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Forum Index : Solar : Solar panels and mirrors
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Now the official rule is dont use mirrors to increase the output of your solar panel, it will void the warrenty and reduce the life. But I wonder if thats just a statement by the manufacturers to make you buy more of their panels. I do have an idea I would like some comments on. See the drawing below. 
The solar panel is in the middle, and the whole assembly is on a solar tracker to keep it facing the sun. The addition of the two mirrors will approximately double the sun light falling on the solar panel, given mirrors dont reflect 100% of the light ( usually only the visible spectrum, they absorb a lot of the infra-red light ). Now this would increase the power output of the panel, by how much I dont know, but say 50%. But the heat will also increase, and this is what is so bad for the solar cells. So I though a couple of 12v PC fans to cycle the air behind the panel. Or even an additional fan facing the front of the panel to blow air over the surface. The fans may drain 5 watts, but on a 80 watt panel the mirrors have given us an extra 40 watts, so we still have a net gain of 35 watts. At $10 a watt thats a big saving. Or is this just crazy talk. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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Gill Senior Member  Joined: 11/11/2006 Location: AustraliaPosts: 669 |
Just too much of an unknown area. I've been running solar as my primary power souce for over 10 years but still havn't finished the tracker let alone the white painted ply concentrating panels. I felt that the white paint reflection would give a defused light and hence less heat. Never got to test it. Your idea worth a try if you've gor an old panel to burn. was working fine... til the smoke got out. Cheers Gill _Cairns, FNQ |
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Trev Guru  Joined: 15/07/2006 Location: AustraliaPosts: 640 |
Hi Glenn, yes the warranty is void for any forms of concentrations. I would be interested though of any real results, if anyone has done it or is prepared to accept damaged panels should that occur by doing such testing. Private email is fine if anyone wants to share with me, but not the world!! My younger brother lives in his car and operates on two 80 watt panels for all his 12v needs. The fridge is the biggest one by Waeco ( 110ltr). He took out the back seat to fit it in. He has experimented a little for only a very short time with a small hand size mirror to boost performance in shady times. It definately works, but how much extra power is possible, and for how long is the big question?????? Trev @ drivebynature.com |
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| AllanS Regular Member  Joined: 05/06/2006 Location: Posts: 67 |
From memory, you get a 4% reduction in output for every 10 degree rise in temperature. Cooling's critical. If you put the cell near your water tank, it wouldn't take much to water-cool it. Anyone see Catalyst last week? Physicists at ANU are making super-thin silicon cells that are cheap and flexible. Origin Energy have thrown $100 million into the hat! They expect to reduce solar panel costs by 75% in one fell swoop. They're talking 5 year payback compared to 20 year. One of the blokes, a wild looking fellow with a gandalfian beard, said "We're so close to the Holy Grail we can smell it!" Sounded very hopeful. Might like to look atthis site He uses a conical concentrator. |
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herbnz Senior Member Joined: 18/02/2007 Location: New ZealandPosts: 258 |
Hi below copy of a response of mine to another forum re heating effects on solar panels mounted on hot roofs. Cooling is not silly even before concentrating light I would love to spray water under panels but to risky uneven temps may crack panels blower i feel be OK tho Herb Posts: 3 Gender: Re: Mounting Photovoltaics on roof Reply #2 - Feb 1st, 2007, 3:05pm Crystalline PV modules lose power at about 0.5 percentper degree Celsius as their temperatures increaseabove the STC rating temperature of 25°C (77°F). Withan NOCT of 47°C (117°F), the module is operating22°C (72°F) above 25°C, and has lost 11 percent of itsrated power. On hot summer days in many parts of thecountry, PV modules are frequently operating at 65°C(149°F), and have lost 20 percent of their rated powerdue to heating. The lost power is largely due toreductions in the peak-power operating voltage point ofthe module as temperatures increase. Above is copied from http://www.nmsu.edu/~tdi/pdf-resources/cc79.pdf. Cell Temperature is above ambeient by the self heating effect due to current flow. It is not uncommon to measure cell temperatures of 75 degress C in an ambeint of of 25 C. if more cooling is provided this .5% loss/ degree C can be recovered. Mounting on a hot roof is not a good way to gain cooling although previous comments about air flow under will make a bad situation better. Myself i have found it easier to mount panels on a free stand on a grass bank maybe easier than roof. I have used old car diff and steel framed bed to mount 4 80 Watt panels no cost hardly. Also i can easierly turn and face the sun one day will add motor and automate. turning panels is another big gain. with the high cost panels thought must be given to efficient operation. Back to top |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Good facts there Herb. I did some reading and from what I can gather, solar concentrators do give some gain in sub tropical areas, ie areas where the light level is down anyway, but at the expense of cell life. In the tropics, its just too hot to use concentrators, the cell temp will go through the roof, loosing efficiency and cell life. As anyone in the tropics would know, if you leave somethine metal out in the sun, like a spanner, you dont dare pick it up. When I was involved with solar racing cars a few years ago, some of the teams carried water bottles in the car. When they needed a bit more power to get up a hill, they would hand spray water over the cells to cool them off and gain a few amps. It worked! Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| petanque don Senior Member Joined: 02/08/2006 Location: AustraliaPosts: 212 |
