August:
I realized I made a poor choice of words in one place below. When I wrote “fused components” I met melted together in a heat failure, not protected by an overcurrent fuse. Wm August: Thank you for the thoughtful reply. I have come to know I can count on you for that. The article you site is interesting, but I do not think it applies. The article is about current in strings, not voltages. This interpretation of considering string currents was first introduced to me by John Berdner (remember him?) in this article <https://millersolar.com/MillerSolar/Resources/ul_fuses.pdf>. The John Berdner white paper is essentially the same information as in the Solar Edge article you cited and is essential information. What is most interesting to me in John’s article is 690.9(A) FPN. It points out that one cannot ignore the possibility of backfeed from inverters. I have on occasion, when using this 690.9(A) exception to avoid combiner fuses, been required by plan checkers to provide documentation from an inverter manufacturer that the inverter proposed was UL certified to not be capable of providing backfeed current. This is in spite of any intuition that one might solidly hold that inverters can’t backfeed DC current. It’s not true just because it seems impossible, or even if the manufacturer says so, it’s only true if a listing agency says it is true. The question I am asking applies to voltage isolation: If I have 850 volts on the output of an optimizer and the optimizer fries, is there any possibility that fused components could connect the 850 volts to the input of the combiner? Most importantly, does a listing agency say it is not possible? If it is not certified, then using optimizers is not a design option. Three persons from Solar Edge have told me the isolation is infallible. I’m not trying to be difficult, but I really think this assertion has to confirmed by a listing agency. I have not seen that yet. Solar Edge has been quick to reply to my voicemails and has expressed a real interest in this project, much to their credit. I will press this point to them and I will post to this forum what I learn. By the way, I am sure you have not forgotten a recent flurry of posts on this site recently about rapid shut down device(s) frying in use. Optimizers are similar devices in the same demanding environment and exposed to high voltages as well. Equipment failure is always a possibility. Thanks again to those many participants who have replied to my question. I am much smarter because of my wrench forum friends. William Miller Miller Solar 17395 Oak Road, Atascadero, CA 93422 805-438-5600 www.millersolar.com CA Lic. 773985 *From:* August Goers [mailto:aug...@luminalt.com] *Sent:* Wednesday, September 8, 2021 4:44 PM *To:* William Miller; RE-wrenches *Subject:* Re: [RE-wrenches] "Re-powering" Aging Utilty Scale PV systems Hi William - You raise a great question - can you install 600 VDC modules on a 1000 VDC SolarEdge system? Of course the DC optimizer output circuit would need to be rewired with 1000 VDC wiring and connectors, but I think the answer is "yes." According to this article <https://www.solaredge.com/sites/default/files/application_notes_string_combiners_na.pdf>, "In a SolarEdge system, the PV modules are isolated from the DC output circuit by the power optimizer." To me, it sounds like there is no risk of going over the max optimizer input voltage. I would want to verify this with SolarEdge prior to designing any systems, but it seems like a good idea to explore! I was recently on another group chat, and someone mentioned being in a similar predicament to you. They want to upgrade an old central inverter. Anyway, they had found that the SMA CORE1 33 kW unit at least can be strung up to work with 600 VDC modules and wiring: https://files.sma.de/downloads/STPCORE1-DS-en-28.pdf?_ga=2.30799225.717469396.1631144387-1894865662.1631144383 I'm sure you'd have to redo a lot of the conduit and wire to accommodate several smaller inverters, but this might be worth exploring as well. August Luminalt On Wed, Sep 8, 2021 at 4:13 PM William Miller <will...@millersolar.com> wrote: Friends: I learned a new buzzword recently: “Re-powering.” It means replacing inverters on an existing PV system of ten or more years old. Due to the high number of systems of this vintage it appears that re-powering has become somewhat of a sub-industry. The big problem is these systems are all 600 Volt limited PV panels, combiners and re-combiners and there are no 600 volt utility grade inverters being manufactured. I am working on a utility scale system <https://millersolar.com/MillerSolar/Portfolio/Commercial/CommercialTracker/CommercialTracker.html> built about 14 years ago that fits the description above. There are two 250KVA Xantrex GT250 inverters and one has failed. The question of the moment is: Repair or replace? Repair: If we fix these inverters, can we count on support in the future? We can negotiate a service contract with Schneider at a cost yet to be revealed. This requires we buy a spare parts kit for about $100K. There are a few other companies that claim to offer repair services on these inverters but none has followed through. Replace: The PV plant is built with panels and BOS all limited to 600 VDC max. There are no more 600 volt input utility scale inverters being built, or at least none that I have found. If we install a 1000 or 1500 volt inverter we may have to replace the entire PV array and BOS. It may be possible to convert the output of the existing panels to a higher voltage with DC-DC converters. Here are the options I see: Optimizers: One purveyor of optimizers is Solar Edge. Solar Edge offers a 100 KVA inverter. This inverter requires DC input of 850 volts. The inverter requires optimizers to obtain this voltage. The question: Do the optimizers isolate the PV from the higher string voltages in the case of a catastrophic failure of one or more of the optimizers? Repower with outboard DC-DC voltage converters, such as provided by Alencon Systems. Solectria has successfully done this. Here <https://alenconsystems.com/learning/pv-retrofits-with-transformerless-inverters/> is a paper on the subject. If anyone has dealt with this issue before I would sure appreciate any wisdom. Here is a link <https://millersolar.com/MillerSolar/case_studies/30-Re-Powering/re-powering.html> to a web-page I built for this project. Thanks, William Miller Miller Solar 17395 Oak Road, Atascadero, CA 93422 805-438-5600 www.millersolar.com CA Lic. 773985 _______________________________________________ List sponsored by Redwood Alliance Pay optional member dues here: http://re-wrenches.org List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org There are two list archives for searching. When one doesn't work, try the other: https://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/ http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: http://www.re-wrenches.org/etiquette.htm Check out or update participant bios: http://www.members.re-wrenches.org
_______________________________________________ List sponsored by Redwood Alliance Pay optional member dues here: http://re-wrenches.org List Address: RE-wrenches@lists.re-wrenches.org Change listserver email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org There are two list archives for searching. When one doesn't work, try the other: https://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/ http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: http://www.re-wrenches.org/etiquette.htm Check out or update participant bios: http://www.members.re-wrenches.org
