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Thread: PV feeder voltage drop - California

  1. #21
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    Break apart into strings

    You can always break your array into multiple strings, with one line to each, to reduce your voltage drop.

  2. #22
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    Quote Originally Posted by ESolar View Post
    You can always break your array into multiple strings, with one line to each, to reduce your voltage drop.
    Well, yes, but then you have a lot of parallel wires. It adds up to a lot of wire one way or the other.

  3. #23
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    Quote Originally Posted by ggunn View Post
    How can something be worse than a worst case?
    You're asking how can a number be larger than the largest number that represents real world possibility? I think you should reread the thread. There's always a number that's larger (or smaller) than the one you should be using.

  4. #24
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    Quote Originally Posted by jaggedben View Post
    You're asking how can a number be larger than the largest number that represents real world possibility? I think you should reread the thread. There's always a number that's larger (or smaller) than the one you should be using.
    I'm not sure what you are driving at. The maximum current that an inverter can produce is documented, and if you use that number to calculate Vd that's the worst it can be. Higher numbers of course exist, but who cares? What am I missing?

  5. #25
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    Quote Originally Posted by ggunn View Post
    I'm not sure what you are driving at. The maximum current that an inverter can produce is documented, and if you use that number to calculate Vd that's the worst it can be. Higher numbers of course exist, but who cares? What am I missing?
    You're missing that the OP's array will never deliver that much power in his case. (Maybe they are planning for future expansion, that's the only reason I can figure for the inverters being so oversized. )

    It's a pithy point, but it underscores pv_noob's observation that there's no firm guidance on the number to use.

  6. #26
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    Quote Originally Posted by jaggedben View Post
    You're missing that the OP's array will never deliver that much power in his case. (Maybe they are planning for future expansion, that's the only reason I can figure for the inverters being so oversized. )

    It's a pithy point, but it underscores pv_noob's observation that there's no firm guidance on the number to use.
    Ah. I use the inverter nameplate current as a worst case scenario irrespective of how loaded the inverter is. When I said that I was responding to the general comment that there isn't any guidance for AC current, not specifically to the OP's system.

  7. #27
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    There was a time in the dark past, 20,000 PV years ago (10 real years) when PV modules were so expensive that inverters were always sized to prevent clipping and therefore were under producing 99% of the time. Under those conditions there was more flexibility in doing voltage drop calculations using less than the max inverter AC output. Now that people are using 1.5 DC/AC ratios we can assume the inverters will be putting out 100% most of the time. So using the max AC output current is more of a given.

    But we still run into the odd ball once in a while. I saw a design a few months ago that was using 3kW out of a 30kW inverter.

  8. #28
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    Quote Originally Posted by ESolar View Post
    You can always break your array into multiple strings, with one line to each, to reduce your voltage drop.
    I don’t think so..

    lowering the voltage on the string will lower the volts dropped but the VD% will stay the same.

    The only way to lower the VD% is to lower the impedance (bigger or shorter wire) or lower the amperage (smaller modules)

    at 10 amps, the VD% over a given wire will be the same at 1 volt or 1,000 volts.

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