small panels > big panels (longevity wise)

[MaximusAnonus]

Hi,
I have another "the local bigshots are suggesting something and I don't quite believe them" question:

I've bought a lot of 550Wp DAH panels a few months back for my own use and mounted them quite successfully on my roofs. These panels are quite big (89 inches tall 45 inches wide) but since I have really good roof access the mounting wasn't THAT painful. Still it took longer then expected so this is probably one of the reasons the big shots aren't using them.

Recently I've been told that I messed up big time and that these "big" panels will be all dead with 4 years. Supposedly they are so big that they flex and the solar cells themselves crack and die really soon. And if the cells don't crack then the outer frame separates from the glass and water damage kill the panels first.
Supposedly only small 400-ish Wp panels are used when you really want your installation to last anything bigger and it's only good for a few years.

Now I find that hard to believe. It sound more like the panels are either too big to be mounted quickly so the companies are trying to dissuade people from wanting them. Or they are too big to reach the mount points easily so the crews mounting them are leaning on the glass too much, cracking the cells during installation which kills the panels within a few years.

Thoughts?

 

[houseofancients]

if you make sure the panels have enough support i dont see why this would become a problem.
my "old" 250w panels had 2 support struts, my much bigger 545w jinko's have 3

 

[sunshine_eggo]

Sounds like fearmongering to me. I doubt the manufacturers would be putting these out with 5+ year defect warranties unless they were engineered to perform as one expects modern panels to perform (25+ year performance life).

 

[MaximusAnonus]

Mine are mounted as per DAHs recommendation at the 55inch mark. They don't flex very much even with my full weight (and I'm a big fatso lol) on the frame. And we don't get that much snow or high winds around here to warrant 3 struts IMHO.

 

[peakbagger]

One comment is on older homes with snow loads, there can be quite a bit of deflection of the roof seasonally. Most new structural elements are designed based on maximum deflection of the span (1/360 or 1/240 are typical) versus the working limits of actual strength of the beams. An older structure frequently has far higher roof deflections especially with snow loads. A two rail racking system would not be impacted by deflection of the roof as the mounting points would pivot slightly to compensate. A taller panel with three rails is more problematical as the racking system has to assume a flat roof, it the plane of the roof is curved due to snow than there will be stress imposed on the panel frames which may be transferred to the actual panels. The same may happen with wind loading although I expect snow is bigger issue. Old roofs will also frequently be permanently curved and I wonder how many installers really take the time to ensure that the three rails are in the same plane?. The temptation would be to just crank up on the clips and get rid of the gaps which would preload the panels with stress.

In this special case larger panels could potentially deteriorate from the increased flexing. One solution would be to mount the panels horizontally and go back to a two rail mount or spend the big bucks and head into the attic and stiffen up the roof joists.

Its interesting in my area of NH, the seasonal snow loads over the long run can be quite high, my town is 95 PSF ground snow load with some elevation modifiers while the town next to me is 115 PSF. Typical loads in the rest of the state are 30 to 40 PSF. Yet there is lot of old 120 year old housing stock and many seasonal homes inthe area, that are still standing. Usually on the rare occasions that roofs fail, its almost always alterations to the original roof design or detail failures where someone long ago took a shortcut like poor toe nailing. In some of these older homes the roofs can deflect so much that chimney flashing has to be done with sliding elements to accommodate the deflection