Science Buddies: "Ask an Expert"

Hi, my scientific question for my project is “Which frequencies of light do air pollutants absorb and would affect solar cell efficiency?â€

Any one has any comment on this project?

[quote="sammhy"]Hi, my scientific question for my project is “Which frequencies of light do air pollutants absorb and would affect solar cell efficiency?â€

Hello. Thanks a lot.
But the EPA website was the one I originally checked. I am just wondering if there is other air pollutants you can suggest to be less toxic and easier to acquire. For example carbon dioxide.
Thank you for your concern.

Hi!
Glad I could help. I actually did a google search and it seems like you could try making carbon dioxide. Here's a link to check out:
http://www.chem.umn.edu/outreach/Card-MakeC02.html
It seems to take a couple of days but hopefully it will help your experiment. Good luck!

sammhy wrote:Hello. Thanks a lot.
But the EPA website was the one I originally checked. I am just wondering if there is other air pollutants you can suggest to be less toxic and easier to acquire. For example carbon dioxide.
Thank you for your concern.

Most of the pollutants that you suggest are colorless gases in 'normal' concentrations; that is, they don't absorb visible light. [I'm assuming you think that the pollutant would reduce efficiency by absorbing some light that the solar cell migh otherwise use. If this isn't your idea, please post back _why_ you think these pollutants would degrade solar cell performance] In a small box, you would have to have extraordinarily high concentrations (and/or pressure) to get a colored atmosphere. In 'real life' solar cell efficiency may be degraded somewhat by pollutants, but the 'path length' of pollutant that the sun goes through to get to a solar cell is so much longer than what you can work with. Look up "beer's law" and then look up some information about how many meters or feet thick a smog layer is, and compare that to your box length.


Louise

Dear Louis,

You are correct, my initial assumption was that air pollutants may some how absorb a certain frequency of light that the solar cell might use. I developed this idea when browsing through abstracts of the previous year Clifornia State Science Fair. Here is a link to the file. http://www.usc.edu/CSSF/Current/Projects/J1025.pdf I was suprised by the drastic change (7% or 10% in some cases).

Would you consider my project to be doable on my own? Is there any way you can think of that I can aquire the pollutant? Thankyou for your concern.

Best,

Sam

sammhy wrote:Dear Louis,

You are correct, my initial assumption was that air pollutants may some how absorb a certain frequency of light that the solar cell might use. I developed this idea when browsing through abstracts of the previous year Clifornia State Science Fair. Here is a link to the file. http://www.usc.edu/CSSF/Current/Projects/J1025.pdf I was suprised by the drastic change (7% or 10% in some cases).

Would you consider my project to be doable on my own? Is there any way you can think of that I can aquire the pollutant? Thankyou for your concern.

Best,

Sam

There isn't really enough information in this abstract to tell exactly how (or how well!) this experiment was done. But the cases with the large changes are NOT gases, they are particles (aersol and car exhaust). The pure gases had _much_ smaller results and I would guess those were within experimental error. You can find out how much light is absorbed by each gas; look up beer's law like I mentioned before. This rule tells you EXACTLY how the absorption changes with distance. Then search for the "extinction coefficient" of the different gases. Do a little research, then tell _me_ if you think this project is feasible (or are you proposing to test the wrong things). I'll let you know if I think you are on the right track.

[Some other things you want to research: 1) smog- what causes the gray color? 2) what type of chemical reactions can occur with Si or GaAs and water or ozone? 3) are Si or GaAs solar cells coated with a protective layer? What do these layers do, if so?]

Hope this helps.

Louise

To do this study you will need to understand something about what it is in sunlight that gets converted to energy.

Then you need to determine if it is blocked by any of the pollutants you study.

Some visible light is blocked by some pollutants, especially particulate pollutants. But things are not always as they seem - you can get sunburned on a cloudy day because the clouds don't block the portion of the sun's slight that causes sunburns. So it is possible a given emission might be opaque to the portion of the sunlight that is used to generate electricity.

