Hi Howie,
I have found one scenario where heat tape can help with snow on solar.
As we know, solar panels warm up in the sun and melt snow even when ambient temperatures are below freezing. The water from this melting snow drips off the array and slush/snow can slide off the panels.
On a cold day, in a well insulated home, or a home with large overhangs, the water dripping off the array will freeze when it hits the roof below the panels. This can create an ice dam that can be an issue for the roof if not properly installed, and also create a barrier to snow shedding from the array. If conditions are right this dam can get quite large and prevent panels from working for a long time in the winter. I have also seen ice dams cause damage to roofs and gutter systems and creep under the lowest row of flat flashings (not micro flashings, yet at least) causing moisture issues.
The is not an issue on all roofs, but can be on many flush mount arrays, on a medium sloped roof (maybe 25-35 degrees), that end maybe 2’ or so from the gutter. Well insulated homes, and/or homes with large overhangs are especially good candidates for this type of ice build up.
In these scenarios a gutter ice melt system that extends up the roof 18” or so can help eliminate this refreeze issue.
I don’t think the cost of the ice melt system installation or operation would be offset by the extra energy you would get from the array, but it would help prevent ice dams which adds additional value.
Personally I would never try to mount any type of ice melt directly to panels. I could see it possibly causing damage to the panels and could also exacerbate this melting/refreeze/ice dam issue if you melt snow when ambient/roof surface temps are below freezing.
Ps. Very interesting vertical east/west video Dave! As we lose net metering here in Illinois people on time of use with east-west arrays will retain the most benefit from their grid tied systems. I hadn’t considered the extreme of vertical bifacial easy-west, but it is very interesting to see some data.
Best,
Garrison
Garrison Riegel
Celestar Solar
(c) 773-515-5168
On Dec 8, 2024, at 8:05 AM, david quattro via RE-wrenches <re-wrenches@lists.re-wrenches.org> wrote:
Here is a very interesting video about vertically mounted bifacial modules - performing surprisingly well.
I'm starting to think that Vertical panels are the only sure fire way to keep them clear. I did a small cabin years ago with 2 panels on the south wall of the cabin. All they wanted is a few lights and cell phone charging
and rarely used in the winter. It worked great. Their Trace 1200 watt inverter was turned off when they were not there and the C40 kept the batteries charged over the winter without any problems. Now I am
stressing over an unreachable camp on an island (you may know this one Kirk) where I updated a 12V system with outback inverter and about 1kw of solar which had been shut down in the winter months. I replaced the inverter with
a VFX3648, added an FM100, Installed 5 kw of PV on a ground mount at 45 degrees (mistake- should have done 60 degrees or more with more space at the bottom but assumed not much snow there, all to run a Starlink and Optics monitoring and lots of cameras. 60 days into this saga today at 4 pm, the signal was lost. Is it snow or ice on the panels, or just lack of enough sun (which has been minimal) which caused low battery cutoff. Batteries are new AGMs and I set cutoff at 45.2. I didn't want to run them too low. If I had some of the panels vertical and 4' above the ground, I could probably be assured that snow would not stay on long. Our problem here in Vermont is that when the clear
weather arrives, it usually comes with frigid cold and ground and pole mounts are kept frozen by the ambient temperature until the sun can warm them up but that doesn't happen with 6" on snow on the face. Only above freezing
temperatures or still air with intense sun will clear them. I'm working on a ground mount now that was started by a previous owner of a property where the base for the ground mount array is a post and beam substructure 4 to 8 feet above the ground. I'm thinking about putting 4 panels vertical and 4 at 45 degree angle on the north edge of the structure and 8 panels at a summer angle on the South edge with adequate space for snow shedding. . We have a temporary array at Approx 35 degree angle that has somewhat shed the snow but with no space for snow buildup, the shedding stops.
I am planning to build a fence around my garden this summer with PV mounted vertically with the stacks of 110 watt modules I have accumulated from repowering pole mounts. South and North side of garden facing south and the east and west sides facing east and west. Any thoughts on this crazy idea?
John Blittersdorf
Off Grid Vermont
Having installed at up to 13,200’ elevation (60° rack mount) and in snow country for most of most of 37 years and dealing with installations by others that almost or
completely come off the roof here is my 0.02:
Low angle roofs less than 35deg seem to take on most of the damage incidents. Avalanches are most prevalent at 32-35+deg. Avys tend not to slide at less than 32 deg.
Is the lower edge of the array shaded or partial shade on part of the array with the low angle winter sun? This allows for ice up on the bottom edge or on a section
of the array.
Is there a drop zone for the snow? I use 5’ min below the leading edge for a mountain install I would increase this to higher.
I know this sounds obvious - Is there a snow fence or obstruction (door shed roof) below the array?
I now install esp. on lower angle roofs a mid-third rail & use 50% more contact to the roof points (cheap array life insurance).
If using a micro inverter or optimizer – attach this to the panel so it flexes with the panel if necessary not the rail mount system. Watch out for bolts that stick
up close to the back sheet.
Happy Hollar Daze all!
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Dana Orzel
GREAT SOLAR WORKS!
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