Q: How does an inverter know what to do: Answer:
Q: How does an inverter know what to do: Answer:
Thanks for the info. I guess my question is in theory with the solar panels connected to the grid how does the resetential system know to push power out to the grid rather than pull it in from the grid? So if two sources (utility and solar panels) are both tied together then why does the home take all of its power from the solar and none from the grid if avalaible. How is it in theory that the excess power is able to be pushed out to the grid?
Does this have something to do with power system stability?
All a grid tie inverter does is push power back to the grid. It cannot power your home at all, if there is no utility. Your home is dependent upon the utility.
How it works is, briefly: The inverter is like a generator that syncs with the utility. If you try to speed it up, it will deliver more power to the utility; if you try to slow ot down, it will deliver less power. The inverter controls it own "speed" (phase) such that power it sucks out of the array and delivers to the utility causes the array voltage to drop (and the array current to rise) to the "Maximum Power Point", which is where the array is most efficient. This has nothing whatsoever to do with your house's consumption.
There are a couple of different types: (1) Dual Metering, and (2) Net Metering.
In dual metering, the PV inverter is connected through an "Export" meter direct to the utility drop though a breaker/AC disconnect. It does not go though your service panel nor your normal "import" electricity meter. You pay one price per KWH for the electricity you consume, as indicated on your "import" meter, and the utility pays you a different (lower) price for the KWHrs you have fed to the grid, as indicated on the "export" meter.
Now some states rightly thought it was so unfair to consumers that they should have to pay 10c/KWH for power they used but only get 5c/KWH for power they generated, that they mandated that utilities should offer the second system - net metering.
In Net Metering, the PV inverter is conncted to a breaker in the main service panel and feeds power back to the grid through your normal meter. So your meter registers the net difference (power used minus power generated) and you pay only for that. So you are effectively getting the same price for your own generation as you pay the utility. In theory, you could have enough panels on your house to gurantee that the meter went net backwards over a 12 month period. However, utilities have negotiated sweet deals with State Utility commissions that say they get to keep the excess over a 12-month period without having to send you a check.
It would seem feasible to have two service connections to your property e.g. one to the house and another to an outbuilding (barn or workshop) and ask for net metering on one and dual metering on the other, if you wanted the best of both worlds.
The above is for grid-tie. There is a whole 'nother type of system which can power your home in the absence of utility power called a "standalone" system, which requires a big storage battery charged by the array.