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What affects the voltage output of a solar panel?

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What affects the voltage output of a solar panel? Planning Aim The aim of the investigation is to find out how the distance between a light point source and a photovoltaic cell affects the output potential difference. Hypothesis I predict that the further the distance, the smaller the output potential distance Inverse square law for light intensity (Taken from the website - http://hyperphysics.phy-astr.gsu.edu/hbase/vision/isql.html#c1) "Inverse square law for light intensity against distance: As the distance between an observer and a light source increases, the observable brightness decreases with d-2. Light spreads out over an increasing area of space to decrease apparent brightness. (Figure 1.1) Figure 1.1 (http://www.astrosociety.org/education/publications/tnl/32/images/fig5.gif) Because, Pin is proportional to area-1 and area is proportional to distance2, therefore Pin is proportional to distance-2 (figure 1.2). This supports my prediction that the output potential difference will be much smaller when the distance between the point source and the PV cell increases. Of course, my hypothesis assumes 100% efficiency and no influence from background light and other factors that may affect the experiment in anyway. 1.2 Prediction of outcome (Pin ? distance-2) Apparatus list The list of apparatus to be used is: Ray box Used as the point source to emit light Clamp This is used to hold the solar cell at 90� to the table firmly Solar cell (photovoltaic cell) To absorb the light and produce a voltage for the experiment Power pack Used to power the ray box Digital voltmeter Used to record the voltage output of the solar cell, digital is used instead of analogue to increase the accuracy of reading Black paper To prevent any light from reflecting off the shiny surface of the table Set square Used to check that the solar cell is 90� to the table Vernier callipers Used to ...read more.


During the trial run, I tried both methods and have come to the conclusion that moving the solar cell is much more difficult compared to moving the ray box as it is harder to position the solar cell at the same angle and spot each time the distance changes. So I shall be moving the ray box to change the distance between the cell and the light source * To increase accuracy in my results, I will record the background reading before and after I record the reading when the ray box is switched on. I can then get an average of the two readings and subtract it from the actual reading. * Instead of ending my experiment at 60cm, I have decided to continue to 100cm to obtain more results and a better graph that is suitable for proper analysis Corrected Method 1. Gather all the equipment 2. Measure the radius of the light bulb using vernier callipers and add it to the distance between the light bulb and the end of the ray box. 3. Plug in the power pack and connect it to the ray box 4. Tape the black paper on the table, with an inch going underneath the ray box 5. Subtract the length measured from step 2 from 10cm and mark that length away from the solar cell on the black paper. 6. Continue marking 5cm increments from the base(10cm) mark until you get to 100cm on the black paper 7. Attach the solar cell to the clamp to a stand. Use a set square to make sure that the solar cell is 90� to the table. 8. Turn on the voltmeter and note down the voltage output without the ray box on. ...read more.


The graph starts to level off as the distances increases. This is caused by the limitation of the solar cell since it is saturated by the light, as discussed in the conclusion. The solar cell was not large enough to obtain a good set of results. An obvious limitation to this experiment was background light. Although background readings were taken and subtracted from the actual reading, the background light could have increased while the reading of the solar cell and the light source was taking place, thus my results unreliable. My measuring technique could also have made my results unreliable. There may have been mistakes when moving the light source away from the solar cell and although may not seem like a huge error, could have affected the graph and results in some way. Another problem I faced was shadows; other people's shadows could have blocked the light source from properly reaching the solar cell and would have affected my results Modifications To overcome the problems identified above, modifications to the investigation could be made. A larger solar cell would mean a larger voltage output, which would give a very accurate reading when d is very small because the solar cell would not saturate. To overcome background light, this investigation should be done in a pitch-black room, something similar to a darkroom used to process film. This would eliminate any background light and give a very reliable and accurate reading. The investigation should also be done so that no reflections or shadows would affect the readings; for example no other people in the room and cover the walls and table with black paper. A machine could be used to clamp the solar cell and move it closer or further away from the light source very accurately and this would almost limit human error and overcome any measuring errors. Thaddeus Cheung (4534) Physics Coursework - Solar Cell ...read more.

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Response to the question

The author has responded well to the task, by developing a suitable experiment to measure how the voltage output from a solar cell is affected by the distance away from a light source it is. They have made a well ...

