I have been following this discussion intently. I hate to say it, but it all sounds like a major case being made for AC-coupled system architecture, and even integrated "AC Batteries" like Powerwalls and Encharge that integrate the battery and inverter into listed Energy Storage Systems. As someone who keeps exploring getting back to DC Coupled systems for some significant reasons, the complexity and lack of standardization makes that a big leap.
I started out with Heart 12V inverters and moved toward Xantrex SW and moved on to Outback GFX and dabbled in other brands before changing businesses and going basically all grid tie with Enphase, later with some Powerwalls and then back into battery backup exclusively with Enphase. In the last three years, I've dabbled with Sol-Ark and done service on a bunch of DC coupled brands (begrudgingly usually). The Enphase system is so limited in terms of max battery capacity, but in terms of design simplicity and safety, I can't think of a better option for consumers right now. The problem of dealing with high ampacity DC circuits keeps me from wanting to jump back into DC Coupled systems despite the advantages of cost, capacity and efficiency for off-grid applications and backup. So from what I'm reading here, the DC charge control is an issue when DC batteries are abruptly disconnected. It seems like an AC-coupled PV system is the answer to that, but it still leaves some DC battery disconnect issues to be considered, especially the remote disconnect issue that can come up. My pipe dream is for Enphase to drastically cut their price and drastically increase their battery capacity, and then get rid of all of the ridiculous communication issues that frustrate me endlessly. Their unique AC coupling that parallels generator output to PV via the System Controller is a novel approach, albeit limited in flexibility. Absent my dreams coming true, maybe someone will come along with an integrated answer that solves some of these DC coupling issues. I'm not holding my breath that standards will be developed. We're more likely to have a slow march toward AC coupling as codes make it harder and harder to comply with the DC issues. Jason Szumlanski Principal Solar Designer | Florida Solar Design Group NABCEP Certified Solar Professional (PVIP) Florida State Certified Solar Contractor CVC56956 On Wed, Feb 1, 2023 at 4:50 PM Brian Mehalic via RE-wrenches < re-wrenches@lists.re-wrenches.org> wrote: > Most firefighters are not electrical engineers; nor are most insurance > agents. However both of those groups are stakeholders with influence over > codes and standards. Some may say too much influence, but the fact of the > matter is that code making is a group/consensus process, and very often > none of the groups get exactly what they want (in fact sometimes a group > accepts exactly what it doesn't want to leverage that for something they > do; yes it often smacks of politics). I would appeal to y'all to submit a > proposal for the 2026 NEC® - they are due by September of this year. Better > yet would be to circulate language that this, or some other, group can work > on, agree on, write a solid technical justification for, and sign their > names to and submit - the more stakeholders that support a proposal the > more weight it has. > > It seems that the PV Industry Forum, or another similar body, may again > begin work to develop PV and storage industry stakeholder-consensus PIs to > submit; in the past this was a very successful endeavor. I'll post on this > list if and when that happens so that anyone that is interested can get > involved, but don't let that possibility keep you from submitting any PIs > on your own. > > Maybe in the meantime, a control system that shuts off the PV, and then > the batteries, would be worth designing. > > Brian Mehalic > > > > > On Wed, Feb 1, 2023 at 2:10 PM James Jefferson Jarvis via RE-wrenches < > re-wrenches@lists.re-wrenches.org> wrote: > >> >> >> On 2/1/2023 2:58 PM, Starlight via RE-wrenches wrote: >> > Have you (or any) installed surge suppression on the PV input side to >> > clamp the open circuit voltage surge? >> >> That's not where the issue is and isn't really a solution. As I >> explained in my previous e-mail, the issue is the open circuit on the >> output leaves no where for the energy in the MPPT controllers inductor >> to go and the only option is for the voltage to rise until it finds >> somewhere to go. >> >> Surge suppressors, such as sold by Midnite Solar, are nothing more than >> Metal Oxide Varistors. Or in the case of Delta, they are pieces of wire >> in sand. They require large rise in voltage before they conduct. >> >> MOVs are sometimes found on the battery side of inverters and charge >> controllers, but their clamp time and voltage before clamping requires >> additional circuitry that works faster to protect fragile semiconductors. >> >> >> If you are proposing using a surge supressor to regulate the voltage of >> an island between a charge controller and an inverter when the battery >> is disconnected, that's also a no go. Once the MOV clamps, it stays >> clamped until voltage goes essentially to zero or until it blows up. >> It's not a regulator. >> >> - >> >> To further stir the pot, it is definitely possible to design electronics >> that can deal with load dumps and survive most anything. Aerospace >> electronics come pretty close. But all that costs money and takes space >> to do. Are we comfortable with requiring $16,000 charge controllers so >> they can handle load dumps reliably from a poorly thought out NEC >> requirement? I think the fossil fuel industry would be very happy with >> the cost of renewable energy electronics being an order of