Understand grid tie system but...

K4ERT
K4ERT Registered Users Posts: 3
in General Solar Power Topics #1
I understand a grid tie system but could someone answer this? Our power company puts in a special meter. What allows this meter to use power I generate before using the grid supplied power. Both are fed into my breaker box,one at top the other at the bottom. I know it works but what makes it work?

Thanks

8 et 250 panels, solaredge 3000 inverter
· Share on Twitter

Comments

  • SkiDoo55
    SkiDoo55 Solar Expert Posts: 414 ✭✭✭
    #2
    Re: Understand grid tie system but...

    Meters are set up to only record in one direction Only. One meter measures power from the solar sytem and the other measures power from the grid.Some newer SMART meter do both internally. On my monthly statement Grid consumption is on Channel "A" and power flow back to the grid is on channel "C"
    GT3.8 w/4600W Trina 230W, TX5000 w/5000W ET-250W, XW4024 w/1500W ET-250W, 4 L16, 5500W Gen. (never had to use) Yet!!
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
    Re: Understand grid tie system but...

    Welcome to the forum.

    The only thing special about the meter is that it is bi-directional, allowing it to record any power pushed back to the grid as well as what your household pulls from the grid.

    There's no magic to grid-tie: it is simply two power sources connected to the same loads. If the output of your GTI is exceeded by the household load demands the additional power needed comes from the grid. If the output of your GTI exceeds the household load demands the surplus power goes back to the grid. All easy and automatic with no wasted solar power potential.
    · Share on Twitter
  • K4ERT
    K4ERT Registered Users Posts: 3
    #4
    Re: Understand grid tie system but...

    How and I guess why is my power used before pulling from the grid? Guess I should not worry about how that part works!
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Re: Understand grid tie system but...
    K4ERT wrote: »
    How and I guess why is my power used before pulling from the grid? Guess I should not worry about how that part works!

    No, you shouldn't worry about it. :)
    I could say "because it's closer" but that isn't true.
    The real reason, simplified, is that as far as the GTI is concerned everything is a load including the grid. As far as the grid is concerned it operates bi-directionally, meaning it can be a load or a source. This is because they are two different types of power sources: the GTI is current-based, the utility grid is Voltage-based. So the GTI tries to push whatever current it can produce, and the grid tries to maintain 'X' Volts against varying load demand. So when the GTI produces current the grid registers this as decreased load demand. That decrease can not only go to zero, but into negative numbers as the grid accepts power from multiple generation sources. It may help to remember the grid does not use one power plant, but several all synchronized in frequency and Voltage. As far as it is concerned the GTI is another such source (albeit one that needs the grid to establish both frequency and Voltage).
    · Share on Twitter
  • K4ERT
    K4ERT Registered Users Posts: 3
    #6
    Re: Understand grid tie system but...

    Think I have a good idea how it works or maybe why it works! Thanks for the comments.
    · Share on Twitter
  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #7
    Re: Understand grid tie system but...
    K4ERT wrote: »
    Think I have a good idea how it works or maybe why it works! Thanks for the comments.
    Your inverter does not know or care whether the electrons it pushes out go to your household loads or out to the grid. A load is a load. If you are using more power than your inverter is putting out the power flow is from the grid into your house. If you are producing more than you are using, the flow is out onto the grid. Don't worry your pretty little head about it; it just works. :D
    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #8
    Re: Understand grid tie system but...

    Or look at gt like your car's electrical system.

    The alternator is the gt inverter. And your car battery is the equivalent to the utility grid.

    Loads are drawing current. They draw from the battery if the car is not running. With the alternator turning, the battery and the alternator share the loads. And as the alternator turns faster, the excess current recharges the battery.

    The utility grid looks almost exactly like a giant AC battery bank and the utility meter keeps track of the energy flow between the house and the utility (both amount of energy and the direction)

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • solarvic
    solarvic Solar Expert Posts: 1,071 ✭✭✭✭
    #9
    Re: Understand grid tie system but...

    I just recently learned how my smart meter measures and how the kwh are metered. Meter has reading a and reading b. Reading A is the kwh you use in your house. Reading b is kwh you generated. If you generate more kwh in reading b than you used in reading a you get the excess kwh credited to your account. For me nov. dec. jan. I use more electric than I generate. For the 3 months of low production kwh will be subtracted from my account. Last year I had to big of a surplus built up in my account so electric co. bought my excess on April bill and credited my account in money value which covered over 4 months of my monthly fee So this year I have been trying to burn up the extra electric so I don,t have an excess. My electric co only paid me wholesale price for the settlement last april. It works out for me as the production of my gas well is declining fast and I have been burning the excess electric to prolong the well a little longer. solarvic
    · Share on Twitter
  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #10
    Re: Understand grid tie system but...
    solarvic wrote: »
    I just recently learned how my smart meter measures and how the kwh are metered. Meter has reading a and reading b. Reading A is the kwh you use in your house. Reading b is kwh you generated.
    How would a single meter on your service know how many kWh you generated? It knows how many kWh flow which way through it, but how would it know whether you generated 100kWh and used 200kWh (net 100kWh from the utility) or used 100kWh and produced nothing (also net 100 kWh from the utility)?
    · Share on Twitter
  • SkiDoo55
    SkiDoo55 Solar Expert Posts: 414 ✭✭✭
    #11
    Re: Understand grid tie system but...

    It just records the directional current flow and records that on separate channels that is recorded and transmitted to the utility. It's like having two separate analog ratcheted watt meters.
    power purchased on one channel
    Power sent to grid
    A minus B = NET Power
    GT3.8 w/4600W Trina 230W, TX5000 w/5000W ET-250W, XW4024 w/1500W ET-250W, 4 L16, 5500W Gen. (never had to use) Yet!!
    · Share on Twitter
  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #12
    Re: Understand grid tie system but...
    ggunn wrote: »
    How would a single meter on your service know how many kWh you generated? It knows how many kWh flow which way through it, but how would it know whether you generated 100kWh and used 200kWh (net 100kWh from the utility) or used 100kWh and produced nothing (also net 100 kWh from the utility)?

    Your right, all they can see is what you actually pushed back into the grid, unless you are like my utility, they put a second smart meter on my solar output. No guerrilla add on here! :-):cry: (although I am setup for it in the back-feed).
    · Share on Twitter

Categories