Community Forums

vsheetz · 03-15-2016, 01:17 PM

Looking for a discussion of the pros and cons of mounting solar panels directly on the roof vs. on racks elevated over vents, A/C units, etc. assuming MPPT controller In both cases.

Pros for mounting over:

Can use physically and wattage larger panels for less cost per watt, and simpler/reduced wiring. Mostly eliminates shading from other equipment on roof.

Cons for mounting over:

Need to remove panel(s) to service equipment underneath. Increased concern of air flow lifting the panels.

Pros/cons of mounting panels directly to the roof pretty much the opposite of the above.

Additional thoughts and considerations? Experiences from those who have mounted over rather than on?

JohnBoyToo · 03-15-2016, 01:23 PM

Vince,
Not that I've done it,
but I think the shading concern is a moot point because if the items next to it are shading the panel, that means the sun is close to the horizon and would think your panel efficiency is close to nil anyway. IMHO of course

Kahoona · 03-15-2016, 01:26 PM

Interesting question. I mounted mine on the roof because I did not want to increase my height. I have also been hit with sudden gusts of wind (in California and Utah) that tore some vents and things from their mounts. I just felt that it was more aerodynamic and less risky to keep them low. I do more time on small roads and on dirt in forests where that would matter though.

Dennis Dean · 03-15-2016, 01:39 PM

So, if I understand this you are considering building some sort of frame to mount your solar panels over your AC units on the roof? Not that I am an experienced RV'er or solar person but that seems like it would be more problematic than useful, unless you use your roof for some reason other than the top of your RV ( sun bathing deck??

) Below is a pretty good video of a major solar install on a bounder with tilting racks. Whether you like or dislike the Wynns it is still a good example of the space and layout of a pretty large solar setup all mounted directly to the roof. Just food for thought.

https://youtu.be/Nq5Wz57zdeI

mel s · 03-15-2016, 01:47 PM

Quote:

Originally Posted by vsheetz

Looking for a discussion of the pros and cons of mounting solar panels directly on the roof vs. on racks elevated over vents, A/C units, etc. assuming MPPT controller In both cases.
Additional thoughts and considerations? Experiences from those who have mounted over rather than on?

vsheetz
I've seen solar panels mounted on on racks elevated over vents, A/C units, etc. on RVs that appear to be permanently parked and on mobile homes....(but never on a "road worthy" RV).

That leads me to the conclusion that for some reason it is seldom, (maybe never?), done by anyone who wants to travel with their RV.

Mel
'96 Safari

Timon · 03-15-2016, 02:27 PM

BatteryPro has done some elevated installations and has posted some of them here. This is just one of them. Yes, that's a total of 14 panels sitting on the roof.

One nice thing about elevating them is you can clear most obstructions even MaxxAir fans which are only about 9" high when open (23"L x 16.4"W x 5"H closed; 9.3"H open). So you really can cover your roof and not raise the height any higher than a dome or trav'ler dish that's down.

In fact I think if you have the Penguin-II, which doesn't have any top air flow restrictions like the Mach 8s, you could let the panel go over the ACs and only be about 1" above them. Done that way I'm guessing you could get 2 or 3KW of solar on the roof. That's no enough to run two or three ACs but it's enough to run one and still charge batteries for the night.

In any case when raising the panels above the roof I'd want a wind deflector at the front of the panels to keep the wind resistance down. You also need to account for the trav'ler so it doesn't shadow any panels when it's up.

Dennis Dean · 03-15-2016, 02:40 PM

Quote:

Originally Posted by Timon

BatteryPro has done some elevated installations and has posted some of them here. This is just one of them. Yes, that's a total of 14 panels sitting on the roof.

That is pretty sweet, I bet it ain't cheap either, but man that is some solar power. I would hate to replace a roof or have to work on any of the fans or A/C units tho, that roof is covered.

vsheetz · 03-15-2016, 03:02 PM

Thanks for the good comments so far.

It's relatively straight forward to elevate the panels using racking system components as used with stick and bricks installations.

Yes, elevated panels can usually be done without increasing the current high point on the roof.

The shading comment above regarding early/late day sun angles is a good point, and shading can be further mitigated by careful selection of panel locations.

I have seen wind deflectors integrated as commented above, which sounds like a good idea.

