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| − | = Solar technologies and techniques =
| + | [[Portal:Solar|►Back to Solar Portal]] |
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| − | Solar energy technologies refer primarily to the use of solar radiation for practical ends. All other renewable energies other than geothermal derive their energy from energy received from the sun. Solar technologies are broadly characterized as either passive or active depending on the way they capture, convert and distribute sunlight. Active solar techniques use photovoltaic panels, pumps, and fans to convert sunlight into useful outputs. Passive solar techniques include selecting materials with favorable thermal properties, designing spaces that naturally circulate air, and referencing the position of a building to the Sun. Active solar technologies increase the supply of energy and are considered supply side technologies, while passive solar technologies reduce the need for alternate resources and are generally considered demand side technologies.
| + | = Overview<br/> = |
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| − | == Solar thermal technologies == | + | {{#widget:YouTube|id=BtbASIJmsjE|width=600px}}<br/> |
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| − | '''Solar thermal technologies''' are harnessing solar energy for thermal energy (heat). Solar thermal technologies comprise flat collectors for low- and medium temperatures and high temperature collectors concentrating sunlight using mirrors and lenses. | + | '''Solar energy''' is the radiant light and heat from the sun that has been harnessed by humans since ancient times using a range of ever-evolving technologies. Solar radiation along with secondary solar resources account for most of the available renewable energy on earth. |
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| − | <br> | + | <u>However, only a minuscule fraction of the available solar energy can be used to:</u> |
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| − | A flat plate is the most common type of solar thermal collector, and is usually used as a solar hot water panel to generate hot water. A weatherproofed, insulated box containing a black metal absorber sheet with built in pipes is placed in the path of sunlight. Solar energy heats up water in the pipes causing it to circulate through the system by natural convection. The water is usually passed to a storage tank located above the collector.
| + | *[[Solar Electric Technologies|Generate Electricity]] |
| | + | *[[Solar Thermal Technologies|Heating]] and [[Cooling|Cooling]] |
| | + | *[[Cooking with the Sun|Cooking]] |
| | + | *[http://en.wikipedia.org/wiki/Solar_desalination Water Desalination] |
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| − | There are many flat-plate collector designs but generally all consist of (1) a flat-plate absorber, which intercepts and absorbs the solar energy, (2) a transparent cover(s) that allows solar energy to pass through but reduces heat loss from the absorber, (3) a heat-transport fluid (air, antifreeze or water) flowing through tubes to remove heat from the absorber, and (4) a heat insulating backing. One flat plate collector is designed to be evacuated, to prevent heat loss. The absorber may be made from one of a wide range of materials, including copper, stainless steel, galvanised steel, aluminium and plastics. When choosing an absorber material, it is important to ensure that it is compatible, from the point of view of corrosion, with the other components in the system and with the heat transfer fluid used. The absorber must also be able to withstand the highest temperature that it might reach on a sunny day when no fluid is flowing in the collector (known as the stagnation temperature). The fluid passageways of the absorber may consist of tubes bonded to an absorbing plate, or may form an integral part of the absorber. Experience has shown that simple mechanical clamping of tubes to an absorber plate is likely to result in an absorber with a poor efficiency. A good thermal bond, such as a braze, weld or high temperature solder is required for tube and plate designs, in order to ensure good heat transfer from the absorbing surface into the fluid. Matt black paints are commonly used for absorber surfaces because they are relatively cheap, simple to apply and may be easily repaired. Paints, however, have the disadvantage that they are usually strong emitters of thermal radiation (infrared), and at high temperature this results in significant heat losses from the front of the collector. Heat losses from the collector can be substantially reduced by the use of absorber coatings known as 'selective surfaces'. These surfaces may be applied by electroplating or by dipping a metal absorber in appropriate chemicals to produce a thin semi-conducting film over the surface. The thin film will be transparent to solar radiation but at the same time appear opaque to thermal radiation. However, these surfaces cannot be produced or applied easily. Flat-plate collectors usually have a transparent cover made of glass or plastic. The cover is required to reduce heat losses from the front of the collector and to protect the absorber and the insulation from the weather. Most covers behave like a greenhouse. They permit solar radiation to pass into the collector, but they absorb the thermal radiation emitted by the hot absorber.
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| − | At night it is possible for the collector to lose heat by radiation and the circulation will be in the opposite direction, so the water will cool. This can be overcome by use of a suitable non-return valve. However, there is a danger with solar collectors when used under clear night conditions (e.g. in arid and semi arid regions) that they can actually freeze even when the ambient temperature is above freezing point. In such conditions it may be necessary to have a primary circuit through the collector filled with antifreeze and a separate indirect hot water cylinder where the water from the collector passes through a copper coil to heat the main water supply. This problem will only apply in certain desert regions in the cold season or at high altitudes in the tropics and sub-tropics.
| + | = Solar Resource Potential = |
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| − | === Costs<br> ===
| + | Solar irradiation data is needed at all levels of solar power development, from initial government planning through to large-scale project development or the calculations needed to size smaller systems. In the past such data was provided at a relatively course level from [https://www.nasa.gov/ NASA] and other global providers, but more recently specialist models have been developed to more precisely calculate global horizontal irradiation (GHI) and direct normal irradiation (DNI) using primarily cloud cover data from satellites. A number of firms now offer such data as a commercial service. Based on this, it is possible to calculate average annual power output from a theoretical photovoltaic power plant (PVOUT), taking into account temperature, tilt, and the efficiency of the equipment being used (solar panels and balance of system components). |
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| − | Low temperature flat-plate solar collectors typically cost 21 US $ per square metre (0,0021 US $ /cm²). Medium to high temperature collectors generally cost around 200 US $ per square metre. F<font face="Verdana" size="2">lat plate collectors are sized at approximately 0,1 square metre (929 cm²) per gallon (3,79 l ) of daily hot water use or 245 cm² per l of hot water. </font>A complete system installed costs around 14 US $/l or 2000 US $ per 150 l.
