Chatted some more details on this over the week.
I have a ponderance that I was hoping someone with knowledge of billing/revenue meters to speak to.
Since we are designing this to work on a US Grid Connected US 240/120 Volt "split-phase" system, we should know how the billing meter really works and reads the energy use, and when getting into the detail portions, I know that I do not know those details.
Per Wiki, the billing formula is:
http://en.wikipedia.org/wiki/Electricity_meterWh = V(IA-IB)/2.
Of course, that being Wiki (which I like . . . . however), it may or may not be the case, and your mileage may vary.
My concern is for an unbalanced load being used at the metering point, and then putting a balanced source (such as inverter) into the mix -- how does one cross from the overall billing consumption range and into the net generation range?
Let me try some numbers for an example --
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Starting point -- No Local Solar/Wind/Inverter Generation.
On Leg A we are using 30 Amps, on Leg B we are using 10 Amps.
Per the equation above, the meter should be showing:
Watts = Volts X (A Amps - B Amps) / 2
Or nominally -- 240 X (30 - 10) / 2 -> 240 X 20 / 2 = 2400 watts.
Does this seem reasonable as Leg A = 120 volts X 30 amps = 3600 watts and Leg B = 120 volts X 10 amps = 1200 watts, for a A + B total of: 4800 watts?
I think wiki must have been trying to say: Watts = V X (IA + IB) / 2.
Otherwise, by the Wiki math, say we were drawing 100 amps on each leg, at 240 volts -- our power use would be metered as zero!?!?
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But let's say W= V X (IA + IB) / 2, and go on with that existing unbalanced load and throw in our local generation.
We turn on our 5000 Watt inverter and start making our local generation. That should be near 20 amps on each of Leg A and Leg B.
So now at the billing/meter point we have:
Leg A = 30 amps being used - 20 amps being generated = 10 amps still being used.
Leg B = 10 amps being used - 20 amps being generated = 10 amps being produced.
So the math for the metering comes out:
Watts = 240 X (+10 + (-10)) / 2 = Zero.
So have we reached the (metering/billing) point of balance while we are still drawing 10 amps on one leg, if at the same time, we are sending up 10 amps on the other?
Any one have any idea if this is really how Billing/Metering really works? Especially with the new electronic DRG (distributed renewable generation) Meters?
Thanks!