Should Solar Face West not South?

RSSfeed
RSSfeed Registered Users Posts: 3,810 ✭✭
in General Solar Power Topics #1
feature-0-1385404947907.jpg A new study from Austin’s Pecan Street Research Institute finds that residential solar PV panels oriented to the west may have more benefits for homeowners — at least in the summer and in Austin, Tex. That research flies in the face of conventional wisdom that PV panels should face south where the amount of sunlight that can hit them is maximized.*

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  • solarix
    solarix Solar Expert Posts: 713 ✭✭
    #2
    Re: Should Solar Face West not South?

    Very true. If - you are on a time-of-use rate plan, and get full retail credit for your afternoon production (in my area it is noon to 7pm, 5 days/week) you will have a larger savings on your utility bill by orienting to the SW. Straight West is not so good though. The grid-tied solar system will produce significantly less power year-round, but your savings will be significantly higher. Here the on-peak rate is 24.4cents/kWh and off-peak is only 6.1 (summer rates). Makes a lot of sense to aim that array for the on-peak times. It helps to have a system sized for this. Too little on-peak production and you are paying the high on-peak rate, and if too little your on-peak credits build up and get paid off at the end of the year at wholesale rates.
    Best part is you are helping the utility too. In the sunbelt, the peak load time of day is late afternoon - around 5pm. SW facing solar arrays are much more helpful to the utility in shaving their peak load. Before too long, when the solar penetration gets above 10%, utilities are going to start saying no thank you to more solar unless we help attack this peak load problem they have. It doesn't matter how much power you make during the day, if the utility has to build more peaking plants - you aren't really helping that much. This is already happening in Hawaii. The electric rates in paradise are so high, people have flocked to solar and the utility there has put a bunch of new interconnects on hold until it is proven that it won't upset their stability.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #3
    Re: Should Solar Face West not South?

    aiming sw may be asked too much of residential solar users because the power production in the winter will royally suck. mounts that can be made to swing more toward the south again would be needed if the owner is to reap any meaningful winter production and it wouldn't have to go real far as sw is 45 degrees off of south. that is far enough to kill production in winter though if not re-aimed.

    as a side benefit though the angle off of the horizon will be lower when aiming sw and in re-aiming to the south for winter use it will already be at a more optimal height, although not the best, for the winter harvest. coming up with good, but cost effective mounts for many pvs to swing for seasonal adjustment is the key dilemma. on roofs it may be difficult, but pole mounts should work. for larger systems many pole mounts would be needed and room for them becomes a problem especially since they must have proper clearances from each other for both sw and south.
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #4
    Re: Should Solar Face West not South?
    solarix wrote: »
    Very true. If - you are on a time-of-use rate plan, and get full retail credit for your afternoon production (in my area it is noon to 7pm, 5 days/week) you will have a larger savings on your utility bill by orienting to the SW.
    But here in Austin we are not on TOU, at least not yet. I toured the Pike Powers (Pecan Street Project) lab a couple of weeks ago and talked to their chief engineer, who is the guy who generated the data for that study; he acknowledges that the study shows what is good for the utility (more help from solar during hours of peak AC usage) but right now not necessarily what is good for the system owner who only reaps the benefit from total kWh production.

    Aside: I really want that guy's job! What a cool assortment of toys he has to play with!
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Re: Should Solar Face West not South?

    East, South, or West,
    Whichever is best
    For your situation:
    Use that declination.
    :D
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  • bill von novak
    bill von novak Solar Expert Posts: 891 ✭✭✭✭
    #6
    Re: Should Solar Face West not South?
    RSSfeed wrote: »
    A new study from Austin’s Pecan Street Research Institute finds that residential solar PV panels oriented to the west may have more benefits for homeowners — at least in the summer and in Austin, Tex.

    And in San Diego due to morning clouds (June Gloom.) SW orientation is ideal.
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  • DaveB
    DaveB Solar Expert Posts: 48 ✭✭✭
    #7
    Re: Should Solar Face West not South?

    I could easily see this as being beneficial for off-grid users. In the summer months I would be producing almost no power from the PV panels when I get up even though the sun is well above the eastern horizon. My electricity usage would then typically drop before the south facing panels finally get the sun. This is why I was thinking of a Wattsun tracker but it may be more economical and reliable to have some panels facing east and/or some west for evening peeks. My first question would be, do you use a single charge controller for the east/west facing panels as the south facing panels?

    Also, if you are using top-of-pole mounts like I am then you can simply turn the west/east facing panels to a more southerly direction for the winter months.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #8
    Re: Should Solar Face West not South?

    In theory, a single MPPT controller should be OK...

    In practice, one engineer that designed MPPT controllers said that he saw substantial improvement if there was a separate MPPT controller per array (i.e., one controller for "east" facing, and a second controller for a "west" facing array).

    Basically, the MPPT controller is, mostly tracking array Vmp which is temperature dependent (Vmp falls as arrays get hotter). If you have different arrays operating at differing temperatures, then there is no "one Vmp:Imp" operating point that is best for both arrays (i.e., the array facing the sun and/or with worse ventilation will be hotter, and need a lower Vmp for optimum Pmp=Vmp*Imp).

    If you have a small system running a PWM controller--Then there is no issue... You have have different panel orientations feeding one PWM controller and there should be no issues (as long as the controller is large enough for the array maximum current, and the Vmp-array is appropriate for the battery bank+PWM controller requirements).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #9
    Re: Should Solar Face West not South?
    DaveB wrote: »
    I could easily see this as being beneficial for off-grid users.
    <snip>
    Also, if you are using top-of-pole mounts like I am then you can simply turn the west/east facing panels to a more southerly direction for the winter months.

    I also have a top-of-pole mount. I find that during the spring and summer months (the sun rises north of east) that tilting the panels so that they are almost horizontal gives me a longer charging day, although with reduced mid-day peaks. It also works well to pick up "cloudshine" on overcast days. When the panels are so close to horizontal, there is not as much to gain by aiming east or west.

    I certainly wouldn't do this if I were grid tied, but being off-grid, my goal is NOT to produce the most power each day... my goal is to keep my batteries charged as long as possible. A longer charging day meets this goal for me.

    Of course, virtual tracking (an east AND a west facing array) accomplishes the same goal (longer charging day). Some folks use a much smaller array facing west because by mid afternoon they are well into absorb or float.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • RandomJoe
    RandomJoe Solar Expert Posts: 472 ✭✭✭
    #10
    Re: Should Solar Face West not South?

    My off-grid system has most panels facing west. Not because of some calculation, but because that's what I have for roof space. Of 2000W in panels, 500W face south and 1500W west. They are wired in four 500W strings and all are tied to the same FM80 CC.

    Never noticed the FM80 having a problem with it, and I get the expected wattage in full summer sun. Winter is tough for me anyway, as even if I could have everything face south the sun dips behind tall trees in the neighbors' yards before the end of the day.

    I ran my setup through the online calculator (PVWatts?) one time and it actually showed I'd produce more over the year with the west-facing panels though I'd get less in winter months. Since I now use my system to load-shave during peak hours in summer - especially when running a mini-split AC mid- to late-afternoon - that's quite useful. Doesn't really matter either way, since I don't have any more south-facing roof space anyway!
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