cost per kWh [RE-wrenches]

[Ray Walters]

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>
> > Don,
> > 0.50 is pretty serious derating from STC to Real World AC. I multiply 
> STC by
> > 0.64 for
> > single crystal and 0.62 for poly and then factor in array azimuth and tilt
>Joel
>I figured this is more conservative than most. Not to quible but I prefer to
>be very conservative estimating offgrid systems. I would go with your derates
>for a battery system -grid connected.
>Best,Don

Hi All;

Windy and I have been using a spreadsheet that you can punch in efficiency 
numbers for  battery storage, inverter, wiring, and PV to battery voltage 
mismatch. I have been using a battery efficiency of 85% (consider day loads 
are higher, night a little lower), inverter at 85 to 92%, wiring at 95% 
(shouldn't be worse than 90%) and with MPPT, I set the mismatch factor at 
98%. This gives a combined factor of  64% to 73%. The only times I have had 
complaints, I was always able to find serious loads that were not in the 
original design.
Don does your 50% factor add a fudge factor for customers' loads not 
accounted for in the original design, or are there  losses I'm not properly 
accounting for?
I've considered adding a temperature derating factor especially for poly 
modules.

Ray

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