Performance of Large Outback system [RE-wrenches]

Darryl Thayer daryl_solar at yahoo.com
Sat Oct 16 12:36:46 PDT 2004


 

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Hi all
Here is and update on my  40 kW Outback 12 pack
inverter system .  Performance so far is good with a
few subtle lessons to be learned.   The highest output
I have seen is 34.5 kW.  This occurred after a
rainfall and the sky cleared, the temperature was
about 40 F, it was near solar noon.  I think the cold
modules and very clear sky and clean collectors helped
the gain.  It was also suggested that I may have had
some cloud edge brightening.   Our fall skies are
never as clear as we see in the spring.  This is
higher than other observations which are about 28-32
kW to the grid.    

The problem that caught me by surprise was a shut down
during my Saturday open house. The skies were clear,
near solar noon, I have about 20 people that I was
explaining the operation to when the 4 GVFX 3648
inverters on phase C shut down.   The remaining
inverters took the load about 30+ kW.  With my clamp
on meter I measured about 4500 watts on one inverter. 
Of course it soon started to flash red and reduced
load to protect itself.  The battery voltage climbed
and the 13 MXs took over controlling the battery
voltage.  I panicked and shut down the system.  I
turned off the single motion switch in the PSAC which
controls the 13 arrays coming into the MX 60s.   I
then called Outback and got help.  Thanks to Greg who
was working on Saturday.

The problem was a high voltage on the AC side causing
shut down.   On weekends when the building load is
very small and I am putting maybe 25 to 30 kW back
onto the grid  the voltage rises exceeding 130 volts,
and when 132 volts is reached the inverters on that
phase shut down.  Then instead of 30 kW on three
phases, I have 30 kW on only two legs being supplied
by the remaining 8 inverters.  The remaining
inverters, one of which I measured at 86 amps, or
about 4500 watts and overloading,  heating up and then
protecting themselves by limiting power to the load. 
The solar was still there and the MX60s ended up
limiting the battery voltage to protect the batteries.
 So no catastrophe, but sure a surprise.  

I need to change the transformer taps to lower the
transformer voltage, and this should stop the above
scenario.  Christopher says that typically the
transformers have 4 volts per tap.     Getting
permission to shut down the building is the problem as
it has two ISPs that need power 24-7 .

The above has happened every weekend, but never during
the week.  I am changing the transformer taps this
coming Friday after midnight.  The system and back up
power will be provided by the UPS during the shutdown.

Thanks Daryl

PS
I just sent some photos to OutBack Power Inc and they
will soon post on their web page. 
In the gallery section.  

I made a presentation to electricians and put together
a power point presentation.  If anyone is interested I
will send via e-mail I think.  However it is rather
large and I am not sure my e-mail will send it.  



		
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