How many solar panels to power a house? (2026)

Most US homes need between 18 and 25 solar panels to cover their electricity use; the national average lands at 21 panels — an 8.2 kW system. Three variables drive that number: annual electricity consumption, peak sun hours at your location, and panel wattage.

The formula

Solar installers use a three-step calculation:

1. Find your annual usage (kWh). Pull 12 months of electric bills and add them up. The average US home used about 10,800 kWh in recent years.
2. Calculate system size (kW). Divide annual usage by your location’s peak sun hours × 365 × 0.8. The 0.8 derate accounts for real-world losses from heat, wiring resistance, and inverter inefficiency.
3. Divide by panel wattage. Most residential panels installed today are 400W. Divide system size in watts by 400.

System size (kW) = Annual kWh ÷ (Peak sun hours × 365 × 0.8)

The 0.8 derate isn’t an arbitrary adjustment. Field data from thousands of installed systems consistently shows production at 75–82% of nameplate capacity under real conditions. Using 0.8 keeps the estimate grounded.

Worked example: average US home

A home using 10,800 kWh per year in a location with 4.5 peak sun hours per day — roughly the national median, representative of Dallas, Kansas City, or Charlotte:

• Production per installed kW: 4.5 × 365 × 0.8 = 1,314 kWh/kW/year
• Required system size: 10,800 ÷ 1,314 = 8.22 kW
• Panel count at 400W each: 8,220 W ÷ 400 W = 20.6 → round up to 21 panels

A 21-panel, 8.4 kW system covers that home’s consumption under average production assumptions. At 2026 installed costs of roughly $2.80–$3.20 per watt, the system runs an estimated $23,500–$26,900 before state or local incentives. Treat these as ballpark figures — get itemized quotes before any financial decisions.

How location changes everything

Peak sun hours range from about 3.5 hours/day in the Pacific Northwest to 5.8 hours/day or higher in the Desert Southwest. That swing alone can mean more than 10 panels’ difference for the same home.

Annual Usage	Seattle, WA (3.5 hrs)	US Average (4.5 hrs)	Phoenix, AZ (5.8 hrs)
7,000 kWh (efficient home)	18 panels	14 panels	11 panels
10,800 kWh (average home)	27 panels	21 panels	16 panels
15,000 kWh (EV + pool)	37 panels	29 panels	23 panels

Assumes 400W panels and a 0.8 production derate throughout.

A Seattle homeowner needs roughly 70% more panels than a Phoenix homeowner with identical usage. That gap affects roof space requirements, structural load, total installed cost, and payback timeline. Your installer should pull location-specific sun-hour data — not just a national average — when modeling your system.

Usage scenarios

Efficient home (7,000 kWh/year). A smaller, well-insulated house with a heat pump and no electric vehicle typically lands here. At 4.5 peak sun hours: roughly 14 panels (a 5.3 kW system). Smaller systems fit most roofs without issue and tend to have shorter payback periods because the upfront cost is lower.

Average home (10,800 kWh/year). A roughly 2,000 sq ft home with central air conditioning and electric appliances. The 21-panel, 8.2 kW result from the worked example applies.

High-consumption home (15,000 kWh/year). An EV charging at home, a pool pump, or electric resistance heating can push annual consumption to 15,000 kWh or more. At 4.5 sun hours, that means 29 panels (11.4 kW). At this system size, check your utility’s interconnection limits — some utilities cap residential systems relative to historical load — before finalizing the design.

Use the solar savings calculator to plug in your actual bill numbers and zip code for a location-specific estimate.

Other factors that shift the count

Panel wattage. A 350W panel requires about 14% more panels than a 400W panel for the same system size. Premium 430W or 450W panels trim the count slightly. Always ask for the specific model and nameplate wattage in any quote — vague references to “high-efficiency panels” mean nothing without a number.

Roof orientation and tilt. A south-facing roof at a tilt matching your latitude produces maximum output. East- or west-facing arrays typically lose 15–20% of annual production compared to due south. Installers should run your specific roof geometry through design software rather than applying a generic adjustment.

Shading. Even partial shading from a chimney, tree, or neighboring structure cuts output — particularly with string inverters, where one shaded panel drags down an entire string. Microinverters or DC power optimizers limit this effect but add cost. If shade affects your roof, request a shading analysis before the design is finalized.

Battery storage. Adding a battery doesn’t change how many panels you need to cover grid consumption. If you want to charge it from solar rather than just using it for grid-supplied backup, consider oversizing the array by 10–20% — and discuss this explicitly with your installer.

Net metering policy. Utilities that credit exported solar at retail rates let your meter effectively run backward on sunny days. States that have moved to lower avoided-cost rates make it more valuable to size close to your actual load rather than exporting heavily.

Roof space

A standard 400W residential panel measures roughly 3.3 ft × 5.4 ft — about 17–18 square feet. Twenty-one panels occupy approximately 360–378 square feet of footprint. Add building-code setbacks from ridges, rakes, and eaves — required for firefighter access — and you need at least 450–550 square feet of clear, well-oriented roof for an average-sized system.

Limited south-facing space? Higher-wattage panels pack more output into the same footprint. Ground-mounted systems work well on properties with adequate yard space and often produce more because you can optimize tilt and avoid shade more easily.

Costs and incentives in 2026

For a full breakdown by system size and state, see how much do solar panels cost?.

The federal residential solar tax credit (IRC §25D) expired December 31, 2025, repealed under the One Big Beautiful Bill Act. A solar system purchased in 2026 earns $0 in federal tax credits. Disregard any quote or promotional material still advertising a “30% federal tax credit” for homeowners — that program is gone.

Two nuances matter:

• Leases and PPAs. When a third-party company owns the system on your roof, they may claim the commercial §48E investment tax credit. That indirect benefit can make lease economics look competitive with a cash purchase in some markets. Compare carefully and read the contract terms.
• State and local incentives. California, New York, Massachusetts, New Jersey, and others maintain state tax credits, rebates, or performance incentives (SRECs) that can meaningfully reduce net cost. These programs change frequently — verify current availability directly with your state energy office or a licensed installer, and never assume an incentive applies without written confirmation.

Always request an itemized quote that separates panel cost, labor, permitting, interconnection fees, and incentives as distinct line items. It’s the only way to compare proposals accurately.

Getting to your number

The formula here gives a reliable starting point. An installer’s final proposal will be refined by your actual utility bills, a shading analysis, roof orientation modeling, and your utility’s net metering tariff.

Before those conversations:

1. Download 12 months of bills or pull your kWh history from your utility’s online portal.
2. Note your address and any planned additions — EV, heat pump, pool pump — expected in the next few years. Size for projected use, not just current consumption.
3. Get at least three quotes from licensed installers. Ask each to show you their production model, not just a panel count and a price.

Before committing to a system size, review solar payback period explained to understand how usage level, local electricity rates, and financing terms interact to determine whether solar makes financial sense for your situation.