Larry and Kent
We did an XW system several months ago, feeding a dedicated loads panel of
course. The owner wanted to fill out the roof space so we added 9 modules w/
190 W Enphase connected to the main panel. My understanding is that when the
grid goes down, the Enphase goes off line, and the XW transfer switch also
isolates from the grid. The XW powers the dedicated loads panel from the
batteries/PV array.
Later , the owner purchased a generator and plugged into the receptacle we had
provided, wired to the AC2 ( GEN )input to the XW. The generator can charge the
batteries, and support the XW output for heavy loads. There is no connection to
the main panel, nor the Enphase inverters.
When the grid comes back online, both the XW and the Enphase take several
minutes to sync to the grid, and then the XW disconnects from the Gen. input
and powers the dedicated loads, sells back to the grid if the PV is producing
more than the dedicated loads are drawing, or allows the grid to 'pass thru ',
thus not depleting the batteries.
After the owner purchased the generator , we tested operation by disconnecting
the AC1 breaker, verifying the Enphase shutdown, turning on many loads in the
dedicated loads panel, and starting the generator to recharge the batteries.
Everything works perfectly.
By the way, we have had no problems with the XW equipment--both 4500W and
6000W. The first XW we did several years ago , when they first became
available, needed a software upgrade, so we purchased the Configuration tool,
which is also handy for some monitoring of performance.
Hope this helps------
Ken Schaal
CommonWealth Solar
----- Original Message -----
From: Kent Osterberg
To: RE-wrenches
Sent: Sunday, March 27, 2011 5:13 PM
Subject: Re: [RE-wrenches] Generator and Enphase
Larry,
The XW has separate Grid and Gen inputs. It's designed to sell power to the
grid and it makes sense that the XW wouldn't sell to the generator. But I don't
think it can stop a microinverter from trying to sell power to the generator.
If the generator is on and the transfer switch is closed, what would stop power
from flowing backwards through the transfer switch?
Kent Osterberg
Blue Mountain Solar
wire...@gmail.com wrote:
This doesn't solve the reliability concern of a contactor but on a webinar
I heard a rep from Schneider say the XW (with GEN and GRID AC IN's) will not
backfeed a generator and will do it without a contactor. Is that true?
Larry Liesner
Wirewiz
Westport, CT
Phone: 203-644-2404
Fax: 203-557-0556
wire...@gmail.com
www.wire-wiz.com
On Mar 27, 2011, at 3:50 PM, Kent Osterberg wrote:
Larry,
Yes, the PV system was straight grid-tie. The back-upped loads were only
covered by the generator (no battery-based inverter was involved). The ATS also
does the generator startup, so an inverter on the backed-upped loads would
require some thinking I haven't done. If the generator startup were changed, my
first thought would be to put the battery-based inverter on the generator side
of the ATS.
Kent Osterberg
Blue Mountain Solar
wire...@gmail.com wrote:
Kent,
Situations vary but this one line helps a lot, thanks.
So, "To PV System" would go to the output of a grid tie inverter and
"To Backed Up Loads" would go to the AC IN (transfer switch) of a battery
inverter.
I have been going to homes with existing 100A gen/utility ATS and
wondering if I could keep it as is and be able to add a grid tie battery backup
to it (using same backup loads). This schematic would work in that situation as
well but wouldn't have the "To Non-Backed UP Loads" tap.
Larry Liesner
Wirewiz
Westport, CT
Phone: 203-644-2404
Fax: 203-557-0556
wire...@gmail.com
www.wire-wiz.com
On Mar 27, 2011, at 2:36 PM, Kent Osterberg wrote:
Larry,
Situations vary so much that this might not be very useful. But here
you go. The attached sketch shows how we recently connected a customer that had
a backup generator and transfer switch that wasn't service rated. There were
nice gutters existing from the original install so accessing points to tap
conductors wasn't difficult. We could have connected the inverters to the
non-backed upped loads panel instead, but the utility requires an accessible
disconnect by the meter so it was more convenient to just get into the gutter.
Kent Osterberg
Blue Mountain Solar
wire...@gmail.com wrote:
Kent, Jason, or anyone else
Would you a have a simple one-line you could share for wiring the
inverter on the utility side of the transfer switch?
Thank you.
Larry Liesner
Wirewiz
Westport, CT
Phone: 203-644-2404
Fax: 203-557-0556
wire...@gmail.com
www.wire-wiz.com
On Mar 26, 2011, at 6:04 PM, Jason Szumlanski wrote:
We’ve explored this strategy many times due to all of the whole
house and critical load generators in Florida. We’ve stayed away from the
contactor solution because of the potential for the NC contactor failing to
open, keeping the inverters “online” when transferred to generator power. While
unlikely, this is a possibility that must be considered.
The other issue presented here is that the inverters will shut
down every time the generator exercises.
The only sure-fire way seems to be wiring the inverter on the
utility side of the transfer switch, as Kent said.
Jason Szumlanski
Fafco Solar
From: re-wrenches-boun...@lists.re-wrenches.org
[mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Kent Osterberg
Sent: Saturday, March 26, 2011 5:56 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Generator and Enphase
Mark,
I agree it is best to wire the inverters on the utility side of
the transfer switch. When that isn't easy, a normally closed contactor that is
opened by generator voltage, will isolate the inverters from the generator and
allow automatic return to utility operation when the generator is off.
Kent Osterberg
Blue Mountain Solar
Mark Frye wrote:
Eric,
I do not have direct experience with this but have been exploring
the issue for a project I am currently doing.
My response will be to take the trouble to interconnect the
Enphase inverters on the line side of the tranfer switch so that the inverters
can never be connected to the generator.
Here are the reasons why:
1 - Enphase states that any such application is considered an
"off-grid" application which voids their warrenty. As I am installing under the
California CSI program, I am required to provide a 10 year manufacture
equipment warranty so I cannot afford to install the inverters in a dis-allowed
manner.
2 - Enphase states that the waveform of the generator may be
"clean" enough such that the inverter may attempt to syncornize and connect to
it as if it were the utility. If this were to happen Enphase believes the
inverters will ruin the generator regulator before the generator ruin the
inverter. I don't want to be the one to run the experiment to find out which
would be which.
3 - I considered a contactor on the output of the inverters, such
that the inverters would isolated by a loss of line voltage, requiring some
form of reset. Ulitmately my customer agreed with me that this was an
undesirable constraint on the operation of an otherwise reliable grid-tied
system and it was not clear that this would satify the warranty issue.
Mark Frye
Berkeley Solar Electric Systems
303 Redbud Way
Nevada City, CA 95959
(530) 401-8024
www.berkeleysolar.com
------------------------------------------------------------------
From: re-wrenches-boun...@lists.re-wrenches.org
[mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of Eric Thomas
Sent: Saturday, March 26, 2011 2:09 PM
To: re-wrenches@lists.re-wrenches.org
Subject: [RE-wrenches] Generator and Enphase
I have a customer with a "30A Mechanically Interlocked Breaker"
for their generator feed at the main panel. My question is: If the home power
is transferred from utility to generator power, will the backfed PV see the
generator as grid power and sync up and produce? This is a nice Honda Generator
so the power should be fairly clean. Any experiences are appreciated.
Take Care,
Eric Thomas
Solar Epiphany LLC
(206) 919-3014
www.solarepiphany.com
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