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 and state wages; typical sizes follow what homeowners actually install.
- 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. Each state’s typical system size starts from Berkeley Lab’s median installed size for single-family homes there, adjusted for local electricity use, sunlight and electricity prices; nine states with too little data are modeled from neighboring states. 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
Each state’s typical size starts from Berkeley Lab’s median installed size for single-family homes in that state, adjusted for local electricity use, sunlight and electricity prices. Nine states with too few installs are modeled from neighboring states. Each state page prints the install year and the number of systems behind its size. Multiplying capacity in watts by the price per watt gives the gross cost.
The June 2026 edition sized systems as average electricity use divided by yearly output per kilowatt. Tested against real installations, that formula landed within 20% of what homeowners actually installed in only 19 of 41 states, so the September 2026 edition replaced it. People size systems to their own home, roof and electricity price, and higher prices lead to bigger systems.
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
From the September 2026 edition, every state page shows one best-case simple payback:
Payback = typical system cost ÷ (system size × yearly kWh per kilowatt × state electricity price)
- 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 average residential price from the U.S. Energy Information Administration, a 12-month average from August 2025 to July 2026, held flat.
- Production: the yearly output of one kilowatt of panels in that state’s sunlight.
- Export value: every kWh counts at the full average price. That is the best case: most utilities credit exported power at less than retail, so most homes take longer.
Simple payback compares the upfront cost with one year of estimated bill savings. It is not a guaranteed outcome; your rate, your export credit and how much of your power you use at home decide your real payback.
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
- National Laboratory of the Rockies: Q1 2025 Solar Photovoltaic System Cost Benchmarks. NLR/OT-7A40-97930; DOI 10.7799/3009689. Dataset updated March 12, 2026.
- Bureau of Labor Statistics: Occupational Employment and Wage Statistics, May 2025. Solar photovoltaic installers (47-2231); electricians (47-2111) where installer wages are unavailable.
- U.S. Energy Information Administration: Form EIA-861, 2024 final data. Final files updated December 3, 2025.
- NREL PVWatts, website version 8.7.4, for local solar-production estimates.
- Lawrence Berkeley National Laboratory: U.S. Distributed Solar and Storage Data, 2026 Data Update (August 2026). The release date is distinct from the installation dates in the dataset.
- IRS: Residential Clean Energy Credit. Guidance on the credit’s end for property placed in service after December 31, 2025.
- DSIRE: Database of State Incentives for Renewables & Efficiency. Program and policy references; individual program dates and eligibility rules apply.
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.