Free Solar Calculators That Actually Work

Every calculator currently published here exposes its inputs, formula, worked example, source links and limitations. We use public laboratory, government and standards-body material where it exists, and label market prices or rules of thumb as planning assumptions rather than facts.

Sizing and yield estimates use user-entered peak-sun-hours and loss assumptions, with NREL PVWatts documentation as the reference model. They are transparent screening calculations, not site-specific weather simulations. A real proposal should be checked against a location-based production model and the equipment manufacturer's data.

Tilt-angle scenarios use absolute latitude as a transparent starting point, with bounded seasonal comparisons. They are first-pass geometry estimates, not site optimisations; nearby obstructions, roof constraints and hourly irradiance can change the best feasible angle.

Cost calculators start from cash-equivalent prices entered by the user or clearly dated public benchmarks. Incentives are not assumed unless a retained tool identifies the applicable authority and date. Results are estimates, never quotes, tax advice or a recommendation to buy equipment.

The current public edition is deliberately limited to reviewed English (United States) pages. Sources are linked beside the claims they support, not collected only in a generic bibliography.

• NREL: PVWatts assumptions, solar-resource terminology and system-loss modelling.
• U.S. Department of Energy: consumer solar, battery, inverter and system-design guidance.
• U.S. Energy Information Administration: dated retail electricity prices used in cost examples.
• Product and test standards: linked only where a retained calculator needs a defined rating or test method.
• Market-price sources: dated and presented as ranges; users replace them with an actual quote.

We built SolarCalculatorHQ as a free planning resource with no account or lead form. Users can enter their own assumptions and inspect the formula, worked example, source references and limitations behind each published result. The calculations are screening estimates to check against site-specific modelling, equipment data and current quotes.

SolarCalculatorHQ is independent. We have no affiliation with installers, manufacturers, or financing providers. There are no referral fees, no lead resale, and no paid placements anywhere on the site. We do not require a signup, an email address, or any personal information to use any tool. Every result is computed in the browser from inputs the user controls, with the formulas and source references shown alongside.

We publish a smaller set on purpose. A calculator is included only when its interface, article, example and source trail have been checked as one unit. Overlapping keyword variants, incomplete translations and tools that could imply an electrical, structural, fire or tax determination are withheld until they can meet that standard.

The site may be funded by display advertising. We are transparent about that because it determines what we will and will not do. We will not sell user data. We will not insert affiliate links into recommendations. We will not write toward a particular installer or product line.

Time-sensitive defaults can change between reviews. Each content page shows its latest review date, and the linked authority or program administrator controls if it conflicts with an older planning value. Readers can report a stale tariff, incentive or code reference through the corrections address on our editorial standards page.