Rain water wear on roof; is it a problem?

[RobBob]

I am getting ready to install a solar system and one concern I have is rainwater wear on the asphalt shingles. Without the panels, rainwater fall uniformly on the roof. However, with panels installed the panels will concentrate several square feet of rainwater in a small area at the bottom edge of the panels. Is wear on the shingles an issue at the bottom of the panels? Or am I being paranoid?
Thank you for your responses.
-RobBob

[DanKegel]

We just asked a roofer a similar question -- whether having a 2nd story downspout pour onto the porch roof instead of making a long downspout to avoid that.
His opinion was that dumping water on the roof from a downspout wasn't a problem.
So there's one data point for you. No idea if this varies by climate or anything. This was in Los Angeles where rain is infrequent but strong.

[inetdog]

We just asked a roofer a similar question -- whether having a 2nd story downspout pour onto the porch roof instead of making a long downspout to avoid that.
His opinion was that dumping water on the roof from a downspout wasn't a problem.
So there's one data point for you. No idea if this varies by climate or anything. This was in Los Angeles where rain is infrequent but strong.

The two potential problems are:
1. The water flow is so strong that it washes the gravel off the roof it is hitting. This is more of a problem if there is debris in the water coming down from the upper roof.
2. If the lower roof is very shallowly pitched, there is a chance that a misdirected flow may cause water to back up under the shingles.

[RobBob]

Queston got a little off track about rain runoff and shingles

The two potential problems are:
1. The water flow is so strong that it washes the gravel off the roof it is hitting. This is more of a problem if there is debris in the water coming down from the upper roof.
2. If the lower roof is very shallowly pitched, there is a chance that a misdirected flow may cause water to back up under the shingles.

I guess my question got a little off track. What I am asking has anybody seen problems with the gravel getting washed off of asphalt shingles due to rainwater running off of the solar panels?

[J.P.M.]

I guess my question got a little off track. What I am asking has anybody seen problems with the gravel getting washed off of asphalt shingles due to rainwater running off of the solar panels?

I haven't but that's because most of the roofs around here are concrete.

However, rainwater rolling off an array and therefore concentrating the runoff to a relatively small area seems to be a problem over time. Several homeowners in my HOA have older solar water heaters. Speaking with them, a couple have had problems with leaks and water damage to the plywood sub roof. Similarly, when I replaced/reoriented my solar water when I bought this house, I had to repair some roof rot - you guessed it - right below the old collector. My educated guess is that a large RATE of water flow in a relatively small area may be too much for the normal situation. I suspect that may be one reason why God made gutters.

All the solar devices on my roof now have match painted (to the tiles) aluminum on the roof below the panels. Fortunately, it doesn't rain much here so the repainting is infrequent (but truth to tell a bit of a PITA).

[SunEagle]

I guess my question got a little off track. What I am asking has anybody seen problems with the gravel getting washed off of asphalt shingles due to rainwater running off of the solar panels?

I would not think that the water "falling" off the end of your solar pv array onto the low part of the roof will do much more "damage" then running off the entire upper part of the roof to the lower. There might be some more "impact" force due to the 4 or 5 inch height of the panels above the roof but not enough to create a significant "water fall" effect.

One thing the pv array will do is prevent the shingles under it from being exposed to direct sunlight which is what heats up the asphalt and loosens the granules. Less granule loss will extend the shingle life span.

What type of shingles do you currently have and how old are they?

[peakbagger]

I have never observed it. What can really impact the life of the roof are a bunch of installers doing an install when its too hot. Asphalt shingles should not be walked on when the outside temp is much over 70 degrees, If they get too warm, anyone stepping on them can scuff off all sorts of granules. Self installers can plan for this but pro installers are paid to install no matter what the weather and that includes superhot conditions.

[quitepossibly]

There are gaps in between the solar panels, so not all of the water is going to "waterfall" on the bottom row.

If you were really concerned about it, you could always reroof the section underneath the solar panels and use something like Grace Ice and Water Shield as the underlayment.