Flat mounting of PV panels. A no-no?

[66788]

I haven't seen addressed the issue of flat mounting PV panels on vehicles. If they are truly flat mounted then they will pool water and collect dirt, debris and other contaminants.

When I mounted the Kyocera panels on my 5th wheel trailer, I had the front of the panel lower than the back. This provided a downward air pressure when traveling, and assured a cleaner panel when it rained, as the rain would wash the debris from the flat surface of the panels, and would not pool on the surface forming a small pond.

Case in point:

https://vanlivingforum.com/attachment.php?aid=1180

Great panels on this vehicle, but the step van is very tall and it will take a ladder and flowing water to clean these panels. By mounting them in an other than level position, the rain will help keep these panels cleaner. In the summer, dust is a problem so they will all need to be cleaned under those circumstances.

 

[Luisafernandes]

I'm going to keep in mind what you said about mounting the solar panel lower in the front for the down pressure when driving. Good tip.
But to keep water off of it I don't think it really matters unless whatever vehicle we drive is always perfectly level when parked.

 

[Seraphim]

Don't need solar panels yet, but I keep them in the back of my mind in case our mobile lifestyle ever changes. We're on the move enough that the truck's two alternators keep the battery bank charged.

I'd considered a folding/tilting rack of some sort, since our truck camper doesn't offer a large open space, and we wouldn't need the panels operational while driving. There's even a mechanism to raise the (now nonexistent) TV a antenna, which could be modified to raise one side of a panel.

Just thinking...

 

[christine]

That's a neat idea, mounting them at an angle. I didn't even think about it when I installed mine. I wonder if that would help or hurt gas milage, if any effect at all.

 

[Van-Tramp]

Aren't these modern panels water proof anyway? Does it even matter if water pools on them? It would only be a thin sheet of water at best and would be blown away the moment you either drive or a breeze passes over them. Obviously you do not want leaves or something else to get stuck to the panels, but that is true no matter if it is flat mounted or at a slight angle. For me, it is a schedule weekly chore to climb up there and make sure my panels are clean and debris free. This would happen no matter the angle I mount them.

I see issues by mounting them at a tilt;
- Any tilt other than front-side-down can cause the panels to be torn off the roof while driving (I've had it happen, not fun... and you could be paying for damage to cars behind you)
- Front-side-down tilt means they have a greater chance of being pelted by road debris kicked up from cars ahead
- Front-side-down tilt will also add stress to the roof at highway speeds. The faster you drive, the more "downforce" being applied to your roof which translates to load on your tires too. It could potentially break through thin fiberglass roofs over time.
- Front-side-down tilt will hurt your MPG at highway speeds with the added drag. The faster you drive, the greater the increase in drag and the greater loss of MPG

 

[Luisafernandes]

Aren't these modern panels water proof anyway? Does it even matter if water pools on them? It would only be a thin sheet of water at best and would be blown away the moment you either drive or a breeze passes over them. Obviously you do not want leaves or something else to get stuck to the panels, but that is true no matter if it is flat mounted or at a slight angle. For me, it is a schedule weekly chore to climb up there and make sure my panels are clean and debris free. This would happen no matter the angle I mount them.

I see issues by mounting them at a tilt;
- Any tilt other than front-side-down can cause the panels to be torn off the roof while driving (I've had it happen, not fun... and you could be paying for damage to cars behind you)
- Front-side-down tilt means they have a greater chance of being pelted by road debris kicked up from cars ahead
- Front-side-down tilt will also add stress to the roof at highway speeds. The faster you drive, the more "downforce" being applied to your roof which translates to load on your tires too. It could potentially break through thin fiberglass roofs over time.
- Front-side-down tilt will hurt your MPG at highway speeds with the added drag. The faster you drive, the greater the increase in drag and the greater loss of MPG

Also very good points! Now, if and when I do get mine they'll be installed level. That's it, not changing my mind again... : )

 

[66788]

Aren't these modern panels water proof anyway? Does it even matter if water pools on them? It would only be a thin sheet of water at best and would be blown away the moment you either drive or a breeze passes over them. Obviously you do not want leaves or something else to get stuck to the panels, but that is true no matter if it is flat mounted or at a slight angle. For me, it is a schedule weekly chore to climb up there and make sure my panels are clean and debris free. This would happen no matter the angle I mount them.

