Do you need a consumption meter to know your monthly (not real time) usage?

[Mike90250]

A GT inverter works by trying to raise the line voltage just a hair above the grid voltage. Thus, it pushes current out toward the grid. If, between the GT inverter and the service entrance point where the grid enters the home, local loads consume some of the power, a reduced amount of the production will get to the grid to spin your meter backwards. If you have no local loads, then the grid will consume all the PV production.

[foo1bar]

That is where I disagreed with DrLumen, who said, "Mechanically, when you are producing power and using it, you are pulling from your array and the grid simultaneously as they are set in parallel in a typical system. You just aren't pulling as much from the grid. It is likely half-and-half if your consumption is equal to what you are producing at that moment. But, in that instance, the other 'half' is going to the grid."

That would be inconsistent with what I have observed. If your consumption is equal to your production then there is nothing going to the grid or anything flowing to the grid.

I do not know for sure what the sentence you quoted is intending to say. (and I didn't look back to check if the quote is accurate).
I think it could be interpreted as "When I am consuming 20A in appliances, hair driers, etc, and the solar panels are producing 15A, then the meter will show 5A flowing in from the POCO"
And "Sometimes you'll be consuming more than you produce and be pulling in power from the grid. Sometimes you won't. When you're using less than your panels produce, the excess is going to the grid."
I think the "half-and-half" and "other-half" verbage is confusing or can be misinterpreted.

As for your statement -
I agree that IF your consumption is equal to your production there is no current flowing to or from the POCO.

One way you can calculate things is to model each side (production and consumption) separately. And then just sum (including signs for the direction) the currents flowing through the line to the POCO. (which is also through the POCO meter)

For example, in the case where consumption is 10A@240V, and production is 10A@240V, your sum is 10A + -10A = 0A.


Because it's single phase (US residential), and I'm simplifying the example to where it's equal currents on the two 'hot' wires, this summation is very simple. But it wouldn't be much different with a 3-phase system like we see in many commercial buildings.

[Ampster]

A GT inverter works by trying to raise the line voltage just a hair above the grid voltage. Thus, it pushes current out toward the grid..........

Thank you @Mike90250 for adding that important aspect that explains the physics. I regret leaving that out of my explanation. The higher voltage if the inverter will flow to the loads and when the loads are satisfied the balance will go out through the meter to the grid.