Methodology

Every threshold on this site is owed to a primary source — and we name it on the page where the number lands. Industry rules of thumb are not a source. Each citation carries the verification date so a reader can see how fresh the underlying release is.

How we source claims, in 30 seconds

Production against NREL PVWatts + NSRDB.
Residential rates against EIA Electric Power Monthly.
Tax-credit timing against IRS Form 5695 (2025) instructions.
Installed $/W against Berkeley Lab Tracking the Sun.
State and utility claims via DSIRE plus the utility tariff itself.
No installer ratings. No lead-gen. No automated state-tax math.

Sourcing tiers

Tier 1 — primary regulatory and scientific. NREL PVWatts (production estimates and NSRDB irradiance), EIA Electric Power Monthly (residential rates and escalator reality check), IRS Form 5695 / Residential Clean Energy Credit (tax-credit eligibility), LBNL Tracking the Sun(installed $/W bands and dealer-fee range), and the DOE Homeowner's Guide to Going Solar (consumer-protection framing). DSIRE is referenced as a pointer for state and utility incentive lookup; we do not make automated state-law claims downstream of it.

Tier 2 — authority explainers.SEIA industry data used only for adoption numbers, never for advocacy claims. LBNL Electricity Markets & Policy reports. Peer-reviewed solar economics papers.

Tier 3 — specific-fact and contract-language. Installer warranty terms cited from public spec sheets when relevant. IRS and FTC enforcement actions when a specific dealer-fee abuse is on the public record.

We do not cite as authority: EnergySage, SolarReviews, Solar-Estimate, Forbes Home Solar, or any installer-affiliated brand-roundup content. These are competitors and lead-gen funnels, not primary sources.

Scope: federal only, no automated state claims

TrueSolarCost does not automate state, utility, or local incentive claims at launch. Federal tax-credit timing is checked on-site against IRS Form 5695. State and local incentives — credits, rebates, sales- and property-tax exemptions, performance payments, and net-metering treatment — should be verified through DSIRE and the homeowner's utility tariff. State-by-state doorway pages, automated state-tax math, and utility-specific calculators are intentionally out of scope until the federal spine is stable.

Calculator inputs and formulas

Each calculator page exposes its inputs, the formula behind the output, and the public source for every constant in the math. The quote calculator additionally surfaces verdict reasoning — which threshold a number tripped, and the source of that threshold — so a reader can audit the audit itself.

Review cadence

IRS guidance and EIA rate releases are re-verified before any publish that surfaces them. NREL and LBNL inputs (production ranges, $/W bands) are re-verified quarterly. DSIRE pointers are re-verified whenever the relevant state surface is touched. Each page lists an Updated date that reflects the most recent re-verification, not the build date.

What we don't do

We don't fabricate homeowner anecdotes. We don't cite publication numbers we haven't verified. We don't present AI-generated rooftops as photographs. When a calculation has a known uncertainty (10-year vs short-term rate escalator, regional production variability, dealer-fee range) we state both bounds rather than rounding to the optimistic one.

Questions or corrections? Contact us.