Calculating Watts AC?

[fafrd]

I’m embarassed to have such a newbie question, but I’m attempting to validate results being reported by my Microinverter gateway and would appreciate clarification on a detail that still leaves me confused:

Is Watts AC calculated as Volts AC x Amos AC or is there some correction factor such as when converting VoltAmpsDC to Watts AC?

My gateway is reporting:
VoltsAC = 249.4VAC
AmpsAC = 0.98A
Power = 265.211W

249.4 x 0.98 = 244.412, so I’m struggling to understand the 7.84% / 20.8W gap to the higher output power that is being reported…

 

[sunshine_eggo]

Watts is always Volts * Amps.

The differences you're seeing may be due to sampling rate, i.e., values are not read/computed at the exact same moment.

 

[fafrd]

Watts is always Volts * Amps.

Thanks, that’s what I thought but reached the point I decided I should confirm.

The differences you're seeing may be due to sampling rate, i.e., values are not read/computed at the exact same moment.

It’s a consistent delta on all measurements throughout the day (and with the gap always in the same direction).

 

[sunshine_eggo]

You're saying Power always reads 15W lower than calculated?

Difference between production and consumption, i.e., the microinverter itself is consuming 15W?

 

[fafrd]

You're saying Power always reads 15W lower than calculated?

Difference between production and consumption, i.e., the microinverter itself is consuming 15W?

The one Microinverter I just checked now has ‘power’ of 230W while VAC x AAC = 183W, so a 20% or 47W gap…

You are thinking ‘power’ represents Vdc x Adc? That would translate to inverter efficiency of 79.4% versus specification of 95.5% (CEC efficiency)…

 

[Mike 134]

When I look at the Energy reported on the inverter web site one display always reads 10% higher than a different page which matches what my wattmeter measures. You'd think the vendor could at least get the numbers to match on their website.

 

[OzSolar]

Watts is always Volts * Amps.

The differences you're seeing may be due to sampling rate, i.e., values are not read/computed at the exact same moment.

AC watts = V x A x Power Factor which often is above .9 so give or take most of the time I ignore PF but I don't forget it's there. So... yeah.. V x A = W for most of the things most of us do most of the time.

I've had a few conversations with some manufacturers over the years about the accuracy of thier meters. More times than not they point out that highly accurate meters will add (significant- implied) cost to their products and some have even offered that if they had thier choice they wouldn't even give us metering because of the people that complain about meter accuracy are most often the worst customers. LOL

Edit: to fix some typos