[RE-wrenches] AC coupled, grid-tied Sunny Island - contactor & bypass

Fri Jan 14 10:07:45 PST 2011

Hi Kelly -

Yes, AC1 from the Sunny Island is always connected to the critical loads
panel. During on-grid operation the critical loads panel is fed solely
through the main panel and transfer switch, not through the Sunny Island.
I see your question about paralleling the critical loads panel through
both the external transfer switch and the Sunny Island. It's been a while
since I've contacted SMA about this but my understanding is that the Sunny
Island is "smart" and since it sees that there is already power on the
critical loads panel it will not backfeed the critical panel until it sees
that the main power goes down.

When the grid power goes down the automatic transfer switch flips very
quickly to backup mode and the Sunny Island immediately kicks in. It
happens so fast that the first few times I was testing it I was caught off
guard and thought that something was wrong. In fact it was flipping to
backup mode so fast that I didn't even see the lights flicker. Even though
this switch is really quick the grid tied inverters still trip off in my
experience.

Does this address your thoughts?

Best,

August

-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Kelly
Keilwitz, Whidbey Sun & Wind
Sent: Friday, January 14, 2011 9:35 AM
To: RE-wrenches
Subject: Re: [RE-wrenches] AC coupled, grid-tied Sunny Island - contactor
& bypass

Hi August,
To make sure I'm clear:
Does the Sunny Island output (AC1) stay connected to the critical load
panel while at the same time fed directly from the main panel?

If so, is there no issue with the critical loads being fed through
multiple paths? And, why, then, would the GD inverters switch off
during the switch if they continue to have an AC signal from the SI's.

If not, you must be switching the critical load panel feed between the
SI AC1 and main, via the transfer switch. And, the drawback would be
that the critical loads would not have an uninterruptible power supply
during a grid outage.

Thanks for your description. This certainly sounds simpler than my plan.

-Kelly

Kelly Keilwitz, P.E.
Whidbey Sun & Wind
Renewable Energy Systems
kelly at whidbeysunwind.com
360-678-7131

On Jan 14, 2011, at 7:23 AM, August Goers wrote:

> Hi Kelly -
>
> Sounds like a fun project. We've got a few 10+ kW grid tied Sunny
> Island
> projects and although they are not with Enphase inverters I thought
> I'd
> pass on how we've been wiring them up with good results.
>
> We tie the solar inverters into the critical loads panel and then
> put a
> transfer switch (either auto or manual depending on the client's
> choice)
> between the main and critical loads panel. The Sunny Island(s) output
> circuit (AC1) is also tied into the critical loads panel and the AC2
> connection is tied into the main. During normal on-grid operation
> the PV
> is tied directly to the main through the critical loads panel and
> transfer
> switch so there are no losses through the Sunny Island. The Sunny
> Island
> at that point is simply keeping the batteries charged though the AC2
> connection and monitoring the grid. When the grid goes down the
> transfer
> switch disconnects the critical loads panel from the main and the
> Sunny
> Island kicks in. The PV inverters shut off immediately during the
> switch
> but then kick into waiting mode once receiving the signal from the
> Sunny
> Island. The PV stays on during the grid outage until the batteries are
> fully charged then the voltage increases until the PV turns off,
> goes back
> into waiting mode and the whole process repeats - this is assuming
> that
> we're getting more PV than load. I've tested both scenarios and if the
> load is larger than the PV then the inverters will stay on
> indefinitely.
>
>
> What was your reasoning for tying the PV into the main and using a
> relay
> to switch to the critical loads panel during a power outage?
>
> Best,
>
> August
>
>
> August Goers
>
> Luminalt Energy Corporation
> 1320 Potrero Avenue
> San Francisco, CA 94110
> m: 415.559.1525
> o: 415.641.4000
> august at luminalt.com
>
> -----Original Message-----
> From: re-wrenches-bounces at lists.re-wrenches.org
> [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Kelly
> Keilwitz, Whidbey Sun & Wind
> Sent: Thursday, January 13, 2011 7:33 PM
> To: RE Wrenches listserve
> Subject: [RE-wrenches] AC coupled, grid-tied Sunny Island -
> contactor &
> bypass
>
> Wrenches,
> We are including 2 Sunny Island inverters into a previously battery-
> less grid tied design utilizing 20 kW of PV on Enphase micro inverters
> and 2 SMA Windy Boy 6000 inverters (10 kW XZERES 442 turbine). Our
> customer wishes to run his fuel generator as little as possible when
> the grid goes down. Nothing is in the power room yet, the house is
> under construction. Only the wind turbine is installed.
>
> With a pass-through limit of 56A, the two Sunny Islands cannot conduct
> the combined RE production to the grid. There is not enough critical
> load demand to justify two more SI's, nor is there space for them. Our
> plan is to connect the micro-inverters (84A, peak) directly to the
> main service (grid) in normal mode, switching to the critical load
> panel (SI AC output) when the grid goes down. The Windy Boys (56A)
> would remain connected to the critical load panel.
>
> I'm hoping that the frequency shifting control of the Windy Boys from
> the SI's will allow the PV micro inverters to connect and stay
> connected to the SI's while there is demand on the critical loads and
> the batteries are charging. When there is more PV output than load
> demand we expect that the SI frequency will rise to the point where
> the micros will go out of spec and disconnect, maybe in a nicely
> staggered pattern.
>
> Questions:
>
> 1. Has anyone experience with this much grid-direct RE capacity and/or
> micro-inverters AC coupled to Sunny Islands? I'm a little scared by a
> previous post from Darryl wherein he found that the RE capacity from
> the GD inverters should be 1/2 that of the battery-based inverters in
> an AC coupled system. Please let me know if you are certain that this
> is not going to work!
>
> 2. Any experience with specifying a contactor/relay to switch the PV
> output? The contactor will be controlled by one of the SI relays.
> Switching from the main panel (grid) to the critical load panel will
> be during a grid outage, so doesn't need to be load-rated, but
> switching back after the grid comes back up could be load-break. Our
> current solution is to use two 80A contactors from Schneider
> (#LC1D80G7) with an intertie kit.
>
> 3. Any suggestions for an inverter bypass (service disconnect) for the
> two SI's? We're considering either a monster 2P2T 200A switch (100 A
> would do), or using a gen-transfer type panel for the critical loads.
>
> Comments and informed opinions quite welcome.
>
> Thanks,
> -Kelly
>
> Kelly Keilwitz, P.E.
> Principal
> Whidbey Sun & Wind
> Renewable Energy Systems
> kelly at whidbeysunwind.com
> PH & FAX: 360.678.7131
> NABCEP Certified PV Installer
> WA Electrical Administrator
>
>
>
>
>
>
>
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