Size the system, price it at 2026 rates, and see the 25-year math
| Region | Peak Sun Hours/Day | Example States | 1 kW Produces/yr |
|---|---|---|---|
| Southwest | 5.5 – 6.5 | AZ, NV, NM, inland CA | 1,600 – 1,900 kWh |
| West & Mountain | 5.0 – 5.5 | CO, UT, TX panhandle, CA coast | 1,460 – 1,600 kWh |
| Southeast & Midwest | 4.3 – 5.0 | TX, FL, GA, NC, TN, KS | 1,250 – 1,460 kWh |
| Northeast & Midwest lakes | 3.8 – 4.3 | NY, PA, OH, MI, MA | 1,110 – 1,250 kWh |
| Pacific Northwest | 3.3 – 3.8 | WA, OR west of Cascades | 960 – 1,110 kWh |
Annual production per kW shown before the ~20% system losses are backed out (the calculator applies them). The national average residential electric rate was 17.45¢/kWh in January 2026 (EIA) and is forecast near 18¢ for the year. Average installed cost is about $2.58/watt nationally in 2026, ranging $2.53–$3.66 by state and system size.
Solar sales pitches love monthly-payment framing because the underlying math flatters them less. This tool runs the full version: how big a system your bill implies, what it should cost at 2026 prices, and what it returns over 25 years with rates rising and panels slowly degrading.
Monthly kWh = bill ÷ rate. Annual usage = monthly kWh × 12. System size (kW) = annual usage × offset ÷ (sun hours × 365 × performance factor), where the performance factor of 0.80 covers inverter conversion, wiring, soiling, heat, and snow. Cost = size in watts × cost per watt, minus any credit you enter. Year-one savings = offset production × rate. Each later year multiplies savings by (1 + escalation) and (1 − degradation). Payback is the first year cumulative savings cross the net cost.
Pull the rate from your bill, not from the national average, because your actual all-in rate (generation plus delivery) is what solar offsets. Find your sun hours in the regional table. Enter any state credit or utility rebate as a percent of cost, or divide a flat-dollar rebate by the gross cost first. If your utility pays solar exports below the retail rate, lower the offset to 80 or 90%, since only self-consumed power saves the full rate.
A $200 monthly bill at $0.175 per kWh is 1,143 kWh a month, 13,714 kWh a year. At 4.5 sun hours with 20% losses, the system needs 13,714 ÷ 1,314 = 10.44 kW, call it 25 panels at 425 watts. At $2.60 per watt that's $27,136 gross, and with the federal credit gone in 2026, $27,136 net too.
Year-one savings are 13,714 kWh × $0.175 = $2,400, a simple payback of 11.3 years. With rates climbing 3% a year and output fading 0.5%, cumulative savings pass the system cost during year 11 and reach about $81,820 by year 25, a net of roughly $54,700 after the equipment. The same system installed a year earlier, with the 30% credit, would have paid back in under 8. The 2026 math still works, it just takes three more years to get there.
A $200 monthly bill at the national average rate of about 17.5 cents per kWh is roughly 13,700 kWh a year, which needs about a 10.4 kW system. That system costs about $27,100 at the 2026 average of $2.60 per watt and saves about $2,400 in year one. Payback runs about 11 years, and 25-year savings total roughly $82,000 with utility rates climbing 3% a year.
No. The residential clean energy credit under Section 25D ended December 31, 2025, when the One Big Beautiful Bill Act terminated it with no phase-down. Systems must have been placed in service by that date to qualify. Some state credits and utility rebates remain, and leases or power purchase agreements from third-party owners can still access commercial credits, so those routes are worth pricing in 2026.
Divide your monthly bill by your rate to get monthly kWh, multiply by 12, then divide by (peak sun hours × 365 × 0.80). The 0.80 factor covers inverter, wiring, soiling, and temperature losses. A home using 13,700 kWh a year at 4.5 daily sun hours needs 13,700 ÷ 1,314, about 10.4 kW.
Typically 9 to 13 years at 2026 prices without the expired federal credit, down from 7 to 10 when the 30% credit applied. High electric rates and strong sunlight push payback toward the low end; cheap power and cloudy skies push it past 15. Systems produce for 25 to 30 years, so most installs still net two to three times their cost over their life.
Savings grow. The calculator compounds utility escalation against your fixed system: at 3% a year, the same kWh that offsets $2,400 in year one offsets about $4,450 by year 20. US residential rates have risen faster than inflation recently, about 6% year over year in mid-2026, so 3% is a conservative planning number.
Yes, at reduced output: heavy clouds cut production to roughly 10 to 25% of rated power, and winter months produce 40 to 60% of summer totals at most US latitudes. The sizing math already handles this because peak sun hours are annual averages. What matters is your yearly total, not any single dark Tuesday.