One way to dramatically reduce energy requirement for cooling is to limit heat transfer through the roof. A common way is via insulation, painting roof with white or IR reflecting paint but another one is via a tropical roof. Tropical roof is a double roof with an air gap allowing free air flow in between. These roofs are still used in tropical climates. See the pictures.
A similar effect can be accomplished by fully populating a roof with solar panels. Ideally slightly larger than a roof to act as mini awnings.
https://www.google.com/search?safe=......0...1c.1.64.psy-ab..0.0.0....0.5xBdyHS2XG8
Since I haven't gotten to this part of my build, this is going to be partly speculation, but based on spending many years living in Texas and Florida I have hope that it will help reduce the heat gain.
My reasoning is:
Paint color on the roof, coatings and such don't matter all that much. (After looking at real studies.)
You can't really do a good job in a van with a radiant barrier. There is just too much metal connecting it all and it is a great conductor.
Thinsulate is easy and works great for winter heat. I did that. It will also help keep it cool if using air conditioning by reducing heat loss.
GD has the best solution to get rid of the heat from radiant heating - vent the roof and vent the floor and with minimal to no power use you can get the inside of the van close to the same temp as the outside shaded temp.
I plan to have 4 100 watt solar panels on the roof of my 170" which will cover a good amount of the roof area. I will also have the GD floor vent and max fans. Rear and CRL windows are dark tinted. I am thinking about 3M Crystalline Film on the windshield
https://www.3m.com/3M/en_US/company...ystalline-Series/?N=5002385+3292716668&rt=rud and wondering if anyone has tried it.
The only practical way to reduce radiant heat gain is to put the van in the shade.
In Texas I have seen many RVs permanently parked under large "carports" or tropical roofs that provide shade above them. High end class A motorhomes have awnings above windows, as do many of the homes in FL.
Solar panels above the roof can partially block the sun from the roof and help, but 4 panels don't even cover half the roof and the side of the van has more surface area than the roof (although off angle).
I am going to try and get the same effect with solar screen, like people use on patios and decks. They often have it roll down in the afternoon like a wall. I don't have a roof rack, but I am going to put a couple short posts in the track and then just attach one side of the screen to them and stretch it to the ground a few feet away from the van and stake it. When parked with the van sideways to the sun this should give me shade with airflow on that side. Plus the screen is see through to an extent. This shouldn't be hard to do from the ground. I am hoping that screen won't catch the wind like an awning does and that I can set it and forget it when parked. Or maybe not stake it, but just set some rocks on it so that if the wind does blow it loose there is nothing hard attached to it to do any damage.
I haven't decide about trying to screen the rest of the roof when parked. It may be a case of the last 20% of the job is 80% more work. If I do, then I will probably just take a piece of the same screen the size of the roof and put it on the post up off the roof at the same height as the solar panels. cut and edge around the solar panels and vents. If I do this I will also use some tent poles to extend it out from the roof track in front over the windshield like an awning. Making it isn't hard, but putting it up there and taking it down on a 4x4 without carrying a step ladder is the part I haven't figured out.
Screen isn't as effective as solid awning, but from my experience parking under trees vs. in the open it might make a huge difference. I am also looking for a solution that isn't expensive and lets me leave the van to go hiking and not worry about the wind picking up. I would welcome comments. (Sorry if I am hijacking your thread)