Hail damage risk

[Brian53713]

Is there increased risk to panels, from hail,with a super flat, summertime angle? Hailstorms are not super common in the area.Renogy 100 W panels.

[J.P.M.]

Is there increased risk to panels, from hail,with a super flat, summertime angle? Hailstorms are not super common in the area.Renogy 100 W panels.

The more vertical an object's velocity vector angle makes with a surface, the greater the normal component of the impact force will be.

So, as a first guess, I'd think that for smooth, mostly flat (but not necessarily horizontal) and mostly isotropic surfaces such as panel or window glazing, for a hail stone of some random size, shape and impact velocity, I'd suspect the greatest probability of breaking the lite will be for the most normal impact angle. Obviously, small stones/objects will not have the same probability of damage as large stones.

Bottom line practical: In a hailstorm, horizontal glazing or surfaces will most likely take more damage than non horizontal surfaces.

The following explains a lot of the basics better than I can:

https://www.donan.com/article/wind-e...ity-and-impact energy/

[Brian53713]

Thank you for that reply, has anyone ever heard of very many instances of solar panel damage from flat or nearly flat positioning, specifically hailstorms ?

[bob-n]

JPM: Clear explanation and great article. Thank you.

JPM answered Brian's question. But I'm still curious about the risk of hail to PV panels, so I did a search for hail damage to solar panels. All of the links that I found said that hail damage to PV panels is statistically extremely unlikely. Most were from solar companies, so you can understand that they're downplaying the risk. The link that describes a severe hail storm at the NREL site in Colorado was perhaps more objective and seemed to be good reading.

https://www.energy.gov/eere/articles/hail-no-national-labs-solar-panels-survive-severe-storm

[J.P.M.]

Thank you for that reply, has anyone ever heard of very many instances of solar panel damage from flat or nearly flat positioning, specifically hailstorms ?

You're welcome.

To be clear, most all rigid panels are flat. A single solar array at a 30 deg. angle to the horizontal is probably considered flat by most definitions of the word except, it seems, when talking about roofs where flat seems to mean, by custom, "mostly horizontal". But this conversation is not about roofs.

Some arrays are "more" horizontal, or oriented more normal to gravity. Similar to saying lead is heavy, or the surface of still water is horizontal, to say a panel or an array is flat is probably trivial, and says nothing about its orientation which does seem to be the focus of this thread.

To your question, such information may well exist, and I may have missed it, but I know of no specific study, work or information, anecdotal or otherwise in the open literature that deals with the rate or incidence of panel failure from hail events specifically as f(panel or array orientation). However, my knowledge of the subject is mostly incomplete and so I'm mostly ignorant in that respect.

FWIW, check your homeowner's coverage. Apparently, some/many carriers exclude or disallow claims made with respect to damage to active solar energy system such as PV or solar thermal devices from damage by most any source(s), (including BTW, golf balls).

Take what you want of the above. Scrap the rest.

[solarix]

Personally, I've never seen or heard of a hail damaged solar panel. The standard rating on PV panels is 1" hail at 90 mph.

[J.P.M.]

If you have horizontal panels during a hailstorm your best friend just might be wind which might decrease the angle. On the other hand it just might increase the velocity.

You know that for sure, right ? Care to share your source(s) of those opinions ?

From what I think I might know about it, based on training and experience, seems to me the wind might be better described as a disinterested observer, at least when it comes to horizontal surfaces.

Theoretical but also practical and actual reality:
The vector component of a hailstone's velocity vector that is normal to a flat (but not necessarily horizontal), smooth surface (such as a lite of glazing) is what does impact damage. The greater the magnitude of that vector, the higher the probability of damage and the higher the probability of greater damage.
The vector component of a hailstone's velocity vector that is parallel to such a surface cannot impart stone impact energy to the surface and so cannot do any impact damage.

Note however, that is different from and not to be confused with the effects of gross wind forces on the entire structure which are off topic for this post.

For hailstone strikes, a horizontal panel or glazing lite is no more than a special (?) orientation case of the above general orientation case.

If the panels are horizontal, the angle of attack ("decrease the angle" as you write) by a stone doesn't matter. What does matter is the vertical component of the stone's velocity vector (for horizontal surfaces, that's the parallel to gravity component of a hailstone's velocity vector). The horizontal component of the stone's velocity vector (which is one component of the stone's velocity vector) doesn't matter.

