Solar Calculator
Estimate your system size, installed cost, and payback using your state's real electricity rate and solar production data.
Assumptions (edit these)
Enter a $/watt installed cost above to see your results.
How this calculator works
System size is your annual electricity use divided by your state's production per kW (from NREL PVWatts), scaled to the offset percentage you choose. Gross cost multiplies that system size by an installed cost-per-watt figure — either a real, sourced figure from LBNL's Tracking the Sun dataset (available for 9states so far) or one you enter yourself. Net cost applies the 2026 federal credit rate (0%, since IRC §25D ended for systems completed after 2025-12-31).
Savings combine self-consumed production (valued at your full retail rate) and exported production (valued at an export credit rate — 100% of retail under full-retail net metering, or a lower editable assumption otherwise). The 25-year total compounds your chosen rate escalation against panel degradation, year by year — not a simple multiplication.
Worked example: a California household using 12,000 kWh/year at California's real $4.25/W cost figure and 5.07 peak sun hours worth of annual production per kW sizes to roughly an 8 kW system — about 20 400W panels — before you edit any assumption.
FAQ
Why does the calculator ask for my own $/watt price for some states?
We only publish an installed cost-per-watt figure when we have a real, sourced number for that state (from LBNL's Tracking the Sun dataset). For states without one yet, enter a quote you've actually received rather than trust a made-up national average.
Does this include the federal tax credit?
No. The federal residential clean energy credit (IRC §25D) does not apply to systems completed after December 31, 2025, so the 2026 default is a 0% federal credit for homeowner-purchased systems. Leased/PPA systems are financed differently — see our lease vs. buy guide.
What assumptions does this calculator make?
Open "Assumptions" above the results to see and edit every input: usage offset target, panel wattage, self-consumption share, export credit rate, rate escalation, and panel degradation. Every default is a documented, real-world estimate — see our methodology page for how each one is chosen.
Data sources
Last updated 2026-09-22
- U.S. Energy Information Administration — Electricity Data Browser — accessed 2026-09-22
- NREL PVWatts — accessed 2026-09-22
- NREL Solar Resource Data — accessed 2026-09-22
- LBNL Tracking the Sun (public data file, host-owned residential systems) — accessed 2026-09-22
Written by GoSolarIndex Team