Installing solar panels

Hi, quick answer, minimum 25mm. Or whatever you think will be enough to ventilate to avoid overheating.

On houses they are on an angle and gap is around 40 mm min most are more than this though. Mine 70mm.
On a van they will be flat/horizontal mounted and to get the ventilation re too hot, they need the 25mm but if you need to you can use a hole saw and "carefully " create holes in the side of the frames ie 4 equally spaced, 19-20mmdia holes per side, maybe more.
This will allow the heat immediately below the panels under surface to be ventilated more easily. No welling up of heat under panel.
Have used a small computer fan and 12v integrated circuit regulator $1:50 to run the fan.
This uses a whopping 0.1 amp of flow but forces air into the space and drives out the hot.
If the fan fails, then all is again as most are with no fan.

Less hot = more amps out of panels, easily overcomes the little fan. 100ma
Fan just runs off the panel output when it is getting sun.

Ross M