I know California has a reputation for being unlike the rest of America, but I’m fairly sure they don’t use Euros.

As even the best places in Europe are worse for PV than almost everywhere in CA, and yet PV is working adequately even in bits of Europe as rubbish as the UK (which is more like southern Alaska), the meme that PV is “just for California” needs to go the way of the dodo: https://solargis.com/maps-and-gis-data/download/world

efficiency drops significantly even they perform "ok" which is not the case for nuclear for example.

I don't know what point you're trying to make here. The efficiency with regard to what?

Joules out per unit of currency in? Joules of electricity out per joules of sunlight in? PV is great at those even in the dark moist British Isles, which are about as bad as southern Alaska.

Nuclear however, is really expensive. Situationally useful, but really expensive — So expensive in fact that it's about the same as using dedicated batteries (rather than hydroelectric or hydrogen or refurbished batteries) to support PV when it's too dark.