I see issues by mounting them at a tilt;
- Any tilt other than front-side-down can cause the panels to be torn off the roof while driving (I've had it happen, not fun... and you could be paying for damage to cars behind you) If the panels are properly installed they will not rip off the roof. Only poorly installed panels will do that.
- Front-side-down tilt means they have a greater chance of being pelted by road debris kicked up from cars ahead The tip is so slight that even a ball bearing would bounce off the panel rather than break it. Don't forget, these are designed to withstand major hailstorms.
- Front-side-down tilt will also add stress to the roof at highway speeds. The faster you drive, the more "downforce" being applied to your roof which translates to load on your tires too. It could potentially break through thin fiberglass roofs over time.
- Front-side-down tilt will hurt your MPG at highway speeds with the added drag. The faster you drive, the greater the increase in drag and the greater loss of MPG

In theory maybe, but in real world numbers I don't think a slight tip down will exert and objectionable force altering wind resistance or damage to the roof. The purpose of a slight tip is to allow the rain to wash the dirt and debris from the panel rather than to let it pool and stick to the panel as it evaporates. Just look at the debris on the panel in the photo above, as well as the pooled water.

Your arguments against tipping have not change my mind at all.

 

[Van-Tramp]

You are certainly welcome to install your panels how you feel is best 66788, but the panels in that pic did not get that way because of how they were mounted, they got that way from lack of regular cleaning as require by any form of mounting. The way you mount them will not change that they require to be wiped down every so often. I've had panels mounted at 30-45 degrees and they still attracted enough dust and debris to require regular cleaning. A 1 or 2 degree angle will have no effect on the regular required cleaning, so there are no benefits, only potential negatives.

If in doubt, I would ask a professional RV solar mounter. He will know what it best, and since I only ever see flat-mounted panels on RVs, I suspect there are good reasons (see above) for that. If I am wrong, I'd love to know.

 

[66788]

You are certainly welcome to install your panels how you feel is best 66788, but the panels in that pic did not get that way because of how they were mounted, they got that way from lack of regular cleaning as require by any form of mounting. The way you mount them will not change that they require to be wiped down every so often. I've had panels mounted at 30-45 degrees and they still attracted enough dust and debris to require regular cleaning. A 1 or 2 degree angle will have no effect on the regular required cleaning, so there are no benefits, only potential negatives.

If in doubt, I would ask a professional RV solar mounter. He will know what it best, and since I only ever see flat-mounted panels on RVs, I suspect there are good reasons (see above) for that. If I am wrong, I'd love to know.

You are right that they all need to be cleaned. A lot of people NEVER clean them and then complain about how poor solar power really is.

I've had flat mounts and slightly tilted mounts, and based upon that experience, prefer the slightly tilted mounts. YMMV.

Since I'm not cleaning any of y'alls panels, mount 'em how you like 'em!

 

[Van-Tramp]

Since I'm not cleaning any of y'alls panels, mount 'em how you like 'em!

LOL

 

[Spaceman Spiff]

I'll jump in

I installed my two 100W panels with a 3° tilt (1" higher in back) as was recommended to me on another forum (forget which). Don't have much experience with them yet, but the more I think about it, I don't think it will accomplish much.

At highway speeds the panels on my camper roof are probably in the low pressure turbulent area, with the majority of the air pushed higher over the roof. So, the panels are probably experiencing very little in the way of forces acting to push them down or tear them off. (The only experiential data I have is I don't get any bugs on the leading edge of the front panel. I would like to test with streamers and a video camera, but I don't have the camera nor the time right now :-/ )

As to the chance of projectiles hitting the panel; it is greater than zero, but has to be very small. And surprisingly, there is a larger trajectory window to hit the rear panel on my camper than the front one!

