Author Topic: Active or passive solar PV hail protection  (Read 5161 times)

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Frank S

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Active or passive solar PV hail protection
« on: August 29, 2014, 02:09:41 AM »
 I was wondering if anyone has given any serious thoughts to a system to afford some protection to an array in the event of a hail storm.
 My array about the only way I have to offer any protection to my panels is to attempt to determine the direction the hail storm may be coming from and try to turn the array away from the onslaught as much as possible
 Last spring we escaped several bad hail storms by shear geographical luck.
 For this reason I am thinking about designing a deploy-able shutter system. for my next array system after we move
  does anyone have any ideas?
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Mary B

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Re: Active or passive solar PV hail protection
« Reply #1 on: August 29, 2014, 03:44:09 AM »
Storm chasers put heavy chicken wire in front of their windows, it breaks the hail into smaller pieces.

Frank S

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Re: Active or passive solar PV hail protection
« Reply #2 on: August 29, 2014, 04:04:40 AM »
Actually I think they may use expanded metal .
 Shading could be a problem even with chicken wire though. that I one reason I am thinking about a stowed deploy-able shutter system.
 Should next year transpire as I hope, I might be increasing to 3 or 4 KW, If so then I will be needing to build 2 or 3 more mounts at which time I plan on adding tracking as well so why not design in a protection system.. It may be that a simple shield mounted from the top of the arrays will be sufficient as the direction of hail large enough to do damage is somewhat predictable depending on wind conditions
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phil b

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Re: Active or passive solar PV hail protection
« Reply #3 on: August 29, 2014, 12:38:19 PM »
I've been thinking about some sort of protection also. I lost 2 out of 8 panels about two years ago to baseball sized hail. People in the area lost new cars, pickups and roofs. I still feel fortunate.

Here's a few of my 'might work' ideas:

1. large hole chicken wire mounted about 4 feet from the panels. That should offer enough bounce to take out most of the energy. Think trampoline.

2. frame mounted panels that can rotate upside down to expose a convex shape of 1/8" steel fixed to the panels' back. That might offer wind protection also.

3. Sun Tuff greenhouse panels mounted a foot or so away from the panels. Gary over on build it solar has some data on them. http://www.builditsolar.com/Experimental/GlazingTransmittance/GlazingTransmittance.htm He got 0.89 light transmittance on the polycarbonate. That wouldn't hurt too bad for the protection it affords. ?

4. Some insurance policies offer protection as a rider to the homeowner's policy.

I could use some new ideas to consider too. I'm still in the building phase of my new container house and the solar panels will be one of the last items to be relocated. In the meantime, they are in use furnishing power for everything that uses 120 VAC, including air conditioning. I really don't want to loose any more panels.   
Phil

Mary B

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Re: Active or passive solar PV hail protection
« Reply #4 on: August 29, 2014, 04:36:58 PM »
I would think a stowable shield would be best. Usually have warning when bad hail is approaching and could deploy it. Protector that slide into the racks in front of the panels.

That polycarbonate sheet becomes brittle with age. One more year and I am going to have to replace it in my solar hot air collector.

phil b

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Re: Active or passive solar PV hail protection
« Reply #5 on: August 29, 2014, 05:53:47 PM »
I would think a stowable shield would be best. Usually have warning when bad hail is approaching and could deploy it. Protector that slide into the racks in front of the panels.

That polycarbonate sheet becomes brittle with age. One more year and I am going to have to replace it in my solar hot air collector.

How old is your polycarb panel? I haven't had a problem with the three year old Sun Tuff panels I have. GaryGary tested a panel that was 9 years old, IIRC. It may be the heat causing deterioration in your panel. Mine have not been subjected to temps above 140 degrees. I have a hot air panel that I need to finish. I guess I'll find out.

If I can find a way to automate the sliding protector, it will work. There's a good chance the hail and high winds will come when I'm away.

There are a few hail sensors on the market but they are pricey. Anyone know where to buy or build one for a reasonable cost?
Phil

Frank S

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Re: Active or passive solar PV hail protection
« Reply #6 on: August 29, 2014, 06:10:20 PM »
Phil what I am thinking of would either slide or be shutters probably controlled by an anemometer.
 My thinking is at least in this part of the country hail is 95% of the time accompanied by wind gusts  in excess of 50 MPH
 there is a wire mesh reinforced clear poly carbonate that has a high resistance to breakage I don't know about the UV life of it or how much light blockage it causes.
 But when open it would resemble the old mobile home shutter glass windows that cranked open or closed
 Or a simple Hat built above the array that might deploy like an iris or a Geisha fan. the problem with those would be creating a high wind load and the need to overcome the sail effect   
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phil b

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Re: Active or passive solar PV hail protection
« Reply #7 on: August 29, 2014, 07:58:40 PM »
Frank S,
My solar panels are surrounded by cattle panels made with 1/4" bar. If there is a difference in output, I don't notice it. Bear in mind, I do have 7100 watts of panels. Small differences aren't too noticeable.

Sliding shudders would work if the slide is sturdy enough and not prone to hanging up.  I'd be interested in what you come up with.

If your panels are to be fixed on both axies, a hinged cover that flips over the panels from the top or bottom may work. A gearbox off an old garden tiller with an electric motor could make short work of it.





Phil

electrondady1

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Re: Active or passive solar PV hail protection
« Reply #8 on: August 30, 2014, 08:59:23 AM »

i would guess with hail that size you would want  to protect them quickly .
mount them like a door with the panels  hinged along one edge,  maybe just pull a pin and let them go edge ways. just a 90 degree rotation down powered by gravity.
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Mary B

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Re: Active or passive solar PV hail protection
« Reply #9 on: August 30, 2014, 04:53:04 PM »
My solar hot air collector has been in use 3 or 4 years and the polcarb has been subjected to 180 degree temps when a friend disconnected the blower power to plug in her laptop. I smelled melting spray foam and tokk the air temp at the outlet of 180, probably was 200+ in the panel

Frank S

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Re: Active or passive solar PV hail protection
« Reply #10 on: August 30, 2014, 07:59:04 PM »

i would guess with hail that size you would want  to protect them quickly .
mount them like a door with the panels  hinged along one edge,  maybe just pull a pin and let them go edge ways. just a 90 degree rotation down powered by gravity.
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 90° or pure vertical is not a perfect solution in many hail storms. the problem is at least in this area hail falls at an angle depending on the wind it can reach 40° off vertical. but 90° &  facing away from the storm with a back shield would certainly do the trick
I live so far outside of the box, when I die they will stretch my carcass over the coffin

Ungrounded Lightning Rod

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Re: Active or passive solar PV hail protection
« Reply #11 on: September 01, 2014, 12:18:36 AM »
"Hardware cloth" or "welded Wire Fencing".  Think coarse window screen with the wires welded where they cross.

The latter is very strong - like 1/32" steel wire welded together with various hole sizes (like 1" x 2")

Mount this sturdily a foot or to so above the panels.  It should break up or catch even basketball-sized hailstones.

Leave it there all the time.  It intercepts very little light - well under a percent.