Recommended height for solar panels

Yes, I mean for heat dissipation, how high above the roof should the panel glass be.

Hi,

While it is good to have 1" of space between the roof and the panel will allow air to circulate below the panel. Panels make more power when cooler.

3" of space will allow to much air below the panel, and can cause problems with the air blowing the panel upwards while driving. You certainly never want the panel higher in the front, and higher in the back can cause excess pressure on the rearward roof mounts. It is not an exact science, just keep it level with the roof. ANd I would never consider mounting on a angled section of a roof like fifth wheels used to have between the lower section and the upper section. Nowdays fifth wheels typically have higher roofs in the living area and do not have that sharply angled roof area.

Check out panels at this place. SunElec.com

Fred.

Snowman9000 wrote:
What I don't know for sure is how high the panels should be off the roof.

There is no precise answer to that. And, as people noted, your question is not quite clear.

If you mean shading on the flat panel - lift them as little as possible, and don't lift higher than needed to clear the obstacles under the panel like plumbing vents, luggage rails etc, and to clear most of the shade except for very early or late in the day when it doesn't matter.

If you mean the clearance under panel for heat dissipation purposes - I would say at least 3/4" from the frame bottom. Then there will be ~1.5" clearance from the actual PV panel because the frame bottom is lower than the back surface of the PV. 1"-2" from the frame bottom is the optimum range, IMO.

If you mean the height of the North side of tilted panel - then I don't know what to answer, there are too many variables.

You specify "how far", how far for what?

Folks, I suffer from providing too much info. I have a good grasp on the shading and locating parameters. What I don't know for sure is how high the panels should be off the roof. Once I know that, I can finish marking the shaded areas on my drawing. I plan to post the finished drawing in a separate thread.

Panel height and no go areas? It depends on the latitude, time of the year (shades are longer in winter), and height of superstructures on the roof.

Like others said, the simplest way is to lay out a piece of cardboard the size of the panel, and see how much shading is there at different times. Lift the cardboard by, say, 3" as the panel frame thickness is ~2" and you need some clearance under the frame.

Empirically, for a flat panel (i.e. surface 3" above the roof) most users are trying to stay 14-18" from the A/C unit and 10-12" from lower structures. Structures that are less than 3" above the roof don't matter, naturally.

If you prefer using your brains, there is indeed a formula that BFL13 has seen somewhere - I think he saw that formula in high school course of trigonometry :)... Or in the 1st semester of the very 1st college course.

Tan S = H/L, where S is the angle of sun over the horizon, H - height of the structure creating the shade, and L - horizontal distance to that structure.

The biggest unknown, as you can see, is the sun altitude over horizon because it varies with time of the year and latitude, and with time of the day. But you can find the sun altitude at noon for your most frequent latitudes.

Keep in mind that H is the height of the structure above the panel surface, not above the roof.

In the end, if you can't clear the shades to your satisfaction, you have 2 choices:
1) wire in parallel (if there is more than 1 panel), or
2) let it be. Like that serial killer said in Mentalist series, "You win some, you lose some".

I always pay attention to others planning solar panels installs on their trailer roof. I will be getting into this probably sooner than I want to haha...

I am at a lost of what you are referring to on your mounting height. I assume you are talking about the height above the roof. I know the smallest shadows walking across your solar panel can really play heck with your outputs. I was playing with a couple of portable units on the ground and a small two-inch aluminum pole shadow was walking my panels and giving me fits.

In my planning I will have two 120WATT Panels mounted long wise on end of my off-road POPUP trailer roof with the fantastic fan door opening in the middle of these two units. My third location will be on the other end of my trailer roof between the air conditioner and the end of the roof. This panel will mount across the roof.

I am planning on at least a mounted height above the existing roof of about 1-1/2 to 3 inches.

The two front solar panels will need to be on a quick disconnect hinge arrangement so that these two units can be used in a portable arrangement on the ground if necessary to stay in the high sun.

I suppose my roof mounted air conditioner may offer some unwanted shade to the one panel mounted mounted close to it...

I too want to get started on my drawings for this. I use LibreOffice 3.4 for my drawings since I can't afford my Autocad LT subscription since retiring... I also have the Adobe Acrobat Pro ver 9.0 where I can capture many drawings from other other places and modify them for my use... Made up a pretty good library of RV items to use.

Roy Ken

Somebody had a good way to measure or calculate shading by the angle from the top of the object causing the shading (a/c shroud say) and the distance of the panel away from the object and the sun's altitude (angle of sun above horizon) Can't remember details

That would be using the height difference, so by raising the panel you shrink that, in effect lowering the object, so you could calculate how much higher for the panel to make the shading stop.

I used to use 1/4" plywood then take disposable camera photos during the day hourly.