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
<mailto: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
<mailto: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
<mailto: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
<mailto: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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