SageBrush wrote:ltbighorn wrote:SageBrush wrote:A dumb question about units:

The x axis shows kVA units, but the numbers are from 0 to ~ 3500 (for the 3500 watt inverter)

Is that correct ? My understanding of electricity is pretty mediocre, and does not go much further than volts * amps = watts.

That's correct and works every time for D.C. power like you get from the panel itself. But the inverter produces AC power and the units for output "power" in AC is known as "VoltAmperes", or VA. That unit means the RMS value of the magnitude of the output power. So, how is that different from Watts? The difference is than in DC power there is no phase angle or any distortion in the waveforms. In AC, there can be both of these things, to the point that if the phase of the current is offset from the phase of the voltage by 90 degrees, no power actually flows. If the phase is more than 90 degrees out, power flows in the opposite direction. There are many different powers which can be calculated in AC systems depending on what you care about. I *think* (without looking it up) the power meter on your house measures the real component of the power which flows (ignoring the imaginary component which just basically just sloshes back and forth and heats up their wires). So, if your inverters do not produce the current in-phase with the voltage, the VA will be higher than the power that is delivered.

Modern solar inverters typically DO produce output current in phase with the voltage waveform, but many, such as the new S280, can be used by the power company to help them correct for problems they have with phase angle. If they do that, the VA out will be higher than the power you get credited for delivering. The efficiency curves will be dictated by the higher VA number.

So, yes, the correct units are VA (or kVA), but in your application, you can just think of kVA as KW and you'll be in good shape.

Aren't you glad you asked?