| + | Solar resource data, including GHI, DNI and PVOUT is now available globally, for free, via the [http://globalsolaratlas.info/ Global Solar Atlas], which is provided by the [http://www.worldbank.org/ World Bank Group]. The same website has downloadable global, regional and country maps available in high resolution. |
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| − | === Maintenance ===
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| − | <span lang="EN-GB" style="mso-ansi-language: en-gb">'''<span style="font-weight: normal; mso-bidi-font-weight: bold">Solar thermal systems are relatively maintenance free and involve on an occasional base the</span>''' checking of the piping for leaks and the cleaning of the collectors. In some regions it may also be necessary to inspect the transfer fluid for freeze protection and to remove the build up of lime scale that chokes the collector and tank recirculating pipes over a period of time.</span><br>
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| − | [[Pico PV test]] | + | = Solar Technologies and Techniques<br/> = |
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| | + | Solar energy technologies refer primarily to the use of solar radiation for practical ends. All other renewable energies other than geothermal derive their energy from energy received from the sun. |
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| | + | Solar technologies are broadly characterized as either passive solar or active solar depending on the way they capture, convert and distribute sunlight. Active solar techniques include the use of [[Solar Cells and Modules|photovoltaic modules]] (also called photovoltaic panels) and [[Solar Thermal Technologies|solar thermal collectors]] (with electrical or mechanical equipment) to convert sunlight into useful outputs. Passive solar techniques include orienting a building to the Sun, selecting materials with favorable thermal mass or light dispersing properties, and designing spaces that naturally circulate air. |
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| | + | Active solar technologies increase the supply of energy and are considered supply side technologies, while passive solar technologies reduce the need for alternate resources and are generally considered demand side technologies.<ref name="http://en.wikipedia.org/wiki/Solar_energy">http://en.wikipedia.org/wiki/Solar_energy</ref><br/> |
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| | + | == Solar Thermal Technologies<br/> == |
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| | + | [[Solar Thermal Technologies|Solar thermal technologies]] are harnessing solar energy for thermal energy (heat). Solar thermal technologies comprise flat collectors for low- and medium temperatures and high temperature collectors concentrating sunlight using mirrors and lenses. |
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| | + | There are even solar thermal system for cooling purposes that work with adsorption, absorption or desiccant cooling<ref>Green Cooling Initiativ: https://www.green-cooling-initiative.org/network/best-practice-examples/</ref>. |
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| | + | == Solar Electric Technologies<br/> == |
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| | + | Sunlight can be directly converted into [[Rural Electrification|electricity]] using '''[[Photovoltaic (PV)|photovoltaics]] (PV)''' and various experimental technologies. |
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| | + | == OTEC - Ocean Thermal Energy Conversion == |
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| | + | [[OTEC - Ocean Thermal Energy Conversion|Ocean Thermal Energy Conversion]] taps into the stored solar energy in the ocean through the difference between the sea-surface temperatures and under 300m depth, which can be harnessed for extracting work through a Rankine cycle. |
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| | + | = Further Information<br/> = |
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| | + | *[[Solar Electric Technologies|Solar Electric Technologies]] |
| | + | *[[Portal:Solar|Solar Portal on energypedia]]<br/> |
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| | + | = References = |
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| | + | <references /><br/> |
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| | + | [[Category:Solar]] |
Solar irradiation data is needed at all levels of solar power development, from initial government planning through to large-scale project development or the calculations needed to size smaller systems. In the past such data was provided at a relatively course level from NASA and other global providers, but more recently specialist models have been developed to more precisely calculate global horizontal irradiation (GHI) and direct normal irradiation (DNI) using primarily cloud cover data from satellites. A number of firms now offer such data as a commercial service. Based on this, it is possible to calculate average annual power output from a theoretical photovoltaic power plant (PVOUT), taking into account temperature, tilt, and the efficiency of the equipment being used (solar panels and balance of system components).
Solar resource data, including GHI, DNI and PVOUT is now available globally, for free, via the Global Solar Atlas, which is provided by the World Bank Group. The same website has downloadable global, regional and country maps available in high resolution.
Solar energy technologies refer primarily to the use of solar radiation for practical ends. All other renewable energies other than geothermal derive their energy from energy received from the sun.
Solar technologies are broadly characterized as either passive solar or active solar depending on the way they capture, convert and distribute sunlight. Active solar techniques include the use of photovoltaic modules (also called photovoltaic panels) and solar thermal collectors (with electrical or mechanical equipment) to convert sunlight into useful outputs. Passive solar techniques include orienting a building to the Sun, selecting materials with favorable thermal mass or light dispersing properties, and designing spaces that naturally circulate air.
Active solar technologies increase the supply of energy and are considered supply side technologies, while passive solar technologies reduce the need for alternate resources and are generally considered demand side technologies.[1]
There are even solar thermal system for cooling purposes that work with adsorption, absorption or desiccant cooling[2].
