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Forum Index : Solar : General Solar Question
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MacGyver Guru  Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Crew I'm 62 (ish) and from memory  it seems to me I recall solar PV cells work at a specific light frequency. If that is true, would it be possible to pass a large amount of white light through a filter, so only the specific frequency needed by the solar cell passes through and then concentrate that onto the cell, leaving the infra-red (heat) out of the equation?
. . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Me Again I took a screen shot on page 2 HERE but it is the wrong file type to copy and paste, so take a look at it, then come back. Scroll down a page or two until you find two little charts that peg frequency against power output. The data presented in the link further supports my theory that silicon cells work over a wide range of wavelengths, but work best with a narrow band of the higher-energy blue-green frequencies of visible light. I'm thinking that if the UV and IR is filtered out of white light, it may mean that we can concentrate visible light onto a cell and kick its output in the ars to give a higher yield while avoiding the heating and UV degradation aspects of the full-spectrum absorption. Comments? . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| neil0mac Senior Member  Joined: 26/12/2009 Location: AustraliaPosts: 210 |
Mac. Interesting find! "if the UV and IR is filtered out of white light" .... suck it and see? I suspect that using a glass UV filter that there is a corresponding (greater or lesser?) loss of other light frequencies. This may be totally wrong, but someone might have a way of testing your idea. The chart that particularly interested was the third one with 'sun', '1/2 sun' etc. plots, because I have seen a reference to '2 suns', 3 suns but the website (www.pvcool.com.au) doesn't show them any more. However, http://pvcool.com.au/oldhtm/DownloadFiles/SP190-FOLDING%20So lar%20Module.pdf does have an interesting chart of irradiation and temperature coefficients. |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Neil I was thinking along the lines of using a frustum (?? I think that's what it's called) which is a section of a 90* cone with a reflective surface. At the center of the frustum, I thought to insert another 90* cone pointing down and reflect a solid conical section of light onto a photo cell. This would effectively make the final image many "suns" and if it were to pass through a blue-green (turquoise?) filter, perhaps the bad UV as well as the heat from the IR could be managed. Just an idea. As for that 3rd chart: I see that it states the terminal voltage is not dependent on the amount of incident light, so evidently, these things are frequency (wavelength) sensitive, eh? Heck, we may be on to something!! . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
[quote]eh? Heck, we may be on to something!! [/quote] Yeha, sunglasses for solar cells. 
Add a hat and coat and we wont even know they are there. 
I would guess it has been tried before (filtering that is) to little advantage or expect industry to have adopted it before now. Pete. Sometimes it just works |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Pete Okay, rain on my parade! I knew I was going out on a limb, but it's Sunday here and raining, so what else was a bloke to do with the day? Still, I don't see any harm in shading the cells with a filter. It's way less complicated than spraying them with a water mist and relying on latent heat of vaporization to keep the temps down. The filter could be held off on stand-off supports to allow air flow between it and the panel and if the wind didn't turn it into a kite, it might be worthwhile.
. . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
I didnt mean to rain on your parade (sounds like you already have enough bad weather )
There is merit in your thinking, and have been guilty of thinking outside the square also. (lot of failures to prove it to) I would think if it was able to squeeze a tad more from the cells with filtering than the big boys would have done it a long time ago. Painting them white might work just as well.  Bit ilke cloud filtering.
