Two steps. First, what your electricity really costs once the fixed charges are split out of the bill. Then, using that number, whether rooftop solar pays back for your house — or doesn't.
Take one recent bill. You need three numbers from it: the total, the kWh used, and the fixed monthly charge (often called "customer charge", "basic service" or "base charge").
The second number is the one that matters for decisions: it is what each kWh you stop buying from the utility saves you. The fixed charge stays whatever you do. We carry it into step 2 automatically.
The bill tells you the total, not where it goes. A plug-in meter sits between the wall and one appliance and counts its kWh. Leave it on a fridge, a dehumidifier or a space heater for a week, multiply the kWh by your price per extra kWh above, and you know what that one appliance costs you a year.
It can't measure hard-wired or 240-volt loads (central AC, electric water heater, most dryers and ovens). If those are your big users, it won't help — and you don't need to buy anything to use the calculator.
The plug-in meter we'd start with: P3 Kill A Watt P4400 →Plain link: we earn nothing if you buy. It doesn't change the math or the verdicts on this page. How we make money.
Every input below is yours to change. The defaults are placeholders, not facts about your house — replace them with your installer's quote and your own production estimate.