How we build & verify our calculators

1. Sources vs. planning assumptions. Source-derived rates and constants come from the utility or agency that sets them — SCE and LADWP tariff pages, the U.S. EIA, the CPUC, the IRS and the DOE/NREL. Third-party blogs are used only to cross-check, never as the primary figure, and we don’t cite ourselves. Where a figure is a Cali Energy planning assumption rather than a published rate (for example a shading derate or a usable-roof factor), it is labeled as such on the tool, with its formula and effect shown.
2. How the effective date is fixed. Each rate is recorded with the date it was checked (for example, “SCE rates verified August 5, 2026”). Utilities may update residential rates multiple times a year, so the date travels with the number.
3. How source conflicts are resolved. When sources disagree, the utility’s own current page wins over third parties, and stale or clearly superseded tables are set aside. Remaining uncertainty (for example, whole-cent rounding of ±0.5¢) is disclosed on the tool.
4. How the arithmetic is checked. Every calculator’s worked examples are computed by hand from the published rates and confirmed against the live tool, so the numbers on the page are reproducible — you can enter the same inputs and get the same result.
5. What “illustrative estimate” means. The tools model published rate structures and typical assumptions. They are estimates, not bills or quotes: your exact charges depend on your rate schedule, billing days, baseline allocation, taxes, credits and CCA status.
6. Why a result is not a quote. A quote requires your actual bill, roof, shading, equipment and interval usage. The calculators are a fast, transparent first pass; a real project figure comes from a full assessment.
7. How to report an error. If a number looks wrong, tell us and we’ll re-check it against the source. Accuracy is the point of the library, so corrections are welcome.
8. Update log. When a tariff or incentive changes, the affected model and its verified date are updated. Each tool shows its own “Updated” date near the top.

Verification registry

Calculators that have completed independent model verification. The rest of the library shows its sources and is being brought to the same standard.

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