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Thread: Enphase Micro Inverter Operation

  1. #31
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    Quote Originally Posted by Smart $ View Post
    No argument. I agree with you. But as a current source, it has to develop a voltage high enough to push that current into a charged system. Let's say the PV system has 2400W available. Local loads are all off. Service voltage is 240V and the inverter "sees" a system impedance of 5 ohms to the grid (includes service transformer). What voltage must be developed at the inverter's terminals to output the entire 2400W (ignoring I²R losses) onto the grid?
    I am not saying that voltage rise does not exist, but in an ideal circuit a current source is perfectly happy to deliver current with a zero voltage differential. Yes, I know that the real world is not ideal and a PV powered inverter is not an ideal current source, but the distinction is, IMO, an important one. It is central to understanding the answer to what is probably the most often asked question about solar power - why a grid tied system must not keep running when the grid goes down. It's not just because it's illegal.

    Current sources can be hard for some folks to wrap their heads around because virtually all the power supplies we come into contact with (batteries and grid power) act as voltage sources and deliver current on demand.

  2. #32
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    Quote Originally Posted by ggunn View Post
    I am not saying that voltage rise does not exist, but in an ideal circuit a current source is perfectly happy to deliver current with a zero voltage differential. Yes, I know that the real world is not ideal and a PV powered inverter is not an ideal current source, but the distinction is, IMO, an important one. It is central to understanding the answer to what is probably the most often asked question about solar power - why a grid tied system must not keep running when the grid goes down. It's not just because it's illegal.

    Current sources can be hard for some folks to wrap their heads around because virtually all the power supplies we come into contact with (batteries and grid power) act as voltage sources and deliver current on demand.
    Okay
    I'll never get there. No matter where I go, I'm always here.

  3. #33
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    Quote Originally Posted by ggunn View Post
    Current sources can be hard for some folks to wrap their heads around because virtually all the power supplies we come into contact with (batteries and grid power) act as voltage sources and deliver current on demand.
    Uh, no. Grid tied systems can, and have, run without the grid. The AC output stage matches volts and cycles to the load and merrily keeps on putting out power. This was not unheard of back before UL1741 came along.

    For some gear, if you can produce a load that looks like the grid (load, not "source"), it will also merrily keep making power.
    Julie in Austin

    Born to brew, forced to work ...

  4. #34
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    Quote Originally Posted by tallgirl View Post
    Uh, no. Grid tied systems can, and have, run without the grid. The AC output stage matches volts and cycles to the load and merrily keeps on putting out power. This was not unheard of back before UL1741 came along.

    For some gear, if you can produce a load that looks like the grid (load, not "source"), it will also merrily keep making power.
    Uh, not exactly.


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    I'll never get there. No matter where I go, I'm always here.

  5. #35
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    Quote Originally Posted by tallgirl View Post
    Uh, no. Grid tied systems can, and have, run without the grid. The AC output stage matches volts and cycles to the load and merrily keeps on putting out power. This was not unheard of back before UL1741 came along.

    For some gear, if you can produce a load that looks like the grid (load, not "source"), it will also merrily keep making power.
    With all due respect, I don't see how this could be, but I am always looking to expand my understanding. Can you point me to a reference?

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