[RE-wrenches] Need info resource re wind & hail damage

David Brearley david.brearley at solarprofessional.com
Fri Mar 9 08:12:42 PST 2012


Allen,

We get so-called Texas-snowstorms down here in Austin, especially in the
spring, which are basically sever thunderstorms producing hail, flash floods
and winds approaching tornado speeds. We lost a roof and some window panes
to one hail storm, and had $5k damage done to the car. A baseball-size hail
stone punched a hole through a friend's windshield, but that's atypical. To
my knowledge none of our customers ever lost a PV module to hail.

The best example I can think of was from the day I flew to Austin on my job
interview. Literally, as the plane was landing, a nasty, isolated spring
thunderstorm was cutting across a swath of the city north of downtown. Near
the hotel where I was staying entire colonies of Grackles (a large, dark,
loud bird common here) were left dead in the road.

The next day we found out that a customer's home had been in the direct path
of the storm. The property is located on the edge of a bluff that runs north
and south through the city, so it was completely exposed. The leaves were
stripped off of the majestic live oaks. The garden was turned instantly to
salsa on the vine. The new coat of paint on the house looked like it had
been sandblasted off. The roof was a total loss, chunked up and beat down.

The only exception was the 300 square feet of roof under the PV array, which
was in perfect shape‹‹as was the PV array itself, in spite of some dings in
the aluminum extrusions. In the end, the insurance company declared the roof
a total loss and paid our labor to uninstall and then reinstall the array.

Clearly, if a baseball-sized hail stone had hit the array, it would have
just punched it's way through the glass. But my experience is that if the
hail storm isn't a windshield breaker, it's probably not PV array breaker.

Good luck, David


On 3/9/12 9:00 AM, "Dave Click" <daveclick at fsec.ucf.edu> wrote:

> Allen, UL 1703 simulates a 1" hailstone @ 50mph by dropping a 1.18lb 2"
> diameter steel ball 51" onto the glass "at any point considered most
> vulnerable." IEC 61215 actually uses a 1" ice ball (what a weird thing
> to use when simulating hail, right?) and shoots it at 11 points on the
> module at 50mph. The test procedure is a bit vague as it seems a
> manufacturer can choose for a tougher hail test-- up to a 3" hail stone
> at 88 mph to better reflect the terminal velocity of larger hail. I've
> never seen a spec sheet indicating that a manufacturer has undergone
> testing for >1" hail, though YouTube shows a Conergy module taking a
> 75mph >2" hailstone.
> 
> http://www.youtube.com/watch?v=8ztdmkcd6lE
> http://www.youtube.com/watch?v=aI6K3xlgYoY
> 
> These impacts are all perpendicular to the module. So any module that's
> listed to either of these standards (preferably both) can take at least
> a 1" hailstone, and likely larger though that's not part of the test.  A
> higher-sloped module should be able to withstand slightly greater
> impacts as the impact wouldn't be perpendicular, but of course higher
> slopes will increase the client's concerns about wind. Speaking of:
> 
> IEC tests a 50psf uplift (wind) and a 113 psf downforce (snow). Unless
> you're on a roof corner or eave in a high-wind area, you won't reach 50
> psf. You could offer that a structural PE could stamp your drawings to
> verify this, and their insurance would cover any issue with wind damage.
> More info on these tests was on the list back around October 7-10,
> subject line "Module Load Rating".
> 
> I understand William's point, but since you're answering a direct
> question from a customer with facts and testing information from
> international standards, I'd say you're in the clear. Saying "I've never
> had a module fly off the roof or get damaged by hail and it's a silly
> thing to worry about" or sending an email each week in continued
> attempts to convince the husband would obviously not be the way to go.
> Of course, once you answer these questions, he'll then point out that
> all that metal on the roof will attract lightning from a 500 mile radius
> and he will ask where in the international standards PV is tested to
> withstand direct strikes... and then note that no standard certifies PV
> to withstand the daily 30-year onslaught of morning dew. Good thing
> you're in the desert.
> 
> Hope this helps.
> DKC
> 
> 
> 
> On 2012/3/8 23:13, Allan Sindelar wrote:
>> Fellow Wrenches,
>> We have an engineer-type whose wife wants badly to do a PV system, but
>> he puts up barriers. In her words:
>> 
>>     Well, I don't know how long ago it was, surely old technology by
>>     now, but some experimental solar panels at Sandia Labs were
>>     shattered by hail and it caused a big controversy. My husband says
>>     it turned him off solar.It comes up every time I talk to him. Either
>>     he is complaining about the wind or the hail or whatever.
>> 
>> I get to respond to this, and am seeking specific assistance: Can anyone
>> send me a link to any formal standards, or reports of aggregated field
>> experiences, indicating that wind and hail (not to leave out "whatever")
>> are not issues of concern when PV modules are installed correctly?
>> Anything that came from Sandia Labs would be ideal, but it just has to
>> be reputable enough to satisfy a grouchy retired national lab engineer.
>> Web links, reports, product warranties, etc. - all good.
>> 
>> Thank you in advance.
>> Allan
>> --
>> *Allan Sindelar*
>> _Allan at positiveenergysolar.com_ <mailto:Allan at positiveenergysolar.com>
>> NABCEP Certified Photovoltaic Installer
>> NABCEP Certified Technical Sales Professional
>> New Mexico EE98J Journeyman Electrician
>> *Positive Energy, Inc.*
>> 3201 Calle Marie
>> Santa Fe, New Mexico 87507
>> *505 424-1112*
>> _www.positiveenergysolar.com_ <http://www.positiveenergysolar.com/>
>> 
>> *
>> *
>> 
>> 
>> 
>> 
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David Brearley, Senior Technical Editor
SolarPro magazine 
NABCEP Certified PV Installer 
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