Photovoltaic cells

[sportygirl101109]

Hi, I am doing a science fair project on whether temperature affcts pv cell's effiency. I was wondering what would be the best way to do my experiment. I went on some other websites and they suggested using a clear box with the pv cell(or cells) inside with a thermometer attached the inside, to moniter the temperature. But i am having a difficult time thinking of a way to generate heat(and control it) to keep the experiment consistant. Also, i can't find a way to measure how much electricity the cells produce and what to use for my light source. Thanks so much for your help!

[Trader]

That's a very interesting experiment!

I've done a bit of background research and it seems like in the case of a a Solar-Pv Ac Water Pumping System, a panel temperature of higher than room temperature negative affects the performance of the photovoltaic cells.

http://www.ars.usda.gov/research/public ... 115=182692

This site appears to explain how you might want to setup your experiment:

http://www.newton.dep.anl.gov/askasci/p ... y05172.htm

To do an experiment to demonstrate the effect, you are also on the right track,
except that the light source should probably go outside the box (most sources
generate heat by themselves, which could throw off your experiment). You need
to deliver a controlled amount and intensity of light to the cell, and control
the cell temperature. Place a thermocouple or other temperature probe on the
back of the cell (make sure it is electrically insulated and does not damage
the cell when you apply it) to measure the temperature, and you will have to
have some sort of means to deliver heated and/or cooled air to the cell to control
the temperature. It would be a good idea to exclude ambient light as well.

To measure the efficiency of the cell, you need to measure the power delivered to
it in the form of light and the power it produces. This can require expensive
equipment, but there are shortcuts.

1) You can measure the power input indirectly by measuring the electrical power
delivered to the artificial light source you are using. This will make the cell
seem quite inefficient (they are only about 15-20% efficient anyway), because you
will be adding in the inefficiency of converting electricity to light in the first
place. This can be fairly low for incandescent bulbs, and they produce a lot of
heat, but they also produce a bunch of light wavelengths. There are more efficient
light sources, such as compact fluorescents and LED's, but they can be more
restricted in the wavelengths they produce. You'll have to experiment to see
what works best.

2) To measure the electrical power delivered and/or produced, you need to measure
the voltage and current, and it may be helpful to measure the time at a certain
set of conditions. Power is measured in Watts, which is voltage multiplied by
current. At the levels of a typical desktop-sized experiment, with a single
small cell (or group of small cells), you may have trouble getting enough
resolution and accuracy in the instruments to see the temperature effect over
a small temperature variation.

I've also found this website: http://solardat.uoregon.edu/download/Le ... _Cells.pdf

This seems to cover the basics of experimenting with PV cells! I'll edit this post later on.

[sportygirl101109]

hey thanks ,

I have been researching and I know i need pv cells, volt meter, a light source, and a thermometer (basic materials). Do you think i need a load resistor specifically a thermistor? Thanks so much

[Trader]

Hi nice to see that you're already starting the materials. If you want to test whether temperature affects a pv cell's efficiency, I think that having a thermistor (where the resistance varies with the temperature) is a good idea. You can see how temperature affects resistance through the thermistor, and through that, the pv cell's efficiency.

However, if you are using a thermistor it may be more of measuring the effect of temperature on resistance (which is a given) on the pv cell's efficiency. If you kept resistance constant however (that is, not using a thermistor), you will be able to directly attribute temperature to increasing/decreasing pv cell efficiency as opposed to the work of the thermistor.

So using a thermistor is definitely one way to do it but it may be more direct (and I think more straightforward might be better) to follow the protocol for example in the experiment listed above (where they directly measure the voltage (or some other way to measure the efficiency of PV cells, i.e. what do the PV cells that you wish to use do?)