net metered system question [RE-wrenches]

[David Palumbo, Independent Power & Light]

wrenches,

	We have a 5.7kw pv array grid tied and set up to sell back thru two
SW4048's. The system is a Y2k "in case of" job. It has over 3,000 amp hours
at 48 volts of battery storage (72 two volt Surrette cells). PV charge
controlling is accomplished with a Pulse Energy Systems PSC 500 control
center. It utilizes a PWM control board and a mercury contactor. The pv is
divided into two 45 amp arrays. One is controlled with the contactor opening
after bulk charge voltage is reached while the other 2,500 watts is pwm
taper charging during absorption and float. Of course under Trace's sell
program the charge controller should only come into use if the grid goes
down for an extended period of time. I understand that our programming
settings should be such that all the pv over what is necessary to maintain
the batteries at float will be sold back to the grid.
	The system has been programmed as follows:
Trace bulk charge voltage 58.6, Abortion time 2 hours,
Float Voltage 54.0 (I don't want to set this any higher because the battery
box vent fans would stay on all the time as they are set to come on at
54.4v).
Pulse Charge Controller settings: Bulk 60.0 volts, Float 55.5 volts,
Equalize automatically every 30 days to 61 volts.
	Both the Trace and Pulse settings are temperature compensated.
The temp comp differential has been running from 1v to 1 1/2 volts (for
example temp comp volts 54.0, actual volts 55.2v.

PROBLEM: It has been observed, on more than one occasion, (I have not
re-visited the site yet so I have not personally checked things out yet, but
a very competent technical person was relaying the info to me via phone
yesterday),
that the pv charge controllers were controlling the pv current at float
voltage,54v temp comp, when observed. The sunlight was strong at that time
so the sell back that should have been occurring was not happening. After
the grid sell back was set up (Dec 2000) we had observed good performance on
sunny days with the meter spinning backwards to the tune of 16 to 20 amps at
120 volts on each SW4048.

The system monitor (TriMetric) picked up some interesting data that shows a
recent power outage that could explain at least part of the problem.
Trimetric high battery voltage 61.9v (Equalized pv actual voltage), and a
low voltage of 48.5v (this would have had to have been a grid power failure
I think).

Any Ideas on what's going on?  Suggestions?

Dave Palumbo
IP&L

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