Solar collector
Solar collector a device is for heat gain from that Solar radiation. A solar collector "collects" and absorbs in the sunlight the contained Energy, whereby contrary to photovoltaischen Plants also that infrared Radiation portion (Radiant heat) one uses with vague light.
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Principle of the solar collector
Solar collectors reaches with the utilization of the solar radiation relatively high Efficiencies - typically between 60 and 75 per cent. In Europe fall in sunshine depending upon Season and Position of the sun between 200 and 1000 wm² (see also Solar constant).
A most important component of the collector is that Absorber, the warmth takes up and it it flowing through Heat distribution medium passes on. With the help of that Liquid this heat distribution medium the warmth from the collector is dissipated and stored afterwards (z.B. over Heat exchanger) or directly as Process heat used.
In order to avoid calorific losses, is a good Isolation the absorber in relation to the environment and also a screen of the warm lines necessarily. According to the isolation technology one differentiates
- Panel collectors, the conventional Isolation materials use;
- Vacuum tube collectors, those those thermal Isolation by Vacuum reach, but are than twice as expensive more;
- Swimming pool absorber, as Low-temperatureCollectors for the swimming pool heating up to be used: They exist usually out Plastic and are not additionally isolated usually at all.
- The simplest design (certainly no collector in the strict sense) is darker, water-filled container with large surface. Sunshine warm up suitable containers in few hours to nearly to Boiling temperature, which in the south is used for centuries. Even in Central Europe can more usually Hose Water temperatures of over 60° reach.
That Solar collector the central component is one thermal solar plant, usually to the warm water production one uses, more rarely also to the space heating support.
A characteristic is that Thermal siphon collector, for solar plants is conceived, without pump according to the force of gravity rotating principle work. That Thermal siphon collector frequently already thereby a complete simple solar plant integrated and represents a hot water tank, like it particularly in southern countries (Greece, Turkey, Israel) on many roofs to find is.
Schematic sketch
Accompanying pattern shows the structure in principle one Panel collector with the most important construction units. The sunbeams breaking in by a glass plate meet on one Absorber. With the impact of the sunbeams short-wave becomes, radiation high-energy converted into long-wave radiation (radiant heat). The warmth freed thereby may not be lost, why the collector is generally thermal insulated.
Warmth, not directly by the absorber taken up or by this as Emission again one radiates, by the windowpane back one reflects. It is thus in the collector imprisoned. This is the effect, often with heat case or Greenhouse effect one describes.
The absorbers heated up transfers the warmth to the heat transfer liquid flowing in firmly with the absorber connected copper or aluminum pipes. This transports the collected heat energy to a consumer or a heat accumulator. There are solar plants with open fluessigkeitskreislauf, with those the absorber is flowed through directly by the industrial water (above all Thermal siphon plants). In regions with larger danger of frost however usually separate fluessigkeitskreislaeufe are used, with those the warmth from in itself closed the solar cycle by Heat exchanger to the industrial water one transfers.
Good panel collectors produce approx.. 450kWh heat energy for each m2 and year, good vacuum collectors to 600kWh/m2a and more.
Absorber technology
That Absorber direct and vague solar radiation is as well as possible to catch and into warmth convert (Absorption). At the same time it is to deliver if possible little warmth again in the form of radiation (Emission). Technically expressed: It is itself selectively held back.
In hot countries frequently absorbers are used, only with so mentioned Solar lacquer "are coated". This solar lacquer is very heatproof and usually black, to reach the optimum absorption values. The emission values are very high and thus bad in addition, at the same time; a large part of the caught warmth is directly again radiated.
In order to minimize the losses of energy, becomes therefore in less sun-spoiled countries up highly selective Coating set, the absorption values over 90 % and emission values under 10 % exhibit.
One of the first coatings, to this requirement corresponded and to be in series manufactured could, were the black in such a way specifiedchromeCoating. It became in one galvanic Procedure on out Copper or Aluminum existing absorber sheet metal applied. Very simplified said it consisted of microscopic chrome villi, those the sunlight between itself caught.
To approximately 1997 the black chrome coating was dominating the market. Meanwhile however newer coatings do not only permit higher ones Efficiencies, separate apply - particularly because of the renouncement of galvanic processes - also under production and RecyclingAspects as more pollution free. A ever less spread alternative to black chrome was one likewise galvanically applied nickel coating ("black nickel").
Most common is today a sputtered layer up Titanium basis with blue color, the absorption values easily worse opposite black chrome exhibits, but but clearly lower emission values and thus altogether a better efficiency achieves. First production stages coatings of this kind were developed in the form of titanium nitrite oxide coatings in Germany and by the company. TiNox [ 1 ] brought on the market. Theoretically also different colors are possible with this coating depending upon layer structure; these achieve however so far no comparable power ratings.
