Methodology
How we calculate.
Every estimate on CleanEnergyCalc traces back to a named, public dataset and a transparent formula. No black boxes, no inflated numbers designed to close a sale. This page explains the data and assumptions behind each category of calculator.
Data foundation
We combine dated public datasets with manufacturer specifications and editable modeling assumptions. Not every default is a measured statistic: installation prices, future rate increases, battery wear, and usage patterns can be illustrative inputs. A source link identifies a reference; it does not mean that agency validates our model or every default.
Data Sources
Electricity-rate data period: June 2026. Electricity rates checked 2026-09-22. Other source-review baseline: 2026-09-06. A review date does not make an older data period current; rates and incentives can change.
Formulas & assumptions
- •Most solar tools use a simplified state annual-average peak-sun-hour model. They do not call the PVWatts API or reproduce a site-specific hourly PVWatts simulation unless a page explicitly says so.
- •Solar ROI applies one editable system-loss factor, then panel degradation from year two. It values self-consumed energy at the retail rate and exported energy at a separate user-entered credit.
- •Simple payback uses first-year net savings. Cash-flow payback separately follows yearly savings, rate escalation, degradation, and entered maintenance costs.
- •Charging cost = vehicle efficiency (kWh/100 mi) × annual miles × electricity rate, with optional time-of-use off-peak pricing.
- •EV-vs-gas comparisons use EIA electricity rates and current fuel-price inputs; maintenance deltas follow DOE estimates.
- •Battery-health and road-trip tools use manufacturer warranty baselines (typically 8 yr / 100k mi) and published consumption figures.
- •Backup sizing is based on user-entered essential loads and stated usable capacity from manufacturer spec sheets.
- •Self-consumption and solar-plus-storage savings are derived from the same EIA rate and NREL production models used elsewhere.
- •Heat-pump operating cost compares modeled annual energy use against gas at user-entered or default fuel prices.
- •IRA rebate eligibility (HOMES / HEAR) follows DOE program rules and income thresholds; amounts are estimates pending state program rollout.
Verified worked example
New York example inputs: 8 kW × $4.10/W (LBNL's 2024 median installed price for New York) = $32,800 gross cost; one conditional state income-tax credit of 25% capped at $5,000; 4.2 peak sun hours/day; one 20% production derate; and 29.49¢/kWh retail value (EIA, June 2026).
Net upfront cost = $32,800 − $5,000 = $27,800. Year-one production is 8 × 4.2 × 365 × 0.80 = 9,811.2 kWh, worth about $2,893 at 29.49¢/kWh. Simple payback is therefore about 9.6 years. With the separate 2.5% rate-growth and 0.5% degradation scenario, cumulative cash-flow payback is about 8.9 years.
This arithmetic example does not establish eligibility or an actual tariff. The New York credit is nonrefundable and depends on qualified expenditures and tax liability. Export value can differ from retail value, so users should replace the annual-average assumption with their utility's estimate.
How often we update
Each dataset shows its actual data period separately from the date we reviewed its source. The current electricity-rate table uses June 2026data; the methodology and cited policy pages were reviewed 2026-09-06. A newer build or review date never changes the underlying data period. Found something out of date? Tell us and we'll fix it.
Estimates, not quotes
Our calculators provide estimates for informational purposes only. Real-world results depend on site-specific conditions — local weather, roof and home characteristics, equipment selected, installer pricing, and utility rate plans. Always obtain multiple professional quotes and consult a tax professional for incentive eligibility before making a decision.