How many solar panels to power a house

The honest answer to "how many panels?" starts with one number: your annual electricity use in kilowatt-hours (kWh). From there it's a short bit of arithmetic, not a mystery. Here's how to get a real count for your own house.

Start with your annual kWh

Your utility bill shows kWh used each month. Add twelve months together, or grab the annual total many utilities print. A typical US home uses 10,000 to 12,000 kWh per year. That single figure drives everything below.

The two-step formula

Step 1 — system size: annual kWh ÷ (peak sun hours × 365 × 0.80)

• Peak sun hours are the equivalent hours of full-strength sun your area gets daily — roughly 3.5 to 4.0 in the cloudy north, 4.5 average, 5.0 to 5.8 in the Southwest.
• 0.80 is a real-world derate for heat, wiring, and inverter losses.

Step 2 — panel count: system watts ÷ panel watts, rounded up.

Worked example: 11,000 kWh ÷ (4.5 × 365 × 0.80) = about 8.4 kW. With 430 W panels: 8,400 ÷ 430 = 20 panels.

Panel wattage changes the count

Modern residential panels run about 400 to 440 watts. Higher-wattage panels get you the same system with fewer pieces, which matters on a small roof:

Will they fit? The roof-space check

Each panel is about 18 square feet. Twenty panels need roughly 360 sq ft of usable, unshaded roof — not counting the setbacks fire codes require around edges and ridges. If your usable area is tight, lean toward higher-wattage panels. For a fuller walkthrough, see how to size a residential solar system.

Should you round up?

A little, if an EV, heat pump, or battery is on the horizon, or your utility pays little for exported power. But many utilities cap interconnection near 100 to 120% of your past usage, so don't oversize blindly — check the rules first.

This is a plan, not an install

These numbers get you a realistic panel count to shop and budget with. The actual wiring, conductor sizing, and grid connection are engineering work, and in nearly every jurisdiction a licensed electrician or PE must design, stamp, and connect a grid-tied system. Use this to walk in informed, then browse the guides to prepare.

Educational reference, reviewed 2026-07. A design aid, not a substitute for a licensed electrician or PE. Confirm the enforced NEC edition and local amendments with your AHJ.