netting? ha! thanks for the funny visual so early in the morning.
Nets are flexible. The energy of the collision goes into accelerating the net at the point of the collision. The net can quickly spread that energy into accelerating the surrounding areas of the net and so on. Unlike with a rigid cover this is not nearly instantaneous, so you don't have all the kinetic energy of the hail being poured into the net at once. That and the ability of the net to rapidly spread energy means that you don't get enough energy anywhere to break the net. It just stretches as it decelerates the hail.
You can see how this works by watching a soccer game and observing how the nets at the goals stop balls. Hailstones that weigh more than a soccer ball are extremely rare, as are hailstones that are falling faster than many strikes and penalty kicks in a professional soccer game, and you don't see many soccer balls breaking through the net.
People have calculated how fast a soccer ball would have to go to get through the net and found that it is over 220 mph. The largest recorded hailstone is estimated to have had a terminal velocity of 168 mph, based on size, mass, and atmospheric conditions. That hailstone had about 16% more kinetic energy than a 220 mph soccer ball and so might have broke the net, but soccer nets are by no means the strongest nets that can made. And remember that was the largest hailstone ever recorded--we are talking a once in decades event.
You want high tensile strength and some level of flexibility/elasticity to absorb the hailstone energy over a greater-than-zero distance. Or to shatter the hailstone well above the solar panel.
Probably too light-blocking to leave up continuously, and maybe awkward and failure-prone to deploy automatically.
So insurance is probably more cost-effective for most installations.
Just because your local car dealership(s) didn't opt for hail protection nets isn't on its own evidence for or against their effectiveness. There are a great many factors that go into such a decision and, unless you were privy to the decisionmaking process itself, whether or not nets were considered -- much less their effectiveness -- is pure speculation on your part.
The point I'm trying to make is just that there are a lot of off-the-shelf (or nearly so) hail protection strategies that seem like they might have better economics than single-axis-tracking installations, which might improve the cost effectiveness of a fixed panel installation to the point where, even in hail-prone regions, it might be doable.
To be clear: anti-hail nets are already a COTS product, just not for this application (as far as I'm aware). Nets are just really, really good at absorbing kinetic energy. I mean, that's effectively what kevlar ("bulletproof") vests are made of -- netting with a very small cell size. But it seems to me like some kind of roll-out kevlar or dyneema netting could be really effective at protecting panels, though I think you'd need some kind of better strategy for safely dispersing the hailstones after they were caught, so you don't end up with a huge collection of hailstones on the net.
I agree that there's probably too much light blocking to leave them up continuously, and I'd also be worried about UV damage. But remember that the comparison here is to single-axis-tracking installations; I think automatic deployment of anti-hail netting could easily be made at least as reliable as the tracking system, if not significantly more so. Maintenance and testing would also be very cheap in comparison, since you could do it at night (ie without affecting power production), and damage to the protection system could be repaired without taking panels offline.
The more I think about it, the more I'd be interested in seeing it deployed.