net-metered efficiency observations [RE-wrenches]

[Kirk Herander]

Bill,

Both the bulk & float voltages are set to 52 volts. So they are temp
comp'ed.  I don't use the "battery sell" feature. The amount of power the
inverter draws at night is dependent upon the float voltage and size of the
battery bank it is trying to hold at that voltage. It can vary. I assume
that the mx-60's are measuring power out of the controller (after the mppt
boost) but that's a question for Chris at Outback.

In terms of expected dc/ac efficiency, I figured about 80% would be
reasonable w/batteries and mppt controllers, but raised the subject to
confirm with others that my assumptions and observations were reasonable.

Kirk
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


> Kirk,
>
> You mentioned that you have set the sell voltage to 52 Volts. Why is the
> sell voltage even being used if this is a net metered system? Normally we
> just set the float voltage to 53.6 V (depending on the battery) since this
> is temperature compensated. The sell voltage is not temperature
compensated.
> Although it may be an okay voltage to keep the battery at year-round,
> regardless of how well controlled the battery temperature is, it should be
> temperature compensated in my view.
>
> You mention that the you think the conversion efficiency is too high. What
> are you expecting? I would say that it could be low. Typical nighttime
> losses should be .5 to .8 kWh since the unit draws about 50 Watts all
night.
> Does the MX60 measure power output or power input?
>
> Bill.

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