Drake, I am the colleague that Jay was talking about. I have long believed that a 100% AC coupled system was a bad idea for fully off-grid systems, primarily because of the black start problem, but I'm not against doing some AC coupled, and some DC coupled. The way the Radian works, you should be able to use any PV inverter, as long as you can put a Frequency-Watt grid profile on it. I haven't done that with the Enphase yet, but it should work great. With the SMA SB, you put it in "Off-Grid" mode, and then it will put out 100% of its power as long as the frequency is below 61 Hz, then it tapers its output linearly from 100% at 61 Hz down to 0% at 62 Hz. Because of this programming, the frequency will never go above slightly over 62 Hz
This would be stated that the curtailment starting frequency of the SB is 61 Hz, and that the ramp-down rate is 100% per Hz, but it is fully adjustable in the settings. Enphase has the ability to be programmed to the following specifications... The following settings define the IQ Microinverter over frequency power limit * Start frequency in Hz (min 60, max 65) - I would use a minimum of 61, but it shouldn't really matter at all for the operation of the equipment. You really don't want it too high because you don't want the loads in the house to have too high of a frequency. * Start delay in milliseconds (min 0, max 10) - this should be 0 * Ramp down rate in %/Hz (min 40%/Hz, max 83.33%/Hz) - this shouldn't really matter either. I'd go close to the high end since the Sunny Boy is 100%/Hz and it works well. The Radian doesn't know what the curtailment starting frequency is, nor what the ramp down rate is, and it really doesn't care. It just knows that when the voltage gets to the absorb voltage (or the float voltage after the absorb timer is over) then it raises the frequency until it achieves the desired effect, so it doesn't matter if the PV inverter has a different power throttling curve, the Radian can simply adjust for however that inverter reacts. You do need to turn on the AC coupling mode. Basically, it should work perfectly if you program it right, and since you already have the DC-coupled portion to prevent the black start problem, you should be set. Michael Morningstar, Looking back, I wasn't totally clear when I was talking to Jay. The system he was talking about is actually grid-tied, but I took it off-grid for a good long while just to test the taper charging and the reactions between the Radian and the Sunny Boys. I wanted to ensure that it was going to work the way I thought it would, and it worked flawlessly, but due to the black start issue, (dark start), I wouldn't design an off-grid system to be fully AC-coupled. You would be correct about Murphy if it were an off-grid system, the dark start issue is something I wouldn't want to mess around with, but being grid-tied, I don't think it will be an issue (unless doomsday shows up). I am caring for an orphaned system nearby that is solely AC coupled using Li batteries, and it's off-grid. I was very much opposed solely AC-coupling off-grid, and this orphaned system just confirms my leeriness to the idea, but it was also a bad selection of equipment for this purpose. They were using the Schneider XW platform, and the problem there is that the XW takes too long to shift frequency, so while it's lagging, the PV is still putting out full power, and then the battery system far overshoots the absorb voltage, and the Li batteries shut off, and then the voltage really spikes and shut the whole system off. I had to just tweak the absorb voltage lower and lower until I found a voltage low enough that by the time the XW shifted frequency, the battery voltage wouldn't be overshooting the correct absorb voltage. It's a functional workaround that's working okay for now. And addressing Ray's statements, I couldn't agree with you more, but here's one other option that (somewhat) relieves the problem... The other thing I've observed is that if you are going to have a solely AC coupled system off-grid, then at least have the low battery cutout on the inverter significantly higher than the low battery disconnect in the batteries, and then get a few external 48 V battery chargers that can charge a fully dead battery (make sure it is the kind that doesn't look for a live voltage before it powers up). Then permanently wire these chargers directly to the generator output so that it can charge the batteries even if the inverter isn't working at all. This will allow the generator to revive a black start scenario no matter what. I think this is still inferior to having part of the array DC coupled, since it does require firing up a generator, but it is a functional workaround that I have been using on the orphaned system and it really does work. That being said, I think I might be able to talk him into getting some DC-coupled PV next spring. Thanks, Kienan Maxfield Solar maxfieldso...@hotmail.com<mailto:maxfieldso...@hotmail.com> (801) 631-5584 ________________________________ From: RE-wrenches <re-wrenches-boun...@lists.re-wrenches.org> on behalf of drake.chamber...@redwoodalliance.org <drake.chamber...