Solar heating

A house fitted with both thermodynamic and photovoltaic panels, used to heat the house

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

• Active solar heating uses sun radiation to heat water either directly or indirectly with the help of a thermodynamic collector.

• Passive solar heating does not require electrical or mechanical equipment, and may rely on the design and structure of the house to collect, store and distribute heat throughout the building (passive solar building design).

Also solar energy can be used to cool (solar cooling).

History

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

How solar heating works

Typical rooftops in Jerusalem

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.

In a simple system the water for consumption or heating can directly be heated in the collectors. If the tank can be installed at a level higher than the collector a pump is not needed: the hot water rises by itself into the tank and the cold water sinks into the collector (Thermosiphon system). This system is cheap and easy to build and can be found in many developing countries.

Central solar heating systems and solar combisystems store summertime solar energy in a seasonal thermal store for later retrieval in the winter. Drake Landing's district heating system operates this way.

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 they reflect almost all incoming light. 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 Heating Capacity 2005-2008 (MW)[1]
#	Country	2005	2006	2007	2008
1	China	55.5	67.9	84.0
2	European Union	11.2	13.5	15.5
3	Turkey	5.7	6.6	7.1
4	Japan	5.0	4.7	4.9
5	Israel	3.3	3.8	3.5
6	Brazil	1.6	2.2	2.5
7	United States	1.6	1.8	1.7
8	Australia	1.2	1.3	1.2
9	India	1.1	1.2	1.5
:)	World (MW)	88	105	126	145

Solar heating in Europe

Solar heating in Europe* (MW heat)[2]
#	Land	2006	2007	2008	Total 2008
1	Germany	1,050	665	1,470	7,766
2	Greece	168	198	209	2,708
3	Austria	205	197	243	2,268
4	Italy	130	172	295	1,124
5	France	154	179	272	1,137
6	Spain	123	183	304	988
7	Cyprus	42	46	48	485
8	Switzerland	36	46	60	416
9	Denmark	18	16	23	293
10	Netherlands	10	14	18	254
11	United Kingdom	38	38	57	270
12	Sweden	20	18	19	202
13	Portugal	14	18	60	223
14	Poland	29	47	91	254
15	Belgium	25	30	64	188
16	Czech Republic	15	18	25	116
17	Slovenia	5	8	11	96
18	Slovakia	6	6	9	67
19	Romania	0	0	6	66
20	Ireland	4	11	31	52
21	Malta	3	4	4	25
22	Bulgaria	2	2	3	22
23	Finland	2	3	3	18
24	Luxembourg	2	2	3	16
25	Hungary	1	6	8	18
26	Latvia	1	1	1	5
27	Lithuania	0	0	1	3
28	Estonia	0	0	0	1
28	EU28 (MW)	2,100	1,920	3,330	19,083
2004-2006 * = The relation between collector area and capacity: m2 = 0.7 kW heat

See also

energy portal

Wikinews has related news: Renewable energy

Wikimedia Commons has media related to: Solar heating

• Renewable energy
• Renewable heat
• Seasonal thermal store
• Solar combisystem
• Solar cooling
• Solar furnace
• Solar gain
• Solar panel
• Timeline of solar cells
• Wood pellets‎

References

External links

• SPF - Institute für Solartechnik - Testing and research competence in Solarthermie
• Polysun - Software to design and simulate solar thermal systems