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Solar Math Pro

Methodology · Overview

Methodology

Reviewed by · Last reviewed .

Every calculator on Solar Math Pro is a real piece of software with tests, a citation, and a named human who reviews it. Here is how the process works, end to end. For category-specific methodology — sources, formula derivations, edge cases, and update protocol — see the per-category pages linked at the bottom of this page. For how Bedrocka Tools operates as a publisher more broadly, see our editorial standards.

Solar Math Pro calculators estimate solar savings, payback, and financing costs based on publicly available data from NREL, EIA, and DSIRE. They do not constitute financial, tax, or installation advice. Individual results depend on site conditions, utility rates, state incentive availability, and financing terms not fully captured in any general-purpose tool. Verify all incentive amounts at dsireusa.org before making an installation decision.

How tools are built

Calculators are written in TypeScript as pure functions inside a shared package (@bedrocka-tools/calc), with Vitest unit tests that cover edge cases: SREC market price changes, net metering compensation rate differences between NEM 1.0 and NEM 3.0 rules, the incentive capture difference between cash purchase and solar lease, and every published sample problem from primary sources. The package has no UI and no side effects — if a calculator gives the wrong answer, there is one file to fix and a failing test that tells us it was wrong.

Formula sourcing — primary sources only

We only cite primary sources. Installer sales materials, blog posts, and third-party solar savings tools are not sources. The named experts whose published research defines this field also inform our methodology: Autumn Proudlove (DSIRE, NC State University) on state incentive program tracking; David Feldman (NREL) on installed cost benchmarks and degradation rates; Jigar Shah (DOE Loan Programs Office) on the current solar market economics; Vikram Aggarwal (EnergySage) on installer market pricing and financing structures; and Lawrence Berkeley National Laboratory on the Tracking the Sun annual dataset covering hundreds of thousands of residential installations. Primary sources we use routinely on this site:

Secondary sources are used only where a primary source does not exist and are always labeled as such.

Review process

  1. Draft: calculator logic and explanatory copy are drafted, sometimes AI-assisted, always with the primary source pulled up in parallel and every non-trivial number checked against it.
  2. SME review: each calculator is reviewed by a named human with domain experience — for solar economics and incentive structure content, Byron Malone; for new tools where installer-market expertise is relevant, we credit domain reviewers on the page.
  3. Citation verification: every URL cited is spot-checked at publish time. DSIRE incentive amounts are verified against the live program page, not cached data.
  4. Publish: with a Last updated stamp and a dateModified schema.org field on every page.

Update cadence

Every calculator is reviewed on a quarterly cadence. In addition, we update immediately on any of the following triggers:

  • DSIRE publishes program changes for states in our incentive stacker
  • NREL releases a new edition of the Tracking the Sun dataset (typically annually in Q4)
  • EIA publishes updated Form EIA-861 annual data with revised state-level utility rates
  • Congress passes legislation affecting residential or commercial solar credits
  • A major state (CA, NY, NJ, MA, TX) changes net metering rules or SREC program structure
  • NREL PVWatts updates its underlying solar resource dataset or default assumptions

Error reporting

If a calculator gives you the wrong answer, we want to hear. Email info@bedrockatools.com with the tool, the inputs you used, and the output you got. We respond to every report within 3 business days; if the tool is wrong, we fix it and publish a correction note on our corrections page.

Per-category methodology

Each calculator category has a dedicated methodology page covering the primary sources, formula derivations, edge cases, and update protocol specific to that category. Calculators marked as launching soon are stubs in active development; the methodology pages are live so readers can evaluate the sourcing before the calculator ships.

  • State Solar Incentives — how the incentive stacker computes the net effect of state income tax credits, property tax exemptions, sales tax exemptions, net metering rates, SREC programs, and utility rebates across all 50 states. Primary sources: DSIRE (dsireusa.org), CA Rev. & Tax Code §17052.1, NY Tax Law §606(g-1), MA G.L. c. 62 §6(d).
  • Solar Lease vs. Buy ROI — 25-year NPV framework comparing cash purchase, solar loan, lease, and PPA structures; who captures the incentives in each case; degradation, utility rate escalation, and discount rate methodology. Primary sources: NREL PVWatts, EIA EIA-861, EnergySage 2024, NREL Tracking the Sun.
  • Battery Storage ROI — time-of-use arbitrage value, virtual net metering, backup power insurance framing, break-even formula, LFP vs. NMC degradation curves, and the §25D expiration caveat for residential installations after December 31, 2025. Primary sources: NREL Tracking the Sun 2024 (LBNL), IRC §48E, EIA TOU rate data.
  • Solar Payback & NPV — why payback period alone is insufficient; 25-year NPV model with NREL PVWatts production, 0.5%/yr degradation, 2.8%/yr utility rate escalation, $17/kW/yr O&M, and inverter replacement modeling. Primary sources: NREL PVWatts, Tracking the Sun, EIA EIA-861, DSIRE.
  • Solar Financing Comparison — five financing structures (cash, secured loan, unsecured loan, lease, PPA) with incentive capture rules for each, HELOC interest deductibility under IRC §163(h)(3)(B), PACE loan lien complications, and interest rate sensitivity analysis. Primary sources: IRC §163, NREL PVWatts, EIA, EnergySage 2024.

Limitations

Calculators on this site are estimates for educational use. Solar economics are highly local — production depends on shading and roof orientation that no general tool can measure, incentive programs change every legislative session, utility rate structures are set by hundreds of individual utilities, and financing terms depend on individual credit profiles. These tools are designed to make you a better-informed buyer of professional advice — from a licensed solar installer, a CPA familiar with energy tax credits, and a financial advisor who can model the investment in the context of your full financial picture. They are not a replacement for that advice.