Guides

These guides explain the rules and assumptions behind the calculator. They are written for a homeowner reading a proposal, not for an installer. Every figure is tied to a named source, and every stated limitation is a real one.

• The 2026 Federal Solar Tax Credit: What Actually Happened — IRS-based explanation of why homeowner-owned solar gets $0 federal credit in 2026, what the installation-completion test means, and where §48E still applies.
• Solar Lease vs Buy in 2026 — A structured comparison of cash, loan and third-party ownership after §25D ended, with the contract terms that actually decide the 25-year result.
• Net Metering vs Net Billing — How full-retail crediting differs from avoided-cost net billing, why NEM 3.0 changed California solar economics, and how to find your utility's export rate.
• Is a Solar Battery Worth It in 2026? — A tariff-first answer: when storage pays for itself under net billing, when it only buys backup, and what the 2026 credit change did to the math.
• How Many Solar Panels Do I Need? — Work from your annual kWh, local sun hours and roof factor to a panel count — with worked examples at 2026 EIA state electricity rates.
• Solar Panel Degradation and Your 25-Year Estimate — Why the 25-year savings number depends on a degradation assumption, what typical warranties actually promise, and how to read the year-by-year table.
• Utility Rate Escalation and Solar Payback — Why a 1% versus 6% electricity price escalation changes a 2026 solar payback more than most hardware choices, and how to stress-test it.
• Solar Payback Explained — Four ways to measure whether solar pays off in 2026 — and why they disagree. Worked with a national-average example and no federal credit.
• State Solar Incentives After §25D Ended — Which statewide residential solar credits and grants we could verify for 2026, which programs depend on registration, and how to confirm yours on DSIRE.
• Roof Orientation, Tilt and Shading — How direction, pitch and shade combine into a single roof factor, and why a mediocre roof changes the required system size rather than just the output.
• Solar Loan vs Cash in 2026 — Dealer fees, APR, total of payments and the 25-year net: how to compare a financed solar purchase against paying cash without a federal credit.
• Inside the 25-Year Cash Flow Model — Every assumption behind the HelioCalc projection: production, degradation, escalation, maintenance, discounting, payback interpolation and IRR.
• Solar Cost and Electricity Rate by State — 2026 — All 50 states and DC with August 2026 EIA residential electricity rates, installed cost benchmarks, solar resource bands and export-credit regimes.
• SRECs, SMART and Performance Incentives — Why per-kWh and per-MWh solar programs exist, how they differ from upfront credits, and why HelioCalc does not fold them into a default estimate.