West-Facing Solar Panels

david3david3 Solar Expert Posts: 37
The roof space that I have available to mount solar panels is facing due west with a 35 degree tilt angle, and I'm at 16 degrees latitude in the Philippines. I've got a space of about 42' x 13' on the roof. I'm hoping to put up 5-6 KW of panels.

Any idea how much of a loss I would incur if I mounted solar panels on this west-facing roof?

My understanding is that the ideal tilt angle is latitude + 15 degrees, to optimize collection during the winter. That would be 31 degrees for me, which is pretty close to the 35 degree tilt of my roof. With the west-facing roof, I think I'd get a little more of the afternoon sun.

I've found an article discussing this here:


This shows examples for a location at 11.4 degrees latitude. According to this source, locations closer to the equator have less system losses due to a 90 degree shift east or west, with this 11.4 degree location showing 96% collection (4% loss). So at 16 degrees latitude, maybe it might not be so bad (perhaps < 10% loss).

The alternative would be to construct a sort-of covered/roofed area over my back yard and mount them flat. The danger there is that the lot to the west of me (next to my back yard) is vacant, and if/when someone buidls a house there, I may have a big problem with shading. So I think they'd be safer on my roof.


  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: West-Facing Solar Panels

    Basically, almost all your charge would be from the afternoon sun, with little or none in the before noon. A huge reduction in what the panels would otherwise be capable of.
  • mike95490mike95490 Solar Expert Posts: 9,362 ✭✭✭✭✭
    Re: West-Facing Solar Panels

    I had a west facing roof, and chose it over the east facet. AM fog and clouds were worse on the east, then the evening marine layer.
    link to sample day attached. (Los Angeles CA) 2:30 pm peak.

    Image source: http://www.mike-burgess.org/PVinfo_2.html (spreadsheet)
    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

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • PhilSPhilS Solar Expert Posts: 370 ✭✭✭
    Re: West-Facing Solar Panels


    ANY "less-than-optimum" panel mounting can be compensated for by adding more panels.

    I'd agree with your initial plan, and just fit as many panels as you can on that space, or at least plan for more panels in the future if you can't install them now.

    Depending on your useage and requirements, I'd think 5 - 6 KW could be sufficient (since we live on less than 3KW and don't get as much sun as you).

  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: West-Facing Solar Panels

    you are correct in that it is an east-west nearly overhead maxima. as was said though the west facing pvs will not reap much of the power coming from the east. if you have roof area on the eastern face you could place some pvs there and it would be recommended to run as separate systems and hence another inverter. if only going with the west facing pvs then i would suggest angling them so they would point more upward if it is possible for you to do. if you have the roof peak shading the array earlier then you should not have the 0 degree or flat arrangement to optimize for solar noon, but probably an offset closer to 20 degrees would be a good compromise angle and is a standard 15 degrees off making the mounts at a more common available angle. you could simplify and leave it at the 35 degree angle, but you will not take good advantage of the higher intensities around solar noon even though it is cheaper in mounting.

    some here may forget that your pvs don't need aimed to the southern sky being you are near the equator as straight up is about optimal.
  • david3david3 Solar Expert Posts: 37
    Re: West-Facing Solar Panels

    Thanks for all the info.

    I've got a smaller section of south-facing roof space, but probably only enough for 12 panels at most. And that section of the roof is more difficult to get to for maintenance and cleaning.

    So if the data in that link (http://www.ftexploring.com/solar-energy/tilt-angle3.htm) is correct, I'd expect a 10% or less penalty for the west-facing roof since I'm close to the equator. Higher latitudes show a 15-30% loss.

    If it's only 10%, it's probably not worth splitting the panels up to mount a smaller portion on the south-facing roof area, though.

    I'm thinking that I'd rather not prop-up the panels to reduce the tilt angle, because that may make them more susceptible to wind damage. I've got typhoons to contend with here, and if the panels are laying broken on the ground, that would be a 100% loss.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: West-Facing Solar Panels

    up to you on this as this is your decision. as to high winds you may find that the winds picking up the pvs will usually not be the case for the damage to them as it would be flying debris that would hurt them.

    let us know how you make out.
  • solarixsolarix Solar Expert Posts: 713 ✭✭
    Re: West-Facing Solar Panels

    The most cost effective thing to do is to mount the west facing roof panels with a southerly tilt of at least 10 degrees. This is easy to do, just use short (about a foot) legs on the back mounting rail. The problem is you have to space out the rows (at least about 2 feet in your latitude) so they do not shade each other. This takes up a lot more space and of course, doesn't look so great, but produces the desired effect of a more south facing array.
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