newbie...north facing sloped roof.

Location: Queen Creek Az
System: 22 Mitsubishi 165E4 Pnels

My question is that I was told the only way I can mount this system to my roof is if I use extended tilt legs to build up and lay the panels in a "flat" orientation. Using this set up...does anyone know the efficiencyu of the system. Will I only produce 30 40 or 50% of potential power?



  • mike95490mike95490 Solar Expert Posts: 9,466 ✭✭✭✭✭
    Re: newbie...north facing sloped roof.

    North roof is a hard situation. (unless you are in Australia)
    You HAVE to use some sort of extended mounts to get the panels out of the winter shade, and the more perpendicular to the sun the panels are, the more power you get. Depending on the expense of mounting, it may not be feasible to use the roof. What about garage, or other outbuildings? Maybe consider pole mounts? Beware of neighboring trees, they can cast shade, and disable the panels output too.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    gen: ,

  • BB.BB. Super Moderators, Administrators Posts: 32,235 admin
    Re: newbie...north facing sloped roof.

    You can try this solar power calculator to compare the issues of tilt and East/West/South orientations to see how much it hurts you...

    From this calculator, the difference for a 2,000 watt system...

    30 Degrees facing south (good setup)--3,732 kWhrs/year
    0 Degrees tilt (your setup?)--3,330 kWhrs/

    Or about a 10% loss... Not a huge loss--but some loss. Also, with the panels flat, they are no longer "self cleaning" from rain and/or hose---may be a big pain to keep clean.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • crewzercrewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: newbie...north facing sloped roof.

    Average insolation over a year in nearby Phoenix for a south-facing array tilted up at altitude latitutude (~34 degrees) is 6.5 hrs/day of “full” Sun. For a horizontally installed array, it’s 5.7 hours/day, or ~12% less. However, the difference is more pronounced in the winter, with 4.9 hours (tilt) vs 3.0 hours (flat) in December, or ~39% less.


    There are a couple of environmental concerns that will compound the reduction. One is that the PV modules will run hotter in the summer due to poor cooling convection, and this will cause the PV array’s output voltage, and therefore its power, to drop.

    Another problem is that the horizontal modules will rapidly accumulate dirt, pollen and other airborne contaminants, and this “film” of crud will reflect/block sunlight and therefore also reduce power output. Accordingly, I’d expect a loss of at least 50% in the winter.

    Jim / crewzer

    Bill!! Good to see you back!  :-)
  • BB.BB. Super Moderators, Administrators Posts: 32,235 admin
    Re: newbie...north facing sloped roof.

    Thanks for the welcome back--nice to be missed... Got back from 2 weeks in Taiwan with family visiting with In-Laws.

    Back to IH8... 10% loss of potential power year over year is not a big problem (you still would be generating more power than my equivalent system near San Francisco, CA)...

    Some of this depends on if you are Grid Tied with yearly net metering or something else like an off-grid system (battery system you can only save power over a few days, with yearly net metering, you can "save power" anytime over an entire year). The link I gave above does also list month to month generation (estimated average) (click on "monthly electricity" link).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: newbie...north facing sloped roof.

    i'd agree w/mike, flat panels would be nearly useless half the year in winter months, I'd pole mount somewhere else - it's expensive enough when it's optimally producing!
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: newbie...north facing sloped roof.

    i too agree with pole mounting unless you'd intend on that many pvs to be mounted that a pole wouldn't support it. with a north facing roof you might as well put in another room there and make the roof naturally face south as you could nearly rebuild the roof with all of the supports that would be needed.
    i was wondering where you disappeared to bill. welcome back.
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