Solar panels vs shade cloth

[noteven]

Has anyone measured roof temperatures in direct sunlight vs underneath a solar panel that is stood off the roof an inch or two on brackets?

I am wondering if panels provide roof cooling like the doubled desert roofs on Land Rovers, Land Cruisers, and "Saudi busses" ?

We have had 4 or 5 clear warm days here - highs in the mid to upper 30s C / high 90s F and warm overnight.

Our sun is high at this time of year. It comes up at 05:00am and sets at 9:50pm.

By mid day on the clear days the air cond is running almost non stop in my camper sitting in direct sunlight.

Today there is some cloud coming through. Immediately after we have cloud shading the air cond starts to catch up and cycle on and off...

So anyways I have thought a shade cloth "awning" that would shade the whole camper roof and walls might make for a more comfortable experience. This trailer has a robust frame and rear bumper that would easily support a double roller affair that could deploy shades side to side...

But such a system would shade rooftop panels when deployed.

So do solar panels act as effective shades or do they begin to pass radiant heat to the roof materials below them and eventually heat up the roof?

[MEXICOWANDERER]

The exterior is aluminum, and few things conduct thermally as good as aluminum. My concrete umbilical is painted OSHA white, while the roof is 3" reinforced concrete covered with tar and solid white pea gravel. The bare concrete ceiling on the inside frequently measures 111F. I audited the shade factor and came to the conclusion, due to heat transfer, the entire structure would have to be shaded.

I would have loved to have a 2-axle U-Haul enclosed trailer with side and end flaps clad plus roof clad in solar voltaic panels. Rig in shade, trailer in full sun.

[Itinerant1]

I think the entire trailer contributes to heat or cold felt. Solar panels are made to produce power and never gave a thought to them shading or help cool the trailer until I turn the A/C on then they're contributing to the power to run the A/C. 😉

[n0arp]

I need to get a IR temp gun out and see, but there is a large difference in roof temps in similar conditions between our two rigs (by feel, when I'm up on the roof on hot days for whatever reasons). We cover almost the entire roof on each rig, but the the truck camper panels are much higher and the roof much cooler to the touch.

That being said, I do feel like it's easier to keep our fifth wheel cool with the panels on, but that is hard to quantify because of other changes we made at the same time we added them.



You can see the panels cover most of the roof, but are only about an inch or inch and a half (it's been a while since I've looked at it) off the surface. The roof is also FlexArmor, which seemed to make a difference itself, and was on there long before we added solar.



Truck camper roof - we still have the 14-5/8" tall factory rooftop AC, so the tops of the panels are 15-3/4" off the roof. Maybe one of these days I'll find a low profile unit, but it's pretty far down the priority list as we're under 13' tall.

[Itinerant1]

Just a follow up. It's 97f ambient, rv roof is showing 97f, top of solar panel 101f, rv roof under solar panel is 104f and that's 4" of space so not much cooling going on.

[noteven]

I suspected there would be some temp gain via the panels.

Thanks for the temp measurements and insulation ideas.

[mr_andyj]

Your roof ceiling structure might be 1 inch thick. Those slats/frame members run side to side. Get some 1 inch thick wood and bolt them the entire length of the trailer, front to back, to the metal slats. This give you 2 inches of structure to place two layers of 1 inch foam board insulation. 1 inch will not be enough insulation! Add 2 inches.

You will add the top layer, then bolt in the wood with self-tapping screws of the right length (1 5/8ths) , then add the second layer, then add some thin venire or 1/8 plywood or paneling for the ceiling. Mark on the walls where the metal slats are and measure out to the center of the wood boards and take notes so after the ceiling goes up you know where the framework is, this helps to know where to screw in the ceiling board too.

And, yes, the panels will keep it cooler a little. The panels just physically cannot transfer al that heat across the air gap.

[Itinerant1]

Nothing scientific here 80f outside ambient with barely a breeze, using the infrared thermometer just hit these spots. 89.9f on the rv roof, 93.2f on top of panel, 94 on roof under the panel.

There is 2" space between bottom aluminum edging around the panel to rv roof and another 2" space from the bottom edging to underside of panel.

Edit: producing 55a, 749w at 10:00

I'll catch a reading later in the day when it's hot.

Looks like this.



The sun is out and suppose to be a warm one today near 95f.

[valhalla360]

The size of the air gap probably makes a big differrnce.

White roof material, reflects heat.
Black solar panels absorb it.

If there is a big gap, good chance the air carries the heat away before it hits the roof.
If there is only 1", good chance it concentrates and then radiates it into the roof.

[Almot]

Panels won't cover your entire roof, and your walls will remain uninsulated. If you're going to sleep in there in a hot weather, there is a lot more work to be done.

[wowens79]

I’m in GA, and have never tried it with an RV, but we have a shade cloth over our deck that gets full afternoon sun. It has made our deck usable in the summer, and as an added bonus shades a French door to our bedroom, and has lowered the temps in that room 5-10 degrees.

[wopachop]

I've wanted to put camo tent over my roof. Rig a way to roll it up on the front. Cut holes for solar panels to get direct light.

Maybe next summer!

[noteven]

Thank you for the replies.

I notice the uninsulated roof of my cargo trailer radiates heat but it is metal and there is no convective air movement when the trailer is closed up.

I'm thinking a set of panels might make an alright double roof.

The plan is to insulated and do a simple build out to make the enclosed trailer a "mini" toyhauler.

[Almot]

When sun is shining directly onto the panels and creating maximum shade footprint, this part of my trailer feels cooler inside. The roof isn't flat, one side of the panel is ~4" above the roof, another side ~2".

[TurnThePage]

My panels are about 5" above the roof. I don't think any heat transfers from them to the roof. Pure shade.