This sort of study will be hard to do without using real sunlight. I worked with a student trying to simulate the damage done to plastic water bottles by sunlight, and "sun-lamps" failed to cause the same effect as real sunlight, their emissions were too different.

If you live in a climate where sunlight is rare, especially in winter, you may have trouble performing your experiments. This is easier to do in Los Angeles or San Diego than in Seattle or New York.

It may also prove challenging generating pollutants safely. It is very dangerous, for example, to collect carbon monoxide from an automobile (doing so in an enclosed room like a garage can actually kill you). Then there is the matter of storing the emissions - if you get a reduction, is it because of the emission or because of whatever jar, bag etc that you are storing the pollutant in?

I find your topic interesting but there are a lot of challenges that may make performing the test quite difficult.

And to top everything off, noxious VOC (volatile organic compound) gases such as nitrogen oxide, carbon monoxide, sulfur hydroxide, etc., accumulate at the inversion layer, commonly seen in dense population (especially in California). To create the same inversion layer in a smaller scale experiment require very unique apparatus to hold the gases in place, and then use a light source that closely mimic the sun light radiation level to power up the solar cells through the gases.

Thanks a lot for your comments!

I am wondering if there were any specific experiments already done to test the effect of pollutants on different frequency of light? I am worried if I am repeating an exact same study already done.
The reason I planned to use artificial light is that I would like to isolate a specific frequency and investigate each pollutant's effect. Moreover, I don't think that I would have easy access to ultraviolet or infrared lights.
My teacher mentioned that it is actually possible to buy small cans of gases such as carbon dioxide, nitrogen dioxide, or sulfur dioxide. Do you think this way to acquire gases is advisable? However, I'm also concern about the way to pump in these gases and to manage concentration. Furthermore, as Louise has mentioned, I am also considering using particle matters or aerosols, yet still facing the problem about materials. Does anyone have idea on acquiring these materials?

Thank you very much!

sammhy wrote:Thanks a lot for your comments!

I am wondering if there were any specific experiments already done to test the effect of pollutants on different frequency of light? I am worried if I am repeating an exact same study already done.
The reason I planned to use artificial light is that I would like to isolate a specific frequency and investigate each pollutant's effect. Moreover, I don't think that I would have easy access to ultraviolet or infrared lights.
My teacher mentioned that it is actually possible to buy small cans of gases such as carbon dioxide, nitrogen dioxide, or sulfur dioxide. Do you think this way to acquire gases is advisable? However, I'm also concern about the way to pump in these gases and to manage concentration. Furthermore, as Louise has mentioned, I am also considering using particle matters or aerosols, yet still facing the problem about materials. Does anyone have idea on acquiring these materials?

Thank you very much!

I think the particle study is more interesting and novel. The absorption of different frequencies of light by gases is well known (this is what I was suggesting you look up with the "extinction coefficient"). This information is available as the "uv-visible spectra" and the "infrared spectra" of the various compounds.

Small bottles of gas are availble, but I would recommend that you work in a hood. Disposal of the gas when you are done is also an issue. You would need to make sure the school can dispose of these wastes safely.

I would look in to the topic of making an aerosol for some ideas of how you might procede.


Louise

Purchasing gases is not a problem if you're living near commercial-industrial parks. I use Carbon dioxide on a daily basis to pump my tires from a bulk tank. Smaller sizes like 10 or 20 oz cans can be purchased either at the bike stores, or welding stores.

Nitrogen oxide is a bit harder to come by in smaller sizes. In large tanks like the 15 to 20 lbs, it's not a problem. I used to use them in labs at the universities as a source for gas mixture and gas spectrometer point setter. But to purchase it in a smaller size would be quite difficult. You can contact the local college and university, or even welding shops, to ask them for a small sample. If you live near by a various gases refill station, they can give you all kind of gases for experiment, since they have an entire lot of bulk tanks ready for distribution. Have them release the gas in a large glass container that is air tight. Flip the glass container up-side-down, pump the gas in, and close the lid tightly before bringing it back to the school gas collection chamber. Keep the glass container up-side-down at all time. Extracting it can be a pain. You have to use pipette large enough to draw in the gas, but small enough to fit your experiment layout.

