SW settings for selling [RE-wrenches]

[Geoff Greenfield]

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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