If the cells on the panel are in series would you need even illumination on the panel to get a consistent output from all segments of the panel? |
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Megawatt Man Senior Member Joined: 03/05/2006 Location: AustraliaPosts: 119 |
On the other hand, when insolation is low, the use of the mirrors as proposed would concentrate the lower levels of radiant energy, possibly up to near the levels that would occur around midday. No more heating over the design maximum midday levels would accrue. So for the early and late hours in the day, you'd receive the same output without thermal stress over and above the panel's normal limits. The trick is measuring just when thermal limits are about to be exceeded and swing the outer mirrors out of the insolation, or maybe swing the whole assembly into a position where incident solar energy remains at the toleable level. Taking a leaf outof the air conditioning engineers' books, use water flow under the panels rather than air if you want to subject the cells to increased insolation and therefore need to remove heat. Water cooled condensors are more efficient than air cooled unit, but you can encounter legionella. Nothing is easy if it's worthwhile. Megawatt Man |
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Storm Regular Member Joined: 12/09/2005 Location: AustraliaPosts: 43 |
During winter months down in S.A. and other lower regions of Australia it gets cold and cloudy, I would think the solar panels could ultilise reflectors without the overheating issues then therfore increasing the total energy over the year (same output in winter as in summer), shorten the payback increase the paypacket. Temp sensors on the panels could operate motorised mirrors so on the hotter days you dont cook your panels, likend to furling, fully automatic. Cooling your panels with electical/audio heatsinks underneath exposed to the shaded air whilst water from a 12v pump runs over the front and returns to a resivior (similar to a water feature). Check these out. [http://www.hydrogen.asn.au/Australian-Solar-Energy.htm |
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| RonS Newbie  Joined: 19/06/2007 Location: AustraliaPosts: 18 |
I agree with Megawattman about water cooling. I have seen used those molded poly-plastic pool heater modules. They have about six or seven (five?) parallel tubes roughly six mm in diameter bonded together. the whole assembly being roughly 70mm wide. You have to muck about with right angle connections to each tube and they tend to leak, but they did cool down the solar panel. Still, as you concentrate more and more light you must eventually reach a point where heat stresses across the thickness of the panel will cause fractures. The one I saw only used something similar to the diagramme above with polished stainless as the mirrors. Don't know what the long term 'survivability' was, though. Probably not too good, I would have thought. No semiconductor has an infinite life and if you stress it, it fails sooner. Avoid strong drink. It makes you shoot at tax collectors ...and miss. |
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Art_ Newbie Joined: 22/10/2007 Location: AustraliaPosts: 30 |
I was going to announce that I had a sacrificial lamb so to speak, but just go outside and try this with one small mirror on your hand, an you'll feel how hot it is instantly. It's astounding. If not actually, then potentially. |
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| Art_ Newbie Joined: 22/10/2007 Location: AustraliaPosts: 30 |
It appears there is no private message system. To Trev: [quote] My younger brother lives in his car and operates on two 80 watt panels for all his 12v needs. [/quote] How exactly do you live in a car? If not actually, then potentially. |
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| petanque don Senior Member Joined: 02/08/2006 Location: AustraliaPosts: 212 |
While heat is an issue in flat panels it would have to be an efficient cooling system to have a net gain. |
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wind-pirate Senior Member Joined: 01/02/2007 Location: CanadaPosts: 101 |
Some intersting thoughts have been projected here. I have (5)-15 watt pannels. I live on the north side of a valley. The sun hits us directly. We can see temps as high as 36c/100f My pannels are on a shingled roof "Brown" facing the south (the sun). We use galvanized sheet metal arond our pannels. They are adjustable, so we can flip then up to about a 30deg angle. We use this on cloudy days summer and winter. We back them off when it realy gets hot. My pannels are three years old now, and are still working fine. Ron THE Pirate. stealing wind & solar energy is fun |
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| davef Guru Joined: 14/05/2006 Location: New ZealandPosts: 499 |
Somewhere on this site he has 9 mirrors shining on one water-cooled panel! HelioTrack |
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