Flat vs tilting panels on RV and wind load.

Skyko · February 2014

I am writing this as a different thread since the other thread devolved into mostly a battery discussion.

I played around a bit more with solar panel ideas and I think it might work to change the layout of the four panels such that they are able to tilt up to 45 degrees and not block each other when tilted. I also mounted them off-center so I can have a path around the panels for servicing/inspection. When we go up to Alaska the sun is going to always be low and the original flat, non-tilting mounting scheme might not be wise (although easier to build).

What do you think about the 37.5" by 66" 265 watt panels in this configuration? Are they too large in physical size to install on a camper/rv? I do not know how the frame/glass will deform under road/wind stress. Should I think about more panels but smaller physical size per panel? Should I just design the frame correctly for the large panels?

Attachment not found.Attachment not found.

vtmaps · February 2014

Re: Flat vs tilting panels on RV and wind load.

Skyko wrote: »

What do you think about the 37.5" by 66" 265 watt panels in this configuration? Are they too large in physical size to install on a camper/rv? I do not know how the frame/glass will deform under road/wind stress. Should I think about more panels but smaller physical size per panel? Should I just design the frame correctly for the large panels?

I don't know much about mounting panels on vehicles, but many boaters and campers (with limited roof space) choose higher efficiency panels.

If you can get the same watts in a smaller package, I suppose that would be beneficial.

--vtMaps

Cariboocoot · February 2014

Re: Flat vs tilting panels on RV and wind load.

I have to ask: what time of year do you go to Alaska? It makes a big difference.
I'm at 52 degrees Latitude and our Summer sun is practically directly overhead. At that time flat panels will do fine (small loss). In Winter that angle changes drastically and all you get is a little ball of flame bobbing up somewhere around due South for a couple of hours midday.

Skyko · February 2014

Re: Flat vs tilting panels on RV and wind load.

We plan to go to Alaska in late April and stay until early fall.

I can see how the tilting would make a huge difference in the spring and fall...but obviously is a hassle in construction and parking orientation.

BB. · February 2014

Re: Flat vs tilting panels on RV and wind load.

You can use PV Watts or Solar Electricity Handbook to estimate the output from different angles/months/locations and see how much differences you will get by playing with the variables.

-Bill

Iceni John · February 2014

Re: Flat vs tilting panels on RV and wind load.

I have a 40' Crown bus that I'm presently putting panels on. I'm making a central walkway between the two roof hatches/vents/exits, and my panels will be hinged to that. The walkway is two 25' lengths of 1.5" x 0.125" 6061 angle that will be bolted through the 18 roof ribs with 36 stainless 3/8" bolts, then with seven pieces of 5-bar 12"-wide treadplate to walk on. It's four inches above the roof surface, to give space underneath for the five weatherproof outlet boxes that are for the panels' two combiner boxes and for PEX water lines for the eventual solar water panels and for washdown outlets to help me clean the panels when needed. I have eight Sharp 255W panels - each panel will sit inside a support frame made from a 16' length of 1.75" x 0.125" 6063 angle (and a bit more to bridge the gap because each frame needs to be 17.5' total length). Now here's the fun part - the four panels on each side of the walkway can be raised up to 50 degrees above horizontal, or they can sit down against the roof at about 20 degrees below horizontal. This will give me almost as good efficiency as having them all hinge up, but with the benefit of easy and safe access to them whenever I need. Having a curved roof has turned out to be an advantage for me: in summer all my panels will be tilted about 20 degrees, and in winter half of them can be raised higher. It's a lot more work to make all this, but the end results will be worth it. When I get my tax refund back I'll be buying two Morningstar 60A MPPT controllers and all their breakers and gauges and whatnots. Fun!

Could you do something like this? None of my panels will ever be shaded this way, and they'll still have good wind-load strength and complete adjustability. Even though my panels already have strong frames, I want to isolate any stresses from windloads and the flexing of driving by having separate support frames for them as well.

Just an idea.

John. in sunny SoCal

westbranch · February 2014

Re: Flat vs tilting panels on RV and wind load.

John, suggest your invesigate the Classic series of controllers, plus the WhizBang Jr. , which adds a lot of functionality to the CC's
Links can be found here:http://www.midnitesolar.com/

Iceni John · February 2014

Re: Flat vs tilting panels on RV and wind load.

westbranch wrote: »

John, suggest your invesigate the Classic series of controllers, plus the WhizBang Jr. , which adds a lot of functionality to the CC's
Links can be found here:http://www.midnitesolar.com/

I need controllers with remote displays (my controllers will be located such that I won't be able to read their displays), and I really don't want fans for cooling. I'm amused that the Comparison Chart doesn't compare them with Morningstar controllers - I wonder why . . .

Yes, they're good controllers, but I think the Morningstars will be the best for what I need. I'll certainly research this further.

Thanks, John

unyalli · February 2014

Re: Flat vs tilting panels on RV and wind load.

John, excellent, pictures and updates please. Subscribed.