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Response to the question

The author has responded well to the task, by developing a suitable experiment to measure how the voltage output from a solar cell is affected by the distance away from a light source it is. They have made a well reasoned hypothesis and confirmed it by analysing their results, using this to come to a well justified conclusion. The question was given as “What affects the voltage output of a solar panel?“, so perhaps they could have also investigated, or at least mentioned, other things which may have an effect, such as the intensity of the light. However, their experiment was clearly carried out very well, and overall their response to the question is very good.

Level of analysis

The author has analysed their results well and compared then to his original hypothesis, using this to come to a well-justified conclusion. However, occasionally they have made minor errors in their analysis, for example they say: “Metre ruler [uncertainty]: +/- .1cm” – we were advised that the uncertainty in a measurement is +/- half the smallest measurable value, so in this case +/- .05cm, because the smallest measureable value is 1mm. However, it’s always better to overestimate rather than underestimate uncertainties so they may not have lost too many marks. I would also have calculated the uncertainties at all the points and plotted uncertainty bars on the graph, which would clearly show how large or small the uncertainties are compared to the values measured (although they have calculated the percentage uncertainties, it is much easier to visualise when they are plotted on a graph with the original data). I would also have plotted one graph with all the recorded data on it, which would show the spread of the data clearly, rather than only using the mean values. I would also have plotted graphs using the original data, rather than only plotting 1/d2 against the voltage output, which would allow more exploration of the relationship between the two. I would also have plotted a line of best fit (excel/ autograph can calculate these and give you its equation, which is really useful, otherwise you could use a more mathematical approach using logarithms. Some exam boards require you to plot them yourself using a pencil, so check with your teacher beforehand!). However, they have used their graphs well to discuss the relationship between the distance and the voltage output, so should have gained good marks for their use of graphs. Another, slightly more important suggestion for improvement is in the scientific explanations given. Their reasoning of the original hypothesis is excellent, however they show at times a lack of understanding about the solar cell, for example, while explaining why “The graph starts to level off as the distances increases” the author claims that this is due to the solar cell being saturated with light, when less light would be reaching the solar cell as the distance increases, so in fact the opposite is true - as the distance increases, the number of photons reaching the solar cell decreases, so less electrons are forced around the circuit. The graph levels off as the distance reaches a limit when the radiation emitted by the light source is not significantly different from the level of background radiation – the ‘noise’ is hiding the signal. To be able to continue the experiment beyond this point, a brighter bulb would have to be used throughout the experiment. Proof reading the report and really thinking about what is happening within the solar cell should help resolve these issues. Despite these mistakes, the author has analysed their results well, using them to come to a good conclusion. They have discussed the causes of uncertainties, and used this to discuss improvements, and explored the relationship between the distance and the voltage produced, showing a good level of analysis.

Quality of writing

Their quality of written communication is generally good, and they have made very few spelling or grammatical errors. The report appears to be very well presented, and they have made good use of graphs and tables to present their results clearly. However, the layout is not perfect - the author has first describes a suitable method, but then does a preliminary experiment which should have been used to come up with this method in the first place. They have also not stated that this is a preliminary experiment, but treated it as if it was the real experiment, except that it doesn’t follow the proposed method. They then have suggested improvements to the experiment that they didn’t actually do based upon the preliminary. I would have described roughly the plan of the actually experiment, without giving any precise lengths or other measurements, then done a preliminary, explaining that this is to work out the most suitable lengths and other measurements to be used. The preliminary should have tested more than three points – I would have recorded the voltage every 10cm until there is no longer any significant change between readings, then plotted all these points on a graph, not just three, which would show the point where the change in distance no longer affects the readings. This would be more useful and make it clearer to the reader what you are doing. Only after these steps would I propose a clear method. This more chronological approach is more conventional and makes it clearer to the reader what you are doing. Another small issue is that they have not clearly labelled their graphs with the units, clear headings, and a description of what the graphs actually is. This makes it slightly confusing to the reader. I would also have used standard units throughout, which makes it much easier to do calculations, as well as being more conventional. Although they have given good headings throughout the report, one stands out as being ‘a bit GCSE’ – “Fair testing” – at A level, we are advised to say ‘reducing uncertainties’ instead. They have also used the word ‘rogue’ instead of ‘anomalous’, which is rather odd, and they have not been able to calculate anomalies as they have not repeated their experiment enough – this can only be done when it has been repeated at least 5 times. However, they have presented their work well, have good spelling and grammar, have used tables and graphs to make their results clearer to the reader, and have shown most of their workings, so the occasional slip in convention could be overlooked.

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