That horizontal component of the stone's vector velocity will not add any force to the impact. So, for horizontal surfaces, the angle of incidence of a hailstone on the surface doesn't really matter. Vector mechanics 101.

The stone's scalar velocity, that is, the numerical magnitude of the vector combination of the magnitude of the velocity components is of interest for a structure's wind loading as noted above. That, however, is a different subject than impact loading and effects.

If the panels are horizontal, only the downward component of the stone's velocity vector is what needs to be considered (as well as stone size, and impact distribution - both spatially and temporally, but those are different subjects than velocity effects).

Regard of surface orientation, if the wind vector has any vertical components, and most wind does, and they are downward, those components will increase the downward stone velocity and so increase the impact on a surface of any upward orientation. Conversely, any upward vertical components of a wind vector will tend to decrease the downward stone velocity and so decrease the impact.

However, vertical components of wind velocities, near the ground anyway, tend to be small relative to stone terminal velocities for stones large enough to cause damage (but that's not true of wind velocities higher in the atmosphere where strong updrafts impart upward stone velocities and thus contribute to hail formation and stone size).

It's also usually assumed that the resultant effects of vertical wind vectors' components, both up and down on the stone velocity vector as it nears the ground, tend to cancel each other. Also, in most cases, again near the ground, and depending on nearby terrain and objects (bluff effects being an example), those vertical vector components are usually small enough relative to a large stone's terminal velocity, and also random enough so that they tend to average out to a net additional stone velocity adder of zero.

Take what you want of the above. Scrap the rest.

[J.P.M.]

The operative word in my hypothetical was "might be". I was keying off your post that said, "The more vertical an object's velocity vector angle makes with a surface, the greater the normal component of the impact force will be." It was purely speculative to invite dialogue about the effect of wind on changing the angle of incidence.

I value the experience of @Solarix and the NREL experience at their site in Colorado as more informative than any of the previous posts including mine. To the original posters question I would now say, not to worry. The panels at the NREL site also appear to be horizontal.

If we're going to attempt to invite dialog, I believe this forum would be better off if we all stuck to what we're pretty sure we think we know rather than what we might want to spout uninformed or useless and non productive and otherwise ignorant crap about. Seems to me that such self imposed selectivity might add some focus and direction to the conversation, improve the content and quality of the content information as well as avoid a lot of misinformational B.S.

I'm sure no one really cares about what any of my opinions might be, but I try - with admittedly incomplete success - to make a point to check reality before I mouth off around here as well as check my ego at the door, and stick to what I think I know based on training and experience that will add to a dialogue or discussion.

Meant as sincere and constructive criticism, you might consider doing something similar. Stop speculating and stick to what you know and what you can back up, not simply what you may think.

To me only, your speculative attempt to invite dialogue was misguided by your ignorance of the subject. Try asking questions instead of bloviating.

[SunEagle]

I would be happy to correct any misinformation I posted about the decrease angles of incidence possibly caused by wind. I probably should have quoted you originally as the authority on angles of incidence. I am always happy to give you an opportunity to demonstrate your superiority. Of course in the end, none of either of our comments actually informed the poster about the probability of damage to his horizontal panels. The moderators might be well advised to remove any of these irrelevant posts.

It is sometimes hard to delete an entire post when there may be some good information in it.

To both Ampster and J.P.M.

Please stop snipping at each other on this thread and any future ones.

[Ampster]

It is sometimes hard to delete an entire post when there may be some good information in it.

.........

I apologize and have deleted my irrelevant posts.
I value the experience of @Solarix and thank @bob-n for the NREL link he posted. The NREL experience at their site in Colorado suggests to me that the chances are less than a thousand to one that hail from a storm like the one that hit their facility in Denver will damage a solar panel. Their panels were horizontal and they reported golf ball size hail. @Solarix explained the standard rating of panels is one inch hail at 90 mph.

To the original posters question I would say, not to worry.

[nwdiver]

Thank you for that reply, has anyone ever heard of very many instances of solar panel damage from flat or nearly flat positioning, specifically hailstorms ?

Hail may not be an issue but dust could be. My panels are ~10 degrees and the dust is unable to run off when it rains on the lower lip so part of the last cell line gets 'shaded'. A flat panel would be far worse. IMO you really need to have an angle of at least ~10 degrees unless you want to clean the panels twice a month.