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@positiveenergysolar.com_ <mailto:al...@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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