Solar Cells - Education

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Solar Cells GCSE

If you are studying for a science GCSE, you should be able to describe how solar energy is being used to generate electricity.

 The light-sensitive photo-cathode

The normal photo-electric effect is applied in the photo-electric cell. The light-sensitive photo-cathode, which is usually installed in an evacuated glass tube, may consist of a very thin film of cesium deposited by vaporisation on to an oxidised silver base.

For greater sensitivity the glass tube may be filled with an inert gas at low pressure. A battery in the external circuit serves to amplify the current by ionisation of the gas filling.

The photo-conductive effect is utilised in the photo-conductive cell. The sensitive material usually employed in this case is cadmium sulphide or cadmium selenide. These substances undergo changes in resistance in the ratio of 109:1 between the extremes of darkness and maximum exposure to light.

When the photo-conductive effect occurs at the P-N boundary of semiconductors or at the boundary between a semiconductor and a metal (e.g., cuprous oxide and copper), a potential difference will develop: this is known as the photo voltaic effect, and a cell of this kind is called a photo-voltaic cell.

These cells generate an electromotive force on their own account, causing a current to flow in the circuit even if no battery is included in the circuit, whereas the photo-conductive cell requires an auxiliary voltage provided by a battery.

Photo-electric cells are used for a wide variety of purposes in control engineering, for precision measuring devices, in exposure meters used in photography, etc They are also used in ‘solar batteries’ as sources of electric power for rockets and satellites used in space research.

For this purpose silicon photo-electric cells are used; about 10% of the radiation energy which they absorb is converted into electric energy.

 

Is China the future?

China, which is expected to double its demand for energy in the next 15 to 20 years, currently consumes 45% of the world’s fossil fuels. This will mean that an additional 45% of oil, gas, coal, and mineral resources will have to be found. In the 1970’s oil was changing hands at around $10 per barrel. Today, new fracking techniques (getting oil, rather than blood out of a stone) will cost at least $80 per barrel, and this cost will increase as the oil rich reserves are quickly used up.

 

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