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The Sun radiates 89 PetaWatts amount of energy at the Earth 24 hours a day, 365 days a year. It is enough to cover the total energy usage of the Earth 6000 times over. The key to endless energy is all around us in the form of sunlight, ripe for the taking. The ability to feasibly harness this energy would surely be the Holy Grail of all energy sources.

The Sun is of course responsible for almost all forms of energy on the earth. Wind and wave power are both driven by heating from the Sun. Fossil fuels contain energy from plants & animals that have soaked up juice from Solar rays. The same goes for Biofuels. About the only energy sources that aren’t derived from the Sun are nuclear, which harnesses atomic energy, and tidal, which harnesses the gravitational energy from the Moon.

Solar power, converting energy from sunlight directly into electricity, comes in two main forms: PhotoVoltaic & Concentrating Solar Power. I’ll explain the difference and talk through some of the considerations that need to be made when choosing one over the other.

Concentrating solar power uses arrays of mirrors to direct sunlight onto a very specific target in order to heat it up to very high temperatures. This is then used as a heat source for a conventional power station (whereby steam drives a turbine which generates electricity). It’s a very simple concept that has been around for more than a century. However, it is far from a simple technology. It requires detailed design to produce a system that is efficient as possible and the manufacture of the huge curved mirrors is quite an engineering feat.

PhotoVoltaic, on the other hand, uses a flat film of semi-conducting material. This has a special property whereby light shining on it will induce an electrical current, which can then be channelled off into the electricity grid.  This method directly transforms the incoming sunlight into electricity although, as always, there is a loss.

Every solar power station varies, but in general the most efficient large scale power stations are built using Concentrating Solar arrays.  It usually pips PhotoVoltaic cells in terms of energy efficiency for large arrays.  However, Concentrating Solar can’t be deployed on a small scale – you need a conventional turbine driven power station that is driven by the solar heat.  On the other hand the effectiveness of PhotoVoltaic solar energy is much more independent of size.  You can have a 1m x 1m PhotoVoltaic panel and it will work in the same way as a 100m x 100m array.  For this reason any small scale solar installation, such as those people often put on their roofs, are almost always PhotoVoltaic solar panels.

Hugely important in the development of solar energy is dealing with the irregularity of sunlight.  At night time or when the sun is hidden behind clouds, the amount of solar energy available is vastly reduced.  Therefore the ability to store the produced energy efficiently is extremely important.  Small scale arrays often work by ‘Net Metering‘, or ‘Feed-In Tariffs‘ as they are known in Europe.  The way it works is that the solar panels on your roof are connected to the energy grid. When there is excess energy to your requirements it will feed the grid and at night, when there is no solar energy, you can draw electricity back from the grid.  You get paid for the energy that you supply to the grid and, depending on local legislation, its usually at a very favourable rate to encourage the uptake of solar energy.

There are various other types of solar power that are also important:

Solar Water Heaters are perhaps the simplest of all types of solar energy.  The idea is simply to place a water tank/pipes in view of sunlight, usually on the roof, and then use this water for various heating functions in your house like showers and filling radiators.  The most common user of Solar Water heating is Israel where it is estimated that they save over two million barrels of oil a year.

Another type of solar power is Solar Chimneys, where in effect you have a very large, thin greenhouse with a chimney in the middle.  The air inside the greenhouse is heated by sunlight causing it to travel up the chimney (hot air rises, remember?).  The hot air will drive a turbine in the chimney, or something similar, which can be used to generate an electrical current.

Update: Interested in Solar Panels? Check out our Win a Solar Panel Competition