What matters most
Model when your home uses electricity, not only how much it uses. The value of energy consumed on site can differ materially from the value of energy exported to the grid.
Understand the applicable tariff
Most new residential systems served by California's large investor-owned utilities fall under the Net Billing Tariff. Export compensation varies by time and is not a simple retail-rate credit. Municipal utilities can use different rules.
Ask the installer to show hourly production, household load, imports, exports, and the exact tariff assumptions used in the proposal.
Battery sizing is an operating question
A battery may shift midday production into higher-value evening hours and provide backup power, but its economics depend on tariff, usable capacity, efficiency, degradation, warranty, and which circuits are backed up. Compare the solar-only case with solar-plus-storage.
Test your assumptions
Use the calculator as a planning model, then replace its defaults with current utility and installer figures.
Open the calculator →Questions to ask before signing
- Which utility tariff and export values are used in the savings model?
- How much production is consumed directly, exported, and stored?
- Which incentives are assumed, and who confirms eligibility?
- What happens to warranty service if the installer closes?
- Does the battery support the intended backup loads during an outage?
Methodology and primary sources
Primary references include CPUC net-metering and net-billing guidance, serving-utility tariffs, US EIA electricity data, NREL PVWatts, and DSIRE. Rules and prices are checked again before any dated figure is published.