Solar heating panels

[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

[medvampire]

That settles it… I tossed them on the ground for now and next year I will add some reflective material under them when I build the racks.
Al.....I am trying to picture a few acres of reflective surface with black pipe. I bet you would blind the air planes as they flew by.

What if a guy did something like this? Think the panel would melt? Have the top adjustable so you could get a ball park aim at the lower solar panel. I have about 5 hours a day due to trees so I want to get the max I can get out of the system.
Steve

[matt4x4]

The more light you can reflect onto it, the better your gain - that would work well.!