magnitude >> more expensive. >> >> >> >> >> > >> > Larry Crutcher >> > Starlight Solar Power Systems >> > >> > >> > >> > On Feb 1, 2023, at 1:23 PM, William Bryce via RE-wrenches >> > <re-wrenches@lists.re-wrenches.org >> > <mailto:re-wrenches@lists.re-wrenches.org>> wrote: >> > >> > I can also backup what Jim has said, and have seen the same gear >> > destroyed by removing the battery abruptly when the controller is under >> > heavy load. They can die, and sometimes die spectacularly. >> > >> > Have seen SolArk inverters integrated MPPT controllers blow up when >> > lithium battery BMS disconnects. Not a field fixable issue. >> > >> > Just flip off the breaker when the solar is working hard and and the >> > SolArk will give up the smoke. >> > >> > Like I originally said, it’s the non talked about issue that is a big >> > issue depending on what gear your using. >> > >> > On Wed, Feb 1, 2023 at 2:49 PM James Jefferson Jarvis via RE-wrenches >> > <re-wrenches@lists.re-wrenches.org >> > <mailto:re-wrenches@lists.re-wrenches.org>> wrote: >> > >> > >> > >> > On 2/1/2023 12:25 PM, Alex MeVay via RE-wrenches wrote: >> > > Although our controllers are probably smaller than what you >> would be >> > > considering in this discussion, surviving a load dump (suddenly >> > > disconnected battery) is an engineering requirement for us, and >> > likely >> > > would be for other responsible MFG's on this list (boB?). The >> charge >> > > controller can either handle full input voltage on the output, or >> > > there is a comparator that will shut the controller down >> instantly >> > > when the output voltage gets too high. >> > >> > So that's part of the picture. >> > >> > The other part of the picture is the rest of the system. The >> discussion >> > and what NEC is mandating is that the battery be disconnected. As >> > far as >> > I can tell, there isn't an explicit requirement in all cases that >> > all of >> > the power inputs into the system are all going to go away at exactly >> > the >> > same time .... or ever. This leaves things like charge controllers >> > getting input power potentially from PV or wind or grid or >> generator or >> > something else. And nothing in the NEC, as far as I can tell, is >> > mandating that all of the DC loads be disconnected. So the loads are >> > online. Now the regulation circuit (switching power supply in the >> case >> > of a MPPT controller) is regulating variable loads and nothing is >> > providing substantial resistance to change. Normally the battery is >> > acting like a very very very big capacitor. But without the battery, >> > there isn't enough damping in the control loops and voltage >> stability >> > will suffer. This is where you get 250 volts on your normally 48 >> volt >> > battery bus. Or 3 volts. Or -80 volts. Or all of those in a >> fraction of >> > second. This sort of thing is hard on electronics and will cause >> > failures. >> > >> > >> > Alex's comment about Genasun's controllers handling full input >> voltage >> > on the output is probably unique to their niche product. Looking at >> > their biggest controller, it appears to support VOC of 34 volts. At >> 34 >> > volts, he can use 50V or 100V rated components on his output. For a >> > 150V >> > input controller, you probably can. But you wouldn't because it >> > would be >> > too expensive. But on a 600V or 1000V controller, there's just no >> way >> > that you do that because 1000V rated components are big and >> expensive >> > and their spacing requirements are huge compared 100V level sort of >> > stuff. So the way bigger MPPT controllers deal with load dump is >> with >> > transient voltage supression or other diodes to handle the voltage >> > spike >> > caused by the inductor when the load goes away. When operated in >> > parameters, these parts don't wear out. But it can be interesting to >> > size them adequately to account for inductance elsewhere in the >> system >> > adding to voltage and energy that has to be absorbed. >> > >> > >> > There is a very simple experiment that anybody can perform to see >> how >> > equipment handles a load dump: Simply wait for a sunny day and turn >> off >> > the battery breaker. If no magic smoke was released, turn back on >> > battery breaker. If still no magic smoke was released, then great, >> your >> > system survived a load dump. >> > >> > If you are at all uncomfortable doing this and/or your system gets >> > destroyed in the process, think back to my earlier security comments >> > about having a self destruct switch on the outside of your building >> > allowing anyone walking by to do this experiment for you. >> > >> > I have personally destroyed Outback, Midnite, and Morningstar >> > controllers inadvertently or intentionally doing load dumps by >> shutting >> > off their output breaker. Typically the TVS diodes short out and >> > secondary over current protection (circuit breaker) trips before >> things >> > catch on fire. Usuaully the UL94V0 rating on the circuit board and >> the >> > box the circuit board is in prevents fire from spreading when >> things do >> > get wild. >> > >> > But I've also seen all of those brands survive a load dump. >> > >> > I have multiple customer who have fielded lithium battery systems to >> > cold locations and have had battery BMS disconnect the battery from >> the >> > rest of the system. Ten's of thousands of dollars of equipment has >> been >> > destroyed in these islanding events. >> > >> > >> > Some thoughts, for what they are worth. >> > >> > -James Jarvis >> > APRS World, LLC >> > >> > >> > _______________________________________________ >> > 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. 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