Recessing Rooftop Solar Panels?

[MuseliMom]

Hi everyone,

We're still planning our bus conversion and doing all the calculations needed (we're still newbies!), so this is perhaps a speculative question, but we're wondering if anyone has recessed their roof-mounted solar panels?

We're doing the calculations about daily usage and wattage, and looking at the various options for panels, batteries, converters, controllers, etc. (our current estimate is about 600-650 watts/day), but when looking through all the information, product specifications, blogs, etc. One thing which appeared constant was that no one seemed to recess roof-mounted solar panels.

We had considered options for recessing the panels to maintain vehicle height, better fuel efficiency, more protection for the panels, etc., but we also realized, we'd lose inside roof/ceiling height. Would recessing solar panels also compromise the roll-over safety structure?

I'm sure we're missing something here, as we couldn't see any skoolies with recessed panels, but I'm just wondering if it's more to do with practical/safety reasons, or whether it's a cost issue.

Any thoughts would be appreciated! Thanks!

[Danjo]

I wouldn’t even consider that for all sorts of reasons.

1. Panels are only 2 1/2” high installed on unistrut.

2. You’d have to install between ribs so the panels would have to be crosswise. If your roof is curved, how would that work?

3. How would you waterproof that?

4. Panels need airflow to stay cool.

5. Too much work for lots of hassle and problems.

[DeMac]

What kind of bus do you own?

[Ronnie]

I would suggest flexible panels that fit the curve of the roof rather then flush mounting.

[rossvtaylor]

I think everyone here agrees that it's not practical to recess the panels. But then again, it's not practical to buy a bus and chop the roof to raise it up...but that happens all the time. But...recessing the panels would create a huge set of issues. You'd essentially have to frame in a shallow pan for the panels, which would trap water and be a pain to create. The flexible panels idea, above, is good. But another is to put the panels on as low as possible (this isn't ideal, from a heating/ventilation perspective) then put a rail on either side, extending just higher than the panels. This offers the protection you seek. If you want stealth panels, you could make those side rails solid...like the RV manufacturers do, to hide all the junk on the roof. As far as fuel efficiency goes...you're driving a shoebox down the road...an extra 2 inches won't make a difference.

I love seeing creativity! But this seems like a TON of work for little gain.

[BeNimble]

What you could do that would be sweet is put them on the roof as normal with curtains so you don't see them and somewhat protected, and then chop the roof off and make it a poptop, so it is very streamlined going down the highway, and then pop it up when you stop. I had this idea in mind for the low floor transit bus. Frontal area is a big issue for MPG, and a bus has a massive amount of it, particular after a roof raise..

https://www.youtube.com/watch?v=KYoj_AKm058

[rffffffff]

What everyone else said seems on point. Full size busses have ribs about every 27 inches so getting them inbetween the ribs would be impractical at best...

In terms of gas mileage though, center mounted panels mounted the long way on the bus, touching each other, with a little custom ramp on the front and back would be fairly stealth and have a small wind impact, and would be hard to see from the ground. It would be a clean look.

[DeMac]

Search 'sasquaters solar'
They have a slide-out design on the roof. The custom housing looks fairly aerodynamic. Not sure if that would fit on a van style bus.

I'm sure you have a drawing or a plan you can show us. After the 5th post, you can upload pix.

[ComfortEagle]

Our goal was to get our panels mounted as close to the roof as we could. And while not flush, the center of the panels are <1in off the roof. However, the particular panels we chose are about 2in thick, and larger 72 cell design.

“Skinnier” (<2in thick) 60 cell panels would be ~1ft less wide (than 72 cell), and would tuck in a bit closer to the roof line. Of course and as mentioned, flexible panels could be a good option if flush mounting the panels is an important design element of your build.

[Rucker]

The bus is a rolling brick. Other than height issues, a couple of inches of added height from the panels will have no effect on mileage, top speed etc.

At this stage of the build you can research solar panel installation, and get a pretty good feel for mounting solutions, wind considerations etc.

I did a little research and, for what it's worth, there's not a lot of gain in tilting the panel, unless you're quite far north in the States (like Michigan). So flat is fine. There are also lots of flexible panels, though I don't know much about them.

Whatever research you do I'm guessing that when you get to this part of the build your primary thoughts will be 'how the hell to I get these suckers bolted down with the least effort?'

