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Nathan, I neither stated nor implied that the SW series could be AC-coupled, because I don't know, friend. I have never had reason to try this. The issue was discussed on this forum several years ago, and I have found two key posts from David Katz of AEE about this topic in my email Wrenches archives. David only addresses compatibility with early Sunny Boys. The SW is true modified sine waveform, so whether is would be capable of providing a reference signal to which a modern grid-tie inverter could latch would be subject to several variables, and would likely vary among inverter brands and models. Here's what David wrote on 4/15/2005, excerpted: I have connected Sunny Boy inverters directly to the output of Xantrex SW inverters and Outback inverters. It works well. The Sunny Boy operates when it sees the SW or Outback output. Sometimes it shuts off when a large load, like a pump is applied to the circuit, because it looks like a grid failure. If the SB shuts off, it waits 5 minutes to turn on. If there is no AC load on the system and the SB is supplying power, you will charge the batteries connected to the SW. You need to put a voltage controlled switch to turn of the AC between the Sunny Boy and the sub panel if the battery voltage gets too high.You mention the GTI below, but have not indicated whether the SW you are considering is or isn't a GTI-equipped model. If it is 4.10/GTI-equipped, I'd suspect it's incompatible with AC-coupling. When one of these is not selling (such as at night), has no loads on it but is grid-connected, it is continually drifting between buy and sell by an amp or two. Note that I have only observed this on the SW's meter display, which is a pretty crude measurement. But I would expect that this would interfere with any GT inverter's latching function, given the mandatory 5-minute waiting period. This is all based on observing one system that we installed around 2002 for a well-known retired movie star. The system remains fully operational today. We had an SW5548 (for most loads) and an SW 4048 (for background loads with surge, like pumps) that were not series-stacked, in a GTWB system, small by today's standards at 4.4kW of PV. Both inverters had GTIs, but only one was set to sell, in order for the two SWs not to argue with each other and to minimize their inherent float inefficiency previously noted. I'd guess your chances of AC-coupling would be better with a pre-GTI unit. Others here may have had more experience with this question. Just to stir the pot some more, here is an email from Lloyd Gomm, then at Xantrex, about the GTI/listing issue from 11/17/2003: Joel Davidson Wrote:AllanNovember 15, 2003 one of our customers (maybe more) with a line-tie SW in Southern California Edison territory got a notice from Xantrex dated October 22, 2003 about a required firmware update. Anyone else get this notice?Joel, this firmware update is necessary for SW inverters tested / listed by UL. This batch of SW's were produced by Xantrex between Q4 2000 and Q4 2001 and, to be clear, were de-listed by UL in November 2001.
Allan Sindelar
al...@positiveenergysolar.com NABCEP Certified Photovoltaic Installer NABCEP Certified Technical Sales Professional New Mexico EE98J Journeyman Electrician Positive Energy, Inc. 3201 Calle Marie Santa Fe, New Mexico 87507 505 424-1112 www.positiveenergysolar.com On 11/22/2011 8:10 AM, Nathan Jones wrote: Bill, I believe Allans post indirectly answered my question. While he did not specifically state the SW could be used in an AC coupled arrangement, I believe it was implied. Since the listing issue, as I understand it, was due to failure to drop out of sell mode in a certain set of circumstances and never had anything to do with the behavior of the inverter in any of its "incoming AC only" settings as far as disconnecting there should not be any question as to its suitability for AC coupling there. The only question would be how they would react and manage backfed AC from a GTI in event of a grid failure. That question is unknown to me and has not been specifically answered yet. Any one have an answer to that? Nathan Jones Power Source Solar Springfield, Mo R 417-827-0738 |
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