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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