Solar Heating

Solar heating is the use 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 pumps that move air or a liquid from the solar collector into the building or storage area.

• 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).

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

How Solar Heating Works

A 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 cylinder.

Other Uses

Solar heating also refers to the heating of any objects, including buildings or 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 most all 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 radiation 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 that have high emissivity for low frequencies but high absorption at higher frequencies will therefore stay much cooler than materials that have high absorption of high frequencies and low emission of low frequencies.

Worldwide

Solar Heating in Europe