Derating for not facing south?

tvengineer
tvengineer Solar Expert Posts: 31
I am seeing more and more "professtional" installations of solar panels on roofs that are not facing south.
I wonder if this is the local "solar experts" just trying to sell systems and not informing the buyer about the losses they will have by facing the panels east or west????

In my situation I have very little south facing roof (and that is pretty much full of PV panels already)

I have plenty of WEST facing roof.. but is there a formula for how much less energy I can recieve by placing panels facing west???

I live in the deep south.. so in summer there is plenty of sun.. and the setting sun in the summer seems (to me anyway) to be very strong on my west side.. but then again.. I am never awake early in the morning to see what it is like on the EASt side ;););)

Louis

Comments

  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Derating for not facing south?

    The PV watts site http://www.pvwatts.org/ addresses this. Also, local micro - climates can have a big influence. I too, had only an east or west face of roof, no south. But my choice was influenced by frequent AM clouds (Marine Layer) and few evening clouds. West was my best choice. Florida is the opposite, face east, for AM harvest, PM heat and thunderstorms/clouds mess up the PM harvest.
    Your Mileage may vary.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Derating for not facing south?

    You can use the PV Watts program to plot out watt*Hours vs time of day (comma delimited file for entire year by hour is available).

    For some places (like Solar Guppy's in Florida) those facing south east actually out perform other south and southwest. Cooler mornings, afternoon thunderstorms, etc.

    Also, if you have grid tied--you can have reasons to face them south west or westerly. For my area, I have summer peak net metering from noon to 6pm week days--and the peak power price is roughly 3x that of off-peak hours--so getting a few more kWhrs in the afternoon would pay back better than balanced or early day production.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Derating for not facing south?

    you may do well in the summer months with pvs aimed east or west and of course there will be losses over what it would be if it where aimed south. the biggest problem would come during the winter when the limited sun times will prevent the sun from actually hitting your pvs at even close to the optimal angle as the sun is literally on the horizon either just rising or setting. the better compromised angles would be those nearer southeast or southwest and which is better can be determined for your location. it is simple common sense though that the best production is when it is aimed directly at the sun. for fixed arrays this would be in the direction the sun is at when it's at its strongest, or due south. the farther off the incident solar rays are from hitting your pvs, the worse the power production will be. some of those installers may just be taking advantage of the home owner especially where no solar surveys are done and the salesman does not warn the home owner of the diminished returns mounting pvs in a non-optimal direction. surprisingly to some, this could also be the case of pvs aimed southerly, but not at an optimal angle with respect to the latitude. this won't be quite as bad as aiming east or west (or anything worse by going more northerly) imho. there are exceptions out there as to the aim south rule of thumb.
  • RandomJoe
    RandomJoe Solar Expert Posts: 472 ✭✭✭
    Re: Derating for not facing south?

    My next set of panels will be going on a west-facing portion of my roof. Primarily because it's the next least-shaded portion of my roof, but also the PV Watts website actually showed I get more power overall (through the course of the year) from a west-facing array than I do from a south-facing one. It doesn't produce as much in winter as the south-facing does, but summertime afternoons more than make up for it.

    If I were to make the arrays adjustable so I could get "optimal" angles for every time of year the south-facing one would do better at all times but mine are parallel with the roof in a fixed angle.
  • tvengineer
    tvengineer Solar Expert Posts: 31
    Re: Derating for not facing south?
    niel wrote: »
    .. some of those installers may just be taking advantage of the home owner especially where no solar surveys are done and the salesman does not warn the home owner of the diminished returns mounting pvs in a non-optimal direction. surprisingly to some,..


    I guess that was my point... In my neighborhood there are at least 3 new installations.. some west.. some east.. does not seem to be any regard to placing them in an optimal location.. just whatever is convinent on the roof... one of them is shaded by another building whenever I happen to look at it.

    I have talked to one of the companies that installs these... and to be brutally honest.. I think that they went into the business when the state and federal incentives went up after hurricane Katrina.. they do a hard sell on the homeowner on just how much money they will get back from the government.. then jack the price of the system up to reap all of the incentives for themselves.. now that I see their installations... I am more convinced that they are really only in it for the $$$
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Derating for not facing south?

    Speaking of which,

    What happened to the tread of the gentleman from Texas who was documenting the installation of his grid tie system. After some folks started to critique some aspects of his installation it disappeared. I went to look for an update the other day, and I can't find it.

    Any body know?

    Tony
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Derating for not facing south?

    Bill "a0128958" thread is here (I think that this is the one you are asking about):

    Illustration of 8 KW (DC) GT Solar PV System Install for Residence in Urban Area

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset