Without knowing the numbers, I'm really just speculating, though; my point is just that it's not a given that this will increase everyone's cost of living.
"Bundling it into construction" as in whoever builds the house pays the upfront cost of the solar installation? This would inevitably pass the cost on through increasing the value of the home. So homes in CA will be harder to afford and mortgages will carry larger payments.
Sure electricity costs will go down some amount to marginally offset the increased mortgage payment. But to definitively claim they will go down _more_ than mortgage payments rise is a ridiculous claim in my opinion because implicit in that claim is the assumption that everyone is missing out on this way to save money and needs the government to impose this mandate for them to realize it.
I think that is an unfounded assumption. It's hard to get an extra loan on top of a mortgage, even if you have a very good use for it. That's why passing the cost on through is not a neutral effect, but a helpful one.