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
ke...@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
ke...@whidbeysunwind.com
PH & FAX: 360.678.7131
NABCEP Certified PV Installer
WA Electrical Administrator
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