Dennis Dean · 03-15-2016, 03:09 PM

anyone have an idea how much weight that adds to the overall coach? I don't think the panels weigh all that much and the mounting hardware all looks like very light weight alum. Just wondering and also if it significantly moves the already top heavy vehicle up more?

Timon · 03-15-2016, 04:44 PM

Quote:

Originally Posted by Dennis Dean

That is pretty sweet, I bet it ain't cheap either, but man that is some solar power. I would hate to replace a roof or have to work on any of the fans or A/C units tho, that roof is covered.

No matter how you mount them solar always makes it harder to work on the roof. However with a rail system you MAY not have as many mount points. Working on equipment shouldn't be that bad since you can just pop out a couple of panels off the rails. Hopefully BatteryPro can chime in.

Quote:

Originally Posted by Dennis Dean

anyone have an idea how much weight that adds to the overall coach? I don't think the panels weigh all that much and the mounting hardware all looks like very light weight alum. Just wondering and also if it significantly moves the already top heavy vehicle up more?

A typical 100 watt panel is about 15 pounds and the 160 watt ones are about 24 pounds. The larger 300 to 400 watt panels get closer to 40 or 50 pounds but you don't need as many.

Dennis Dean · 03-16-2016, 05:33 AM

Quote:

Originally Posted by Timon

A typical 100 watt panel is about 15 pounds and the 160 watt ones are about 24 pounds.

Thanks John, so about 160 lbs for 6 panels(including hardware), that's not bad and don't see it increasing any top weight issue.

Smitty77 · 03-16-2016, 08:49 AM

Vince,

One key advantage of the S&B Rack application for RV Solar Panel usage, is that the panels do remain cooler. When I check things out from time to time, I always notice a little less output from the panel mounted directly to the roof, at times when I do this a peak sun/heat times, I've seen as much as a 4-5% lower output. And yes, it is the furthest run, but IMO very little drop page is a result of the extra 4-5' of wire run.

I know you have seen the pictures of my install, and the added angle sheet metal to help guide tree limbs up and over the panels, vs the potential of bering caught under the rack, which is a potential downside to rack mounting on RV's.

I have zero concerns with the wind or driving air force on these panels. Very solidly mounted.

A final advantage on how we mounted ours, and done so on purpose, was I straddled the shower skylight. Yes, and the DW does not like this, it does reduce the light let into that part of the coach. I estimate a 40% reduction. But, it also shades this skylight, which all but eliminates solar heat gain into the coach. And that is IMO worth the reduced light. And, in rain or hail, much quieter inside

!

Though as I think you know, I added the 5th panel to avoid needing to tilt the panels on the roof. I did not research this part of using a rack system, so do not know if a tilting option is available or not. (You may have seen in my other thread where I posted the pictures. That I may add one or two smaller portable panels, carried in our future toad trucks shell, for times we're in heavier shaded areas. But you know, that generator still runs fine too

!

I'm real happy with the rack system, and glad we did this on our install.

In short, yes unusual with me, the positives outweigh the negatives, at least for my needs

!

Looking forward to seeing what you end up with, as you previous coaches system was well thought out.

Best,
Smitty

Timon · 03-17-2016, 01:21 AM

I've been thinking about how to tilt when using a rack. I think you can just use solar L brackets to act as a hinge sitting on top of the rack. Really not that much different than mounting flat on the roof. I've been looking at the various rack manufactures to see what's stock tha might be useable.

OMT, I think this would work best with the large panels going across the entire width of the coach.

Smitty77 · 03-17-2016, 03:21 PM

Timon - Please share the results of your tilting investigation in regards to rack mounted SP's.

Mine are not the biggest, but were geared for residential and commercial markets. Certainly much larger size, and wattage, then the AM Solar RV Right Sized recommended panel choices. (Not a ding to their panels, as they're good, and are as said 'right sized'. Also, many people will not want to use a rack mount SP system on their RV. Having the smaller panel, allows for placement out towards the edges of the roof, away from as many as possible self inflicted shadowing objects as possible. And, while still leaving a 'access path' for walking on the roof.)

Here is a link to some pictures of the X's 5 Panasonic 240S 48V panels on my roof:
http://www.irv2.com/forums/f56/roof-...cs-280334.html

Best,
Smitty