Solar Panel Count & Payback
Panel count and system kW from your utility bills, the roof area it takes, production by climate, the 2026 tax-credit reality, and payback in years.
Panels need about 21 sq ft each at 400 W, and racking gaps mean a residential array runs about 4.5 DC watts per sq ft of roof, not the 19 W per sq ft the module itself rates.
How the math works
- System size: kW needed = annual kWh × target offset ÷ production ratio. The production ratio is annual kWh per kW-DC installed: 1.10 in the northern states, 1.25 mid-latitude, 1.40 sun belt, 1.55 desert.
- Panels: panel count = kW-DC × 1,000 ÷ nameplate watts, rounded up, and the system is rounded up with it. Arrays size in whole panels, not whole kW.
- Roof area: a module is nameplate watts ÷ 19 W per sq ft (a 400 W panel is 21 sq ft), and the array footprint runs about 4.5 DC watts per sq ft of roof once racking gaps, fire pathways, and obstructions are respected.
- 2026 incentives: the residential federal tax credit (25D) ends for owner-owned systems placed in service after Dec 31, 2025, so a 2026 purchased system carries no 30% federal credit. Third-party-owned (lease/PPA) systems can still draw the 48C code. State, utility, and SREC money is entered separately, and it is the money that closes the gap in 2026.
- Payback: annual kWh × your rate = annual savings; net cost ÷ savings = simple payback. Anything under 8 years is a good buy in 2026 with a loan at today’s rates; over 12 years, the equipment replacement math stops working.
How many solar panels for a 10,000 kWh home?
A 1.25 production-ratio home needs 8 kW-DC to offset 100%: 20 panels of 400 W, 8 kW, about 1,780 sq ft of roof at 4.5 DC watts per sq ft, and roughly 20,000 to 24,000 gross in 2026.
How many square feet of roof per solar panel?
About 21 sq ft of module for a 400 W panel, and 22 to 24 sq ft of roof per panel once you include the racking gaps, the fire access pathway, and the roof edges. Count on 4.5 DC watts per sq ft of usable roof.
Is solar worth it in 2026 without the federal credit?
Owner-owned cash and loan systems in 2026 lose the 30% credit, so payback stretches to 9 to 14 years in most of the country. Leases and PPAs keep federal support, and state rebates, SREC markets, and 1:1 export utilities are where owned systems still pencil.