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Thread: California to require solar panels on all new homes

  1. #51
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    Quote Originally Posted by ggunn View Post
    True enough, but how would you get the inverter output to track the load?
    It would not be trivial, but IMHO would be do-able.

    You could not simply set the inverter for constant voltage output, because you would also need to manage the array voltage so that the power output of the array would match the power consumption of the load.

    This might simply 'magically' work if the array voltage is being bucked in the inverter to produce output. If you are on the part of the power curve where current drops if voltage increases (out of the part of the IV curve where the array looks like constant current) then if the load drops, the array voltage will go up and its power will go down. Sounds reasonably stable to me.

    If you are on the constant current part of the power curve, then you need an inverter that can deal with the fact that the system is _unstable_; if the output power drops, then the array voltage will increase leading to more power from the array. You would either need a dump resistor, or be very very smart about quickly increasing output voltage (slightly, still in tolerance) to increase output power faster than array power is increasing, and get back to the target steady point.

    Hmm. I think I know which part of the power curve I would use

    -Jon

  2. #52
    Join Date
    Jun 2004
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    Cherry Valley NY, Seattle, WA
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    Quote Originally Posted by winnie View Post
    You could not simply set the inverter for constant voltage output, because you would also need to manage the array voltage so that the power output of the array would match the power consumption of the load.
    But with PV we can just open circuit it if we dont need/want the power. GTI's already do this if array power exceeds inverter capability.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

  3. #53
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    May 2011
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    Quote Originally Posted by ggunn View Post
    True enough, but how would you get the inverter output to track the load?
    FWIW, this isn't so hard in a grid tied situation either. Just put a meter at the point of entry to the house (or wherever you're trying to reduce the load to zero).

    SolarEdge's StorEdge inverter will do this. You can set an export limit, the limit can be zero, and it will do a decent job of matching inverter output to local load with no exports. You'll get a few watts going back and forth but nothing the utility would be likely to care about.

  4. #54
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    Oct 2009
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    The bottom line for me is that as a PV design engineer I am limited to designing systems with equipment that actually exists. If and when someone comes out with a GT inverter without batteries that will merrily keep supplying power when the grid goes away, I'll use it. Until then, conjecture is fun but that's all it is.

    I'll just add that I believe that the odds of us (most of us with limited exposure to PV systems) coming up with an inverter design concept which hasn't been considered by the design engineers at all the inverter companies in the world are vanishingly small.

  5. #55
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    Oct 2007
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    Quote Originally Posted by ggunn View Post
    The bottom line for me is that as a PV design engineer I am limited to designing systems with equipment that actually exists. If and when someone comes out with a GT inverter without batteries that will merrily keep supplying power when the grid goes away, I'll use it. Until then, conjecture is fun but that's all it is.

    I'll just add that I believe that the odds of us (most of us with limited exposure to PV systems) coming up with an inverter design concept which hasn't been considered by the design engineers at all the inverter companies in the world are vanishingly small.
    What is the raw, unsubsidized by any credit, off-set, or government-largess-of-any-kind cost for a 3kW array on a south-facing, second story, simple roof in your area? Grid-tied only. Here in NJ I hear numbers of around $30,000.

  6. #56
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    May 2011
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    Quote Originally Posted by gadfly56 View Post
    What is the raw, unsubsidized by any credit, off-set, or government-largess-of-any-kind cost for a 3kW array on a south-facing, second story, simple roof in your area? Grid-tied only. Here in NJ I hear numbers of around $30,000.
    I think you must mean a 10kW array.

    For a 3kW array around here it would be about $10,500, installed. There are economies of scale.

  7. #57
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    Oct 2009
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    Quote Originally Posted by jaggedben View Post
    I think you must mean a 10kW array.

    For a 3kW array around here it would be about $10,500, installed. There are economies of scale.
    It's not my department but I would agree that ~$3/W will get you pretty close.

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