[RE-wrenches] Generator and Enphase
Ken Schaal
ken at commonwealthsolar.com
Sun Mar 27 18:15:22 PDT 2011
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
wirewiz at 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
wirewiz at 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
wirewiz at 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
wirewiz at 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
wirewiz at 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
wirewiz at 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-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at 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-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Eric Thomas
Sent: Saturday, March 26, 2011 2:09 PM
To: re-wrenches at 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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