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How does that work? Solar Panels

How does that work? Solar Panels

You’ve probably all used them at some point, maybe in a wristwatch, to heat water in a house or even to light up a garden path. The fact is, they are used in all sorts of applications, but do you know how they turn the Sun’s rays into electricity? The Null investigates.

In a nutshell, the cells you see on solar panels are photovoltaic cells (PV cells), which are semiconductors commonly made from silicon. When light strikes the cells, some of that light energy is absorbed inside the semiconductor itself, and this causes electrons inside to become loose allowing them to move about. The PV cells then use electric fields to channel the electrons around the cell, and as they pass over metal contacts at the top and bottom of the cell, a current is formed which can be drawn off and used outside the cell. This current, along with the cell’s electric field, gives us the power of the solar cell.

But, there can be a lot more to it than that, as you might expect.

A silicon solar cell is not pure silicon, mainly because in its pure form, it does not conduct electricity that well. So, to enhance the silicon there are several impurities added to it. This gives us N-type and P-type silicon, enhanced with phosphorus and boron respectively. Put these together in a solar cell and you have the makings of a good energy producer. When light hits the cells, electrons on the N-type side lift up and rush over to the other type, and find places to rest on the P-type side. The moving electrons generate current, the electric field in the cell generates voltage and together they make power.

Sadly there is a lot of wastage, with only about 10-25% of the light actually absorbed by the cells. Light is made up of different wavelengths (which we see as colours), and some are not powerful enough to knock electrons around the cell, while others have too much power, but any surplus power is wasted and not re-used. There is also a lot of resistance within the silicon, and it’s not the best conductor!

The final design of the cell comes in the layers that make it up. Because silicon is highly reflective (think of a sandy beach and the glare from the sun) there is a lot of waste if the light doesn’t enter the cells. Therefore, an anti-reflective cover is added, along with a glass plate to protect it from the elements.

So, once you have your panels made, how do you power your house with them? Firstly you need to have your roof at the correct angle and (if you’re in the UK) pointing south. Some solar panels have a tracker that follows the sun throughout the day, but they are mega-expensive! You then need batteries, because when the sun doesn’t shine (and let’s face it, in the UK that’s quite a lot of the time!) you’ll need to store the energy you make on one sunny day, so you can use it on another cloudy one. You can, however, power many smaller devices if you set them up correctly - and it’s all free!

Other solar uses

The main benefit of solar power is that it’s very reliable and needs very little maintenance - great in remote areas. It’s now become common to see it in a number of everyday processes: on offshore buoys, lighthouses, aircraft warning lights and on the top of many street lights and road traffic signs.

Another application of solar power has been in space. Most of the major vehicles in space are powered by solar energy. This includes the Hubble space telescope, many satellites and planetary rovers such as the Mars lander. The international space station will also have its share of solar cells, in fact some 250,000 cells will line the solar array arranged on the surface of four, 72 metre-long gold coloured wings that will power much of the unit - enough to power a small town.

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20 Jul 2011
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