Frequently Asked Questions

Common questions about Solar Scores, ROI calculations, and our data sources.

What is the Solar Score and how is it calculated?

The Solar Score (0–100) is a composite metric comparing solar potential across states. It combines three factors: solar irradiance (40% weight, from NREL data), estimated payback period (30%), and incentive program density (30%, from DSIRE). Each factor is normalized relative to other states, then weighted and summed. A higher score means better overall solar economics in that state.

Where does the solar irradiance data come from?

Solar irradiance data comes from NREL's National Solar Radiation Database (NSRDB), which provides average peak sun hours per day by state. Peak sun hours are a standardized measure of how much solar energy is available in a location.

Where do electricity rates come from?

Electricity rate data comes from the U.S. Energy Information Administration (EIA) Form 861, an annual survey of electric utilities. We use residential average rates by state from the 2024 release.

What incentives does PlainSolarData track?

We track state and utility incentive programs from DSIRE USA — the Database of State Incentives for Renewables and Efficiency. This includes state tax credits, rebates, property tax exemptions, sales tax exemptions, and net metering policies. Federal incentives like the Investment Tax Credit (ITC) are not included in DSIRE counts but are referenced in explanatory content.

How accurate is the ROI Calculator?

The calculator uses state-level average data from NREL and EIA to produce estimates. Actual solar ROI depends heavily on your specific property (roof orientation, shading, size), local utility rates and net metering policy, installer pricing, and financing structure. Treat calculator outputs as a rough starting point, not a financial projection.

Does PlainSolarData recommend solar installers?

No. PlainSolarData is an informational resource only. We do not recommend, rank, or receive compensation from solar installers. Always get multiple quotes from licensed local installers before making a solar decision.

Why does my state score low even though it gets a lot of sun?

The Solar Score weighs three factors: irradiance, payback period, and incentive density. A state with high sun hours can still score lower if it has poor incentive programs, high installation costs relative to electricity savings, or both. States with high electricity rates tend to have shorter payback periods even with average sun.

How often is the data updated?

NREL, EIA, and DSIRE publish updated data annually. We update our database when major new releases are available, typically in the first quarter of each year.