[RE-wrenches] PV and Roof Flammability

[Matt Lafferty]

Wrenches,

I'm coming from a perspective of comparing "beneath array" areas to "not
beneath array" areas of the same roof. Regarding flammability, I don't
really care what the source of ignition is in this conversation. I prefer to
think that the PV isn't the cause, frankly. Would rather think in terms of
flying embers from a fire in the area (wild fire, neighbor's house on fire,
chimney, etc.), but I don't think we can discount any cause out of hand.

I think it is very important to understand that the UL tests are designed to
emulate pre and early-stage combustion, as opposed to emulating a
fully-involved fire situation. This is important because it marks the
difference between "fire resistant" and "fire proof" materials. Only fire
proof materials would survive to pass a full-on fire test. These tests
essentially test the fire resistance of roofing materials. 

Another element to understand is that these tests only test from the top.
They don't emulate an attic-fire burning thru the sheathing and engulfing
the roofing materials from the back. 

Based on observation and farm boy commons, it seems to me that the biggest
problem area is low-profile, flush mounted arrays over petroleum-based
roofing materials. These are parallel to and close to the roof surface. Most
commonly with horizontal rails below the surface of the modules, thereby
reducing the effective clearance to the roof by the height of the rail.
Which dramatically reduces convection. This mounting configuration
concentrates heat onto the roof surface and traps roof gasses beneath the
array from otherwise normal ventilation.

Gassing is normal and occurs throughout the life of most roofing materials.
Petroleum based roofing products tend to gas at a declining rate throughout
their life cycle. This gassing is not generally combustible in these
concentrations. Combustible gasses are created when a roofing material
begins to burn. Early-stage combustion. If these combustible gasses are not
allowed to evacuate quickly, the fire is exacerbated.... Gaining heat and
intensity quickly. Flame spread.

Once the roofing material is fully involved, meaning self-sustained burning,
it's probably not gonna matter much whether there is an array above it or
not unless someone is there to fight the fire. 

The "chimney" effect behind a tilted array would have three primary effects
on this cycle. The first effect is that normal gassing would occur similarly
to adjacent roof sections not covered by the array. The second is that,
during pre and early-stage combustion, the combustible gasses will not
concentrate between the module and the roof, effectively reducing the fuel
and heat concentration by some amount. Possibly to a level that is equal to
adjacent roof sections not covered by the array. Possibly even extinguishing
an ember or small flame in a manner similar to blowing on a lit match. The
third effect would occur once the roofing material is fully involved. In
this part of the cycle, the chimney effect could certainly draw more air
into the fire, possibly increasing its intensity, much like blowing into the
base of a campfire.

>From a pure flammability perspective, I like the tilted array better than
the flush array. My reasoning is primarily that normal aging will be more
likely and, if an ember were to reach the roof beneath the module, it is
more likely to self-extinguish or at least act like the adjacent roof. These
characteristics reduce the overall liklihood of actually catching fire in
the first place. Which I like. 

In the event that the roof beneath a tilted array were to become involved
and induce an adverse chimney effect, the fire would be WAY more accessible
to a water hose than with a flush mounted array. 

Another negative that a flush mounted array has in the fully involved
scenario, is that it's gonna melt down for sure. If this is happening during
daylight hours, it may contribute more ignition source from the DC arcing
and sparking in close proximity to the already flaming roof. 

The real question at hand is to determine the affect(s) on roofing
flammability caused by mounting PV above the roof materials and compare that
to the flammability of identical roofing material, on an adjacent surface
without an array above it. Part of a comprehensive study will include
evaluation of various mounting methods, on different slopes, above various
roofing materials. Anything less is suspect and must be discounted. 

For example, if the tests are only performed on a flat, level plane, they
won't properly model real-world sloped-roof installations. Similarly, if the
tests are only performed at a single low-angle pitch, they are incomplete. 

Ryan is right. At some point, we have to accept that collateral damage will
occur. As part of that, we must determine how
much/many/frequent/catastrophic is acceptable. My definition of
acceptability goes like this: Collateral damage is acceptable as long as
it's somebody else's customer.

I would guess that we all share a similar definition when we get right down
to it. Which sort of causes a problem, doesn't it? This is at the heart of
why I am in favor of responsible testing to determine the truth in this
matter. Because we all want it to be somebody else's customer and we can't
make sure it's not our customer unless we understand how to do that. We
won't really understand how to do that unless somebody goes thru the
exercise of testing stuff and telling us what the results are.

I suspect that testing will show that most common sloped-roof materials will
maintain their UL rating as long as there is something like a 6" clearance
up-slope for convection. Meaning 6" between the roof surface and any
horizontal rails. I don't think one can honestly argue that "there's an
array over that piece of roof so hot embers can't get onto the roof surface
in that area". Sort of like having a disaster response plan composed of "It
will never happen". 

I say be proactive on this issue or somebody else will make decisions for
us. We just might learn something important along the way and avoid some
really hard lessons in the future. Even if it's somebody else's customer.

Like all of us, I am concerned about further limitations on PV deployments.
The CalFire guidelines pretty much strangle a lot of potential residential
installations and, in my opinion, are overkill that provides very limited
benefit. That sucks. Bonehead AHJs cause a lot of grief. That sucks.
Uncertainty about materials supply or incentives... That sucks too. Big oak
tree in the neighbor's yard. That sucks. Foreman quits to go into business
for himself. That sucks. Third microinverter failure in a week. That sucks.
When it comes down to it, we have to deal with all kinds of things that suck
on a daily basis. Some avoidable and some not. Let's avoid the avoidable
ones.

