Hacker News Reader

Comment by mikece | Hacker News Reader

I wonder how much efficiency would be lost by using a thicker glass -- or even bulletproof material -- on the panels. I imagine this has been considered but there are technical and financial reasons not to.

View on HN

There is no such thing as material that is "bulletproof", only varying levels of bullet resistance can be certified to specific and highly complex applications of materials or combinations of materials.

You know how car safety is complex and isn't solely attributable to any one system or component, like a seatbelt, or airbags, but rather the combined effects of the whole system of components, in that specific application? Bullet resistance is similar.

My idea for this is basically an enormous, rail-guided heavy, metal garage door that can be raised remotely to cover the entire installation from above. You could even power it with a small power reserve battery that got recharged from the panels, have it automatically get raised when the barometric pressure went too low or after a weather alert for hail came in, etc.

Trying to engineer resistance into the panels for the top 0.1% most extreme hail load is going to increase the cost for everyone, including those who never even get pea-sized hail. Seems wasteful to me.

I imagine having automation to turn the panels vertical during a hail would have saved a good portion of them. I assume these already have motors for turning, so it should be relatively cheap.

And that system would pay for itself at the first event.

But most places will suffer 0 events on this scale in their lifetime, so it's not clear it would pay for itself on average.

Sure, then don't do it, and instead pay into a risk pool, aka insurance.

Would it not be sufficient to angle the panels to 90 degrees so that they're sitting vertical instead of angled to the sun. That would at least minimize the surface are exposed to the falling hail (unless it's really falling at an angle).

I'm guessing the top edges of the panels are (or could be made) strong enough to handle a direct hit.

* * * * * | | | | | \ \ \ \ ---------- instead of. -----------

That would mean mounting the panels a lot higher, and not all panels are mounted on motors due to cost already. The real question is how many panels will be damaged by hail in a 10 year period and back-calculate what it's worth to protect them.

That would exactly negate the efficiency of the panel. You want the normal of the panel to be pointing at the sun which is generally towards the clouds emitting hail. Or are you suggesting an automated panel movement when hail is approaching?

>Or are you suggesting an automated panel movement when hail is approaching?

Yes, big Red Button to re-orient all panels when hail is approaching. Some of these farms are massive so I think it would save enough of them to make it a cost-effective feature. Not sure how much human monitoring goes on though, or if an automated system would be better in case it happens e.g. late at night.

(sorry about the formatting +embarrassed smiley+ )

I think the question is all about cost. How much would it cost to add such a system? And how much is hail damage insurance on those panels? How much does your insurance decrease if you had such a system?

So long as the system costs more than the insurance savings, it won't be common. However, if your insurer starts demanding it, then it will be installed everywhere quickly.

It’s cheaper to just replace the panels if it happens (and probably get a capacity upgrade)

Even clear glass heats up so it takes some of the energy the panel wants.

Why not just put a wire mesh cage above them? You only care about hailstones larger than a certain size, so the mesh is going to be pretty open and won't have much impact on collection. Galvanized steel is cheap and will do fine, no recycling issues either.

I reckon you could suspend a net above each solar panel. Just make the gaps a bit smaller than the diameter of a hailstone that would cause damage.

That'd be quite a bit cheaper.

I think you'd need a kevlar net to catch baseball sized hail going 150mph and that won't be cheap.

Nets have their own issues as they can ensnare birds and trap debris blown around by the wind.

Nets which could be deployed (manually or automatically) during periods of high-risk for hail might be an alternative.

Minimises the risks you highlight, maximises protection of the solar panels themselves.

In this case, the netting need not even be particularly transparent. You're looking for loss-minimisation, rather than maximising electrical production at all times. So a fairly thick or heavy webbing might work.

Keep in mind that as the damage inflicted increases with the kinetic energy, that is, with the square of velocity, even a net or webbing which permitted contact of hail with panels but at significantly reduced speed should serve to avoid most damage.

I'd put my money on something lighter that has enough elasticity to take the punches without shattering

Reply on news.ycombinator.com