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. Split into independent calculators built by individuals (like this one), and the government and institutional tools behind a lot of the underlying data.
Independent calculators
- CleanEnergyCalc — a big set of free, no-signup calculators for solar, EVs, heat pumps and rebates, built on EIA/DOE/NLR 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.
- sun-calc.com — a great integration of the Google Solar API (tilt, azimuth, shade) with NLR PVWatts v8, turning the two into monthly kWh. The return calculations are outdated and inaccurate, so take the monthly kWh and feed those into the calculator here for the money side.
- Google Project Sunroof — satellite-based roof potential and a rough savings estimate.
- startOFFgrid — calculators and guides for off-grid solar and battery setups — RVs, vans, cabins, and full off-grid homes — a category the grid-tied tools here don't cover. Independently run and affiliate-funded.
Government & institutional tools
The lab is now the National Laboratory of the Rockies, and its tools answer on nlr.gov. The old nrel.gov addresses no longer resolve, so the links below go to the new ones.
- NLR System Advisor Model (SAM) — a free desktop app for detailed cash-flow and performance modeling.
- NLR REopt — a free techno-economic optimizer (more oriented to commercial and resilience cases).
- OpenEI — open datasets, including the Utility Rate Database of machine-readable tariffs for most US utilities.
- pvlib python — an open-source library for modeling PV output, if you code.
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.
- NLR PVWatts — free first-year production estimate for any address; the tool's production model is 896 saved PVWatts v8 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.
- NLR — PV Lifetime Project — the field data behind the 0.5%/yr default.
- NLR 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.