[quote]so what else was a bloke to do with the day? [/quote] You could take the wife out for lunch?? ....Ha, ha. Then you did say it was only a wet day and not that hell has frozen over 
Pete. Sometimes it just works |
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Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Mac, the way I read it, on the subject of PV cells, is that they turn *light* into electricity. Meaning visible light, not UV or IR radiation. The amorphous type cells do some more selective light spectrum thing but AFAIK also on visible light. If fancy filters would do any good why are they not already fitted to every solar panel? Perhaps a bit of googling finds you a doctoral thesis on the subject to chew on for a while Klaus |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Tink It's not a big deal. I ran across the charts while looking for something else and thought it interesting. I recall most PV cells are already a blue color, so maybe they already filter everything except the blue part of the visible spectrum anyway, I dunno. It was just a passing thought. Thanks for your input. If I run across anything earth-shattering, I'll post it. . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| neil0mac Senior Member Joined: 26/12/2009 Location: AustraliaPosts: 210 |
And it does ... http://en.wikipedia.org/wiki/Solar_cell (long article!). |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Neil Great find! You were spot on when you said the article was long. I found this quote about two feet down the page: "Amorphous silicon has a higher bandgap (1.7 eV) than crystalline silicon (c-Si) (1.1 eV), which means it absorbs the visible part of the solar spectrum more strongly than the infrared portion of the spectrum." This further leads me to believe that electricity production is frequency based. Further down the page, they talk about "CPV" (concentrated photo voltaic) and mention that heat is a problem. I would think filtering out the IR and active air circulation would be key. Like Pete & Klaus siad, if it were a big deal, industry would already be one it like a chicken on a bug (paraphrased). Still, I think I'll do a little "tinkering" of my own to see if I can make a better mouse trap. Hmmm . . . . last time I said that I got into quite a fray with someone asking if my better mouse trap were better than Pete's (?) cats. Anyway, you get the drift. . . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
Hi Mac, do a google on Sanyo HIT cells. These are a hybrid. There are also hybrid GAS cells as well.[not easy to buy though]. Hybrid cells capture a wider section of the solar energy spectrum. The Sanyo HIT cell panel I have has an efficiency similar to SunPower modules. Gordon. become more energy aware |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Gordon Thanks. Actually, I was merely looking at a way to improve on the existing silicon cells in widespread use today. According to that 3rd graph, they use the entire spectrum and I was interested in filtering out the destructive UV as well as the hot IR, that's all. I'll just have to try it out, but all my "toys" are in storage until the end of March 2011. Guess I'll have to wait. Waaaaa! 
. . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Me again! I copied this from that really-long article mentioned a reply or two back: Air mass has an effect on power output. In space, where there is no atmosphere, the spectrum of the sun is relatively unfiltered. However, on earth, with air filtering the incoming light, the solar spectrum changes. To account for the spectral differences, a system was devised to calculate this filtering effect. Simply, the filtering effect ranges from Air Mass 0 (AM0) in space, to approximately Air Mass 1.5 on Earth. Multiplying the spectral differences by the quantum efficiency of the solar cell in question will yield the efficiency of the device. For example, a silicon solar cell in space might have an efficiency of 14% at AM0, but have an efficiency of 16% on earth at AM 1.5. Terrestrial efficiencies typically are greater than space efficiencies. It looks to me like air actually "pre-filters" some of the bad stuff out already. This leads me to believe we may be able to boost the production even a bit more by adding a filter or two of our own. Like I said earlier on, I can't do much hands-on experimenting for a while, so all this is theory. When the time arrives (March) I will dabble with this a bit to see if adding a blue-green filter improves output enough to even bother with. Oh! Oh! Further on down that long page, in reference to the Mildura Concentrating Solar Power Station somewhere in Australia,I found this too: "The modules include a specially-designed filter (bold and underlines added by moi) that removes harmful UV radiation that reduces the operating efficiency and life of traditional PV technology. The modules are also cooled, which increases their effective operating life and their efficiency". Hmmmm . . . . . . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| RossW Guru Joined: 25/02/2006 Location: AustraliaPosts: 495 |
A thought or two. Optical bandpass filters are moderately expensive. Those with low attenuation in the passband are generally very expensive. (And using anything with non-trivial attenuation in the passband is a very bad idea!) Filters get hot (where do you think all that blocked energy goes?) There are a number of material that have very different reflectivity at different wavelengths. For example, have you ever wondered why chrome bumber bars get so stinking hot out in the sun, when you'd THINK that being so shiny they'd stay relatively cool? The answer is that they are quite reflective in the visible part of the spectrum, but are far from it in other parts of the spectrum. If you make your (concentrating) reflectors out of the right materials, you may be able to avoid having to spend big money on filters and cooling systems, keep your panels easily accessable for cleaning, and achieve all the tricky work in the surface coating of your reflectors. |
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| GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
