SMA Sunny Island three phase multi clustering [RE-wrenches]

[John Berdner]

Larry/Wrenches:
 
Your concern regarding balancing of the solar resource is certainly
valid.
You can only estimate the loads so closely and even then you will never
get it perfectly right.

You can help to balance the generation side by using the programmable
control relays in the Sunny Islands.
For example you can program one of the relays to close when you reach a
specific state of charge or when the battery goes into absorption phase.
 You would then use one (or more) external power relays to transfer the
output of the Sunny Boy from one cluster to another.  This helps to
balance the solar resource across the various clusters and maximize the
use of the solar resource.  I do not have a diagram of this yet but we
hope to have several applications notes regarding the use of the control
relays completed after the first of the year.
 
If I understand your comment regarding bypassing of the sub-panels back
to the generator it should still be possible to do this using multiple
smaller bypass switches one for each sub panel rather than a single
large bypass switch.
 
Best Regards,
 
John Berdner
 

>>> larry at starlightsolar.com 11/30/2007 09:27:06 AM >>>

Thank you John. My main concern with not having a common battery bank
is 
the distribution of the PV resource. Obviously I want to use all of the

PV, all the time. With 4 clusters on this system, would it be better to

use SB grid tie inverters instead of splitting up the PV into 4
charging 
systems? Would this allow the SI's to better balance the charging of
the 
4 banks or would your description below be more efficient? Do you have
a 
diagram showing the relay configuration? I don't see anything in the 
manual about this.

In this system all 3-phase sets will be paralleled. I do not think we 
can break up the AC distribution into sub panels because the owner
wants 
to be able to bypass back to the generator. I will look at this further

though.

Thank you,

Larry Crutcher
Starlight Solar



John 

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