The only downside with drawing these kinds of analogies is that you're still paying an operating cost for the unused portion of your production server.

The light falling on a solar panel is free.

Yeah there's theoretical lost revenue, but that's a theoretical loss versus a real loss from operating costs.

If you want to be pedantic, hail falling on solar panels isn't free and happens sometimes. But adding up these kinds of cost requires a large dose of pedantry, because the costs are so small compared to the cost of operating devices that have moving parts.

(Pedantry is fun, of course. I love it.)