Israel mandated roof top solar water heaters for a while (since 1980 according to [0], but essentially every building built since 1960 or so has one). It's relatively cheap, pays for itself in 3-5 years, and is carbon neutral. This stores energy as hot water, not using PV panels (such as those discussed in the article). A relatively small panel per apartment is sufficient.
I do not claim that the California directive is sensible, but it is worth comparing to a somewhat similar directive that has been in place for 40 years with great effect - reducing grid energy production by 8%, saving everyone money (if the article is to be trusted), and only being a minor eye sore ....
Residential solar thermal no longer makes any kind of economic sense. These existing mandates only show how government regulations can serve to ossify bad practices and harm innovation.
Not a citation, but when I last looked at it for a cabin, the plumbing costs, pumps, and extra stuff required in addition to the normal heater drove the cost so high that it was just cheaper to add more PV panels, which have been coming down because they are made in great volume.
Someplace without freezing weather, or someone who might just say “too cloudy too long, no warm shower today” might have a different calculus.
As far as sun goes, Israel is comparable to California, and all data I was able to find is along the lines of "8% less energy production required, 3-5 years ROI".
To me that does make economic sense, both at the state level and at the individual level; why do you call it a "bad practice"?.
AFAIK, the laws do allow PV panels instead of solar thermal. I'm not aware of any innovation harmed by such a mandate in either Israel or Portugal. Do you?
I do not claim that the California directive is sensible, but it is worth comparing to a somewhat similar directive that has been in place for 40 years with great effect - reducing grid energy production by 8%, saving everyone money (if the article is to be trusted), and only being a minor eye sore ....
[0] https://www.reuters.com/article/idUS311612153620110318