Solar Heating  Printable view
 
Fig. 1   This railing becomes hot in sunlight
Fig. 2   An artwork showing Archimedes directing sunlight onto enemy ships with a mirror

Touch a metal railing outdoors on a sunny day and you will find that it is quite hot. This is due to the radiation from the sun. For the same reason, we feel warmer in sunlight than in shade.

The Earth receives a huge amount of radiation from the sun every day. Most of the energy required to sustain life on Earth actually comes from this radiation. This huge amount of energy keeps the Earth warm and makes it suitable for various forms of life to flourish. The uneven distribution of solar heating on the Earth causes the wind to blow. The heat from the sun also evaporates water from the oceans, lakes and rivers, initiating the water cycle.

In ancient times, people were already able to convert heat from the sun for various purposes. It is said that the Greek mathematician Archimedes had made use of sunlight to defend Syracuse from attack. He used a mirror to direct beams of sunlight onto enemy ships, causing them to burn.

In this module, we will learn how the heat from the sun has contributed to modern day living, such as heating water, warming buildings, cooking food and providing a warm environment in greenhouses.


Applications of solar heating

Although the amount of radiation from the sun is enormous, it 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. Clouds can reflect or scatter solar radiation before it reaches the ground. Applications of solar heating are therefore only practicable in areas where bright sunlight is available throughout the year.