PG&E customers over the next few years may see some big changes in their monthly bills, as compliance with a new state law expands. Right now, bills are based on how much electricity and gas a customer uses. A new proposal would add a fixed monthly charge based on the household income levels of the customer. Along with the monthly charge, the utility would then cut electricity rates by 33%, which could be less expensive for customers who can control their usage. The state Public Utilities Commission will have to make a decision on a final rate and billing structure by July of next year.