Jeff

dkpro1 · February 2014

Re: Flat vs tilting panels on RV and wind load.

Attachment not found.

unyalli wrote: »

John, excellent, pictures and updates please. Subscribed.

Jeff

This is what you need

unyalli · February 2014

Re: Flat vs tilting panels on RV and wind load.

dkpro1 wrote: »

Attachment not found.

This is what you need

Oh man, what a setup. More details please, are those aluminum bars? How are you attached to the roof?

Jeff

Iceni John · February 2014

Re: Flat vs tilting panels on RV and wind load.

dkpro1 wrote: »

Attachment not found.

This is what you need

Er, no!

I don't see how they can raise more than they are in the photo, about 20 degrees. That's OK for Southern California latitude in the summer, but too low for winter use there or for further north. Also, I don't see how they can be raised the opposite way - if you could only park pointing to the west they wouldn't do much good. (At least, north of the equator!) I also wonder about their ability to withstand desert wind gusts which can come out of nowhere and be surprisingly strong - the photo looks like it's taken just south of Quartszite AZ, where it can get very windy at times.

John

zoneblue · February 2014

Re: Flat vs tilting panels on RV and wind load.

Iceni John wrote: »

I need controllers with remote displays (my controllers will be located such that I won't be able to read their displays), and I really don't want fans for cooling.

You can remote mount the MNGP (grpahics panel, it clips off, and connects via telephone type wire and plugs.

I'm amused that the Comparison Chart doesn't compare them with Morningstar controllers - I wonder why . . .

Quite. They reportedly invested in extensive performance comparison, but didnt publish the results! Other than that summary table, which is a pity. But I later heard robin or bob say that the morningstar and classic were on par in terms of daily yeild. A poster here had something to do with the design of the morningstar mmp60, and beleived they were efficient.

Yes, they're good controllers, but I think the Morningstars will be the best for what I need. I'll certainly research this further.

Classic is something of a forum favorite, but im interested what folk think about build quality and support from morningstar.

dkpro1 · February 2014

Re: Flat vs tilting panels on RV and wind load.

Iceni John wrote: »

Er, no!

I don't see how they can raise more than they are in the photo, about 20 degrees. That's OK for Southern California latitude in the summer, but too low for winter use there or for further north. Also, I don't see how they can be raised the opposite way - if you could only park pointing to the west they wouldn't do much good. (At least, north of the equator!) I also wonder about their ability to withstand desert wind gusts which can come out of nowhere and be surprisingly strong - the photo looks like it's taken just south of Quartszite AZ, where it can get very windy at times.

John

Yes John it only tilt's 28 deg but that's all i need the sys. is just huge 1.9 kw tilt maily to make sure of no shading..... 24 foot 4x2 aluminum tubing with 8x 4 inch toggle bolts into roof along with sealer holding down very very strong

PS its a motor home they go south for winter don't need much tilt

unyalli · February 2014

Re: Flat vs tilting panels on RV and wind load.

dkpro1 wrote: »

the sys. is huge 1.9 kw

Wow, you could run a 15k btu ac off that.

dkpro1 wrote: »

24 foot 4x2 aluminum tubing with 8x 4 inch toggle bolts into roof

Did you hit the trusses? How did you locate them?

Jeff

Cariboocoot · February 2014

Re: Flat vs tilting panels on RV and wind load.

Nothing wrong with Morningstar controllers at all. I often recommend them when I think they're the right choice for the application.
I also often recommend the MidNite Classic when I think that is the right choice for the application. The difference is often whether or not the extra features/abilities of the Classic are worth the extra money for what it will be used for. Sometimes they're not.

As for the differences in controller efficiency, this is a small percentage among the top brands and not really a critical concern for most cases. If one or three percent is make/break on your system the system is designed wrong and isn't going to work well anyway. You need quite a bit of latitude because every day on this Earth is not the same for loads and sun. People who try to get away with minimum battery bank and (especially) minimum panels are always disappointed with the result.

If you try to 'live on the edge' don't be surprised if you fall off.

zoneblue · February 2014

Re: Flat vs tilting panels on RV and wind load.

Coot, you are of course right. But in terms of heat, an efficiency difference of 3% might not sound much, but lets say at 2400W, the difference in heat dissipated into a controller is 2400W * 0.03 = 72W. Now thats a fair bit of (extra) heat for any product to have to manage, and has got to affect product life and reliability in the longer term.

Cariboocoot · February 2014

Re: Flat vs tilting panels on RV and wind load.

zoneblue wrote: »

Coot, you are of course right. But in terms of heat, an efficiency difference of 3% might not sound much, but lets say at 2400W, the difference in heat dissipated into a controller is 2400W * 0.03 = 72W. Now thats a fair bit of (extra) heat for any product to have to manage, and has got to affect product life and reliability in the longer term.

Yes and the more efficient controllers use cooling fans which ... draw ... power ... uh ...

