Projects that either (a) incur ≥5% of total project costs or (b) begin physical work of a significant nature before July 4, 2026 lock in the full 30% ITC for up to 4 years of continued construction.¹ After that date the credit phases down sharply for commercial projects.

SAFE HARBOR — IRS NOTICE 2018-59

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Chris LeVeck
Chief Executive Officer and Founder

1. Federal Investment Tax Credit — IRC §48E (Inflation Reduction Act of 2022). Base rate 30% for projects meeting prevailing-wage and apprenticeship requirements. Safe-harbor "beginning of construction" rules per IRS Notice 2018-59. Deadline shown reflects the current scheduled phase-down. Verify with your tax advisor.
2. 25-year cumulative bill savings minus net system cost. Assumes 0.5% annual module degradation and 3% annual utility rate escalation. Savings capped at modeled annual bill (cannot offset more than consumed).
3. System size = rooftop area × 65% usable-roof factor × 17 W/sqft installed density. Usable-roof factor accounts for setbacks, HVAC, walkways, and array spacing. Density is typical for modern monocrystalline modules on a flat commercial roof.
4. Year-one production = kW_DC × site irradiance (peak sun hours/day) × 365 × performance ratio (0.78). Irradiance derived from NREL NSRDB state averages (1998–2020). Performance ratio is a PVWatts-style aggregate of inverter, soiling, wiring, and temperature losses.
5. Installed cost = $1.65/W_DC, NREL Annual Technology Baseline 2024 commercial rooftop benchmark. Actual installed cost varies with site complexity, interconnection, prevailing wage requirements, and EPC scope.
6. Modified Accelerated Cost Recovery System (MACRS) 5-year depreciation plus 40% first-year bonus depreciation per current IRC §168. Depreciable basis reduced by half the ITC per IRC §50(c)(3). Tax-shield value modeled at 21% federal corporate rate; state tax benefits not included.

Electricity rates are EIA Electric Power Monthly state commercial averages (2024). Building energy intensities from EIA CBECS 2018 and MECS 2018. This calculator is a planning estimate for educational purposes, not a binding quote.