Mount Flat Or At Angle?

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Hello everybody, my first post here.
It is time to go to a solar panel for our travel trailer and I have this question. I see many of them mounted on the roof of trailers and some are mounted flat and some are mounted at an angle! In talking with a number of other RV`rs I get almost an even split on wether the panel should be mounted flat or at an angle. Factors such as how the Rv is parked in relationship to the sun is a big part of the conversations with many claiming mounting flat just plain uncomplicates things. I`m planning on doing my own fabrication of the mounting system and so far things are getting more complicated by the minute. So, how much extra efficiency can the angle mount have over the flat mount??
Thanks,
Richard

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  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
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    Re: Mount Flat Or At Angle?

    Tilting the modules up at an angle of between local latitude and latitude minus ~15 degrees and aiming them to the south works best in terms of energy production in the summer. Travel trailers see most of their use in late spring, summer and early fall, so mounting the PV modules "flat" typically works well enough during that period. A benefit is that you don't have to worry about the southern orientation. A complication, however, is that dirt, pollen road grime and bird souvenirs collect and "pool" on the modules. For example, the frame edges don't allow rain to drain away, and, once the puddles dry, the module glass is left covered with a carpet of crud, which blocks sunlight and reduces energy production.. So, you'll have to make a point of going up on the roof and cleaning the modules with a glass cleaner and old newspaper.

    Also, try to install the modules with a couple of inches of free air space beneath them, rather than attach them directly to the roof. Modules can get pretty hot in the summer (>140 F), and a little air circulation beneath 'em will help cool 'em a bit as well as hopefully avoid damage to the trailer's roof material. I used Yakima cross bars and angle aluminum to secure my PV modules above the roof on my old camper.

    Give us an idea of where you camp, and we can probably provide insolation data for various tilt angles for that (those) location(s).

    HTH,
    Jim / crewzer
  • BB.
    BB. Super Moderators, Administrators Posts: 33,497 admin
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    Re: Mount Flat Or At Angle?

    The answer to the question depends on where your trailer will be and what time(s) of year you will be using it.... For example, if you are in the southern US and only use the RV during the summer--you will be pretty happy with a simple to fabricate and install flat rack.

    If you are in the northern US and do a lot of snow camping--then you will want the panels to tilt up to both catch the sun and keep them free of snow.

    You can check here for the number of equivalent hours of sun per day, any month and by year to see how you would be affected with different tilt angles for any major section of the US... If you are out of the US, there are other sites that have similar information.

    http://rredc.nrel.gov/solar/pubs/redbook/

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2
    System2 Posts: 6,290 admin
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    Re: Mount Flat Or At Angle?


    Thanks for the replies, late spring, summer, and early fall use will be here in eastern oregon with hopefully very little snow to put up with. Late fall, winter, and early spring use will be in south eastern California (desert), along with Arizona, etc. I have just come up with a nice cedar frame design that will allow the panel to pivot 360 deg. and either lay flat or tilt to almost any angle. Tomorrow looks to be a good day to start construction, we`ll see how things go, sometimes something looks good on paper but in the flesh ???!!!
    Again, thanks for the kind words, see ya!
    Richard
  • System2
    System2 Posts: 6,290 admin
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    Re: Mount Flat Or At Angle?

    I just had mine mounted flat about 2" off the roof of my rv. I drove into severe head winds through the desert for about 300 miles and they are as solid as ever. Just me but we do a lot of movements rom campground to campground and, inevitably, I would forget to secure/flatten tilted panels before traveling.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,497 admin
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    Re: Mount Flat Or At Angle?

    One caution about the cedar frame... Most high performance solar panels are basically big panes of glass. And wood frames tend to be heavy/bulky and not always easy to make stiff and resistant to flexing...

    If the wood frames themselves tend to twist when you pickup one corner--there is the possibility that the solar panels could twist and shatter...

    Tilting panels will generate more power (especially in northern latitudes) and be much better at shedding dirt, etc... But high wind loads and stiff structures are pretty much a requirement to ensure that your panels last a long time. I believe (I am not a structural engineer) that you should plan on the structure withstanding 75-125 lbs per sq foot (wind/snow loads) if left unattended (where you cannot lay them back down in the wind and sweep snow). Don't give the frames a chance to flop in the wind.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2
    System2 Posts: 6,290 admin
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    Re: Mount Flat Or At Angle?


    Yes, it would be a calamity if one left the solar panel assy. up instead of down! Yikes! That would really ruin an otherwise great day!
    BB, I`m going to try and make the panel assy. as rigid as possible, with gussets, screws, glue, and anything else I can think off. My experiece has been that a wood frame can be made quite rigid and flex free doing the right things. Anyway, I`m going to give it a go. By tomorrow evening I should know more about wether my grand scheme will fly or not.
    Richard
  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
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    Re: Mount Flat Or At Angle?
    Thanks for the replies, late spring, summer, and early fall use will be here in eastern oregon with hopefully very little snow to put up with. Late fall, winter, and early spring use will be in south eastern California (desert), along with Arizona, etc.

    Richard,

    Using Eugene, OR, for an “eastern Oregon” reference, you won’t see a lot a difference between flat and tilted modules from late spring to early fall April – September).

    See: http://rredc.nrel.gov/solar/old_data/nsrdb/redbook/sum2/24221.txt

    Using Phoenix, AZ as a reference for late fall through early spring in southeastern CA and AZ, it would definitely be helpful to be able to face the modules to the south and tilt them up to ~48 degrees from the horizontal.

    See: http://rredc.nrel.gov/solar/old_data/nsrdb/redbook/sum2/23183.txt

    HTH,
    Jim / crewzer