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

Fri Jan 14 10:22:40 PST 2011

August,
If the SI does, indeed, shut out the pass-through AC channel when the  
critical load panel is connected directly to the grid this is  
certainly a simpler solution. That would explain why the GD inverters  
would drop out during a switch.
Is the switch-over is fast enough that time-keeping gizmos will not  
have to be reset? Ours is an on-grid customer, with on-grid  
expectations.

We'll confirm that this connection is approved by SMA.

Thanks, again.
-Kelly

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

On Jan 14, 2011, at 10:07 AM, August Goers wrote:

> 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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