Sizing guide · updated October 23, 2026

How many solar panels do I need?

Short answer: divide the kWh you use in a year by what 1 kW of panels makes in a year where you live. The average U.S. home bought 863 kWh a month in 2024 (EIA), about 10,359 kWh a year. At the median state output of 1,367 kWh per kW (PVWatts), that is a 7.6 kW system, or about 19 panels of 400 W. By state, covering the local average home takes anywhere from 10 panels (California) to 27 (Washington).

This guide sizes a grid-tied home system for a target share of your yearly bill. It uses two published data sets: EIA's 2024 average residential use and bill for every state (EIA Electric Sales, Revenue, and Average Price, Table 5A), and the annual output of 1 kW of panels by state from NREL/NLR PVWatts v8 (state table). Off-grid cabins and RVs size differently (for the worst month, with days of battery), so see the off-grid cabin and RV solar guides for those.

The four-step method

1. Add up 12 months of kWh. Use the "kWh used" line on each bill, not the dollar total, and add all 12 months so summer AC and winter heat both count. One month × 12 is a rough fallback. If you already have solar, your bill shows net purchases, not use; EIA flags the same problem in its own averages (EIA FAQ).
2. Find your kWh per kW. Run your address in PVWatts with a 1 kW system, or use your state's figure in the table below. PVWatts already includes its default 14% system losses (soiling 2%, shading 3%, mismatch 2%, wiring 2%, connections 0.5%, light-induced degradation 1.5%, nameplate 1%, availability 3%) plus a 96% inverter (PVWatts system losses).
3. System kW = yearly kWh × offset ÷ kWh per kW. Offset is the share you want to cover: 100% for a full net-metering offset, less under export-credit plans valued below retail (see below).
4. Panels = system kW × 1,000 ÷ panel watts, rounded up. Then check roof space: about 21 sq ft per panel.

Run your own numbers in the calculator

Panels needed for the average home, by state

Each row covers 100% of that state's 2024 average residential use with 400 W panels on a typical, unshaded fixed array. Panel area uses the Qcells Q.TRON BLK M-G2+ footprint (1,722 × 1,134 mm). Click a state for its daily-use and battery table.

Use: EIA 2024 average monthly consumption and bill per residential customer, Table 5A (EIA). Output: annual kWh per kW from PVWatts v8 state averages (state table); your address can differ by 10% or more with roof direction, tilt and shade. U.S. average 863 kWh/mo and $142/mo. EIA counts grid purchases, so states with lots of rooftop solar (Hawaii, California) show lower "use" than homes actually consume.

By your own usage

Find your monthly average in the left column. Four states show the range from cloudy to sunny: Washington is among the lowest-output states in the lower 48, Arizona among the highest (only New Mexico edges it).

System kW = monthly kWh × 12 ÷ kWh per kW; 400 W panels rounded up. For other panel sizes, multiply the kW by 1,000 and divide by the panel's rated watts (a 435 W panel needs about 8% fewer panels than a 400 W one).

What changes the panel count

• Panel wattage. Residential panels now commonly run 400–440 W; the Qcells Q.TRON BLK M-G2+ series spans 420–440 W in the same 1,722 × 1,134 mm frame (Qcells). Higher-watt panels shrink the count, not the kW you need.
• Roof direction and shade. PVWatts' default assumes only 3% shading loss from distant obstructions; trees or a chimney on the array need a site survey (PVWatts manual). An east- or west-facing roof makes less than a south-facing one; PVWatts lets you set azimuth and tilt.
• Aging. After initial light-induced degradation, panels typically lose about 0.5% a year (PVWatts manual). That compounds to about 12% less output by year 25, so a system sized to exactly 100% today covers about 88% then. Adding a panel or two of margin is reasonable.
• New loads. Plan for what's coming. Example (our assumption, not a rating): an EV driven 12,000 miles a year at 0.30 kWh per mile adds 3,600 kWh a year, about 7 more 400 W panels in Michigan or 7 in Texas. Check your car's rated kWh/100 mi on fueleconomy.gov. Heat pumps and induction ranges add load too.
• Clipping and inverter size. Arrays are usually built with more DC panel watts than inverter AC watts; PVWatts' default DC-to-AC ratio is 1.2, and the annual kWh per kW already reflects that.

Should you size for 100%?

That depends on how your utility pays for exported power. With full retail net metering, a system that makes 100% of your yearly kWh roughly zeroes the energy part of the bill (fixed customer charges remain). Under export-credit tariffs, the math changes: California's Net Billing Tariff, for interconnection applications on or after April 15, 2023, credits exports at avoided-cost values that are generally low at midday (CPUC). Under rules like that, a smaller array matched to daytime use, or solar plus a battery that shifts midday output to evening, usually pays back better than a big array exporting cheap power. Ask your utility which tariff applies before choosing an offset.

How many batteries?

Batteries are sized by the kWh you want to use when the sun is down or the grid is out, not by panel count. The average U.S. home uses about 28.4 kWh a day. A Tesla Powerwall 3 stores 13.5 kWh and delivers up to 11.5 kW continuous with 185 A locked-rotor start capability (Tesla datasheet), so about two cover an average day for a whole home, while one unit can cover a smaller essentials-only load. For portable or DIY backup, size from the essentials you'd actually run:

• How much battery storage do I need? (kWh, kW and motor-start sizing for home batteries)
• Battery for 1 day of essentials and 3 days of essentials
• Grid-tie vs battery backup: a grid-tie system without a battery shuts off in an outage.
• LiFePO4 vs NMC vs lead-acid

Incentives in 2026

The 30% federal Residential Clean Energy Credit (Section 25D) is not available for expenditures made after December 31, 2025, and for solar, the expenditure counts when installation is completed, so a system finished in 2026 does not qualify (IRS). State, local and utility rebates still exist in some areas; search your ZIP in DSIRE. The DOE's homeowner's guide to solar covers financing, permits and choosing an installer.

Questions

Sources

• U.S. EIA, Electric Sales, Revenue, and Average Price, 2024 data, Table 5A (state average monthly kWh and bill); Today in Energy, 2024 bills; FAQ: How much electricity does an American home use?
• NLR (formerly NREL), PVWatts calculator, system losses help, PVWatts Version 5 manual (loss categories, ~0.5%/yr degradation); nrel.gov domain retirement notice
• State PVWatts v8 averages: TheGreenWatt peak sun hours by state (used across SolarSized; see methodology)
• Qcells, Q.TRON BLK M-G2+ product page and datasheet
• Tesla, Powerwall 3 datasheet (North America)
• IRS, Residential Clean Energy Credit; CPUC, Net Energy Metering and Net Billing; DSIRE incentives database; DOE, Homeowner's guide to going solar

Run the calculator · Peak sun hours by state · How the math works