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 <http://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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