Solar heating panels

[medvampire]

Getting ready to set up some solar heating panels and was wondering.
Temporary going to lay them on the ground would it be better to lay black plastic, tar paper, or just bare ground under them?
Steve

[CarlD]

Just bare ground is fine. The heat bakes through so you don't get that slimey, wormey, bug-filled muck that you normally get from something on the ground. You get dead grass either way, but it won't be disgusting when you lift the panels up--it will be dry and baked. It will heat the ground around it, and that ground will go on heating the water after the sun passes, passing it back to the panel. Done this a couple of times.

[matt4x4]

I used my useless winter cover as a barrier under my panels and landscape edging around the perimeter, then spread 3/4" pea gravel around and between the panels - gives it a nice finished look and I don't have to deal with Grass/weeds growing up around the panels.

[Poconos]

After several years of having my homebrew array laying on tarpaper I gave up. It doesn't last. Had to replace every year. Bought some rolled roofing this Spring and so far shows no sign of deterioration. Tarpaper would have been pretty ratty by now. Got the cheapest stuff I could find at Home Depot. Time will tell.
Al

[medvampire]

Thanks for the answers. I am going to build racks in the spring and plan to use rolled roofing to underlay the panels.
Steve

[matt4x4]

If you're going to build racks for your panels, I presume you will use wood - possibly PT. In this case, I don't think any underlay is needed, it will certainly NOT help with heat gain, the only possible extra heat gain I could see is if you were to use something reflective like aluminum foil or the silver foil covered foam boards used in house construction. Reason being, the black underlay would actually absorb heat that's allready in your panels, where the reflective would bounce the heat trying to push through the panels right back at them.

The only reasons I used my black winter cover as underlay on the ground was to keep the weeds down and that I had it kicking around and it saved me from buying tons of landscape fabric which is also black, however, for a raised install I would not use it.

[Poconos]

Just to clarify a little more, I have both a 4x20' mat that is on a flat rack made from plywood and 2x4's. Mat lays right on the wood. My field heater is 1200' of 1/2" black poly pipe and because there are significant gaps between the pipes the roofing does help by keeping the entire surface they're layng on hot so the hot roofing radiates and heats the pipes on the sides where the sun doesn't hit directly. At least that's my thinking. Also prevents weeds from growing.
Al

[ShelleyAnn]

Steve -

Just been there/done that. You'll notice that if there isn't a border around the mat, a hard rain will kick up all kinds of dust and mud all over the solar panel that will need to be washed off to maintain the blackness/efficienty of the panel. If you don't mind that...nothing else is needed.

Shelley

[matt4x4]

yes! Keep it clean AND keep those pesky dogs off it, I had to repair mine this spring, didn't use the typical plug it method, just "welded" it with some of the same plastic so i could keep teh trace working and not lose efficiency.

Poconos - wrt your field system, I understand why you have the black under it, but with the mats you would get a slight negative effect.
have you ever tried reflective under the field system? I'd be interested to see if it improves - it probably would because instead of the underneath absorbing heat, it would reflect it back onto even the undersides of the pipes.

You can get thermal blankets at camping stores that are reflective plastic sheets big enough to wrap a person up - very thin, but very effective and cheap - they'd work.

[Poconos]

Never tried the reflective stuff. Probably would be more efficient but I'm wondering how it would hold up. The area is quite windy at times and even the tarpaper would blow and tear sometimes. I'm also not interested in squeezing the last % of efficiency from the thing either. I've got a lot of space back there so if I ever decide I need more heat I'll just add more pipe and roofing. Can you imagine a couple acres covered with 1/2 black pipe?
Al