# How do I measure the irradiance of a particular wavelength?

I am still a high school student and I want to do an experiment on a solar panel. I want filter out red light and then focus is it onto a solar panel and measure various intensities and how it relates to the variation of power output from the solar panel.
For this I suppose I should measure the irradiance. But I am not exactly sure on how to do this. Because I am measuring the Irradiance of a particular wavelength does the unit W·m−2 change?

Thanks alot.
Dilan

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I am still a high school student and I want to do an experiment on a solar panel. I want filter out red light and then focus is it onto a solar panel and measure various intensities and how it relates to the variation of power output from the solar panel.
For this I suppose I should measure the irradiance. But I am not exactly sure on how to do this. Because I am measuring the Irradiance of a particular wavelength does the unit W·m−2 change?

Thanks alot.
Dilan
Cool project.
http://rredc.nrel.gov/solar/spectra/am1.5/ASTMG173/ASTMG173.html

Here are a few books:
1) Jenny Nelson. (2003). The Physics of Solar Cells. Imperial College Press, Covent Garden, London.
2) Harold J. Hovel. (1975). Semiconductors and Semimetals. Academic Press, New York, New York.
3) Antonio Luque, Steven Hegedus. (2003). Handbook of Photovoltaic Science and Engineering. John Wiley & Sons, Hoboken, NJ.

I highly recommend using (3). If you have access to a university library, you can check out an eBook copy.

(2) FANTASTIC book. I would also get this.

I don't know how long this link will be up:
http://www.eas.asu.edu/~roedel/eee498s07/index.html

but take a look at "Analytical Paper - Solar Cell Operation"

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Claude Bile
Sounds like an interesting project, here are a couple of suggestions.

Depending on what you are using to filter the incoming light, you may want to consider measuring the transmission spectrum of your filters. Good quality commercial filters will have the transmission spectrum supplied to you, in which case this wont be necessary, but if you are using something crude like cellophane, a direct measurement would be very useful.

Typically to measure irradiance you simply take a power measurement and divide it by the area of your detector. There are a number of different detectors you can use, thermocouples and PIN photodiodes are probably the most common.

The units you should use should be W.m^-2 as per usual. You may come across something called the spectral power or spectral irradiance if you do some reading, which will have gnarly units like W.nm^-1 or W.m^-2.nm^-1 - something like that - this unit is essentially power (or irradiance) as a function of wavelength, with the integral of the curve being the total power (or irradiance) across all wavelengths. Since you are inevitably integrating over a finite bandwidth, you should continue to use W.m^-2.

Claude.

NoTime
Homework Helper
If you are trying to measure spectral response of the solar panel. Then different color LEDs could be a possibility instead of filters. You could get a fair idea of the output intensity from the data sheets for the devices.

Claude Bile
That's a good idea, using LEDs, I would say that would be the cheapest way in fact to get a known spectrum going into your solar cell.

Claude.

thanks

hi,
Claude, yes as you have mentioned I am going to use cellophane (or glass paper). I've searched for 1 week in my country for colour filters and couldn't find any. Even to find a solar panel it was really difficult, but I managed to get a panel that's of dimentions 46cm *29.5cm. The only solution for this would be LEDs, but I am not sure whether the power of LEDs will be enough for a fairly large solar panel. Using LEDs will give me precision, but I was wondering whether the power given of by alot of LEDs will be enough for me to collect sufficient data.

NoTime
Homework Helper
Large panels like the one you have, are a collection of single solar cells. For purposes of testing it will far easier to illuminate a single cell (a few cm^2) than a panel as the parts of the panel that don't get illuminated will just be resistors and diode drops.
A few LEDs will cover a single cell, but for the panel you have it might be hundreds.

You can work out the LED power requirements from the data sheets.

Large panels like the one you have, are a collection of single solar cells. For purposes of testing it will far easier to illuminate a single cell (a few cm^2) than a panel as the parts of the panel that don't get illuminated will just be resistors and diode drops.
A few LEDs will cover a single cell, but for the panel you have it might be hundreds.

You can work out the LED power requirements from the data sheets.
They are designed to withstand the environment. I have heard that they can be quite difficult to take apart, so be careful.

NoTime