[RE-wrenches] AC coupled GT Sunny Island w Enphase; string optimizers

[Kelly Keilwitz, Whidbey Sun & Wind]

Wrenches,
Here's an update on this configuration (20kW Enphase, AC coupled to  
Sunny Islands) you should know about:

Enphase will not support and warranty the use of their micro inverters  
in an AC-coupled installation with battery-based inverters. Enphase  
approved this verbally with us in design, but balked when we asked  
them to back it up in writing. Their issue/point is that AC-coupling   
violates the UL1741 listing.

Thus, we're revising the design to use Sunny Boy string inverters. Our  
customer would still like the module-level monitoring and optimization  
offered by the micro-inverters (there is some shading issue), so we're  
considering using string optimizers. We have not used string- 
optimization, yet. It looks like the leading options are Solar Magic  
and Tigo.

Any preferences, cautions, or advice with choosing and using  
optimizers would be appreciated.

Thanks,

-Kelly

Kelly Keilwitz, P.E.
Principal
Whidbey Sun & Wind
Renewable Energy Systems
NABCEP Certified PV Installer
WA Electrical Administrator
987 Wanamaker Rd.
Coupeville, WA 98239
kelly at whidbeysunwind.com
PH & FAX: 360.678.7131









On Jan 13, 2011, at 7:33 PM, Kelly Keilwitz, Whidbey Sun & Wind wrote:

> 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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