Links
The resources this calculator is built on, and the ones I'd point a friend to. Three buckets: other free tools, primary data sources, and sites that explain solar well. Found a good one I'm missing? Let me know.
Similar free projects
Other free tools and open resources — no paywall, and little or no sales funnel.
- CleanEnergyCalc — a big set of free, no-signup calculators for solar, EVs, heat pumps and rebates, built on EIA/DOE/NREL data. Jiseok is doing some great work here.
- Plugin Solar — Balcony Solar Savings Calculator — savings estimator for plug-in / balcony solar, a category most US tools ignore.
- NEM 3 Calculator — a free, no-signup payback estimator focused on PG&E net billing, working the hourly avoided-cost rates and battery value in detail.
- Google Project Sunroof — satellite-based roof potential and a rough savings estimate.
- NREL System Advisor Model (SAM) — a free desktop app for detailed cash-flow and performance modeling.
- NREL REopt — a free techno-economic optimizer (more oriented to commercial and resilience cases).
- pvlib python — an open-source library for modeling PV output, if you code.
- OpenEI — open datasets, including the Utility Rate Database of machine-readable tariffs for most US utilities.
Data sources
Primary data and official references — much of what the calculator's fixed assumptions are built from. The How it works page ties each number to its source.
- NREL PVWatts — free first-year production estimate for any address; the tool's production model is 112 saved PVWatts runs.
- EPA eGRID — grid CO₂ intensity by region; feeds the "Our future" carbon lens.
- CPUC Avoided Cost Calculator (E3) — the model California uses to set the value of exported solar.
- PG&E Energy Export Credit values (full hourly data) — the month × hour export-price sheets behind the $0.06/kWh net-billing default.
- SDG&E export pricing — SDG&E's equivalent export-price files.
- DSIRE — the database of every US state and utility solar incentive and net-metering rule (browse all programs).
- EIA Electric Power Monthly — authoritative US retail electricity rates by state, updated monthly.
- EIA Annual Energy Outlook — long-run federal projections for electricity and fuel prices.
- LBNL — Tracking the Sun — annual report on what US residential solar actually costs to install.
- LBNL — A Review of Value of Solar Studies (2025) — a survey of what distributed solar is worth to the grid.
- LBNL — One Year In: Impacts of NEM 3.0 — early data on how California's net-billing switch changed payback.
- NREL — PV Degradation Rates — the field data behind the 0.5%/yr default.
- NREL Annual Technology Baseline — cost and performance baselines for solar and storage.
- PV Value® — the Appraisal-Institute-endorsed method for valuing solar at a home sale.
- fueleconomy.gov — EV label guide — the source of the 33.7 kWh-per-gallon gasoline-equivalent figure.
- EPA Social Cost of Greenhouse Gases — the basis for the social-cost-of-carbon slider.
- IEA PVPS Task 12 — life-cycle carbon footprint of PV manufacturing.
Informative sites
Good places to learn, get context, or follow the industry. Not data the calculator uses — just worth reading.
- DOE — Homeowner's Guide to Going Solar — a plain-language government primer; a good first read.
- Clean Energy Reviews — genuinely technical, well-written explainers on panels, inverters and batteries.
- EnergySage — Solar learning center — solid explainers (it's also a quote marketplace, so expect a sign-up prompt).
- Canary Media — nonprofit clean-energy journalism.
- pv magazine USA — industry news, policy and technology.
- Electrek — solar and EV news for a general audience.
- Rewiring America — home-electrification guidance and research.
- SEIA — the US solar trade association; policy tracking and statistics.
- CALSSA — the California Solar & Storage Association; NEM 3 explainers and advocacy.
- Solar Rights Alliance — consumer-side advocacy on California solar policy.
- r/solar — an active community; useful for quote sanity-checks and installer experiences.