net-metered efficiency observations [RE-wrenches]

[Todd Cory, Mt. Shasta Energy Services]

Kirk,

I assume you have 4 kW on a 5548. Did you take the reading the next morning, so
the wasteful and unnecessary SW  floating the batteries all night was subtracted
from your gross production on the meter? I have many winter weeks where there is
not enough sunshine to even make up for the SW wastes. So net efficiency will be
better in the high production summer months than in the winter. I have plans to
retire my old 4024 and install an outback GVFX with a smarter silent sell
feature.

Todd



Kirk Herander wrote:

> I have a net-metered system: 4 kw of pv on Zomeworks trackers, regulated
> by -2- Outback MX-60's. The sell voltage is set to 52 volts, and the mx-60's
> are in MPPT bulk charge all day, except for occassional auto-recal. Using
> the form 12s meter to measure PV power converted to AC in a 48 vdc battery
> based Xantrex SW system, I observed the following. On a recent sunny day,
> the AC kilowatt-hr meter registered 20 kwh. The total DC kwh registered on
> the mx 60's was 23.8 kwh for the day. So this gives an dc/ac conversion
> efficiency of about 84%. Although this might be a somewhat simplistic means
> of measuring conversion efficiency, is 84% reasonable for a battery-based
> system w/MPPT controllers? I might of thought it to be a little less than
> this......
>
> Vermont Solar Engineering
> Kirk Herander
> North American Board of Certified Energy Practitioners
> Certified Solar PV Installer(TM)
> Xantrex Certified Dealer Charter Member
> NYSERDA-eligible installer
> Vermont Solar and Wind Partner

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