system expansion [RE-wrenches]

[John Berdner]

Larry/Wrenches:
 
A couple of points here if I read your questions correctly.
 
1) The Sunny Islands (SI) have a grid disconnect relay in them that
allow a maximum pass through current of 56 Amps continuous which is
equal to a 70 Amp breaker.  This creates one limitation since the total
maximum PV current that can be fed through the SI is limited by the 70
amp breaker.
A single SI would be limited to a 70 Amp breaker at 120 Vac (or 35 Amp
breaker at 240 Vac with an autoformer).  In order to handle the SB6000
plus the SB3000 you would need a split phase pair of SI's. 
 
2) The critical load sub panel is fed by the 70 Amp breaker via the SI.
 When calculating the total of all supply sources for the critical load
sub panel you have the 70 Amp breaker feeding the SI, the 40 Amp breaker
for the SB6000, and the 20 Amp breaker for the SB3000.  This gives you a
total of 130 Amps of breakers that can supply the critical loads sub
panel.  Effectively this means you need a panel that is rated for at
least 125 Amps to meet the 120% rule for conductors and bus bars
(assuming this is residential).  
 
3) In the main service panel you are also limited to 120% of 200 Amps
so you would be forced to do a line side tap if you need more than 40
Amps of PV.  This is true for the combination of the SB6000 plus the
SB3000 (60 Amps total breakers) or for the SI plus Sunny Boy (SB) set up
with a 70 Amp breaker. 
 
4)  If you want to use an existing 60 Amp fused disconnect you can
program the SI for a maximum supply breaker (or fuse) of 60 Amps.  This
will prevent nuisance tripping of the 60 Amp fuse or breaker but... 
Some AHJ's are requiring a 70 Amp fuse or breaker since this is the
maximum rating of the inverter's pass through current even though this
current can be limited electronically by the SI.  
 
5) Lastly, you should plan on adding an RS485 communications link
between the SI's and the SB's.  This is suggested so that the SI's can
control the output power of the SB's when the grid goes down.  If the
communications link is not used, the SI's will automatically trip the
SB's offline when the batteries are full and the load current is less
than the generation current. While this approach does work, it is a
brute force method.  In contrast, the communication link allows the SB's
to stay online but the SI will command them to derate their output power
to match the loads.  The message displayed when the SI's are controlling
the SB output power is "derating ##" (where ## is the percentage the
SB's are derated)
 
I hope this helps.
 
Best Regards,
 
John Berdner
 

>>> sunmountain at netstep.net 8/16/2007 04:58:15 PM >>>

Wrenches,

I just finished a system for a client with 36 Sanyo 200"s. 4 strings 
of 6 modules each feed a SunnyBoy 6000. 2 strings of 6 modules each 
feed a SunnyBoy 3000. We did a tap on the main service entrance 
conductors between the utility meter and the main ( new 200 amp ) 
service panel.
Now that wen are done the customer wants to add batteries to the 
system. So we are looking at a Sunny Island and a step up 
transformer or possibly two Sunny Islands depending on critical loads 
to be run.
The questions are how to reconfigure the wiring from the Sunny Boys 
since they will now go to the critical loads panel rather than to the 
tap on the service entrance wiring. The Sunny Island will go to the 
main service entrance panel.
We have 60 amps ( 40 amps for the Sunny Boy 6000 and 20 amps for the 
Sunny Boy 3000 ) coming from the two inverters combined into one 60 
amp outside disconnect to satisfy the local utility requirement of 
only one disconnect switch for the whole system.
The Sunny Island requires a 70 amp breaker.

Any suggestions on how to set up the critical loads sub panel so to 
not violate an code requirements?
Does the Sunny Island fall under the 120% rule since it is a 70 amp 
breaker and a 200 amp main service panel.
Anyone done this set up before?


Thanks

Larry Brown
Sun Mountain
Olivebridge, New York




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