Solar Power and Grid tie-in help

Discussion in 'General Electronics Chat' started by t00t, Jun 4, 2015.

  1. t00t

    Thread Starter Member

    Jan 22, 2015
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    Have been reading up on solar power .

    There is a thing I do not understand .

    1) I know for the grid tie-in to happen you need an inverter to change DC to AC and make sure you have the same 60Hz . Thing is I cannot understand how in electrical terms do you feed the power back ? From what I know power substations do not store electricity right ? So how is it exactly that the power get feed back to the grid ?

    Thank you
     
  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    The power doesn't get stored anywhere, but used as you produce it by other customers.

    Power you make and supply to the grid need not be produced by the utility, that is why they "buy" it from you.
     
  3. t00t

    Thread Starter Member

    Jan 22, 2015
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    Yeah but unless there is a wire connecting me to my neighbor else I don't see how can the power goes over .
     
  4. Externet

    AAC Fanatic!

    Nov 29, 2005
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    Without having studied it, I would say the frequency has to be perfectly synchronized in phase and the voltage outputted by the inverter has to be a tiny bit higher than the present in the mains in order to inject it back.

    There is a new trend to use micro inverters that usually attach to the back of each solar panel, and connect directly to mains. Search for micro inverters.

    There is a wire connecting you and the neighbors. Your wall outlet connects to your power meter and then to the power pole and then to the neighbors meters and to their outlets.
     
  5. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    grid tie inverter systems synchronize with the 60 Hz grid power and feed into your electric panel by slightly raising the voltage above the level present on your utility service lines.
    They will NOT work to provide you electric power in cases of a grid service interruption. If the grid goes down the inverter shuts down as well
     
  6. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    By direct connection. You literally plug your inverter into the mains. If your inverter output voltage is higher than the mains voltage, current will flow *into* the mains. The voltage difference can be small, and the inverters I've seen do the adjusting automatically.

    ak
     
  7. wayneh

    Expert

    Sep 9, 2010
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    I had wondered about this same question and assumed this explanation is the only one that could work; in phase but higher amplitude.

    But I'm still wondering about the details. Does the local inverter apply, say, 121V to a 120V supply? Or more like 125V?

    On one hand it seems like you'd need a reasonable excess ∆V to move much power "uphill". But on the other hand the supply must have an impedance approaching zero, so it can sink enormous current without much of a ∆V. If you were changing the voltage of the supply even a small amount, it seems like that would create problems for your neighbors.
     
  8. t00t

    Thread Starter Member

    Jan 22, 2015
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    So in electron terms , when I feed power back the electrons in the wire ( current ) flows to my neighbor's house ?

    So in AC voltage terms, when i get a + 230 V my neighbor is getting a - 230 V ? and some of the -230 V is from the solar panel ?

    Thank You
     
  9. crutschow

    Expert

    Mar 14, 2008
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    The power from the inverter goes into the grid and basically disappears as part of the power on the grid.
    The extra voltage required by the inverter to push the current into the grid is just to overcome whatever wire resistance there is between the inverter and where it ends up being used by other customers. Most of this resistance is likely from the wiring between the inverter and the neighborhood distribution transformer.
    Typically this extra voltage would be quite small.
    The voltage at the customers is infinitesimally unchanged by this.
     
  10. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    your inverter becomes just another generator like your utility company uses, just much smaller. any local perbutations are swampped by the large capacity of the power grid. how excess power is distributed back onto the powerlines is academic, it could be flowing among large numbers of local outlets around you as appliances and lights are switched on or off, always changing
     
  11. wayneh

    Expert

    Sep 9, 2010
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    All makes good sense. I guess the local grid-tie inverter monitors and controls how much current is being placed onto the grid? The small excess voltage driving this current just goes where it needs to?
     
  12. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    I can guarantee you that wire is already there.

    What do you think the power grid is anyway?
     
  13. crutschow

    Expert

    Mar 14, 2008
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    The excess voltage is dropped in the line resistance between the inverter and the grid.
     
  14. t00t

    Thread Starter Member

    Jan 22, 2015
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    Can you try and explain the academic part ? That is the part I am asking about . Thank you .
     
  15. ian field

    Distinguished Member

    Oct 27, 2012
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    One of the Australian magazines said something about the inverters slightly leading the phase of the mains to avoid a large number of inverters installed in an area pushing the voltage up over tolerance.

    Didn't really absorb the details, I was only glazing over the article out of idle curiosity.
     
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