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Thread: Inverter Running at 66% or Transformer

  1. #21
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    Cherry Valley NY, Seattle, WA
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    Quote Originally Posted by pv_n00b View Post
    The general rule of thumb is that there is little penalty for bucking and a more significant penalty for boosting..... and a 240Vac system needs ±340Vdc. Just ballpark figures but it gives an idea.

    So here in the northeast where it's cold, some quick and dirty calcs show it's actually tough to keep array voltage above the peak voltage for a 240v system with 600 volt strings.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

  2. #22
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    Quote Originally Posted by electrofelon View Post
    So here in the northeast where it's cold, some quick and dirty calcs show it's actually tough to keep array voltage above the peak voltage for a 240v system with 600 volt strings.
    Funny, I always thought that the string voltages (both VOC and VMP) rise as temperature decreases. That is why you need to know the minimum operating temperature (usually just after dawn on a clear winter night) and the temperature coefficient of voltage with temperature to make sure that the maximum input voltage of the inverter is not exceeded.
    Or do you mean that by keeping the winter voltage safe you are perhaps reducing the summer noon voltage below the minimum operating voltage?

  3. #23
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    Quote Originally Posted by GoldDigger View Post
    Funny, I always thought that the string voltages (both VOC and VMP) rise as temperature decreases. That is why you need to know the minimum operating temperature (usually just after dawn on a clear winter night) and the temperature coefficient of voltage with temperature to make sure that the maximum input voltage of the inverter is not exceeded.
    Or do you mean that by keeping the winter voltage safe you are perhaps reducing the summer noon voltage below the minimum operating voltage?

    Yeah the latter. Figuring around -25 F for a low and hot summer day in the sun around 130 results in a very wide voltage range.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

  4. #24
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    Quote Originally Posted by electrofelon View Post
    Yeah the latter. Figuring around -25 F for a low and hot summer day in the sun around 130 results in a very wide voltage range.
    That's why the first generation SMA transformerless inverters were such a pain here in Texas. Usually there was only one string length that would work, and even then if the grid were to glitch in the middle of the day the PV system would not restart until the next morning.

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