Need a little help...

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johnT
johnT Registered Users Posts: 15 ✭✭
in Solar Beginners Corner #1
I have a friend who is getting ready to set up his solar panels, and is planning on turning them east, or just slightly southeast. His reason is because someone told him that his batteries will be at their lowest state of discharge first thing in the morning, so turning them east would get them charging/charged quicker. I have tried to explain why true south is way to go, but he seems stuck on it for some reason (I am still a beginner myself, so can't blame him for not taking my word on it). I thought maybe if I could get anybody here to write a beginners version of "why south" then I could show him different peoples views/opinions and it might turn him around before it's too late. I should mention he has total control over which way they will end up facing, so he CAN point them south, he is just choosing not to at this point. thanks
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
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    Re: Need a little help...

    I hate to tell you this but your friend may well be right, depending on what is usage patterns are and how far East the pnels are twisted.

    Yes, panels will out out their maximum if pointed solar South. However, on an off-grid system this means you get peak production midday when the batteries may already be charged from morning sun anyway and there may not be any loads to run. Hence the reasoning behind a little earlier exposure to get the charge cycle start (and completed) sooner.

    However, this just means you shift the 'midday power surplus' to a different time of day; you may still have power available that you can't realize because there's no place for it to go. This is why trackers were invented; to gain total Watt hours over the day.

    The 'new' solution to this has been nicknamed "stationary tracking" and involves dividing up the array so that there's charge current available as soon as possible followed by enough panel facing South and even Southwest so the output through the day can sustain Float until there's not enough sun.

    Simple? No, it's not. :roll:
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #3
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    Re: Need a little help...

    he may be right only to a point. if near the ocean reflections can add to the power harvested (new word to use that i like thanks to another poster). now the main direction of south has the highest overall solar intensity and is close to the center of the day allowing the most collection unless there are storms in the afternoon then by all means swing it more easterly.

    due east i would not do as that would put the mid-day sun at 90 degrees off the pvs and no direct solar insolation will occur at the best time of the day. if one is concerned with putting more in sooner then a slight easterly twist is fine by up to around 20 or so degrees, but i would go no more than 10-15 degrees to capitalize on the better solar intensities of the mid-day. if he has morning rains/fogs then do not aim easterly, but if i miss my guess here you would probably have storms primarily in the afternoon times and the best sun up to the mid-day so 10-15 degrees more easterly off of true south is still good. also, do not go by magnetic north/south as that has errors from the true north/south and needs to be compensated for.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #4
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    Re: Need a little help...

    There are various programs to predict solar output... PV Watts is one of the simplest to use. Just pick a station nearest to you (with similar weather patterns). And it takes into account local weather patterns (if you have afternoon thunder showers, point the array a little bit east of south can generate more power--for example).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • gww1
    gww1 Solar Expert Posts: 963 ✭✭
    #5
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    Re: Need a little help...

    Which effects power most? coolness of the morning or fog in the morning?
    thanks
    gww
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #6
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    Re: Need a little help...

    Coolness may gain you 5-10%... fog will cut you by 50-95+% (depending on how deep the marine layer is in you area).

    With PV Watts--They do have an "hour by hour" output you can load into a spread sheet. The data is actual "typical" day measurements--So you can probably find one of the typical days with morning fog/overcast and see how much it reduces the output.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • gww1
    gww1 Solar Expert Posts: 963 ✭✭
    #7
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    Re: Need a little help...

    Bill
    Thanks
    gww
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