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GridPermit Methodology

This page has two parts: how we verify the facts in our solar permit guides (all 50 states), and exactly what our California-only savings calculator does and doesn't calculate. Where we don't yet have real data, either way, we say so directly instead of guessing.

Part 1: The California savings calculator

Current scope: California only. The sections below describe exactly what today's estimator calculates: no more, no less. This tool is separate from the solar permit guides described in Part 2.

1. What the ZIP code check actually does

We check that the ZIP code you enter falls within California's ZIP code range (90001–96162). That's a structural range check, not a lookup of your address, your utility company, or your specific rate schedule. We do not yet identify whether you're a PG&E, SCE, SDG&E, or municipal utility customer.

2. System size estimate: the only number we calculate today

The "Illustrative System Size" figure is your entered monthly bill divided by one flat placeholder rate of $0.30/kWh, then divided by one flat placeholder solar-yield assumption of 1,400 kWh per installed kW per year. Both numbers are fixed placeholders applied to every California ZIP code the same way. They are not your utility's actual rate, not a regional average, and not adjusted for your city's actual solar irradiance. Real utility-specific rate data and location-specific solar production data are planned but not yet built.

3. Battery sizing

We show a typical residential battery range (10–20 kWh) as general background information. We do not calculate a battery size specific to your household's usage pattern.

4. Savings and payback: Coming Soon

We deliberately do not show a dollar savings figure or a payback period today. Producing an honest number requires real utility rate schedules (including time-of-use and NEM 3.0 export rates), which we have not yet integrated. Rather than estimate this with invented assumptions, we label it "Coming Soon" until it's built on real data.

5. Limitations

Every figure on this site is informational only and does not reflect your roof, shading, equipment selection, financing terms, or your actual utility's rate schedule. Nothing here is engineering, financial, or tax advice. Confirm any real figures with a qualified installer and your utility before making a decision.

Part 2: How we verify solar permit guides

Our solar permit guides, for all 50 states, are built from a separate, source-linked verification process, not the calculator above. Each city guide only publishes facts that came from an official source: a city or county government page, an adopted municipal code section, a utility's own program page, or a state energy-commission or public-utilities-commission document. Every fact on a guide page links directly to the source it came from and shows a confidence score (High, Medium, or Low) reflecting how directly that source supports it. California is our deepest-coverage state today (see California guides), but the same verification bar applies everywhere.

Before a city's guide page is published, the underlying record is run through an automated validator that checks for schema consistency, dangling or duplicate source citations, and internally impossible values (like a review timeline where the minimum is longer than the maximum). A city is only published once it clears two bars at once: most of the fact categories we track are populated with real, sourced information, and the record passes validation with no errors. If a city's record doesn't yet clear that bar, usually because an official source couldn't be reached or a specific fact (like an exact fee amount or review timeline) was never stated anywhere we could verify, we keep it unpublished rather than publish a thin or partly-guessed page. We do not fill a missing fact with an estimate, a typical value from a similar city, or an inference from a neighboring jurisdiction's rules.

Utility-wide facts (for example, a utility's own interconnection program page, which is the same for every city that utility serves) may be reused across multiple city records once verified, but only when we've independently confirmed that utility actually serves that city, and the record says so explicitly rather than implying the fact was re-verified city-by-city.

Every guide page states the date it was last verified. Facts on this site can go stale as cities and utilities change their rules. Always confirm current requirements with the listed permit authority and utility before relying on anything here for a real project.

What "READY" means, and what happens when sources disagree

A city's record is scored on two independent measures: completeness (what share of the fact categories we track, including permit authority, required documents, inspection steps, fees, eligibility, and others, have real, sourced values instead of "not yet verified") and a validation score (a deduction-based score starting at 100 that's reduced for validator warnings, such as an official source URL that couldn't be confirmed reachable). A record is only marked READY and published as a public guide page when completeness is at least 80% and the validation score is at least 85 with zero validator errors. A record with real but sparser sourcing (completeness at least 50%, score at least 75) is tracked internally as LIMITED and not published as a standalone page; everything below that is NOT_READY. This threshold is the same fixed rule applied to every city: no city is published on a lower bar than another.

When two official sources disagree on a fact (for example, a city's own page states one fee and a county-hosted mirror of the same ordinance states another), we cite the more direct, more current source (normally the city or utility's own official site over a secondary mirror) and note the discrepancy in the fact's notes rather than silently picking one. If neither source can be confirmed current, we leave the field unverified rather than guess.

GridPermit is not the city, the utility, the CCA, or any government agency. We independently compile and link to their own public information. If you find a fact on a guide page that's inaccurate, out of date, or contradicts the source it cites, please contact us with the city name and the specific fact; we review corrections against the cited source (or a newer official source, if the old one has moved or changed) and update or remove the fact rather than leave a known error live.