Solar panel edges / prevent wind? (not sure what to call them)

[desmo907]

Not sure what to call them but I notice some new panels around town and they have something on the edge that is like a wedge - perhaps to prevent wind from coming under the panel?
I assume they are add-ons and they look nice too.
Wonder what they are called, can they be attached to any panel (easily) and costs.
I have the Phono 204w poly panels..

Thoughts?

[J.P.M.]

Not sure what to call them but I notice some new panels around town and they have something on the edge that is like a wedge - perhaps to prevent wind from coming under the panel?
I assume they are add-ons and they look nice too.
Wonder what they are called, can they be attached to any panel (easily) and costs.
I have the Phono 204w poly panels..

Thoughts?

They probably don't hurt and might help a bit with efficiency by reducing array temps. a bit from reduction of the "bluff" effects possibly caused by the flat edges of panels that are mostly vertical to the wind.

I doubt however, that would produce a noticeable effect and is probably not measureable.

One thought: For arrays very close to the roof deck (~ <3" or so), I might consider mounting them slope side down to perhaps improve air flow beneath the array. But I'm pretty sure most folks would get them for aesthetic reasons with not much concern for efficiency or array temps, and in any case, probably not worth the price for the possible and small efficiency improvement achieved.

[emartin00]

I'm assuming what you are referring to is the wind deflector. All of the new "rail-less" systems use them, as well as some traditional systems. They aid in reducing the uplift forces from wind, and also help them meet the fire code requirements.
They are system specific, so you probably won't find one to fit your existing system.

[J.P.M.]

I'm assuming what you are referring to is the wind deflector. All of the new "rail-less" systems use them, as well as some traditional systems. They aid in reducing the uplift forces from wind, and also help them meet the fire code requirements.
They are system specific, so you probably won't find one to fit your existing system.

How do they reduce uplift ?

[Raul]

Over here those terminal end are used on flat roof floated ballasted instals only. They serve one purpose , stoping vermins and birds to house under panels . On a roof slope the racking is strong enough to handle the winds and air circulation should not be blocked to aid cool the panels as a loft space can get much hotter than a flat roof void.

[emartin00]

How do they reduce uplift ?

By stopping excess wind from coming up under the panels. It's not the main purpose, but does have an effect.

[J.P.M.]

By stopping excess wind from coming up under the panels. It's not the main purpose, but does have an effect.

If you are referring to the possibility of reducing the possibility of up lift, I seriously doubt such devices have any measureable effect at all.

Thinking about it a bit, I suppose, in theory anyway, and perhaps under steady state conditions (uniform wind vector and no overlying gust conditions), I'd think that a tapered leading edge might channel a bit more air flow over the top face of an array. That would allow an increase in wind vector magnitude over the face of the array. The venturi effect caused by the increased (relative) velocity would then cause a slight uplift.

Sometimes, "booster mirrors" are added to arrays, in the past, usually for solar thermal collectors. The wind calcs for such design considerations are concerned with forces caused by the reflectors and their size, not the forces induced by the wind when it's under an array that is parallel and, say, 6" from a roof deck. Those forces, such as they exist at all, are basically calcd' as stagnation forces (how Pitot tubes work) or sometimes as a form of what are sometimes called "velocity head" forces, and are uplift in nature.

In both cases, such forces (venturi or velocity head induced pressure differences) are, in all likelihood, miniscule compared to the normal (both senses of the word as in customary or expected, and also vertical) and constant weight loads imposed on the supporting structure (a roof ?), which, for PV anyway, is quite small, and in most cases often dwarfed by other possible loadings such as seismic.

Those tapered edge additions do nothing to an array other than make it look different, with beauty being in the eye, and perhaps, and in theory only maybe, impair efficiency a bit.

[emartin00]

Those tapered edge additions do nothing to an array other than make it look different, with beauty being in the eye, and perhaps, and in theory only maybe, impair efficiency a bit.

I beg to differ. Ask SolarCity to leave them off. They won't, because the system does not pass the fire testing required by UL without them.
It depends on the system obviously. Most traditional rail systems will pass without the wind deflectors, but rail-less systems will not.

[J.P.M.]

I beg to differ. Ask SolarCity to leave them off. They won't, because the system does not pass the fire testing required by UL without them.
It depends on the system obviously. Most traditional rail systems will pass without the wind deflectors, but rail-less systems will not.

I believe what you write. What SolarCity is saying is something I'm ignorant of at this time, so I can't and won't challenge it, but I'm dubious of what you were told until I check further. Perhaps my cynicism will prove unfounded in this case. In any case, it doesn't sound like the reasons you were given for such deflectors have much to do with changing uplift characteristics.

Further, if rail-less systems result in an array being closer to a roof and thus reducing the free space beneath an array, and thus reducing air flow and thus increasing array temps. with a corresponding decrease in efficiency, and perhaps a shorter potential service life, I'd wonder about the efficacy or wisdom of such a design other than to reduce first cost in some way at the expense of quality and robustness of design - something of a dubious and short sighted goal in my book.

[emartin00]

I believe what you write. What SolarCity is saying is something I'm ignorant of at this time, so I can't and won't challenge it, but I'm dubious of what you were told until I check further. Perhaps my cynicism will prove unfounded in this case. In any case, it doesn't sound like the reasons you were given for such deflectors have much to do with changing uplift characteristics.

Further, if rail-less systems result in an array being closer to a roof and thus reducing the free space beneath an array, and thus reducing air flow and thus increasing array temps. with a corresponding decrease in efficiency, and perhaps a shorter potential service life, I'd wonder about the efficacy or wisdom of such a design other than to reduce first cost in some way at the expense of quality and robustness of design - something of a dubious and short sighted goal in my book.

You don't have to take my word for it. Just ask any of the manufacturers (Zep, QuickMount, Ecolibrium, etc).

Rail-less systems aren't necessarily any lower to the roof than tradition rail system. In fact, they typically are about the same height. I believe the rails on a traditional system help reduce the spread of flame, and without them, you need an additional piece.

[J.P.M.]

You don't have to take my word for it. Just ask any of the manufacturers (Zep, QuickMount, Ecolibrium, etc).

Rail-less systems aren't necessarily any lower to the roof than tradition rail system. In fact, they typically are about the same height. I believe the rails on a traditional system help reduce the spread of flame, and without them, you need an additional piece.

I choose to take you at your word. As for height, of the several arrays with tapered edges I've seen up close and personal (four I believe at this time, all from SolarCity), all of those had about 1" -2" of clearance. Guess I better get up to date on mounting systems.