$0.02001

Solar Janitor

PS... On a brainstorm note: It occurs to me that laying a corrugated metal
roof skin over the top of an existing roof material should effectively
increase the fire resistant characteristics to an acceptable level. A
physical barrier. A roof condom. I figure that you wouldn't need to attach
it to the roof... Just secure it to the standoffs and rails, attach some
stiffener system to eliminate the wind-rattle, and you're golden. Just a
thought.


-----Original Message-----
From: Michael Welch
Sent: Thursday, September 23, 2010 12:50 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] PV and Roof Flammability

Hi gang. It seems to me that an upward sloping gap between the flammable
roofing materials and the PV modules would result in a chimney effect for
any fire in the roofing materials whether the fire is a result of the PV
system or not.

Combine that with the modules blocking access to a roofing fire, and maybe
you have their concern.

Just guessing here.

Ryan LeBlanc wrote at 12:43 PM 9/23/2010:
 
>Good points all,
>
>Has anyone had an experience where you've seen new shingles and PV 
>installed at the same time, where the shingles became prematurely 
>brittle beneath the array, where you could say for sure it was PV's 
>fault?  I too have tried to keep an eye on that, but I never can pin it 
>on PV, most are still retrofits, not lending any credible data.
> 
>As long as the PV doesn't cause the fire, due to:
>- Ground-faulted or otherwise compromised wiring
>- Melted cheap-o junction boxes (lowest cost import products)
>- Improperly wired roof mounted combiners (reverse polarity)
>- Conduit/expansion fitting errors (like the TARGET fire)
>- The fact that they simply will be in the way if firefighters have to 
>vent...
>
>Are we saying there is evidence that the "PV shade structure" can 
>increase the flammability of the roof product from combustion, due to
proximity?
>Trapping a combustible level of heat beneath the array that can dry out 
>and set fire to comp shingle? Hypothesis = 1 in a billion, necessary to 
>look at, sure.  Maybe 1 in a 1/2 billion for wood shake.
>
>Solutions I see then:
>-They can be stuck to the roof, no air gap no problem.  Well, except no 
>possibility of removal for firefighters.
>-Integrated into the roof, then maintenance and wiring is buried.
>-0-5" (or whatever), no go due to too close.
>-5" (or whatever) and higher, Ok, due to adequate airflow and lack of 
>proximity.
>
>So now we're going to need PV compatible roof product ratings?  PV has 
>a great track record ratio of installs to related fires, and this is 
>with a majority of installers NOT really knowing what their doing, me 
>included.  I hope we don't have to get more expensive as a result, 
>let's make the roofers tell us which ones are not compatible, and then 
>we can just tell them to stop installing it.  PV is too important. :o)
>
>I have to believe that having a roof covered by PV, especially in CA, 
>could also Help Prevent fires from falling embers from forest and field 
>fires, the occasional PG&E GAS LINE EXPLOSION BLOWING UP WHOLE
NEIGHBORHOODS, etc.
>
>Most material science would indicate that shading of the roof, the 
>overwhelming majority of the time, will extend roofing product 
>lifespan, often significantly, and help keep the attic a bit cooler.
>
>Let's not let officials overdo it, as I get more frustrated and 
>educated about this overly passive and tolerant society of ours, I'm 
>beginning to believe a little collateral damage is completely 
>acceptable.  It obviously is for the big boys of energy, money,
automobiles, policy, etc.
>
>*See BURNING THE FUTURE (Coal), GASLAND (Natural Gas), FLOW (For Love 
>of Water), all the oil movies (oil), The Cove (Dolphins)... etc.
>
>We could probably have a roof fire per day, and still be doing better 
>than these "A" for alternative holes, except we'd get blitzed by the bad
guys.
>Thanks again for keeping watch guys.
>
>$.0001
>
>P.S. WHERE IS OUR FEED-IN TARIFF?... oh what, the PPA's have it 
>covered, oh yeah, they don't want one, great for us.  Is anyone 
>watch-dogging these PV finance guys?  They're the ones that scare me 
>the most, you know, the ones that get lost at the "T" for
"truth-in-lending".
>
>Thanks for your relentless service to the industry that could save 
>America, if only they would let us.
>
>Ryan J. LeBlanc
>NABCEPT Certified Solar PV Installer
>Cell: 707.591.1950
>Direct: 707.536.9839
>ryan at NaturalEnergyWorks.com
>http://www.NaturalEnergyWorks.com
>
>
>
>
>_______________________________________________
>List sponsored by Home Power magazine
>
>List Address: RE-wrenches at lists.re-wrenches.org
>
>Options & settings:
>http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
>
>List-Archive: 
>http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org
>
>List rules & etiquette:
>www.re-wrenches.org/etiquette.htm
>
>Check out participant bios:
>www.members.re-wrenches.org


_______________________________________________
List sponsored by Home Power magazine

List Address: RE-wrenches at lists.re-wrenches.org

Options & settings:
http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org

List-Archive:
http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org

List rules & etiquette:
www.re-wrenches.org/etiquette.htm

Check out participant bios:
www.members.re-wrenches.org