Slightly west of South?

cdre
cdre Solar Expert Posts: 78 ✭✭
in Solar Beginners Corner #1
I recently ran a number of models to see what different orientation of PV arrays would produce. Interestingly, SSW proved to produce more than plain 'ole South. I was a reference in another post recently saying that generally just west of south is where you see the best results.

Is that true? And if so, why? Does if have to do with more clouds in the morning than in the afternoon? Some other non-astronomic reason?
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  • HandyBob
    HandyBob Banned Posts: 31 ✭
    #2
    Re: Slightly west of South?

    That is going to vary widely with the climate and whether using MPPT or PWM. Many places have more afternoon clouds, some have morning fog. Cooler temps in the morning make MPPT work better, but can also lead to higher humidity in the air and thus less solar energy passing through it. I have designed a solar heated home that is just coming out of the ground. I saw some people saying to orient the solar wall east, some west & everybody had some theory. The fact for me was that orienting slightly east of south will supply quicker morning heat. I don't need a test to prove that.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,623 admin
    #3
    Re: Slightly west of South?

    PV Watts is actual measurements of solar energy--So if you have AM clouds/haze, it will take that into account.

    For Florida, facing south east is better--PM Thunderstorms reduces output. Plus something that PV Watts (I think) does not account for, cool morning with higher Vmp-array (Power=V*I) vs warm summer afternoons (which depresses array operating voltage).

    For Grid Tied systems with Time of Use billing, South West gives more afternoon power, which for the plan I am on, gives me more $$$ credits ("6 months of summer"--I get paid $0.30 per kWH credits between noon and 6pm on weekdays. Off peak, I only get $0.10 per kWH--So for me, 3x more credits for afternoon power generated.

    However, my roof faces south east--Such is life. And I have a redwood tree on a neighbor's property (south east) that is growing like a weed (no problem 10 years ago, now--Hate to go look). And some oaks south west... Mostly, does not affect my non-winter power (at least for now).

    I would suggest looking a conservation vs spending too much time and money on S/SE/SW orientation issues/questions and/or spending lots of money on racking to "tweak" the orientation.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • cdre
    cdre Solar Expert Posts: 78 ✭✭
    #4
    Re: Slightly west of South?

    Makes sense. Regarding the data PVwatts provides, if you export the"daily" results, it gives a ton of info to include panel temp. To run my models, I put together a matrix to parse out the info and average it out by the hour. Very useful data. Only concern I have is that it looks to reflect a single year. Could be misleading as weather patterns can change dramatically from year to year.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,623 admin
    #5
    Re: Slightly west of South?

    PV Watts is typically a compilation of 20 years or so of solar data. The dates in PV Watts detailed output (as I understand) is "real data" from a statistically "average day"... If you look closer, you will find the years will (usually) be different on different days.

    I don't remember temperature data, but that may because of the PV Watts I typically use to answer questions (older, simpler version).

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