuated area inside the inner tube and cause absorber corrosion in particular when made from dissimilar materials galvanic corrosion.
A Barium flash getter pump is commonly evaporated inside the high vacuum gap in between tubes to keep the internal pressure stable through time. The high temperatures that can occur inside evacuated tubes may require special design to prevent overheating. Some evacuated tube collectors 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. A longstanding argument exists between proponents of these two technologies.
Some of this can be related to the structure of evacuated tube collectors which have a discontinuous absorbance area. An array of evacuated tubes collectors on a roof has space between the individual tubes and a vacuum gap between each tube and its absorber inside, covering only a fraction of the installation area on a roof. If evacuated tubes are compared with flat-plate collectors on the basis of the area of roof occupied gross area , a different conclusion might be reached than if the absorber or aperture areas were compared.
The recent revision of the ISO standard  states that the efficiency of solar thermal collectors should be measured in terms of gross area and this might favour flat plates in respect to evacuated tube collectors in direct comparisons. Flat-plate collectors usually lose more heat to the environment than evacuated tubes because there is no insulation at the glass side. Although several European companies manufacture evacuated tube collectors mainly glass-metal type , the evacuated tube market is dominated by manufacturers in China, with some companies having track records of 15—30 years or more.
There is no unambiguous evidence that the two designs differ in long-term reliability. However, evacuated tube technology especially for newer variants with glass-metal seals and heat pipes still needs 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 heat pipe tube is lost it can be easily be replaced with minimal effort.
In most climates, flat plate collectors will generally be more cost-effective than evacuated tubes. Unglazed flat plate collectors are the preferred devices for heating swimming pool water.
Evacuated tube collectors have less aerodynamic drag, which may allow for a simpler installation on roofs in windy locations. 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. Flat plate collectors might be easier to clean.
Other properties, such as appearance and ease of installation are more subjective and difficult to compare. Evacuated flat plate solar collectors provide all the advantages of both flat plate and evacuated tube collectors combined together. They surround a large area metal sheet absorber with high vacuum inside a flat envelope made of glass and metal.
They offer the highest energy conversion efficiency of any non-concentrating solar thermal collector,  but require sophisticated technology for manufacturing. They should not be confused with flat plate collectors featuring low vacuum inside.
Evacuated flat plate solar collectors require both a glass-metal seal to join the glass plate to the rest of the metal envelope and an internal structure to support such plate against atmospheric pressure.
The absorber has to be segmented or provided with suitable holes to accommodate such structure. ISBN Copyright year Number of pages Your email address. I recommend this publication for the following reasons. Cite this book There are two ways to cite this book:. Edited Volume and chapters are indexed in Show more. Table of Contents Open access peer-reviewed chapters. Available on. It provides ten thousand times more energy than is actually used worldwide, however, it is not so easy to obtain it, although it is not impossible either.
It reaches us through electromagnetic radiation and can therefore be used to obtain electrical and thermal energy. This requires the use of solar panels , which capture the radiation and convert it into energy for human consumption. Three ways of using solar energy are highlighted: Photovoltaics obtained through photovoltaic solar panels and used to generate electricity , solar thermal energy collected through solar collectors and transformed into thermal energy and passive solar energy which is not obtained through any device, but uses solar radiation to position buildings so that they are naturally lit and heated.
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[Solar collector book pdf free
In concentrating solar-thermal power CSP plants, collectors reflect and concentrate sunlight and redirect it to a receiver, where it is converted to heat and then used to generate electricity. In tower or central receiver plants, mirrors, known as heliostats, track the sun on two axes, with each heliostat typically on its own base, foundation, and motor to direct sunlight onto the receiver at the top of a tower.
In parabolic trough plants, mirrors line the inside of a trough-shaped array, which follows the sun in only one direction, and concentrates the light on a linear receiver pipe. Learn more about how CSP works. Collectors are the starting point for the conversion of sunlight into energy.
They must be designed to efficiently concentrate light while minimizing fabrication, installation, and operating costs. Collectors that can cost-effectively achieve high concentrations of sunlight are able to directly improve the efficiency of the receiver. Currently, collectors can comprise 25 percent or more of the total system capital costs for CSP plants.
The U. SETO funds research and development in this area to improve the performance and lower the cost of solar collectors and produce prototypes that demonstrate the viability of advanced technologies for future integration in CSP plants. In particular, SETO-funded projects are working to develop solutions that enable a solar collector field to fully operate without any human input, reducing operating costs and maximizing thermal energy collection efficiency.
To view specific solar collector projects, search the Solar Energy Research Database. What are Solar Collectors? Why are Solar Collectors Important? SETO Research in Solar Collectors SETO funds research and development in this area to improve the performance and lower the cost of solar collectors and produce prototypes that demonstrate the viability of advanced technologies for future integration in CSP plants.