A further new development is those sunselectCoating of the glass and coating manufacturer Interpane [ 2 ], a Ceramic metal structure (probably likewise on titanium basis), like the titanium nitrite oxide coatings in the vacuumSputterProcedure is applied and likewise black-bluish gleams.
Both coatings can be applied so far only on absorber sheet metals from copper; appropriate techniques for aluminum absorbers are only since short on the market. Also these aluminum absorbers use however for the temperature heat sink by means of the "solar liquid" (see in addition Thermal solar plant) a pipework system from copper, by laser welding methods with the absorber one connects.
Apart from the coating absorbers of different manufacturers differ also in their structure in principle. Absorbers are frequent, the out particulars Finn exist, about 10-15 cm narrow strips, on their back a thin pipe in each case is welded on, at both ends into a collecting pipe to be then soldered, so that a kind "harp" develops. Besides it gives Surface absorber, those out of only one absorber sheet metal exist; the pipework system is with these usually zigzag-like on the back up-soldered or welded. A third design are those Cushion absorber. Like surface absorbers they consist of a only one continuous absorber sheet metal, on however back instead of a piping the pressformed second sheet metal is applied; the heat transfer liquid flows between these two sheet metals.
In principle point Surface absorber the best power ratings up. Since at the beginning of the manufacturers could process the new highly selective coating only copper sheets, the certain width did not exceed, particularly in older collector models absorber Finns are used still predominantly. Besides absorber Finns permit more different collector designs.
Solar glass
The glass used for the collector is to let break in as much as possible radiation high-energy into the collector and only from the absorber emitted or reflected radiant heat again back in the collector inside to reflect.
For high speed collectors therefore today usually a special becomes Solar glass used, these requirements better fulfills than normal Fensterglas. Chemically it differs from this mainly by the smaller Eisengehalt. This difference becomes optically visible with the view of the edge of a solar windowpane: While fensterglas works with the view of the edge greenish, solar glass is clear also from this line of sight.
A further requirement is the breaking strength opposite hail and snow load (similar as with rooflights), with as small a disk thickness as possible to be reached is.
Inventor
The principle of the Solarthermie is for a long time used: Burning and Hollow mirror there were Antique ones already in that. The use of solar power goes on the Greek mathematician and inventor Archimedes of Syrakus (285-212 v. Chr) back, allegedly by brennspiegeln the Roman fleet in fire set.
In 18. Century invented the natural scientist Horace Bénédict de Saussure the forerunners of the today's solar heat collectors. He built in 18. Jhd. a simple holzkasten also black soil and glasabdeckung. With this first solar collector it reached a temperature of 87°C.
Historical for the use of the Photovoltaik
Center 19. Century succeeded it to the Frenchman Mouchot for the first time, the solar power in Electricity to convert. The principle of the Photovoltaik became already 1839 of the Frenchman Becquerel developed and by the employment of Silicon as semiconductor material approx.. 80 years later into an efficient form transfers. The Photovoltaik became a firm component that Space travel and often those secures Current supply of space probes.
Areas of application: Household to industry
Most well-known application out Solar power won heat is those Warm water production in Household. During suitable interpretation of Collector surface and Storage volume it is enough with us during the entire Summer half-year to washing and bathing.
First wide applications were since that Energy crisis that 1970erYears the heating of public and increasingly also private Swimming pools. Also Industrial companies use the solar power for a long time as contribution to Process energy, whereby at least a preliminary heating of the heat distribution media is possible. Also warming up Biomass cultures - for instance to the production of Fermentation gas is long to Ready for the market one prospered.
Is somewhat more fastidious in that Building services the solar Heating or those Cooling. With sucked. Energy house a nearly complete assumption of the heating is possible by the solar radiation. With standard heaters it can contribute those in the yearly cut up to some decimal per cent to the heating energy and therefore Heating costs lower noticeably. One Amortization the relatively expensive wide collectors and that Armatures is according to firm names in cca. to expect 20 years.
Around also on cloudy to guarantee and rainy days sufficient hot waters, is in that Thermal solar plant usually Heat accumulator inserted, for households - depending upon Family size - from approximately 300 to 1000 litres water filling is enough. Usual market devices heat the lower half, their convection in sufficient sunshine then the whole Storage water heater warmed up. In covered weather is one Additional heating system with river or that Boiler usually.
From the thermal solar collectors to to differentiate are those Solar cells and/or. Solar modules, those Solar power in electricity convert (Photovoltaik).
See also: Thermal solar plant, Thermochemical heat accumulator, Solar furnace, Upwind power station
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