Anyway, to the matter at hand: the Fronius does sound like it's keeping a record of what's being collected; for now we will believe what it says. The other meter, installed by the power company, is telling you what? Does it directly read 540 KWh or does it read something else? You did some calculations that didn't go anywhere. If the meter displays kiloWatt-hours, then the voltage doesn't matter much to its reading.
You're concerned about a fairly large loss; 174/714 = 25% You haven't given enough information to know if that's all due to the transformer. The step-up transformer needs a 1:5 ratio to go from 120 to 600 volts. There probably is a loss through that transformer. Can you tell us more about how the Fronius manages the grid-tie connection? Does it shut itself down at night? Does the inverter collect other data about power output? Steven Fahey
