solar heating

solar heating

[soh-ler-heet]

Use of solar radiation to heat water or air in buildings. There are two types: passive and active. Passive heating relies on architectural design; the building's siting, orientation, layout, materials, and construction are utilized to maximize the heating effect of sunlight falling on it. A well-insulated building with a large south-facing window, for instance, can trap heat on sunny days and reduce reliance on gas, oil, or electricity. Brick, stone, or tile capacity walls are often incorporated to absorb the sun's energy and radiate it into the interior, usually after a time lag of several hours. In active solar heating, mechanical means are used to collect, store, and distribute solar energy. In liquid-based systems, a blackened metal plate on the exterior absorbs sunlight and traps heat, which is transferred to a carrier fluid. Alternatively, fluid may be pumped through a glass tube or volume of space onto which sunlight has been focused by mirrors. After picking up heat from the collector, the warm fluid is pumped to an insulated storage tank. The system can supply a home with hot water from the tank or provide space heating with the warmed water flowing through tubes in floors and ceilings.

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Solar heating is the usage of solar energy to provide process, space or water heating. See also Solar thermal energy. The heating of water is covered in solar hot water. Solar heating design is divided into two groups:

History

The very first solar heating factory in the world was built by Jewish immigrants, from South Africa, in Ashqelon Israel in 1952. In 1980 a law was passed in Israel making solar heating mandatory.

How solar heating works

A typical household solar heating system consists of a solar panel (or solar collector) with a heat transfer fluid flowing through it to transport the heat energy collected to somewhere useful, usually a hot water tank or household radiators. The solar panel is located somewhere with good light levels throughout the day, often on the roof of the building. A pump pushes the heat transfer liquid (often just treated water) through the panel. The heat is thus taken from the panel and transferred to a storage container.

Other uses

Solar heating also refers to the heating of any objects, including buildings, cars, through solar radiation. Solar heating depends on the solar radiation, surface area, surface reflectance, surface emissivity, ambient temperature, and thermal convection from wind. With objects on Earth, solar heating reaches a state of temperature equilibrium as the heat imparted by the sun is offset by the heat given off through reflection, radiation, and convection. White objects stay dramatically cooler than other objects because the most important variables are characteristics of the surface, reflectance, emissivity, convection and surface area. Silvery objects get hot even though they are excellent reflectors because they are very poor in heat emission. Human skin, and many other living surfaces, like tree leaves, have near perfect emissivity (~1.0), and so stay pretty cool. A perfect sunscreen is a dye that perfectly absorbs, with high emissivity, or perfectly reflects, ultraviolet and infrared while being transparent in visible light.

It is worth noting that it is impossible for any material to be a good absorber of a given frequency and at the same time a poor emitter of the same frequency (or the other way around). The difference in absorption and emission arises because the radiation emitted by a relatively cold object like a human, has much lower frequency than the radiation emitted by a hot object like the sun. Materials which have high emissivity for low frequencies but high absorption at higher frequencies will therefore stay much cooler than materials which have high absorption of high frequencies and low emission of low frequencies.

Worldwide

Solar Hot Water Installed Capacity 2005
Country million m2 GWth
China 79.3 55.5
EU 16.0 11.2
Turkey 8.1 5.7
Japan 7.2 5.0
Israel 4.7 3.3
Brazil 2.3 1.6
United States 2.3 1.6
Australia 1.7 1.2
India 1.5 1.1
World 125 88

Solar heating in Europe

Solar heating systems with glazed collectors* (kWth)
Country Total (2007) Added in 2007 Added in 2006 Added in 2005 Added in 2004
Germany 6 295 800 665 000 1 050 000 665 000 525 000
Greece 2 499 140 198 100 168 000 154 350 150 500
Austria 2 024 839 196 700 204 868 163 429 127 816
Italy 770 161 171 500 130 200 88 941 68 417
Spain 674 916 183 400 122 500 74 760 63 000
France 609 420 178 500 154 000 85 050 36 400
Cyprus 437 640 45 500 42 000 35 000 21 000
Switzerland 356 286 45 802 36 304 27 392 21 812
Denmark 269 696 16 100 17 710 14 875 14 000
Netherlands 236 839 13 930 10 280 14 174 18 410
UK 213 444 37 800 37 800 19 600 17 500
Sweden 183 676 17 826 19 977 15 835 14 041

Poland 164 428 46 900 28 980 19 390 20 230
Portugal 144 165 17 500 14 000 11 200 7 000
Belgium 102 283 29 400 24 945 14 164 10 290
Czech Republic 92 211 17 500 15 421 10 885 8 575
Slovenia 84 910 8 400 4 830 3 360 1 260
Slovakia 57 225 6 300 5 950 5 250 3 850
Romania 48 720 350 280 280 280
Ireland 21 553 10 500 3 500 2 450 1 400
Malta 20 552 3 850 3 150 2 800 2 951
Bulgaria 17 570 1 750 1 540 1 400 1 260
Finland 14 345 2 800 2 380 1 668 1 141
Luxembourg 13 230 2 100 1 750 1 330 1 190
Hungary 9 975 5 600 700 700 1 050
Latvia 3 745 1 050 840 700 350
Lithuania 2 415 490 420 350 350
Estonia 1 029 245 210 175 175
Total GWth 15.37 1.92 2.10 1.43 1.14
* = The relation between collector area and capacity is 1 m2 = 0.7 kWthermal

See also

References

External links

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