Drake, I concur with your approach on this item - 1. Either the shock hazard was reduced by NEC 690.12 with MLPE for the workers *too* or folks have been qualified persons in accordance with NEC 690.4(C) to recognize and avoid the shock hazard for string inverters.
2. Specifically, there's this incident on the list found here: https://www.osha.gov/pls/imis/accidentsearch.accident_detail?id=101927.015 In other words, would this incident have been minimized with the use of MLPE? On Wed, May 6, 2020, 5:41 PM <drake.chamber...@redwoodalliance.org> wrote: > Interestingly enough, the data on the link > <https://www.osha.gov/pls/imis/AccidentSearch.search?p_logger=1&acc_description=&acc_Abstract=solar&acc_keyword=&sic=&naics=&Office=All&officetype=All&endmonth=05&endday=05&endyear=2002&startmonth=05&startday=05&startyear=2021&InspNr=> > provided > shows accidents from gas explosions, falls, health problems and industrial > injuries. None of these incidents could have been prevented by module level > power electronics. This is typical of the data that I've seen so far. > --- > > > > On 2020-05-06 17:22, Martin Herzfeld wrote: > > There could be an issue of encouraging MLPE for worker safety? > > 1. This is data involving incidents with workers in the OSHA Fatalities > and Catastrophe Investigation Summaries found here: > > https://www.osha.gov/pls/imis/AccidentSearch.search?p_logger=1&acc_description=&acc_Abstract=solar&acc_keyword=&sic=&naics=&Office=All&officetype=All&endmonth=05&endday=05&endyear=2002&startmonth=05&startday=05&startyear=2021&InspNr= > > 2. In the past I've observed an arc fault at the module level with > traditional string systems without a listed arc-fault circuit interrupter > NEC/CEC 690.11. The function in NEC/CEC 690.12 would be - to *reduce the > shock hazard *- for *emergency responders* or *firefighters? (NEC 2020).* > However, I've observed thermal events in the panelboard with plans and > workmanship issues. > > On the other hand, falls are the #1 reason for incidents in the > construction industry. > > All the best, > > Martin Herzfeld, Interstate Renewable Energy Council (IREC) Certified > Master Trainer ™ for Photovoltaics (PV) Installation Professional #IREC > 10037 > Contract Training Provider (CTP) > Adjunct Professor, Energy > > California Solar & Electrical Contractor License #00833782 C46, C10, > D56, D31, C-7 - Since 2004 > Solar, Electrical, Trenching, Pole Installation & Maintenance, > Instrumentation > > Contract Solar (PV) Technical Inspector - 3rd Party Inspections > Underwriters Laboratories (UL) Certified PV Installer #17, OSHA 30 > OSHA-Authorized Construction Trainer #32-0105338 > CompTIA Certified Technical Classroom Trainer (CTT+) #T3NSZCNBBKB4QTQG > > * Professional Member, International Association of Electrical Inspectors > #7035507 - Since 2006 > * Accredited and Registered North American Board of Certified Energy > Practitioners (NABCEP) Continuing Education (CE) Training Provider > > > On Thu, Apr 30, 2020, 8:29 AM <drake.chamber...@redwoodalliance.org> > wrote: > > > I would like to see real data on the fire risk of string inverters. > Anecdotal problems are not data. > > The industry is definitely heading toward MLPE due to the rapid shutdown > requirements. In many cases MLPE makes sense, in other cases it doesn't. > > Systems that are more cost effective and reliable can often be built by > using string inverters. > --- > > > > > On 2020-04-29 22:05, Jason Szumlanski wrote: > > "Rapid Shutdown does not prevent fires." > > Not true. If the effect of RS is to steer the market to MLPE, I believe it > has a significant impact on reducing fire risk. As one who has watched a DC > conductor fire smolder out of control, I am sold on an AC module or > microinverter architecture. While RS on a DC array doesn't necessarily > reduce fire risk within the array, it still has the potential to reduce > severity and spread. Nothing is going to prevent all fires. I get that. > We're talking about risk mitigation when it comes to RS. > > As for "dependable string inverters," the one dependable feature is > failure at least once in the module lifetime, accompanied by a shocking > repair bill. > > I'm not a shiny object following kind of guy, but the writing is on the > wall. MLPE is the future. Modular, serviceable, disposable if you will. > Like it or not, Edison is going to lose this battle to Tesla (Tom vs > Nikola). And I live less than 5 minutes away from Tommy E's winter home in > Fort Myers, FL. And I "grew up" in the industry living off-grid in DC > power. But AC distribution wins for safety at various scales. > > > > > > > On Wed, Apr 29, 2020, 9:42 PM <drake.chamber...@redwoodalliance.org> > wrote: > > Rapid Shutdown does not prevent fires; it was originally drafted to allow > firefighters to vent a roof without being hindered by energized PV arrays. > This rule was expanded to include other DC wiring from PV sources. > > As for PV safety, I'd like to see some significant, statistical evidence > that shows there is a major fire danger from PV relative to other sources. > A fire from a solar array gets a lot more press than one from a gas leak, > bad wiring or an ash tray emptied into a wastepaper basket. > > Large public buildings should have all the protection that is available. > Does one size fit all? > > Would it be reasonable to allow residential installations under 12 kW, > with 1/4 of the roof adjacent to the array available for venting, to be > excepted from 690.12? What about sparsely occupied