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
_______________________________________________
_______________________________________________
List sponsored by Home Power magazine
List Address: RE-wrenches@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
