Solar energy can be converted directly into other forms of energy, such as heat and electricity.
The major disadvantages of solar energy are:
- our inability to control or predict how much solar energy arrives on the earth's surface at any place and,
- our technology to date requires that a large surface is required for collection of useful amounts of solar energy.
The strength of the solar energy available at any point on the earth depends, on the day of the year, the time of day, and the latitude of the collection point. The amount of energy collected can be further changed depending on the orientation and shape of the object doing the collection. Insolation is a measurement of the amount of solar energy that reaches the surface of the Earth. The amount of insolation an area receives depends upon the Sun's angle, the amount of dust and water vapour in the air, and the amount of cloud cover. Less than half of the radiation energy we receive from the sun makes it to the ground. The rest is absorbed by the atmosphere or reflected back out into space.
The strength of solar radiation at the outer edge of the earth's atmosphere when the earth is taken to be at its average distance from the sun is called the solar constant, the mean value of which is 1.37 106 ergs per sec per cm2, or about 2 calories per min per cm2.
Solar energy is used for heating water for domestic use, space heating of buildings, drying agricultural products, and generating electrical energy.
One of the first examples of using solar energy was the used of a solar collector box to cook food during an expedition into Africa in the 1830's by British astronomer John Herschel. Today it is used widely for many things. Solar thermal or heat energy is used widely in Australia for heating water for our domestic use in Solar Water heaters. This is an excellent and economic energy solution as, by using the sun's heat for making our hot water, we cut down on the amount of fossil fuels needed to be burnt to supply electricity to do the same thing. The technology is now developing which will use solar thermal energy to produce steam at high enough temperatures and pressures to drive steam turbines for electricity generations.
We are also able to harness radiant or solar light energy. Radiant energy is produced in the sun as a result of nuclear fusion reactions and is transmitted to the earth through space by electromagnetic radiation in quanta or packets of energy called photons. This light energy can be utilised by a process called photovoltaics, which produces electricity directly (Photo meaning light and voltaics relating to electricity). This process is being used more and more as the technology is developed and becomes more economic. It is used widely in solar powered calculators and other such devices.
How many ways can you think of that the sun's energy is used directly today?