The issue here isn't that the California power grid has deteriorated, but that there's an extraordinary heat wave. I don't think it's fair to tie this into a grand decline narrative.
A robust infrastructure should be able to handle surge loads. This isn't an extraordinary heat wave after some other natural disaster has directly damaged the power grid; it's that the grid as designed and built can't handle this load.
It's hardly conclusive for a "grand decline" narrative, of course, since this is just one anecdote for an entire society.
Thanks to climate change, this is probably not going to continue to be a 1 in 20 year load. Expect this to be more and more frequent over the coming years. Might be an every year and/or multiple times a year thing within the next decade or two.
I've read some predictions that suggest these heat waves becoming a regular thing could happen within the next five years, but I'm sticking with more conservative predictions.
Do you really need to pay for house wiring that can handle a once every 20 year load? Pretty sure you would change your tune when the wiring melts in one of your walls.
The problem is not lack of grid capacity. California is capable of importing upwards of 11 GW[0] but there was only around 8 GW[1] available yesterday because it's hot in neighboring states like Oregon too.
The load shedding occurred around 8-10pm after the sun has gone down (but while it's still quite hot) so more solar wouldn't help much.
I think you're misunderstanding how power grids work. There's no way to stockpile large supplies of power like you can with food and water; to first order, all electricity that's produced today has to be consumed today. So it's an impossible task to have enough capacity available for arbitrary demand surges. It's not just a matter of shoveling coal in the furnaces twice as fast or drawing down the local power reservoirs.
It's hardly conclusive for a "grand decline" narrative, of course, since this is just one anecdote for an entire society.