Trevor built the EcoGen Solar Cost Index and owns its inputs, weights and refresh schedule. In the home improvement and residential solar industry since 2016, he sets the assumption set that every cost, payback and worth-it page on this site runs on. Last index refresh: June 2, 2026.
Key takeaways
- The EcoGen Solar Cost Index is one number per state: the standardized installed price of residential solar in dollars per watt, before incentives, for a typical home system.
- Version 1 (2026) covers 52 states and territories. It blends two national marketplace price sets at fixed weights and checks the result against transacted prices from the Lawrence Berkeley National Laboratory where that data exists (19 states).
- Prices are as of March 1, 2026. The typical system size, production and payback figures on every cost page come from the same assumption set, version v1-2026.
- The index is maintained by Trevor Guilday, EcoGen America’s founder. Every cost page names it once, in its methodology note, and links here.
Every solar cost page on EcoGen America carries one sentence that begins “Methodology:” and names the EcoGen Solar Cost Index. This page is what that sentence points to. It explains where each state’s price per watt comes from, what the typical system behind the dollar figures is, and which assumptions turn a price into a payback year, so you can check any number on this site against its source.
What the EcoGen Solar Cost Index Is
The index is a single installed price per watt for each state, before any incentive, for a typical residential rooftop system. It is a standardized figure, not a quote: the same recipe is applied to every state so that a Connecticut price and a Georgia price mean the same thing. Version 1 for 2026 covers 52 states and territories, from Arizona at $2.39/W to North Dakota at $3.83/W.
Inputs and Weights
Version 1 blends two national marketplace datasets that publish state-level installed prices from real quotes: EnergySage marketplace pricing, weighted 60%, and SolarReviews state pricing, weighted 40%. The weights favor the larger quote pool. Where the two sources diverge by roughly 20% or more, the state is flagged in the index file and the divergence is noted in the confidence field rather than averaged away silently.
Where the Lawrence Berkeley National Laboratory publishes transacted prices for a state in its annual Tracking the Sun data update, the blended figure is benchmarked against that transacted price. 19 states have LBNL coverage in this version; the rest are marked as triangulated from marketplace data only, and their confidence field says so.
The Typical System Behind Every Dollar Figure
A price per watt only becomes a dollar figure once you pick a system size. Each state’s typical system is sized from the state’s average residential consumption (EIA-861, 2024) and its production factor, the annual kilowatt-hours one kilowatt of panels produces at the state’s reference location (NREL PVWatts, largest city). The gross cost on a cost page is that size multiplied by the index price. Cost tables then price a range of sizes at the same per-watt figure, labeled as gross before incentives.
Payback Assumptions, Version v1-2026
- 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 is the installed cost divided by the first year’s bill savings. It does not change with system size, and no page on this site says it does; what sizing changes is how much of the 25-year value leaks to a low export rate.
How Often It Changes, and How You Can Tell
Prices carry an as-of date (March 1, 2026 for this version) and every state row records when each source was retrieved. When the index is refreshed, every page that depends on it is recomputed in full, headline price and every dependent figure together, so a page never mixes two versions. The version name, v1-2026, appears in the assumption set on every row.
What the Index Is Not
- It is not a quote. Your installer’s price depends on your roof, your equipment and your utility; the index tells you whether that quote is in the state’s normal range.
- It is not a ranking of installers. No company’s price feeds it, and no installer is scored by it.
- It is not influenced by who pays EcoGen America. Lead partners have no input into the index or the assumption set.
Where the Data Lives
The index file holds, for every state, the price per watt, the two source prices and their weights, the LBNL benchmark where available, the typical system size and gross cost, the production factor, the residential rate and its 5-year growth, the net-metering regime and export credit rate with its primary source, the federal credit status, lease and PPA legality, the license requirement, and the retrieval date of every source. Requests to see a state’s row can go to the founders through the contact page.
EcoGen Solar Cost Index FAQs
Is the EcoGen Solar Cost Index the price I will pay?
No. It is the standardized installed price per watt for a typical system in your state, before incentives. Use it to judge whether a quote sits inside your state’s normal range.
Where do the prices come from?
Version 1 blends EnergySage marketplace pricing (60%) and SolarReviews state pricing (40%), checked against Lawrence Berkeley National Laboratory transacted prices where the lab publishes them for the state.
Who maintains the index?
Trevor Guilday, EcoGen America’s founder, owns the inputs, weights, assumption set and refresh schedule.
How often is it updated?
Each version carries a price as-of date and per-source retrieval dates. When a refresh ships, every dependent page is recomputed in full so no page mixes two versions.
References & Research Sources
- Lawrence Berkeley National Laboratory. Tracking the Sun, 2025 Data Update (transacted residential PV prices by state, 2024 installs). emp.lbl.gov. Accessed June 11, 2026.
- U.S. Energy Information Administration. Form EIA-861, 2024, Parts A and D (residential customers and consumption by utility). eia.gov. Accessed June 10, 2026.
- National Renewable Energy Laboratory. PVWatts Calculator (production factor at each state’s reference city). pvwatts.nrel.gov. Accessed June 2026.
- Internal Revenue Service. One Big Beautiful Bill provisions, FAQs on Sections 25C, 25D, 25E, 30C, 30D, 45L, 45W and 179D (Public Law 119-21). irs.gov. Accessed June 10, 2026.
- DSIRE, N.C. Clean Energy Technology Center. 3rd-Party Solar PPA Policies map, May 2026. Accessed June 10, 2026.
- U.S. Census Bureau. American Community Survey 2024 1-year, table B25077 (median owner-occupied home value). Accessed June 10, 2026.
- EnergySage marketplace state pricing and SolarReviews state pricing, retrieved June 11, 2026 (scored inputs; cited as plain text).