Heat pipes and specturaly selective window glazing for solar panel heat dissapation.

[orochi8]

Im just curious to know what you guys all think of these two technologies and whether or not they would prove effective in use with a solar panel to help avoid the problem of over heating.

I would assume that spectraly selective windows glazings would be an ideal solution in many respects, but the films available right now are engineered to provide better insulation in home windows, so who knows if they would allow enough of the spectrum a PV needs through. Im guessing that idealy we would want only the infra red to be reflected, but Im not really familiar with exactly what light the PV can make use of and what it cant. Apparently, there are kits you can purchas for retrofitting your older windows with a spectraly selective film, so it might be worth it for someone to check it out.

The other means of heat controll that comes to mind are heat pipes. They dont really dissapate heat all that well by themselves, but they do a pretty decent job of moving it from one side of the pipe to the other, and Im told they are actually fairly afordable. If you where to fit the back of your solar panel with a heat sync and some heat pipes, then run the heat pipes to a shaded area with a seccondary heat sync, it might substancialy reduce the amount of heat in and near the panel itself. The one major hitch being that the heat pipe needs to have gravity working on its side. Which is to say it needs to be standing verticaly with the area that you want to cool touching the bottom of the heat pipe, and the area you want to disapate the heat from at the top. This seems problematic, as anything you put above the panels, is likely to shade them. If anyone has some ideas though, pleast make a comment.

-Orochi

[Vtbsr]

Hello orochi, I don't think you have to worry about the slight loss of output of your PV's. In the winter they will put out more. The PV will still put out a higher potential than the volts of a 12 v battery on a hot day. On solar hot water pannels you want a low iron glass cover to get the most btu. Regular glass will look a little green on the edge and low iron will be clear. I assume the PV cover glass is the same low iron. On your house glazing low e glass will cut out 30% of the incoming solar gain, but will help retain heat at night. Regular thermal pane 20% and low iron less than 10%. I always thought that regular thermal pane on the south side and low e for everything else. If you could have a outside robotic insulated shutter you would realy help your heat loss. With walls at r19 and windows at r 3 the windows are the major loss area. The problem with inside window quilts is that the glazing drops below 32 deg. and the house humid air condenses on the cold glass. When you open the quilt the glass warms up and the frost melts running on the sill. Just my 2 cents

[scottsAI]

Yes, at 150 degrees F or so, power output can drop 20%.

The power drop is 0.5% per degree C.

So, building a system to lower the temperature is a good thing!

With that said, what will it cost to build a system to lower the temp 70 some degrees? Or even lower, must stay above the due point. Power gets better colder.

Lest say you have 10 free air panels, they get heated to 150'F.

At 70'F you get the same power out with 8 panels, save the cost of two panels.

What will the equipment to cool the 8 panels cost? How much power does it need?

Every system I have seen or devised cost more than the cost of two additional panels.

If you have a cold water stream near by, that may be worth considering.

The same thing applies to trackers, I thought they were great. Until I looked at the cost

I may be able to build my own tracker for a lower cost, but for all the work I may not do it. I have seen some simple single axis trackers. Manually change second axis.

Power voltage tracking: the cost is below the cost of the replacement panels therefore, it's worth doing.

If the solution is break even, then you have to consider other benefits, time etc.

I have looked into using films in front of the solar panel. The film claimed 85% visible light transmission with 80% heat reflection. (not sure if the heat is right).

The film by itself was not cost effective. 85% light = 85% power, the temperature would have to stay below 90'F to brake even. I did not think it would. Ambient temp is almost that high. With the 20% heat that gets through, not good.

I figured if I used Mirrors to increase the light to 2x...

Please understand, generally when using mirrors a tracker is required.

Since I needed a tracker I could shape the solar panels to reflect the heat back to a single point heating a sterling engine (we are thinking big here). The sterling engine would be operated to cool the solar panels. The interesting thing about the heat is it produced more power than the solar panel! I started loosing interest in solar electric panels. Maybe consider the heat engine.

I searched and found a solar cell designed for 350 suns., yes 350 suns! rated to 1000 suns, the efficiency dropped above 350 suns. Was a three junction solar cell, efficiency was 32% at 350 suns. Normal panels are around 12-15%. Been three years, military is buying all they can produce for a huge price, dropped any plans to use them.

Last year found a two junction solar cell, 21% at 30 suns. Just as costly.

Normal solar panels if used with mirrors will void the warranties. The solar cells all required 25'C temperature. How do you keep a solar cell at 25'C with 350 suns?

Keep thinking up ideas. And remember:

Have fun.

[orochi8]

God, I WISH heat engines where a viable option. If I had a machine shop of my own, and engineering knowledge up the wazoo, they might make sense. Currently though, they just dont even come near being reasonably priced from what I can tell. It would seem that a stirling generator will set you back about 15,000-20,000. Plus, stirling engines have an entire set of issues all their own. For one thing, the whole temperature differential thing is a pain. Cooling of course becomes a far more significant factor than it is with PV, so we get right back to your concerns about the cost of a cooling system, not to mention the engine needs to be built for a specific heat range to be efficient. Then of course there is the weight, which isnt a big deal for eveyone, but for someone like me that is planning on hauling all this stuff arround with me in a vehicle, it can be problematic. Please do let me know if you find a source of inexpensive stirling engines though. Hell, if you can even find plans for a fairly efficient stirling engine design that could be built primarily with stock components or something, Id love to hear about it. It sure would be fun to fool arround with some parabolic dishes and fiber optics to see how much I funnel into one of those things.

Thanks for the input.

-Orochi

[Psycogeek]

use the heat on purpose, is the only viable thing i could figure.

have a pre water heater running behind them.

use aluminum backings, they are basically heat sinks of sorts, instead of the usual plastic or wood, and make all the rest of the open surfaces chrome , bet that would cost some money, untill it Aged, and those things held up lots better.

tried some films stuff, Poof power gone to fast, but i didnt have IR only types.