Sulfur dioxide can be extremely dangerous if you have a specific allergy, and can be extremely irritating if it gets into your lungs. Just be careful. Sulfur dioxide can be collected by just burning coals. Of course, you have other gases from burning coal, but 23% of the gas giving up is sulfur dioxide. If you can burn the coal in the gas collection chamber for about 5 minutes, there's plenty of sulfur dioxide in the gas mix to give you a great start on the experiment. Just make sure there's no other volatile and flammable gases near you during the lighting and burning period, or your lab experiment may go up in smoke...literally!

Hi. I investigated more in aerosols and partculates. I found out that all aerosol both absorb and scatter radiation. There is a Single Scattering Albedo (SSA) that measures the light absorption of light. For example, a major atmospheric abosrber that has a SSA of 0.23 is Black Carbon, which arises from combustion of fossil fuel.
I am wondering if I can probably collect this particulate matter with a baloon from the car exhaustion tube, while the car engine is on. Is this method feasible and safe? I would also like to vary and test some other particulate matters through frequencies of light.
Thank you very much.

Sam

Hi Sam!
Black carbon is definitely a significant atmospheric absorber. Collecting black carbon from a car exhaust tube might be a bit dangerous, but if you do, make sure that you try not to breathe it in. Black carbon is also produced when coal is burned so maybe that could be an alternative to using the car exhaust. Good luck!

sammhy wrote:Hi. I investigated more in aerosols and partculates. I found out that all aerosol both absorb and scatter radiation. There is a Single Scattering Albedo (SSA) that measures the light absorption of light. For example, a major atmospheric abosrber that has a SSA of 0.23 is Black Carbon, which arises from combustion of fossil fuel.
I am wondering if I can probably collect this particulate matter with a baloon from the car exhaustion tube, while the car engine is on. Is this method feasible and safe? I would also like to vary and test some other particulate matters through frequencies of light.
Thank you very much.

Sam

I think this is a really good research idea. I think a balloon is not a good idea, car exhaust is hot! [Also, the exhaust pipe isreally hot, you could burn yourself badly by touching it] Could you test particles of different sizes that aren't necessarily pollutants. For example, flour. Charcoal is carbon-could you grind it finely enough? (Check with your folks !before! you grind up charcoal in the blender. ) Don't use the stuff with lighter fluid. These some examples... maybe you can come up with more.
Decide what it is you want to test and then think how you could model that.

Louise

If you put a balloon on a car exhaust pipe the most likely result is the baloon would pop, or if it survived you'll stall the engine by messing up the oxygen flow. At least that's how a carburator car would work, I'm not as certain in these days of fuel injection on most cars.

If the car was in neutral (stick) or park (automatic) and there was somebody in the driver seat to ensure it did not go anywhere, and you did not attempt this in an enclosed space, it would probably be reasonably safe except for the risk of breathing the fumes or burning yourself on the tailpipe (they get quite hot). You'd have to collect it when the entire car was "cold", or the baloon would melt.

I don't recommend this - both for the difficulty of doing it safely and because even if you succeed the result will contain lots of elements other than what you are looking for. The suggestions of purchasing gaseous elements directly would keep it to one dependent variable, although there is still the difficulty of separating the results from the container you have placed the gas in (you'd need an identical container with ordinary air in it as a control)

The kind of charcoal you buy for a BBQ these days is usually saturated with the equivalent of lighter fluid or other chemical to make it ignite quickly. This will also ruin your results, as it mixes other products into your air.

Even if you get normal charcoal that is "just' charcoal, you still have the problem of ensuring a measured amount of gas result. Grinding it fine, measuring it and burning it to ash under something that collects all the gas is probably the only way and that is going to take something more sophisticated than you can easily do at home. I would talk to a chemistry instructor about what resources they have. At minimum, a fume hood would be prudent and some sort of crucible to ensure fire safety.

Anything involving generating gas via combustion is very difficult to control and will have some safety issues.