A solar salesperson usually wants one number off your bill — the monthly dollar amount — because it makes the pitch easy. That number is the least useful thing on the page.

Three things to find

1. Twelve months of kilowatt-hours, not one month.California usage swings hard with the seasons — a July bill and a March bill can describe two different households. Your utility publishes twelve months in your online account. Anyone sizing a system off one bill is guessing.
2. The name of your rate schedule.It’s printed on the bill — something like E-TOU-C, TOU-D-4-9PM, E-ELEC or EV2-A. That code tells you whether you’re billed by how much you use or by when, and it sets the hours that matter. The single most informative thing on the page.
3. When you actually use power.A household home all day uses solar as it’s produced. One that’s empty until six and then cooks, charges a car and runs the AC uses power exactly when the sun is going down. Same annual total, completely different answer.

Tiered or time-of-use

Tiered: price depends on how much.

A baseline allowance of cheaper kilowatt-hours, set by climate zone and season; usage above it costs more. The first kilowatt-hours solar offsets are the most expensive ones you buy, so the value tapers as the system grows.

Time-of-use: price depends on when.

Now the default for new residential accounts, and effectively mandatory once you have solar. Peak hours are the expensive ones — on the three big investor-owned utilities, 4–9pm.

The part most people are never told

Under the Net Billing Tariff — what people call NEM 3.0 — the electricity you buy and the electricity you sell are priced differently.

You’re billed the full retail rate for every kilowatt-hour you import, and credited a much lower avoided-cost rate for every one you export. The gap between those two numbers is the entire economics of a modern solar system.

It’s deliberate policy, not a mistake: a retail rate bundles transmission, distribution and fixed costs, while avoided cost is roughly just the generation slice. The consequence is that solar stopped being a game of producing as much as possible and became a game of using what you produce.

Unless you’re on a municipal utility

Cities that run their own utility — Los Angeles, Sacramento, Pasadena, Glendale, Azusa and others — aren’t under the same tariff, and several still credit exports at or near retail. If that’s you, most of what you read about NEM 3.0 doesn’t describe your situation, and the battery case is a different conversation. Check the name on your bill first.

Two things that hide the truth

The blended rate.

Dividing your total bill by your total kilowatt-hours gives an average, and the average conceals the structure. A household averaging thirty-something cents might pay far more at peak and far less overnight. That spread is where the money is.

“One hundred percent offset.”

A system sized to produce as many kilowatt-hours in a year as you consume does not produce a zero bill. Production and consumption happen at different hours and are priced differently, and there are fixed charges for being connected at all. Annual offset and bill offset are two different numbers.

A rough sanity check

As a rough check on whether a proposed array is in the right range — not a design, and not a promise — a well-oriented kilowatt in California tends to produce around 1,400 to 1,700 kilowatt-hours a year. Shading, orientation and pitch all move that. If a proposal implies dramatically more, ask what assumption is doing the work.