How Many Solar Panels Do I Need to Power a House?

Short answer: the average US home, using about 865 kWh a month, needs around 20 solar panels of 400 W (an 8 kW system) where there are 4.5 peak sun hours a day. In a cloudier place with 3.5 sun hours, the same home needs about 26; in sunny Arizona or southern California, about 17. A typical UK home needs about 9 panels, and a typical Australian home about 10.

Enter your own bill and location in the solar panel calculator for an exact figure, roof area and cost.

The formula

system size (kW) = yearly kWh ÷ (peak sun hours × 365 × 0.8)
panels needed    = system size × 1,000 ÷ panel watts (round up)

The 0.8 is a performance factor: real systems lose about 20% to heat, wiring, inverter conversion, dirt and shading compared with their label rating. Peak sun hours are the equivalent number of hours a day of full, 1,000 W per m² sunlight averaged across the year, not the hours of daylight.

Worked example: the average US home

1. Yearly use: 865 kWh × 12 = 10,380 kWh.
2. System size: 10,380 ÷ (4.5 × 365 × 0.8) = 7.9 kW.
3. Panels: 7,900 ÷ 400 = 19.75, so 20 panels (8 kW).
4. Expected output: 8 kW × 4.5 × 365 × 0.8 ≈ 10,500 kWh a year, just over 100% of use.
5. Roof space: with modern panels of about 21% efficiency, roughly 38 m² or 410 sq ft, before gaps and setbacks.

Panels needed by usage and sunshine

Number of 400 W panels to cover 100% of yearly use:

Rough peak sun hours: Seattle and the Northeast about 3.5, the Midwest about 4, the Southeast and California coast about 4.5 to 5, the desert Southwest 5.5 to 6. UK about 2.5 to 3, Canada 3.2 to 4.2, Australia 3.8 to 5.5.

By country

Should you cover 100% of your use?

Not always. Where exports are credited at far less than you pay for electricity (common in the US, and true of most UK and Australian export tariffs), the best value often comes from a system sized to the electricity you use during the day, plus a battery if it pays. Covering 100% makes most sense under full retail net metering. The solar payback calculator shows how the split between self-use and exports changes your payback, and is solar still worth it in 2026 works through the numbers now the 30% credit has ended.

Things that change the answer

• Roof direction and tilt: south-facing (north-facing in Australia) is best; east or west roofs produce roughly 10% to 20% less.
• Shading from trees, chimneys or neighbouring buildings can cut output sharply.
• Future loads: an electric car adds about 3,600 kWh a year (about 7 more 400 W panels at 4.5 sun hours); a heat pump can add several thousand more.
• Panel wattage: fewer, larger panels need the same roof area, because area depends on total watts and panel efficiency.

Frequently asked questions

How many solar panels does it take to run a house off-grid?

Usually 25% to 50% more than a grid-tied system, sized for the darkest month rather than the yearly average, plus enough battery for several cloudy days.

How many solar panels do I need for 1,000 kWh a month?

About 23 panels of 400 W with 4.5 sun hours, or 26 with 4 sun hours.

How much does a solar panel produce per day?

A 400 W panel produces about 1.4 kWh a day at 4.5 sun hours. See how many kWh a solar panel produces per day.

Sources

• US Energy Information Administration, average US household electricity use.
• NREL, PVWatts calculator (solar resource and typical system losses).
• Ofgem typical consumption values; Australian and Canadian averages as used in our calculators.

Checked October 22, 2026.