For water runnoff, I think this is more important if you are stationary, as motion will remove any standing water. I haven't seen any data on what standing water does to the output of the panels, but I know when rainwater around here is left to evaporate, it leaves a film that has to be scrubbed off.

Downside of slightly tilted panels is having to park facing south to maximize panel output.

Would I tilt the panels if I had to remount? I'm undecided. When I first looked at them after I mounted them, I thought the rake was excessive. I am going to go with them this way this winter and reassess next summer. I made accommodation to adjust them flat, all I have to do is remount the rear RED Loctited bolts :s

-- Spiff

 

[GotSmart]

At last, positive entertainment and learning at the same time.

Since I am about one month from installing my panels, I find this debate timely. With pictures in my mind of slow motion camera action of a bug giving its guts in an attempt to get back at a solar panel, to images of SuperBird Solar panel wings (too many CarToons as a child!!!) My imagination is going wild.

I am thinking of a wooden platform on a van rack with a couple panels raised an inch in the back to keep the water from pooling. To optimize solar intake, panels should always be facing the sun. The systems I installed had a much higher, about 70* I think. Hardly what a person driving would do, but doable when camping. I will look into a locking rod system so the panels can be raised when I want to.

 

[Optimistic Paranoid]

I am thinking of a wooden platform on a van rack with a couple panels raised an inch in the back to keep the water from pooling. To optimize solar intake, panels should always be facing the sun. The systems I installed had a much higher, about 70* I think. Hardly what a person driving would do, but doable when camping. I will look into a locking rod system so the panels can be raised when I want to.

A couple of points to keep in mind . . .

I've seen reports of tilted solar panels being ripped off of rvs roofs when a sudden, strong wind gust gets behind them from just the right direction.

Also, you'll now have to space the panels in such a way that one doesn't shadow another when they are tilted. Sometimes easy to do, sometimes not so much, depending on roof size, number of panels, other junk like roof vents, etc.

Regards
John

 

[66788]

The amount of tilting necessary on flat panels would not be affected by wind gusts or shadowing. We are talking 3 to 5 degrees here...

 

[riffraff]

while were on the subject.. I suppose mine are probably a bit dirty having had them installed for over a month now. Just go up on a ladder and use some windex?

 

[highdesertranger]

I find this thread very interesting. both sides have good points. I was thinking of tilting mine when I permanently mount mine. but I was thinking along the lines of 1%. going to have to do some more figuring on this one. highdesertranger

 

[66788]

I've seen reports of tilted solar panels being ripped off of rvs roofs when a sudden, strong wind gust gets behind them from just the right direction.

Regards
John

I"m betting the panels in those reports were inadequately mounted to standard RV construction consisting of sheet metal screws into 1/4 inch plywood, often times rotten plywood as well. I suspect that sheet metal screws into most surfaces are inadequate to mount heavy photovoltaic panels. Through bolts with large surface reinforcement on both sides of the vehicle's roof are recommended. A fender washer at minimum, or a reinforcement of greater surface area.

A properly mounted panel will withstand 100 mph winds. An improperly mounted panel will be, well, gone with the wind.

 

[GotSmart]

I have seen winds that will take the bark from a Basset Hound. I can see a large flat object ripped off of its mounts by not having it fastened properly.

Overkill is my friend!

 

[akrvbob]

Very few of us will ever park our vans at dead plumb and level.

If you are in an RV you probably do some leveling of it but ii doubt if it's ever perfect. And if you were worried about it you can set the level off very slightly. For my trailer I use 1 inch leveling blocks for side-to-side leveling and the odds of it being perfect are very unlikely. If it's at all close I don't even bother with those.
Bob

 

[66788]

Case closed.

I'll be cleaning my panels less...