In a previous life as a chemical analyst, I had access to bandpass interference filters. These appeared silvery, and most were under 1mm thick, with 99% transmission at the middle of the bandpass wavelengths. As RossW has mentioned, the cost is significant. I see the cost of solar panels dropping continually. At the moment there is not much benefit cost wise. If panel prices rise again, then other options may be economically viable. Gordon. become more energy aware |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Crew Okay, maybe a blue filter isn't high on the priority list, but a tracker, I'm told, will increase efficiency something like 40%. To that end, I've decided to make one. I'll be copying the Mother Earth News' design except that I intend filling it with liquid propane instead of CFC's. Here's a link in case you don't know what I'm talking about. Unfortunately, there seem to be no pictures, so you'll have to use your imagination. Being a plumbing contractor, I should be able to knock this one out some morning soon. My plan is to make one "master" unit and have it drive several "slave" units. A "unit", by the way, will be nothing more than a flat Kyocera solar panel mounted on an axis at my mean azimuth (34* I think) and aimed south. This way, it should pretty-much follow the sun's circular pathway through the sky on a year-round basis, without much trouble. If everything goes per plan, it should be pointing due west at sunset and as soon as the morning sun's rays heat one of the receivers, it should move everybody back to an east-facing direction and that's that (in a perfect world). I know Murphy will be hiding in the wings, so I'll be patient and take pictures along the way so I can participate in 4m show 'n tell eventually. I looked around a bit and came up with a "photo" of sorts. Looks like a "screen shot" is the wrong file type, so here's another link to a page with pictures of what I'm going to build. And as if that weren't enough, here's yet another link to make things more understandable. I built one of these back in the day when we all thought CFCs were not harmful to anything and any bloke could buy the stuff. Not so, apparently, and now days you have to have all kinds of licenses and permits and insurance and such to even handle the stuff. Lord help you if you are caught letting any "go" into the atmosphere! That's why I'm going to use liquid propane. It's relatively cheap and easy to handle and not very harmful (no smoking please!) if it gets loose. The only thing I'll change from the pictures shown is, I found that the little sunlight barrier works better if it is both taller and mounted between the tank and the panel. You have to be mindful of where you attach the hoses from the expansion tanks to the piston so it tilts the correct way is all. . . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
Hi Mac, yes, these sun trackers have been around for many years. I remember them back in the late 80's. Operation is affected by wind. The wind tends to wobble the units without the dual cylinder. The simplest had no moving parts and required no electricity. The liquid was pushed around by pressure difference to maintain solar tracking. Even when panels were very expensive, they were not that popular though. Gordon. become more energy aware |
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| MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329 |
Gordon Thanks for jogging my memory. Now that you mention it, I remember I had similar problems with wind not so much shaking things, but instead, actively cooling the cylinders. With that in mind, I think I'll cook up a way to shelter the drive panel and have it drive another panel at a 2:1 ratio so its motion will make a flat-plate mirror bisect the angle between the sun and a fixed target (the solar array). Not sure if that will actually work without an active Y-axis control; we'll see. I've done this before, but used a fancy electronic dual-axis thingy loaned to me by a friend to keep things in alignment. If tilting the mirror at the mean azimuth and then bisecting the angle between it and the sun while things rotate about that mean longitude works, it'd be something everyone using solar photovoltaics could use. The trick is to make this thing entirely mechanical and make the drive plate move twice as fast as the reflector plate. I've figured out a way to do it mechanically, but will just have to build it. You know what they say about a picture being worth a thousand words, right? This is one of those occasions. I can likely build it faster than I can accurately describe it using only words. By the way, the mechanics are easy as pie (at least on paper). Of course, that little chill I felt as I sensed I am being watched made me turn just in time to see Muphy dodge back into a shadow!
. . . . . Mac Nothing difficult is ever easy! Perhaps better stated in the words of Morgan Freeman, "Where there is no struggle, there is no progress!" Copeville, Texas |
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| Tinker Guru Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Mac, if you search the messages you'll find a home built dual axis tracker built by me. It uses a timer to track the sun at hourly intervals and has now been in use for a year. I have 2 x 210W sunpower panels on it which replace the 3KWh daily draw from my 500Ah/24V battery bank easily, often by midday. Using a timer requires only minute driving power, all the switching & motor electrics are off normally and the timer sends 12V power up to the motors for a few seconds each hour. BTW, you should look up a 'sun position calculator' there are plenty free ones on the net. For my location (lat 31 deg. South) the sun moves over a 120 degree azimuth in Winter and a 240 deg azimuth in Summer so its not quite as simple as a "circular path". You have to fit gas shocks to stabilize the panels. With just 2 panels mine wobbled alarmingly in high wind on the shaft and were giving the worm drive gear a hard time until I fitted the gas shocks. Klaus |
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