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Solar energy is the radiant light and heat from the Sun that has been harnessed to generate thermal or electrical energy.
Types of Solar Collection
People have been harnessing solar energy for thousands of years. Building designs take advantage of solar energy to heat during the winter, with large low windows facing the winter sun. Technology related to the harnessing of solar energy has developed greatly over the years such that sunlight can be very efficiently absorbed as heat and even converted into electricity.
There are essentially two main types of solar collection, thermal and photovoltaic.
Thermal solar involves absorbing sunlight and converting that into heat. This is much easier and more efficient than converting sunlight into electricity, as sunlight is already heat radiation from the sun!
Low temperature solar thermal is primarily used for pool heating, normally made of a rubber/plastic piping. A large surface area of the roof is covered with the “webbing” of pipes through which pool water is circulated. This system is very effective during warm weather, but cannot provide heat in cool weather due to the heat loss.
For low temperature applications (<150oC / 304oF), a dark surface is used to absorb the sunlight. Technological developments over the past 20 years have resulted in surfaces that can absorb as much as 93% of available sunlight, and only reflect a very small amount. This means that solar collector systems can reach efficiency levels in excess of 75%!
For high temperature applications requiring steam production, concentrating thermal solar is used. This involves using an array of mirrors which focus the sun’s rays onto a absorber tube, or sometimes even a tower. This method is similar to using a magnifying glass to focus the sun’s rays, the result being extremely high temperatures, enabling the production of steam for electricity production. This system is able to be used in regions with high solar radiation levels and plenty of open space. Due to the size and complexity of these systems, they are only really viable for commercial applications.
Photovoltaic (PV) uses silicone crystals, sliced into thin layers which have the special property of creating electricity when exposed to sunlight. PV is a viable renewable energy option, but has the disadvantage of high cost and relatively low efficiency. Commercially available panels have peak efficiency levels of around 15%, although this is set to improve with continued research.