SW settings for selling [RE-wrenches]

Wed Sep 29 21:01:19 PDT 2004

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Geoff,

Some thoughts:

 - Spread the float voltage on the MX60 more away from the float of the
SW. For a 24V unit, we use a spread of at LEAST 0.5VDC, due to
measurement errors. Got to keep the MX 60's from regulating off.

 - Even better, turn off the float mode on the MX60s. Let them only bulk
all the time. The SW will sell it away whenever grid connected, and a
little heavy charge during an outage will not hurt the batteries.

(Basically, need to make sure the MX60 NEVER stops charging the
batteries under grid-tie situation.)

 - these are wet batteries. Boost the bulk charge up to ~29.5VDC on the
SW, and to ~30VDC on the MX60s. Yes, water will be needed, but you said
you wanted to keep them from sulfating, and industrials still will not
need water often. And, they will only get up to bulk rarely, unless grid
power is off frequently.

 - Set float to ~27.2 to 27.6.

Try this and email me in the morning :) Oops, it is morning here.

Jeff Wolfe

-----Original Message-----
From: Geoff Greenfield [mailto:Geoff at Third-Sun.Com] 
Sent: Wednesday, September 29, 2004 11:07 AM
To: RE-wrenches at topica.com
Subject: SW settings for selling [RE-wrenches]

Esteemed wrenches - especially those with many SW utility tie
applications in their past... I ended up spec-ing an SW before the
outback had grid-tie compliance.  This is my lone SW in grid tie and I
admit to complete bafflement and novice-ness in this application!  Our
goal is to power loads in an outage, maximize our "sold" power and
maintain long life/low maint on the batts.

I have a 24 V system with 2,800 watts of PV, a 2200 amp hour Industrial
2 volt cell based battery and an SW4024.  It powers 6 priority loads
(lights, computers and 2 fridges) and is set up to sell excess.  We are
in O-hi-O and have about 4.2 hours/day this time of year. Batteries have
needed water once - we want to really minimize watering and wear yet
avoid sulphation.

We have a mechanical kwh-hour meter set up to record "sold" power and
power to the subpanel (and may have a problem with the wiring as we
tried to integrate the sub panel and the line to the main here).  This
unit registers
558 kwh (over 206 days of operation averages 2.7 kwh/day).  I thought
this should be more like 8-9 kwh/day allowing for losses.

We have two sub arrays feeding MX-60s (this should have been a 48 VDC
system but that's another story).  The wonderful log function of the
controllers tells me: that the two arrays combine to produce 11.5
kwh/day average 14.4 best day.  Sub array A always outperforms B (eg:
7.6 vs 5.2) - I attribute this to panel tolerances (lets get those glass
manufacturer's to tighten
up!) and array layout/AM shading.  THE BIG CLUE: the MX60 on A has 7
days out of the 14 looked at (spread out) with float minutes in the
240-290 range
(4-5 hours!).  No floating on the lower power array (Chris - normal way
these things work together? - no hub)

DAY OF VISIT:
(overcast but sunny - MX60 in mppt and sweep... I failed to record amps
in but I would have registered an unusual situation so lets assume
around 35 amps each sub array output)

The trimet read 23.9 Blo and 29 Bhi (I reset and will check those out
again) It was holding at 26.9 VDC +/- .5 and was showing -4 to +4 amps
in/out of the battery.

The SW meter showed line tie yellow, AC1 good, float was green and the
Inv charge amps AC was around -10 to -13.  The AC input was also around
-13 amps.  The mechanical meter was slowly moving to the right
(producing).

My settings:
Sell, bulk 28.8, absorb time 0, float 26.8, max charge amps 18, grid
usage charge time 21 start, 21 end, bulk trigger 0, MX 60 I need to
recheck these, but I think they are the out of the box settings 28.6 /
27.2 / 2 hour timer

MY REQUEST:
I welcome input on what was going on the day of my visit, fine tuning my
settings (Including MX60?), why I may be floating with the MX60s, and
someone to hit me on the head and tell me to re-wire the kwh meter
(probably switch it over to 2 meters, one for buy/sell to main and one
for power out to sub-panel... but we thought we tested it and had it
working under all situations).

Sincerely,

Geoff Greenfield
NABCEP Certified Solar PV Installer TM
GLREA Certified Photovoltaic Systems Integrator/Installer License Number
0211-01

THIRD SUN SOLAR AND WIND POWER Ltd.
340 West State Street, Unit 25
Athens, OH 45701

Phone (740) 597-3111
Fax   (740) 597-1548

www.third-sun.com

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