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Solar cells

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Solar cells

This case study involves researching about solar cells and study the effect internal resistance has on its efficiency. This ties up with our practical investigation where we investigate the internal resistance of a power supply.image02.jpgimage00.png

Sunlight can be converted into electrical energy using photovoltaic cells also known as solar cells.  Photovoltaic (PV) cells are made of materials called semiconductors such as silicon. When light strikes the cell, a certain portion of it is absorbed within the semiconductor material[1]. The energy absorbed by the semiconductor from the light knocks electrons loose, allowing them to flow freely thus making an electric current. Unlike on Earth, there is no atmosphere in space blocking sun light so there is a good supply of sun light energy if positioned correctly, but the disadvantage is that the longer they stay exposed to extreme high temperature the more likely for them to get damaged. Temperature also has a major impact on the internal resistance of the solar cell. This could be detrimental to the space program being undertaken. In this case study, I aim to investigate the internal resistance of a power supply and link the results to a power supply in space i.e. a solar cell.

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This p.d. will be less than the e.m.f. E by an amount of Ir called the lost volts. Combining these two together gives:

        V= E – Ir

The lost volts tell us the energy transferred to the internal resistance of the supply. If you short circuit a battery with a piece of wire, a big current will flow, and the battery may get warm as energy is transferred within it. This is risky as a large flow of current could cause serious injuries or electrocution. Precautions can be put in place to reduce the risk of this by for example introducing a resistor to the circuit.

In general, internal resistance will rise during discharge due to the active materials within the battery being used[3]. However, the rate of change during discharge is not consistent but is affected by external factors like temperature which affects internal resistance. In colder temperatures the chemical reactions in the battery occur slowly due to slow movement of electrolytes which in turn increase internal resistance but reduce when temperature increases. This is particularly important with solar cells because of constant exposure to sunlight in space.

image04.png[4]Figure 2image01.png

The disadvantage of internal resistance can be seen in the headlamps of cars.

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  • Energizer - http://data.energizer.com/PDFs/BatteryIR.pdf.  (Last Accessed: 08/04/10)

Energizer is a company that produces portable power sources in the form of batteries. The website provides technical details about the performances of their products. Information are reliable but very difficult to understand.

  • Energizer - http://data.energizer.com/PDFs/BatteryIR.pdf (Last Accessed: 08/04/10)
  • Cnet - http://news.cnet.com/8301-11128_3-10355500-54.html?part=rss&subj=news&tag=2547-1_3-0-20 (last Accessed: 08/04/10)

Cnet is a website dedicated to providing the latest technology and gadget news. As a regular reader information from the website is most of the time accurate and reliable but from time to time, I found that the information can be wrong.

  • David S, Keith G, Robert H. (2000) Physics 1, Cambridge: Cambridge University Press. (Last Accessed: 08/04/10)

[1]How Stuff Works - http://science.howstuffworks.com/solar-cell1.htm. (last Accessed : 08/04/10)

[2]Figure 1 ActewAGL Always - http://www.actewagl.com.au/education/_lib/images/energy/energy07.jpg. (last Accessed : 08/04/10)

[3]Energizer - http://data.energizer.com/PDFs/BatteryIR.pdf (Last Accessed: 08/04/10)

[4]Figure 2 Energizer - http://data.energizer.com/PDFs/BatteryIR.pdf.  (Last Accessed: 08/04/10)

[5] David S, Keith G, Robert H. (2000) Physics 1, Cambridge: Cambridge University Press.

[6] Cnet - http://news.cnet.com/8301-11128_3-10355500-54.html?part=rss&subj=news&tag=2547-1_3-0-20 (last Accessed : 08/04/10)

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Response to the question

Though candidate gives an introduction, it is a little brief, they have stated what they plan to discuss which is good but you should also include a brief introduction of your topic, in this case that could be a description ...

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Response to the question

Though candidate gives an introduction, it is a little brief, they have stated what they plan to discuss which is good but you should also include a brief introduction of your topic, in this case that could be a description of solar cells and perhaps what they are made of and their main purpose. However the candidate gives a fairly in depth response overall and they have provided a suitable amount of detail.

Level of analysis

The candidate demonstrates a good understanding of physics principles and they have used appropriate scientific terms throughout. In addition to this the candidate has taken the initiative to do independent research and has sensibly included a list of the sources they have used in their work. This additional information shows an interest in your subject and can make the essay more enjoyable to read. However the candidate has not written a conclusion and this is a mistake. A conclusion gives you the chance to leave the reader with a good impression, the key things you should include are a summary of your key points and ideas and a personal response to the topic as this helps you draw the essay to a close.

Quality of writing

This piece of work is very well written, it is coherent, the information is laid out clearly and is easy to follow. In addition to this there are no grammatical or spelling errors.

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