On grid w/battery [RE-wrenches]

[Joel Davidson]

One of our customers with an SW4048 battery PV system tried running his system
yesterday at 60V with 5 each 12 volt batteries. Here are his own words.

I was able to carry out an experiment running my system at 60V today. The
morning clouds disappeared
at around 10AM, leaving a clear blue sky that lasted until about 2PM. My array
points at exactly 180 degrees,
and using the NOAA Solar Position Calculator, I determined the solar zenith
would occur at 1:07 PM.

At 12:10, I shut everything down and re-wired my battery array for a 2 X 5
configuration. Measured voltage
was 63.5 V.

I bypassed the C60, running a wire directly from the 60A breaker to the 250A
breaker. I powered up the
inverter and programmed the high battery cutout voltage to 66V (highest
possible) and the float to 64V
(highest possible). Cutting in the solar array, everything settled down within a
minute, and the only noticeable
difference was a reduction in loudness coming from both the inverter and the
GTI.

Per my plan, I watched the output of the solar array until just after the
zenith, and then reconfigured the system
back to 48V in less than 5 minutes at 1:14PM.

I fully expected to see the power output elevate somewhat higher than the
highest I've seen in the last week,
however, I did not. The numbers captured by the logger show that power output
was exactly the same; the
higher voltage came with a proportional drop in current. I'm not sure what can
be concluded reliably, but here's
what comes to mind:

With an ambient temperature of 72 degrees and no wind, my solar array was almost
certainly operating under
PTC conditions. The PW1000 specs assume STC conditions. I think it's probable
that module operating
voltage has only a small effect on power output, at least under PTC conditions,
which would explain why I saw
no measurable difference between running my system at 13V and 16V per module.

(Joel's comment - PV customers are wonderful!)

Bill Brooks wrote:

> Joel,
>
> If you use the SW as a non-PV UPS, you may end up increasing your losses
> rather than reducing them. The float charge for an AGM battery is about
> 50-Watts (more for flooded and some gels). Without PV you will end up
> charging 24-hours a day unless you set it up to bump the battery once a day.
>
> Every inverter has low load losses, so installing a new inverter will
> decrease your low irradiance power output--no matter how good it is. I would
> encourage you to stay away from the batteryless UT-SW-PV series inverters
> since they definitely max power track worse than a battery-based system.
>
> Bill.

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