William, Yes, I think we both agree - the SolarEdge system should be designed *and listed* to work with 600 VDC modules, even if the optimizer-output side is running at 850 VDC. Has SolarEdge given you any indication about whether this is a supported setup?
August On Thu, Sep 9, 2021 at 10:11 AM William Miller <will...@millersolar.com> wrote: > August: > > > > I am not worried about the inverter backfeeding. I only brought that up > because there was a precedent set that in order to rule out an electronic > assembly backfeeding, it had to be listed as such. > > > > Here is what I am worried about: I am worried about the high voltage on > the output of an optimizer crossing over the optimizer in a failure > condition and energizing the input circuit of the optimizer. > > > > If I understand the design process correctly, manufacturing to high > standards is not enough—a listing with a recognized agency to that effect > is also required. > > > > Thanks again for thinking and writing about this. Your experience and > expertise is valued. > > > > William > > > > 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:* Thursday, September 9, 2021 9:34 AM > *To:* William Miller > *Cc:* RE-wrenches; Greg Notley; jonathan.sm...@solaredge.com; > rya...@solaredge.com; Garrett Duffy > *Subject:* Re: [RE-wrenches] "Re-powering" Aging Utilty Scale PV systems > > > > 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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