[RE-wrenches] RE-wrenches Digest, Vol 4, Issue 135

[Greg Egan]

Doug & Todd,

We install here in Fairbanks, AK and I'm a big believer in a really 
steep tilt angle.  85 degrees or more.  One reason is that it's got to 
be steep enough to shed snow.  If you're array is under snow you're not 
going to get much performance if any.  Second is we get most of our 
sunshine in the springtime.  We get more hours of possible sunshine in 
the summer but as a rule summers are cloudier, so if you miss out on the 
spring sun you lose a lot.  Third is during snow season you definitely 
get some benefit from snow reflection.  I personally have seen a 10% 
boost but some have told me they've seen higher.

  We have some pretty cold temperatures so even if it's sunny out it can 
be well below 0.  Our snow doesn't melt off the panels fast like it must 
in some warmer climes.  I like pole mounts as well because they're easy 
to clean, easy to adjust and will never cause a roof to leak.  Of course 
there are places where they just don't fit for one reason or another.

If you have a pole mount with plenty of room under it for snow (or 
someone who's good with a snow shovel), you can do really well in the 
winter with snow reflection and then adjust as needed for the summer 
months.  If you're going to put something high on a pole you want to 
make sure your foundation and the pole can handle the extra stress.  
Using a structural engineer is better than guesting and you'll sleep a 
lot better during wind storms.

Last, I don't know how they stand up to heavy loads but Sharp NU-U240F1 
(240 watt panel) has two beams that kind of separates the panel in to 
3rds.  This should make it stronger since structurally it's closer to 3 
- 80 watt modules than one 240 watt panel

Best,

Greg Egan
NABCEP Certified PV
Remote Power Inc.
Fairbanks, AK
>
> Hi Doug,
>
> I had a customer's roof mount system break modules this spring after yet another record Mount Shasta snow event. This one brought 8' in 10 days.
>
> The situation here was 15 Evergreen 190 watt modules (rated for 80#/sq ft), on a DP&W power rail mount, on a 6/12 pitch, comp roof. Ice dams were not removed so the bottom edge of 5 module's frames were peeled off the glass... without the frame's support, 2 of the module's glass broke. Evergreen did not warranty the damage.
>
>  From Evergreen:
>
> "The observed damage is attributable to weather related effects, not manufacturing or workmanship issues with the panels.
>
> You are correct, we do guarantee our panels for up to 80 pounds / sq. ft.  However, that is for a uniform load.  The installation manual, page 3 (attached), has the following warning:
>
> The maximum permissible loads apply to uniformly distributed
> wind or snow loading. Care should be taken to avoid mounting
> panels in areas that are prone to drifting snow, icicle and/or ice dam
> formation."
>
> I have come to the conclusion that the only real way to mount PV modules in heavy snow country is on a pole mount with a steep winter angle and enough ground clearance (minimum 6' from the bottom edge of the array to the ground) to allow the snow to keep sliding off the array all winter. A roof mount might still work, but it would need to be greater than ~8/12 pitch (not so good for summer production) and accessible to manual snow removal in those critical situations like we had here a couple of weeks ago.
>
> One of my most difficult challenges is trying to design my installations to mitigate winter snow damage. I realize very few list members have to deal with these kinds of severe conditions, but any feedback on my empirical conclusions would be welcome.
>
> Todd
>
>> Wrenches,
>>
>> Can anyone recommend a panel that is built with more strength or
>> ability to handle greater load.
>> I am installing on a shallow pitched roof and am concerned about snow
>> build up in this particular location.
>> I know you guys out in the Sierra's get a lot more snow than we do.
>> What modules are up to the challenge?
>> Are there any new military spec modules like the old MSX 120's?
>> Any experience or guidance is appreciated.
>>
>> Doug Wells
>> Morrisville, VT 05661
>> NABCEP Certified PV
>> Vermont Solar Partner
>> The Solar Specialists
>> www.thesolarspecialists.com
>> 802-498-5856
>> _______________________________________________
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