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. What are others finding?
I'd love to hear about favored options for complying with rapid shutdown. Any success stories? or better yet, any early failures?
--
Corey Shalanski
Jah Light Solar
Portland, Jamaica _______________________________________________
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