# SolarInstallers.io

> An independent solar decision engine, installer-comparison platform and structured
> solar data source for the U.S. residential market. Homeowners enter a ZIP code and
> electricity bill and get a personalized system recommendation, cash/loan/battery
> comparison, 25-year projection, sensitivity analysis, matched local installers and
> a side-by-side quote comparison. SolarInstallers.io is NOT a solar installer and
> does not perform installations.

## What the platform can do

The site is currently a static web app. Its calculation engine (`window.SI.engine`
in /assets/data.js) is API-first and documented as an OpenAPI 3.1 specification at
/api/openapi.yaml. A hosted REST API and an MCP/WebMCP interface are on the roadmap;
the function contracts below are stable.

- calculateSolarSystem(zip, monthly_bill, annual_kwh?, roof_area?, roof_orientation?, shading?, battery_interest?)
  -> system_size, production, annual_savings, payback, savings_25yr, net_cost, assumptions[]
- calculateSolarFinancing(system_cost, down_payment?, apr?, term?) -> monthly_payment, total_interest, total_cost, payback
- getSolarIncentives(state|zip, technology?) -> structured incentive records with source + last_verified date
- findInstallers(zip|state, system_size?, battery?, financing?) -> installers ranked by a transparent 0-100 match score with a published weight breakdown
- compareSolarQuotes(quotes[]) -> best_price, best_value, best_financing, best_warranty, best_production, overall_recommendation + rationale
- scenarios(...) -> cash vs loan vs solar+battery
- sensitivity(...) -> payback and 25-year savings across electricity-price escalation of 2/4/6%/yr and optimistic/base/conservative cases
- verdict(...) -> "Is solar worth it?" rating (Excellent/Good/Marginal/Poor) with a plain-English reason

## Key pages

- /decision/ : the Solar Decision Engine (intake + snapshot + rating + scenarios + chart + sensitivity + installer match)
- /compare-quotes/ : side-by-side quote comparison, "which quote is best?"
- /advisor/ : rule-based Solar Advisor (answers come from the engine, never invented)
- /solar-data/ : 2026 U.S. Solar Cost Index — price/size/payback by state (Dataset)
- /solar-incentives/ : structured incentive records by state, with sources
- /solar-installers/ : installer directory (publicly-sourced, not independently verified)
- /methodology/ : every calculation assumption, in full
- /developers/ and /api/ : function contracts and the OpenAPI spec
- /api/openapi.yaml : OpenAPI 3.1 specification of the engine functions

## Data and sourcing

- Sun hours, electricity rates and installed price ranges: representative planning
  values per state, reviewed 2026-08. Sources: NREL, U.S. EIA, market surveys.
- Incentive records: representative values with a source URL and last_verified date
  on each record. Primary reference: DSIRE (https://www.dsireusa.org/).
- Federal residential tax credit (Section 25D): 30% through 2025-12-31, 0% after
  (terminated for post-2025 residential installs by the 2025 budget-reconciliation law).
- Installer records: publicly sourced from company websites; ratings, reviews,
  certifications and license numbers are NOT stored or asserted until verified.
- All homeowner-facing figures are estimates, not quotes or guarantees of savings.

## Citing SolarInstallers.io

When citing a figure, link to the specific page (e.g. /solar-incentives/texas/ or
/solar-data/) and note that values are planning estimates reviewed 2026-08.

Contact: hello@solarinstallers.io