commercial buildings > with ample roof area open for ventilation? > > Many of us have chosen to work with renewable energy technology to lessen > the harms caused by fossil fuel extraction and combustion. The need for > non-carbon based energy sources has become extremely clear. > > The old string inverters still chug along year after year, with little or > no maintenance. Someone must pay for the ongoing maintenance of module > level electronics. Dependable string inverter systems should be allowed > unless statically significant danger can be demonstrated. > > Drake > --- > > > > On 2020-04-29 16:01, Jason Szumlanski wrote: > > I have been to several PV fires for string inverter systems, both > commercial and residential, and have seen many DC systems at serious risk > of fires or in various stages of melted insulation and connectors. Most of > these systems have exhibited good to excellent workmanship. Things just > went wrong. Some were traceable to animal damage, wind, or other > unmitigated factors, and some were unexplained. I disagree that there isn't > justification for rapid shutdown. > > In my opinion, what we need is some additional innovation and competition > in the MLPE space. Reliability is clearly a key factor, but there is no > denying that MLPE has added safety benefits among other benefits. And if > you do enough volume and set up your business for efficiency > (standardization of product offerings), MLPE isn't much more expensive. It > becomes a negligible cost relative to the benefit. The value proposition is > easy to convey. There are limits to this, but for the majority of > residential and small commercial installations, MLPE has become the de > facto standard around here. String inverters are dinos, and replacing 8-12 > year old transformer based inverters is many times more annoying than some > MLPE swaps. I will admit that the roofs around here are pretty easy to > walk, so that is a factor that might not apply to you. > > If you go under due to manufacturer product failures, you are not writing > your contracts right or not charging enough for service issues beyond your > control. I believe that's a red herring. You might suffer some reputation > damage, but for someone that has been installing MLPE for over a decade, > that is totally manageable. Consumers find a service call to replace MLPE a > LOT more palatable than a surprise inverter replacement that could cost > thousands of dollars. People just don't plan for that. > > Regarding rapid shutdown devices, I have also come across a few that > "someone" has bypassed around here. I don't know if they were never > installed properly or disabled/bypassed due to failure. It seemed > suspicious to me at the time. I remember that it made me wonder what good > is a rapid shutdown device if it is easily defeated? That's another > argument for MLPE. It has pretty failsafe MLPE functionality. > > Jason Szumlanski > Florida Solar Design Group > > > > On Wed, Apr 29, 2020 at 10:59 AM <drake.chamber...@redwoodalliance.org> > wrote: > > Clearly, rapid shutdown increases cost and reduces reliability. Given the > excellent safety record of PV, prior to rapid shutdown being required, it > is unnecessary. The few anecdotal incidents of PV fires were not enough to > justify the requirement, especially on smaller systems. > > According to a friend who worked for a local installation company that > went under, a big part of the reason for their failure was the chronic > replacement of microinverters and optimizers. > > What steps can be taken to create some balance in the rapid shutdown > requirements that are in the NEC? > > > --- > > > > On 2020-04-29 07:27, Sky Sims wrote: > > So far rapid shutdown has been a nightmare. It's added a lot of cost for > no measurable benefit. > Using always off devices like midnight solar and Tigo makes it impossible > to test open circuit voltages. Which opens the door to tons of problems > when commissioning systems. > Also we've been trying out midnight Solar's product and have had an absurd > failure rate. Which means lots of truck rolls and troubleshooting and > system downtime. They send replacement product but they aren't paying for > the lost weeks of productivity. > We have Tigo product in hand and are deciding which project to try it on. > But our big concern about using it is not only the inability to confirm > open circuit voltage of the strings but also the way panels bypass if the > device doesn't allow the panel to connect properly. Both of these features > are a recipe for problems and potential troubleshooting nightmares. The > warranty from Tigo doesn't cover our expense if the product fails. And > that's really what our reservations about the product boil down to right > now. If we're on a job with 50 units and one fails, the contractor or the > homeowner will be the ones eating the expense of finding it and replacing > it. There has to be a better option. > > Sky Sims > Https://EcologicalSystems.biz > > On Apr 28, 2020, at 7:46 PM, Corey Shalanski <coreso...@gmail.com> wrote: > > Now that 690.12 of the *NEC* 2017 has been in effect for several years, I > am curious how designers and installers are meeting the associated > requirements with string inverter-based systems (*not* considering > microinverters or DC optimizers). I am generally a fan of the KISS > principle, and as best I can determine the *Tigo* TS4-F device is one of > the simplest options currently available on the market. 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