All utilities have usage based costs and large fixed costs. Historically, all utilities have charged solely on usage. The problem is when you have solar, or solar + battery, your usage goes way down. Unfortunately the grid still needs to be maintained and power plants at peak times (maybe a bit lower, but still high) still need to be paid for.

With usage based bills, people with solar pay less than their fair share for the maintenance component of a utility's cost, which means that this cost is larger for the other rate payers. On top of this California has huge subsidies to early rooftop solar adopters. This structure hurts lower income people more since lower income people are more likely to rent and apartments don't have as much space for / not as interested in rooftop solar.

So the CPUC started exploring different models for adding a bigger fixed charge to the bill and lowering the per-kwh cost. Of course the rooftop solar installers hated this as did the different "equity groups." Which is where you got the idea to adjust the fixed charge based on income.

I don't think it's a great idea but I at least understand where the CPUC is coming from. We probably need more innovation in utility pricing models.