Measurement of kWh: Sunpower Inverter vs Revenue Grade Meter

[Ian S]

Okay, my little test has been going for over two days now: comparing kWh displayed on my Sunpower 7000 inverter vs that displayed on the meter that APS installed to measure my production. The latter is a separate smart meter from the one used for billing purposes. Both the inverter and the production meter keep track of total kWh produced but as others seem to have found discrepancies between output measure independently from their inverter, I thought I'd see if there was a similar issue with my Sunpower inverter. Technique was simple: wait for the APS meter to cycle to the total kWh display and record it then immediately go to the inverter and record what it displayed

APS meter: Start 26480 kWh - End 26564 kWh. Change: 84 kWh
SP Inverter: Start 36404 kWh - End 36488 kWh. Change: 84 kWh

So far, the correlation looks fine but I'll report back maybe after a couple of weeks observations.

[J.P.M.]

Okay, my little test has been going for over two days now: comparing kWh displayed on my Sunpower 7000 inverter vs that displayed on the meter that APS installed to measure my production. The latter is a separate smart meter from the one used for billing purposes. Both the inverter and the production meter keep track of total kWh produced but as others seem to have found discrepancies between output measure independently from their inverter, I thought I'd see if there was a similar issue with my Sunpower inverter. Technique was simple: wait for the APS meter to cycle to the total kWh display and record it then immediately go to the inverter and record what it displayed

APS meter: Start 26480 kWh - End 26564 kWh. Change: 84 kWh
SP Inverter: Start 36404 kWh - End 36488 kWh. Change: 84 kWh

So far, the correlation looks fine but I'll report back maybe after a couple of weeks observations.

Thank you.

[Ian S]

Update: After 24 days, The APS meter is reading 27460 kWh for a total change of 980 kWh while the SunPower inverter is reading 37387 kWh for a total change of 983 kWh. So the inverter is about 0.31% high compared to the utility meter.

[J.P.M.]

Update: After 24 days, The APS meter is reading 27460 kWh for a total change of 980 kWh while the SunPower inverter is reading 37387 kWh for a total change of 983 kWh. So the inverter is about 0.31% high compared to the utility meter.

Looks to be fair agreement. You got a good one.

[SunEagle]

Update: After 24 days, The APS meter is reading 27460 kWh for a total change of 980 kWh while the SunPower inverter is reading 37387 kWh for a total change of 983 kWh. So the inverter is about 0.31% high compared to the utility meter.

I would call that close enough to both "meters" being pretty accurate. Of course that 0.31% difference might grow over multiple months. Keep us informed of your measurements.

[Sunking]

Well within tolerance

[sensij]

I would call that close enough to both "meters" being pretty accurate. Of course that 0.31% difference might grow over multiple months. Keep us informed of your measurements.

Yes... a pair of Class 0.2 revenue meters could disagree by more than that and still be in compliance. Based on PVOutput data, I suspect this result would replicate for many or most SMA inverters, but have no firm examples to support it.