If you invest in a coal or gas power plant, there are times where supply outstrips demand, spot prices drop below your marginal costs, so you have to shut down your plant, making your capital investment seem wasted, too.

There also basically always is more supply than demand because customers value reliability (possibly more so at times where demand is high)

What’s different here is that, for solar panels and wind power, the marginal costs of producing electricity are zero, that solar panel ownership is way more distributed, and that supply varies with the weather.

The main question for both cases though is whether the investment makes sense in the long-term.