Solar power comes from the sun. Beams of sunshine are waves of light and heat energy, radiated across 93 million miles of space to reach our earth in about eight minutes.
Why has the Sun got so much Energy?
Our sun is a star. Like all stars, it is a spinning ball of hot gases, with no solid surface. Relative to other stars, our sun is medium-sized; there are bigger stars and there are much smaller stars. But compared to the earth, the sun is gigantic. The earth is around 8,000 miles in diameter, while the sun’s diameter is 900,000 miles. The centre is the hottest part, and the temperature there is hotter than anything we can possibly imagine; in fact, it is reckoned to be around 15 million degrees Celsius. That’s a lot of thermal energy.
How We Use Solar Energy
Solar power is still thought of as an emerging technology, although people have been inventing ways of using sunlight for their own purposes for a very long time. One early recorded use tells how a British astronomer on an expedition to Africa during the early 19th century used sunlight to cook food, via a solar thermal collector box, and these devices are still sometimes used today.
However, during the last few decades we have become acutely aware of the need to explore alternatives to fossil-fuel energy. Consequently the use of solar energy has become more mainstream, but scientists are still experimenting with new ways of deriving maximum benefit from this completely non-polluting source of renewable energy.
There are two basic ways of harnessing solar energy: firstly, by converting it directly into thermal energy; and secondly, by converting it into electricity, which can then be used for a variety of applications.
Converting solar energy into thermal energy can be effective on a large scale or on a small scale. A good domestic installation can be expected to produce around 50 per cent of the total amount of hot water needed throughout the year; during a good summer it should be able to provide sufficient energy to heat all the water needed, but in winter its contribution is likely to be small.
Electricity from Solar Energy
Producing electricity from solar power can be done on a small scale, using photovoltaic panels installed on the roof, but for households looking to adopt solar technology this is generally less cost-effective than installing a solar water heating system.
Larger scale electricity generation is achieved through solar thermal power plants, which use a process that starts by heating liquid to produce steam, and the steam is then used to drive the turbines. The first step, therefore, is to collect sufficient solar thermal energy to produce the steam. CSP systems, for Collecting Solar Power, can take the form of a dish, or a trough, or a tower.
In each case the idea is to collect sunshine on a large surface, and use a system of mirrors or lenses, linked to a tracking system, to focus the sunlight into a concentrated beam. The dish system, called a ‘parabolic dish’, works by reflecting the light from the whole of its surface area onto a receiver positioned at its focal point and tracking the sun along two axes. Parabolic dishes are a very effective collecting system. A solar trough is a linear reflector. The advantages of the trough are that it makes effective use of the space it occupies, and the tracker system has to operate along only a single axis; this is considered the most cost-effective option.
Solar power towers are a simple system but they too are effective. They depend on a series of tracking reflectors, called heliostats, which concentrate sunlight on a central receiver mounted on top of the tower.
Limitations of Solar Energy
The drawback of solar energy is that it is only available when the sun’s rays reach us. In fact, strong sunshine is not always necessary; photovoltaic cells collect energy on a cloudy day, but not overnight. It is advantageous if solar energy can be stored, and most systems incorporate ways of doing this. However, solar energy is generally used in conjunction with other types of energy, rather than as a stand-alone energy source. Installing the necessary equipment can be expensive, but once installed, the cost savings should over time more than repay the investment.
In environmental terms, solar power itself causes no pollution, although the construction process and the materials used for solar installations may have environmental implications. Solar power is completely renewable. It will be there for as long as the sun itself continues to exist in its present form, and harnessing solar energy for our own purposes will have no effect on the lifespan of the sun – which is likely to be approximately another five billion years.