Our Methodology

Data Sources

All data is sourced from four public datasets:

• Solar Resource Data: NREL National Solar Radiation Database (NSRDB) — average peak sun hours and irradiance by state.
• Electricity Rates: U.S. Energy Information Administration (EIA) Form 861 (2024) — residential electricity rates by state.
• Incentive Programs: DSIRE USA (Database of State Incentives for Renewables & Efficiency) — state and utility incentives, tax credits, rebates, net metering policies.
• System Costs: NREL Annual Technology Baseline (ATB) and Lawrence Berkeley National Laboratory Tracking the Sun report.

Solar Score Calculation

The Solar Score (0–100) is a composite metric combining three weighted factors:

• Solar Irradiance (40%): Average peak sun hours per day from NREL NSRDB. More sun means more electricity produced per system.
• Payback Period (30%): Estimated years to break even on system cost. Shorter payback means better ROI.
• Incentive Density (30%): Number and diversity of available incentive programs from DSIRE. More programs mean more ways to reduce upfront costs.

Each factor is normalized to a 0–100 scale relative to other states, then weighted and summed. The score provides a quick relative comparison across states — it is not a prediction of individual installation outcomes.

ROI Calculator Methodology

The ROI Calculator estimates solar system performance using state average data:

• System size is estimated from your monthly electricity bill and state electricity rate (from EIA Form 861).
• Annual production uses state-level NREL irradiance, a standard roof orientation factor, and 80% system efficiency.
• Costs use NREL average installed cost per watt for each state.
• Savings are calculated at current electricity rates without projecting future rate changes.
• 25-year savings subtract the upfront system cost and assume no panel degradation over the period.

These are estimates based on state averages. Actual results vary by property, system design, installer pricing, and utility tariff structure.

Data Vintage

NREL, EIA, and DSIRE release updated data annually. We update our database when new releases become available, typically in the first quarter each year. Current data primarily reflects 2024 EIA rates.

Processing Pipeline

Our ETL pipeline combines data from four sources into a unified state-level solar intelligence database:

• Download NREL NSRDB solar irradiance data and compute state-level average peak sun hours from geographic sampling points
• Download EIA Form 861 residential electricity rate data and extract the average residential rate per kWh for each state
• Catalog DSIRE incentive programs by state, counting and classifying each active program (tax credits, rebates, net metering, SRECs, property tax exemptions)
• Estimate system costs per watt using NREL Annual Technology Baseline and Lawrence Berkeley Lab market data
• Compute Solar Scores, payback periods, and 25-year savings estimates from the combined dataset

No data is fabricated or editorially modified. Solar resource measurements come from NREL satellite and ground-station observations, electricity rates come from utility self-reporting to the EIA, and incentive program details come from DSIRE's continuously maintained database.

Limitations

• Solar Scores use state-level averages — local irradiance, shading, and roof orientation vary significantly within states.
• ROI estimates do not account for utility net metering caps, interconnection delays, or future policy changes.
• DSIRE incentive counts change frequently as programs expire or are created.
• System cost estimates reflect market averages and do not account for installer-specific pricing, permitting costs, or equipment brand premiums.
• Panel degradation over 25 years is not modeled, which means long-term savings estimates are slightly optimistic.
• This site does not provide financial, tax, or investment advice.

Editorial Workflow

Content on PlainSolarData is compiled by our editorial team from official source data. Raw data from NREL (NSRDB irradiance, ATB installed costs), EIA Form 861 (residential electricity rates), DOE Solar Programs, DSIRE (state and utility incentives), and state utility reporting is ingested by our continuous editorial pipeline; narrative framing, guide text, Solar Score commentary, and methodology writeups are drafted by our editorial team from source data and then reviewed line-by-line by the PlainSolarData Editorial team at Kiznis Studio before publication. No page on PlainSolarData is published without human review. We do not accept payment for coverage, placement, or rankings — state rankings and incentive counts are computed directly from the underlying federal and DSIRE data.

Not Affiliated

PlainSolarData is not affiliated with NREL, EIA, DSIRE, the U.S. Department of Energy, or any government agency, utility, or solar installer.

Frequently Asked Questions

Where does PlainSolarData's solar data come from?

Solar irradiance comes from the NREL National Solar Radiation Database (NSRDB). Residential electricity rates come from EIA Form 861 (2024 release). Installed system costs come from NREL Annual Technology Baseline (ATB) and Lawrence Berkeley National Laboratory's Tracking the Sun report. State and utility incentive programs come from DSIRE, maintained by the N.C. Clean Energy Technology Center. All sources are public government or publicly funded research data.

How is the Solar Score calculated?

The Solar Score (0–100) is a composite metric combining three weighted factors: solar irradiance (40%) from NREL NSRDB, estimated payback period (30%) from combined cost and rate data, and incentive density (30%) from DSIRE program counts. Each factor is normalized across all 50 states, then weighted and summed. The score is a relative state-to-state comparison, not a prediction of individual system performance.

How often is the data updated?

EIA publishes Form 861 electricity rate data annually, typically in the fall. NREL NSRDB and ATB cost data update annually. DSIRE updates incentive program listings on a rolling basis as programs are created, modified, or expire. PlainSolarData refreshes its database within weeks of each upstream release — typically a full rebuild in the first quarter each year. Every page displays the vintage year of the underlying data.

Does PlainSolarData earn commission from solar installers or quote referrals?

No. PlainSolarData does not accept referral fees, commissions, lead-generation payments, or sponsored placements from solar installers, equipment manufacturers, utilities, or financing providers. We are not a quote service. Our only revenue is contextual display advertising served by Google AdSense — advertisers have no influence over which states or incentive programs we cover or how we rank them.