There has been an interesting discussion on the ProMaster Forum on whether or not a PV panel mounted on the roof of the van increases heat gain to the interior of the van on a sunny day, and, if so, how much.
I did a test on my van measuring the temperatures on the roof both under the PV panel and on adjacent parts of the roof. Bottom line is that for the sunny, no wind day I did the test, the heat gain to the interior of the van for the part of the roof under the PV panel was about 35% greater than the heat gain for other parts of the roof for our white roof van.
I did several runs, but this one is representative:
- Ambient temperature: 73F
- Full sun: 790 watts/sqmeter on PV panel surface
- Inside van temperature: 78F
- Wind speed: 0 to 4 mph (near calm)
- PV panel top surface temperature: 157F
- Roof temperature under the PV panel: 136F
- Roof temperature outside the PV panel: 119F
So, the roof is about 17 F warmer under the PV panel than away from it. If you were trying to maintain the temperature inside the van at 70F, then the heat gain for the part of the roof under the PV panel would be about 35% greater per sqft than the gain from rest of roof.
This is with a white roof van, as RD pointed out on the forum, the difference would likely be less with a dark roof as the roof runs hotter.
Looking under the PV panel (which has been raised up a bit to get the thermocouple to the middle of it). The surface mount thermocouple is the small patch of tan and has an adhesive coating to make good thermal contact with the van roof.Surface mount thermocouple adhered to top surface of PV panel.