Solar Heating  Printable view

Solar energy is essential to life on Earth. The energy from the sun keeps the Earth warm and supports life. The energy of wind also comes from the sun. Solar radiation heats up air. Warm air rises and surrounding air move in to fill its place. This movement of air is wind. The kinetic energy of wind can be used to generate electricity.

Solar heating is also essential to the water cycle. Solar radiation heats up water in the sea, causing it to evaporate. When the water vapour cools and condenses, it falls as rain. When rainwater forms rivers or flows down from high places, the gravitational potential energy of the water can be used to generate electricity.

Fig. 1   The energy of wind comes ultimately from the sun. A windmill can convert the kinetic energy of wind into electrical energy. (Photo credit: HEC) Fig. 2   The gravitational potential energy of water in a waterfall also comes ultimately from the sun.
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The amount of solar energy is unevenly distributed around the Earth and varies with time. Regions close to the equator receive much more sunlight than those at higher latitudes. In places of high latitudes, much more solar radiation is received in summer than in winter. The amount of cloud in the sky also affects the solar energy received in a place.

We can use the heat from the sun for many purposes, for example, heating water, warming buildings, cooking food and providing a warm environment in greenhouses.

Solar water heating

Fig. 3   Solar water heaters placed on top of buildings (Photo credit: Ku, Jean and NREL/DOE)

In Hong Kong, solar water heaters are used to heat water in some government properties. In Shek Kwu Chau Treatment and Rehabilitation Centre, solar water heaters are used to provide hot water for forty showers per day. Solar water heaters are also used in Sheung Shui Slaughterhouse to provide hot water for washing down the slaughter hall after slaughtering. At Shing Mun Valley swimming pool, solar water heaters are used as one of the energy sources for heating the pool.