@redwoodalliance.org> Sent: Friday, November 1, 2019 10:33 AM To: RE-wrenches <re-wrenches@lists.re-wrenches.org> Subject: Re: [RE-wrenches] Off Grid Optimizers I agree completely that AC coupled systems are far better off if they have a battery charging method completely independent of the off-grid inverter. Some DC coupled solar is the best way to go. The system I'm considering already has 2820 W of DC coupled PV. Drake ----- Original Message ----- From: "RE-wrenches" <re-wrenches@lists.re-wrenches.org> To: <re-wrenches@lists.re-wrenches.org> Cc: Sent: Thu, 31 Oct 2019 19:33:11 -0600 Subject: Re: [RE-wrenches] Off Grid Optimizers We've discussed AC coupled many times. Aside from the issues Michael brought up, I need to remind that not having at least some DC PV charging means that when the AC system shuts down for any reason, so does all the PV charging. If Li+ batteries get discharged to their low voltage shut off: Dark Starts anyone? With lead acid, DC coupled PV is just as critical to keep the battery from sulfating. Which would you want? Scenario 1:Come back to trouble shoot a system shutdown, try to reboot, only to find no battery voltage to even test with. or Scenario 2: You will have a battery that is being charged, if not already at full charge. For GTB?, you decide how important this issue is, but for Off grid you are putting your customer in serious jeopardy without power. Unless they have a manual bypass, the generator won't pass through to the loads, or charge the battery either. This is not theory, We've had to fix these, and in some cases replace the battery bank that was damaged after sitting dead too long. My previous post in favor of AC coupling was only as a supplement to a solid DC PV system, or for module level optimization in partial shade conditions. Ray Walters Remote Solar 303 505-8760 On 11/1/19 1:08 PM, Michael Morningstar wrote: You know Murphy? That is Murphy of Murphy’s Law? He’s gotta just love the idea of AC coupled off-grid systems. The OB, SB, Li system Jay described is going to keep him (Murphy) and the installer very busy at some point. The further away the system is from civilization, the higher the odds of chicanery and headaches. Systems that need backup safety controls seem inherently risky too. On Oct 31, 2019, at 11:06 AM, jay <jay.pe...@gmail.com<mailto:jay.pe...@gmail.com>> wrote: HI Drake, I was just talking with a colleague the other day about a project he did. New Radian, AC coupling, lithium batteries, SB inverters. Everything is working just as it should with the GT inverters tapering during AC coupling frequency shift mode. I would say you are fine, and while I can’t say for sure if the Enphase will work that way, they should as they are all designed to the same parameters rule 21. I always do recommend a aux relay for backup/shutoff should there be some kind of issue. With the Envoy you’ll be able to see that tapering as well. Seems like a good option for your application jay On Oct 31, 2019, at 9:49 AM, Drake <drake.chamber...@redwoodalliance.org<mailto:drake.chamber...@redwoodalliance.org>> wrote: Hi Jay, Between 2160 and 2880 Watts of added array. We will be using a new Radian. Drake At 11:49 AM 10/31/2019, you wrote: How many watts are you adding as ac coupling? And presuming its an older 8k radian? Jay _______________________________________________ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org<mailto:RE-wrenches@lists.re-wrenches.org> Change listserver email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules & etiquette: www.re-wrenches.org/etiquette.htm<http://www.re-wrenches.org/etiquette.htm> Check out or update participant bios: www.members.re-wrenches.org<http://www.members.re-wrenches.org> _______________________________________________ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org<mailto:RE-wrenches@lists.re-wrenches.org> Change listserver email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules & etiquette: www.re-wrenches.org/etiquette.htm<http://www.re-wrenches.org/etiquette.htm> Check out or update participant bios: www.members.re-wrenches.org<http://www.members.re-wrenches.org> _______________________________________________ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org<mailto:RE-wrenches@lists.re-wrenches.org> Change listserver email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules & etiquette: www.re-wrenches.org/etiquette.htm<http://www.re-wrenches.org/etiquette.htm> Check out or update participant bios: www.members.re-wrenches.org<http://www.members.re-wrenches.org> Michael Morningstar Morningstar Electric PO Box 1494 Mount Shasta, California 96067 530-921-0560 CSLB 949635 _______________________________________________ List sponsored by Redwood Alliance List Address: RE-wrenches@lists.re-wrenches.org<mailto:RE-wrenches@lists.re-wrenches.org> Change listserver email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html List rules & etiquette: www.re-wrenches.org/etiquette.htm<http://www.re-wrenches.org/etiquette.htm> Check out or update participant bios: www.members.re-wrenches.org<http://www.members.re-wrenches.org>
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