ratcheting cyclometers [RE-wrenches]

[Kelly Keilwitz]

Hi Todd,

The grid-feed to the critical load subpanel is irrelevant as far as the
Green Tags payments go. The customer is paid for all AC production from PV
(only - how to seperate out the wind production is another twist),  whether
they use the actual power or it makes it to the grid. We put the Green Tags
meter between the inverter and the main panel breaker. We want to use a
ratcheting meter so the customer doesn't loose credit for grid energy used
to charge the batteries, power the inverter, or supply the critical (backup)
loads. In these recent systems the subpanel loads are small (e.g. duplex
plug and power room lights) or only to be used when the grid is down. As I
see it, the only significant time that the customers would not be credited
for their use of renewable energy (what a concept!) is during the short
duration when the grid is down.

With significant subpanel loads like you describe I could see that a
sizeable portion of the PV AC production could be going to the subpanel and
bypassing the Green Tags meter. In that case, I see the importance of
metering the subpanel feed. But, is it possible to distinguish between grid
feed and PV feed to the subpanel?

The net metering - a seperate agreement with the Utility - is accounted for
with a utility-owned, dual readout digital net meter. The renewable energy
used by the customer (at the main service panel) could be calculated as the
Green Tags meter reading minus the net meter "out" reading.

-Kelly

Todd wrote:
> Power generated is power supplied to the back up sub panel and any excess
> generation delivered to the grid. The power to the sub panel is not only
> supplied when the grid is down. When the grid is up the inverter's xfer
switch
> feeds grid power to these loads as well. (In my home this is all 120 volt
> loads.) Not metering this feed would result in a highly inaccurate
measurement
> of PV power being generated.
>
> Todd
>
>
> Kelly Keilwitz wrote:
>
> > Hi Jeff,
> > Yes, in order to completely measure all of the RE AC output from the
system
> > the throughput to the subpanel loads should also be measured. However,
> > since these systems are battery backup for a few loads where the grid
might
> > normally be down for 24 hours per year I disagree that the power to the
> > subpanel is substantial (in these cases). The benefit in accuracy
doesn't
> > seem worth the extra cost and complexity of metering the subpanel AC
output
> > in addition to the grid AC out/input from the inverter to me.
>
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