Wrenches.
I need some help on inverter sizing. In Montana we have a lot of
cold weather with bright sun. What about the following
With an array of 50 panels at 235-watts, I would select an 11.4 KW
string inverter. The string sizing chart says the 11.4 KW inverter
would be fine, but it also says a 10 KW inverter would be fine.
Best guess is that my nominal 11,750 watt DC array would make about
80% conversion to AC with irradiance of 1000 watts at 77°F, so
9,400 watts AC. Either inverter doing fine.
On a clear cool day insolation would still be 1000 watts, temp would
go to 0°F or -18°C, so my 11,750 watt DC array would be 14,217 watts
DC times 80% is 11,374 watts AC. 11.4 KW inverter working fine,
10 KW inverter ignoring over 10% of array.
We have pretty clear air and some high elevations, and code figures
possible plus 25% over nominal on irradiance. So possible 1200
watts irradiance and still moderately cold, 0°F, so 11,750 x 1.2 x
1.21 is 17,061watts DC times 80% is 13, 648 watts AC. My 11.4 KW
inverter is ignoring 16% of the array and my 10 KW inverter is
ignoring 27% of my array.
Now I decide to go to a micro-inverter instead. 50 microinverters
in this case. So my maximum AC output is now 50 x 190 or 9,500
watts. I could be producing 13,648 watts AC but my micro-inverters
are limiting me to 9,500 watts. Not all the time, and not that
much that much of the time, but in cold clear climates a fair amount
of the time.
Am I missing something here?
Thanks
Lee Tavenner
Solar Plexus
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