I wonder which would be worse for adding heat to an RV: the radiant, lower efficiency controller like an XW or the fan-cooled, higher efficiency controller like a Classic? So many variables!

It's a bit of a "pick your poison" situation. Like trading off power loss in wiring for power loss in conversion (array to system Voltage ratio).

Now if we ever get panels up to >80% efficiency these small amounts are going to matter big time.

vtmaps · February 2014

Re: Flat vs tilting panels on RV and wind load.

Cariboocoot wrote:

If one or three percent is make/break on your system the system is designed wrong and isn't going to work well anyway.

zoneblue wrote: »

But in terms of heat, an efficiency difference of 3% might not sound much, but lets say at 2400W, the difference in heat dissipated into a controller is 2400W * 0.03 = 72W. Now thats a fair bit of (extra) heat for any product to have to manage, and has got to affect product life and reliability in the longer term.

I agree with both points, but it brings up the whole issue of specifications and ratings. When a device (generator, inverter, controller, etc) is rated 2400 watts, what does that mean? Depending on the meaning of the rating, it may or may not be good design practice to operate the device at that power continuously.

Regarding the issue at hand (morningstar vs classic) is it better to run 40 or 60 amps through a 60 amp morningstar or a 96 amp classic?

--vtMaps

BB. · February 2014

Re: Flat vs tilting panels on RV and wind load.

If you have a dusty/buggy environment, I would like to avoid systems that bring outside air into the electronics.

Those with no fans and external heatsinks are great (in my humble opinion), those with external heatsinks and fans are not bad (as long as the fans are easy to change).

One person here simply took an external heatsink GT Inverter (Schneider/Xantrex) and used a simple office desk top fan bolted to the garage rafters, on an AC lamp timer, pointed at his one (or two) GT inverters--Worked great, was cheap, and he only ran the fans in hot weather (prevent heat buildup in the corner of the garage--As I recall).

-Bill

Cariboocoot · February 2014

Re: Flat vs tilting panels on RV and wind load.

vtmaps wrote: »

I agree with both points, but it brings up the whole issue of specifications and ratings. When a device (generator, inverter, controller, etc) is rated 2400 watts, what does that mean? Depending on the meaning of the rating, it may or may not be good design practice to operate the device at that power continuously.

Regarding the issue at hand (morningstar vs classic) is it better to run 40 or 60 amps through a 60 amp morningstar or a 96 amp classic?

--vtMaps

Most of the controllers say "no derating necessary" (and then the NEC comes along and argues with that) but that would be in a solar application where they are not actually going to see full current for 3+ hours. Put them in a wind turbine application where the current is steady and its another story.

Basically if you have something rated for 'X' Amps and you use it at 0.8X Amps it will run cooler, no matter who made it or what the design. This usually equates to longer life of the unit (other factors being equal). That's physics. So a controller rated for 96 Amps asked to handle 60 Amps would last longer, but in absolute heat output terms would be the same as the 60 Amp controller unless the 96 Amp controller is more efficient: it is the efficiency difference that alters how much power is going to heat. Thus we have zoneblue's calc on the 72W of heat from 3% difference in efficiency for a fixed power allotment.

So in theory the Classic used at the same 60 Amp power level will have two advantages: more efficiency so less heat is produced and components better able to withstand that heat (because they are design to handle 50% more current).

In practice Bill's observation will make more difference: environment. Suck dust into your Classic and it will lose some of its heat dissipating ability causing it to run hotter, possibly more so than a unit with just passive cooling. Likewise any passive-only unit can have problems if natural convection is not good enough to move air over the cooling fins and in that same location the fan-cooled unit can perform better (even for identical current ratings such as the XW & the FM60).

Gosh, it's never simple is it?

scrubjaysnest · November 2014

Re: Flat vs tilting panels on RV and wind load.

Your wind loading will be your highway speed, with the panels lying flat this hasn't been a problem for a proper attachment system. This summer while camped I had ours propped up with 2x6's on the roof and they handled 40 mph gusts without a problem. That was most likely pure luck.

Reed · November 2014

Re: Flat vs tilting panels on RV and wind load.

We full time and primarily boondock/dispersed camp/bush camp and have had wind gusts in NM, AZ and MT that rocked the 34' 5th wheel (60 mph or greater). Gusts can occur with little warning and I would worry about panels and mountings being damaged. That said, I have to say that the setup is the best I have ever seen and it looks quite strong. I particularly like the idea that each set of four panels is adjusted simultaneously. I had only seen panels with individual tilting adjustments.

We do have 6 x 235 W panels. Was curious a month ago and wandered around the roof with a cardboard template of one of our panels (fancy term for a cut piece of approximately 2' x 6' cardboard, forget the exact dimensions) and found that we did have room for two more panels as currently set up and three more if we moved one panel.

We'e "Goldilockers" as in "not to hot and not to cold, just right!" When it looks like attached photo, time to head south. We were on way to Yucatan and Belize.
Reed and Elaine

Flat vs tilting panels on RV and wind load.

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