EcoGen Solar Cost Index Methodology

Trevor Guilday
Index maintained by Trevor Guilday, Founder of EcoGen America
The EcoGen data and analytics team, led by Trevor Guilday, builds the Index and maintains its methodology. Current cost-model edition: September 2026.

Key takeaways

  • A state cost benchmark, not a quote for your home.
  • Built from a federal system-cost benchmark, state wages and household system sizing.
  • Calibrated to marketplace quotes; checked against installed prices in 21 states.
  • The national benchmark gives equal weight to all 50 states and DC.

This page explains the September 2026 cost methodology. For the structure of the underlying records, see the EcoGen Solar Database.

What the EcoGen Solar Cost Index Is

The Index is a modeled installed price per watt for a representative residential solar system, before incentives. A consistent method makes state benchmarks comparable. Your equipment, roof, utility and financing can change the price you are offered.

How the September 2026 Model Works

The EcoGen Solar Cost Index, September 2026 edition, is built by the EcoGen data and analytics team, led by Trevor Guilday. It starts from the Q1 2025 Solar Photovoltaic System Cost Benchmarks published by the Department of Energy‘s National Laboratory of the Rockies (formerly NREL). That benchmark breaks the price of a home solar system into cost categories, from equipment to field labor and office costs.

We adjust the labor costs for each state using Bureau of Labor Statistics wage data for solar installers, or for electricians where installer wages are not published. We size a typical household system for each state from U.S. Energy Information Administration electricity-use data and local sunlight. Each state’s figure comes from EcoGen’s proprietary cost model, calibrated against current marketplace quote data from across the country.

Then we check the result against what homeowners actually paid. In the 21 states covered by Lawrence Berkeley National Laboratory‘s 2026 transacted-price data, each state’s figure is compared with real installed prices. The national figure is the plain average of the 50 states and the District of Columbia.

The federal benchmark is the starting cost structure; quotes calibrate the model; completed-installation prices provide a separate cross-check. These are different types of evidence.

The Typical System Behind Every Dollar Figure

We size a representative system using U.S. Energy Information Administration household electricity-use data and local sunlight. Annual electricity use divided by expected annual generation per kilowatt gives a representative capacity. Multiplying capacity in watts by the modeled price per watt gives a gross cost estimate.

This is a comparison scenario, not an engineering design for every household. Check the system size and included work before comparing a quote.

Payback Assumptions

The payback assumptions are set separately from the cost method and did not change with the September 2026 edition.

  • Federal credit: the 25D residential credit is $0 for host-owned systems placed in service after December 31, 2025 (Public Law 119-21). The 48E credit reaches third-party-owned systems only, where leases and power purchase agreements are legal.
  • Electricity price: the state’s residential rate (EIA), escalated each year at the state’s own 5-year compound annual growth rate, floored at 2% and capped at 4%.
  • Panel degradation: 0.5% per year.
  • Horizon: 25 years.
  • Export value: the state’s actual net-metering or net-billing regime and export credit rate, read from the utility tariff or statute, not a national average. The primary source for each state is recorded in the index file.

Simple payback compares the upfront cost with estimated annual bill savings. The result depends on production, self-consumption, export rates and the other scenario assumptions; it is not a guaranteed outcome.

How Often It Changes, and How You Can Tell

September 2026 identifies this model edition. It does not mean every underlying source was collected in September. Check a figure’s model edition, source observation period and retrieval date when comparing editions.

Source updates and model revisions are different. A model revision should be identified explicitly so older results remain interpretable.

What the Index Is Not

  • It is not a personalized quote or a guarantee of savings.
  • It is not an installer ranking or a verification badge.
  • It is not a nationwide transaction average: the installed-price cross-check covers 21 states.
  • It is not endorsed by the agencies or laboratories whose data it uses.

Where the Data Lives

The EcoGen Solar Database explains the state records, the distinction between inputs and calculated outputs, and the limits of state-level comparisons.

The national price-per-watt benchmark is the plain average of the 50 states and Washington, DC: add the 51 values and divide by 51. It is not weighted by population or installation volume. Puerto Rico is not part of this national average.

EcoGen Solar Cost Index FAQs

Is the Index the price I will pay?

No. It provides context for comparing quotes with a similar system size and scope.

Who builds the Index?

The EcoGen data and analytics team, led by Trevor Guilday.

Does 2026 data mean installations completed in 2026?

Not necessarily. A dataset’s release year and the dates of its installations are different. The installed-price comparison is separate from current marketplace quote calibration.

Where can I report a discrepancy?

Email contact@ecogenamerica.com with the state, figure and supporting source.

References & Research Sources

These are the source editions used for the September 2026 cost method and its supporting assumptions. Current marketplace quote data also calibrates EcoGen’s proprietary model. Organization links identify source publishers, not EcoGen partners.

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