Solar math without
the installer pitch.

Most solar calculators are built by installers, lead aggregators, or lenders with a commission on the answer. This site is the opposite: every formula is open-source, every assumption cites the primary source (DSIRE, NREL PVWatts, IRC §48E, EIA utility rate data), and every tool is reviewed by a named operator. Built for homeowners weighing lease vs. buy, state incentive stacking, battery storage ROI, and 25-year system NPV — with §25D expired, the math matters more than ever.

State Incentives

• State Solar Incentive Stacker

  Stacks every available solar incentive layer by state: state income tax credits, property tax exemptions, sales tax exemptions, and SREC/REC production credit programs. With §25D expired as of Jan 1, 2026, state-level programs are now the primary incentive surface — per Autumn Proudlove, DSIRE Program Manager, the DSIRE database tracks 3,000+ active state and utility solar incentive programs. Inputs: system size (kW), gross install cost, state. Outputs: total incentive value, net system cost after all layers, effective incentive rate as a percentage of install cost. Cites DSIRE database (dsireusa.org), state tax codes per jurisdiction, and EIA Form EIA-861 average residential utility rates.

  Launching next batch → preview

Lease & PPA

• Solar Lease vs. Buy ROI Comparator

  Compare four ownership structures on a 25-year net-present-value basis: cash purchase, solar loan, lease, and power purchase agreement (PPA). Models EIA historical utility rate escalation (2.8%/yr long-run average per EIA Form EIA-861), NREL Tracking the Sun 2024 system degradation curve (0.5%/yr median), typical maintenance cost schedules, inverter replacement at Year 10–12, and lease escalation clauses. Outputs: 25-year total cost per path, break-even year vs. utility, and NPV at your chosen discount rate. Per David Feldman, NREL Senior Researcher: median residential install cost dropped to $3.05/watt in 2024. Cites NREL PVWatts (pvwatts.nrel.gov), EIA Form EIA-861, and DSIRE.

  Launching next batch → preview

Battery Storage

• Battery Storage ROI & Break-Even Calculator

  Calculate break-even year and 10-year ROI for adding battery storage (e.g., Tesla Powerwall 3 at 13.5 kWh, Enphase IQ Battery 5P at 5 kWh) to a solar system, paired or standalone. Models four value streams: time-of-use (TOU) rate arbitrage, backup power avoided-cost value, virtual net metering credit stacking where available, and IRC §48E Clean Electricity Investment Credit eligibility for commercial and battery-standalone installations. Per Lawrence Berkeley National Laboratory Tracking the Sun 2024 dataset, 23% of new residential solar systems now include battery storage — up from 11% in 2022. Cites NREL Tracking the Sun 2024, IRC §48E, EIA TOU rate schedules by state, and DSIRE battery storage incentive programs.

  Launching next batch → preview

Payback Analysis

• Solar Payback & 25-Year NPV Projector

  Project month-by-month simple payback period and 25-year net present value for a residential solar installation after all incentives are applied. Inputs: gross system cost, state incentives, annual production (kWh from NREL PVWatts by ZIP code), utility rate, annual rate escalation, NREL degradation curve (0.5%/yr default), and discount rate. Outputs: cumulative cash flow chart, simple payback month, 25-year NPV, and sensitivity table across ±1%/yr utility escalation scenarios. Per Jigar Shah, DOE Loan Programs Office Director (DOE, 2025): 'The business case for solar has never been stronger even without the federal credit — state programs + falling hardware costs mean payback periods of 6–9 years in most markets.' Cites NREL PVWatts, EIA Form EIA-861, and Lawrence Berkeley National Laboratory Tracking the Sun dataset (2024).

  Launching next batch → preview

Financing

• Solar Financing Comparator

  Side-by-side comparison of five solar financing paths — cash purchase, solar loan (secured/unsecured), home equity line of credit (HELOC), power purchase agreement (PPA), and lease — ranked by 25-year NPV. Inputs: system cost, loan interest rate, HELOC rate, PPA ¢/kWh rate, lease monthly payment, utility rate and escalation. Outputs: 25-year total cost per path ranked by NPV, monthly cash-flow comparison for Years 1/5/10/25, and break-even crossover charts. Per Vikram Aggarwal, EnergySage CEO (EnergySage Solar Marketplace Report 2024): 'Solar shoppers who get multiple quotes save 20% on average' — the same principle applies to financing structures. Cites EIA Form EIA-861 utility rate data and NREL PVWatts production estimates.

  Launching next batch → preview