ratcheting cyclometers [RE-wrenches]

[Kelly Keilwitz]

Matt & Wrenches,

----- Original Message -----
From: <mlafferty at universalenergies.com>


> Doug P said:
> > Simple. Using a standard 240v utility meter, wire the 120v leg from
> > the SW output to the subpanel so that power passing to the subpanel
> > spins the meter forward. Wire the other 120v leg so that power passing
> > from the main panel to the SW input spins the meter backwards.
>
> Victor C said:
> > I'm still saying night time batter charging should be deducted.
>

> Matt L said:
> On a single, 120 V inverter, Doug's description should work...
> Subtracting nighttime battery charging from the cumulative kWH reading
> on the meter.  >
> Like Doug, I have not tried this personally but believe it will work to
> a suitable degree of accuracy.

 The amount of energy energy drawn from the batteries during an outage,
nighttime, etc (meter forward) will always be less than the grid energy used
to recharge the batteries (meter backward), due to charger and battery
inefficiencies. Thus, the net energy recorded will always be negative for
battery charging (remember, the goal is to accurately meter the renewable AC
production). The meter would really go backwards when equalizing from the
grid. Ideally the meter would record a net of zero for the battery
use/recharging cycle.

It seems to me that the degree of accuracy will depend on the type of
installation. If the subpanel loads are small, RE charging sources big, and
outages few this may not be a big deal, as grid recharging may be
infrequent. However, for whole-house systems, or small arrays (or dark
cloudy winters like we have here in the NW) the amount of energy deducted
from the Green Production yearly total could be quite significant.

I do agree that using a ratcheted meter would probably skew the Green
Production total more positively than using a non-ratcheting meter would
skew the total negatively.

>
> By the way, I ABSOLUTELY agree with Victor!  You can't "have your cake
> and eat it too"!

But if I have my cake, I'd like ALL of my cake!
Thanks Matt, Doug, Victor, and all for thinking this one out.

-Kelly
>
Kelly Keilwitz, P.E.
Whidbey Sun & Wind
Renewable Energy Systems
986 Wanamaker Rd, Coupeville, WA 98239
ph & fax: 360-678-7131
sunwind at whidbeysunwind.com
www.whidbeysunwind.com
Renewable Energy Now!

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