Scenario basic help please

Scenario Manager sounds like a good fit for this. I’d probably create a scenario for each tariff period, such as the old rates, current rates, and any major changes, then use the same consumption and solar figures to see how the final bill changes. Excel lets you switch between those saved sets of values without manually replacing the figures each time.

Another simple option is to keep the different electricity rates in a small table and select the period you want to calculate. That might be easier if you mainly want to compare historical bills. I’ve been doing something similar when checking electricity costs, and I also keep copies of bills using Source Website so I can refer back to them later.