Hi William - I think I'm picking up on a couple of separate issues here. First, the question is whether you can install a module rated for 600 VDC max on a 1000 VDC SolarEdge system. I realize that the article I linked to was talking about string combiners and currents, but the isolation between the module side and output side of the optimizer was the point. The max input voltage on the optimizers is less than 100 VDC, so it would seem safe to connect a module rated at 600 VDC. Keep in mind that this is just the maximum system voltage, not the Voc, Vmp, etc. Still, I would want to verify this with SolarEdge prior to proceeding with system design.
Your second issue related to whether the inverter will backfeed in a fault condition is addressed in that article. I haven't done my homework to know whether the inverter listings test for this particular fault situation. I know that most string inverters (or maybe all?) that we've designed with over the last 15 years say that they don't contribute reverse fault current, so we don't count that current in our calculations for fusing. So getting back to your question - what happens if the optimizers fail, will modules be destroyed too? I'm sure SolarEdge's design team hopes the answer is no. Depending on how they fail, who knows? Let's hope they are designed and manufactured to the highest standards. August On Wed, Sep 8, 2021 at 11:11 PM William Miller <will...@millersolar.com> wrote: > 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 > >
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