[RE-wrenches] SI/SB MicroGrid - Recovery From Low Battery Shut Off

Sun Jun 7 20:08:45 PDT 2015

Do these same concerns apply to XW? There is a minimum battery (I think
100Ah) required.

Bill Dorsett

From: RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] On
Behalf Of Drake
Sent: Sunday, June 07, 2015 11:16 AM
To: RE-wrenches
Subject: Re: [RE-wrenches] SI/SB MicroGrid - Recovery From Low Battery Shut
Off

That is what we did for our home system. The main impetus was to keep the
batteries charged without having to charge from the grid using the on-board
battery chargers. Grid charging uses a lot of utility power. 

This system has stacked Outback inverters. We keep the backup inverters
turned off at the Mate, but with the instrumentation running. If we did have
a low battery situation, the voltage would rise enough to start the system
back up from the 80 W of DC coupled PV. 

Another way to recover from low battery shutdown would be to program the
shut down parameters below battery voltage when the sun came back out. Also,
it is likely that if the system were completely turned off at the DC
breaker, the battery voltage would rise enough to start the inverter(s) when
solar resources improved. 

At 05:51 PM 6/6/2015, you wrote:

Years ago, when I was researching SB/SI microgrid solutions for a Ted Turner
high-end off grid rich man's lodge, John Berdner (at that time the head of
SMA-America) had made me the same recommendation: that a small amount of PV
be wired as a DC charge-controller-based input. This was a final fail-safe
approach, in case the array was insufficient and the gennie didn't start. It
would bring the batteries to a minimal voltage level, such that the SB/SI
system would return to operation once the batteries recovered.
Allan

Allan Sindelar
allan at sindelarsolar.com
NABCEP Certified PV Installation Professional
NABCEP Certified Technical Sales Professional
New Mexico EE98J Journeyman Electrician
Founder (Retired), Positive Energy, Inc.
505 780-2738 cell

On 6/6/2015 8:23 AM, Mac Lewis wrote:

Hi Mark, 

The Sunny Island has various battery protection modes and will shutdown
based on user programmable state of charge levels. Level 2 battery
protection will start the Sunny Island every 2 hours in an attempt to get
charge into the batteries.  You should set this level up at times when
energy input is likely.  See page 113-114 here:
http://files.sma.de/dl/15216/SI4548-6048-US-BE-en-20.pdf  If it doesn't get
any charging to the batteries for 10 minutes, it will shut down and wait
again.

This is an advantage of having at least some DC coupled solar input.

On Sat, Jun 6, 2015 at 7:39 AM, Mark Frye <markf at berkeleysolar.com > wrote:

Hi Guys,

Just wondering about how a SI/SB microgrid works. If all the PV is connected
to SB inverters, what happens if the loads manage to drain the batteries to
their low voltage shutdown? Wouldn't the SB stop providing the AC sync so
then the SB wouldn't have anything to sync to even if they had power
available from the PV?

How is this handled? It seems to me you would always want to have some
amount of PV DC coupled.

Thanks,

Mark Frye

Berkeley Solar Electric Systems

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