I'm reminded of Bush calling for the US to return to the moon by 2020 -- a proposal Obama quietly nixed.
I'd much rather we say, "We're going to increase renewables by X% every year, starting now, to reach the goal of 100% renewables by 2045."
Another problem is that nobody else (at this scale at least) got there so it's hard to anticipate all the challenges. Germany, normally at 36% renewable energy, managed to reach that magic 100% figure on a winter early-morning this year. But nothing close to sustained generation. And they plan to get to 100% in 2060+. So California, currently at ~44% renewable energy, could be the first to hit the sustained 100%.
Another problem is that everyone defines "100% clean energy" in different ways, by leaving some sectors out of the count. Will this target cover electrical power or also aims at replacing all non-renewable sources of power for all applications?
Instead say, "we will drop it by 10% in 3 years." Now you're telling me some useful truth to which I can hold you accountable (ooh, politicians HATE that). Incidentally, 10% in 3 years would be a perfect milestone to 100% in 30 years, so if these politicians WERE being honest (they're not), then they should have no reason to refuse the 10% in 3 years idea.
"This bill would state that it is the policy of the state that eligible renewable energy resources and zero-carbon resources supply 100% of retail sales of electricity to California end-use customers and 100% of electricity procured to serve all state agencies by December 31, 2045."
Source: https://leginfo.legislature.ca.gov/faces/billTextClient.xhtm...
From this I take they don't plan to necessarily eliminate all carbon emitting energy sources but rather just the ones used to produce electricity. This would make the goal a little more achievable but also makes it a moving target. As different industries move from burning carbon based fuel to electricity the demand also increases which will still affect the balance between clean and dirty energy.
There are plans to ban ICE engines and other fuel burning applications so the demand for electricity will see a sharp rise. It's more that achievable to be 100% green in 2045 assuming the energy consumption trend of the past. But the future will probably see that trend go from relatively linear to something exponential for at least a few decades until the switch is done. Covering that difference will be the real challenge.
As always, devil's in the details. In the meantime, the headline looks impressive, which is frankly all these critters care about.