[BeNimble]

Originally Posted by Rucker

The bus is a rolling brick. Other than height issues, a couple of inches of added height from the panels will have no effect on mileage, top speed etc.

Drag is computed by coefficient x frontal area.
If a Bus has a 1.0 coefficient of drag of a brick, the frontal area IS EVEN MORE IMPORTANT. The amount of drag directly effects the MPG. The required power goes up by the square of the speed too, so 50 vs 60 is big difference.

Here is some fun reading...https://history.nasa.gov/monograph46.pdf



The Crowns rounded corners are a big deal. For a school bus that spends most its time stoping and starting and going maybe 40, drag is not a big deal. It is for a highway vehicle like a travel bus or a semi-truck that spend almost all its time on the highway at speed.

If fuel mileage doesn't matter, then the next time I hear get a diesel they get better mileage I'm going to post a reply saying WTF does that matter! ;)

[Iceni John]

I have eight 255W 60-cell panels on my bus, all individually tiltable and all hinged from a central walkway I built between the two roof hatches. At 60+ MPH I don't hear any wind noise at all from the walkway or panels. They lay down against the roof at 21 degrees down when stowed for travel, and can be raised to level (kinda pointless!), or 21 degrees up (for summer) or 33 degrees up (for spring or fall) or 45 degrees up (for winter). Most importantly, they all have good airflow under them while driving or parked, so their thermal derating is no worse than ambient air temperature. I also put two water outlets on the walkway so it's easy and safe to wash the inevitable bird crap and dust off the panels to maximize their solar harvest: flat-mount panels get really dirty really quickly, so you'd better have a good way to easily wash them!

There's no need to overthink this - it ain't rocket surgery to make effective panel mounts for a curved roof, just common sense and sweat equity. And please don't use those godawful stick-on flexy panels that are bloody useless!

John

[Willie_McCoy]

Originally Posted by Iceni John

I have eight 255W 60-cell panels on my bus, all individually tiltable and all hinged from a central walkway I built between the two roof hatches.

Do you have pictures of this setup anywhere that I can take a look at? I am in the product acquisition stage of the solar build with work expected to begin in the spring when the weather breaks. Would like to see what you have done here as I dont doubt that it is top notch

[Iceni John]

Originally Posted by Willie_McCoy

Do you have pictures of this setup anywhere that I can take a look at? I am in the product acquisition stage of the solar build with work expected to begin in the spring when the weather breaks. Would like to see what you have done here as I dont doubt that it is top notch

Sorry, no photos (I'm photographically challenged!), but YouTube has a short video titled Buses Gone Wild VII, or something like that, showing when six of us at one of our annual Crown get-togethers at my friend's house a few years ago decided to drive into town and make nuisances of ourselves there: mine's the third bus, showing when I had made the panels' support frames but before I had loaded the panels themselves into their frames.

John

[Doktari]

Recessing panels does not seem worthwhile in my mind. I’m thinking of adding tree branch deflectors on the front and back of my solar array as they will be elevated from the roof 12” on a rack. Just some angle iron to push branches up and over. My not very scientific experience is that having elevated stuff on the roof of my bus has very little effect on my mpg. And empty or fully loaded it’s about the same mpg. I drive slower when loaded so maybe that’s partly why.

[captnredbeerd]

We did a low profile solar mount. Sometimes people don’t even realize it’s up there. Included pic of the mounting with z brackets from renogy, bc when I was building planning I would have wanted to know—how do they actually attach these things?! FYI, installed these while the interior ceiling was down.

[kazetsukai]

To give another perspective, my setup is the opposite of low profile.

My 10 305W panels are up on strut, strut which itself is on L brackets. The panels themselves clear the roof by a little over 5, maybe 6 inches. I did a trip from NH to KY with this configuration... any worry I have is with winds from the side, and even in that case the extra clearance allows air to flow underneath. I want to put a wind shroud down the length of the bus, but haven't actually needed to yet.

I'm about to put another 10, 315W panels up, for a little over 6200W. Still working out the design, where half will slide out when parked, before I update my build page.

[Ronnie]

More mounting pics. I did an aluminum angle iron frame with tabs at each rib to hold it. Note this is a construction picture and the wires are not laying loose like in the photo.