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

Fri Mar 9 13:54:59 PST 2012

Hi folks,

I have heard of a whole array being smashed by hail at Waterloo near the
Sydney airport.

Hail does not always fall straight down.

Usually the hail comes in from the South in this part of the world, and as
the arrays are pointing North, damage is rare.

This storm swung back and came in from the North due to a wind change, and
hit the array perpendicular.

The same storm hit Canon/Unisolar style panels with no glass on the Sydney
Olympic Stadium and no damage ensued.

For this reason, arrays in Australia that I have designed for
telecommunications are all thin film with no glass.

Maybe your client would consider this option. 

Carl Emerson
Free Power Co.
Web   www.freepower.co.nz

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

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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