How Many Solar Panels Do I Need?

Step 1: Calculate Your Annual Electricity Consumption

Your electricity bill is the most important document in this whole process. Pull the last 12 months of statements and add up the kilowatt-hours — not the dollar amounts, which fluctuate with rates. Many utilities print a rolling 12-month total on each bill, which makes this easy.

The national average is about 10,500 kWh per year (EIA). The exact figure shifts with the weather and the year: EIA reported 10,791 kWh per residential customer for 2022, and about 865 kWh per month (roughly 10,400 kWh per year) for 2024. That average hides large regional differences. In EIA’s 2022 data, the average household in Louisiana, where air conditioning runs for much of the year, used 14,774 kWh, while the average in Hawaii used 6,178 kWh. If your real usage is 40% above the national average and you size to the average, your system will be undersized from day one.

Once you have your annual total, convert it to a daily average by dividing by 365. A home using 10,500 kWh annually consumes roughly 28.8 kWh per day. You will use that daily figure in the formula in Step 3.

Two practical notes before moving on. First, if you plan to add an electric vehicle, include that load now. At 12,000 miles per year and 0.25 to 0.35 kWh per mile, an EV adds roughly 3,000 to 4,200 kWh per year. Second, a heat pump or electric water heater can shift your consumption substantially. Sizing a solar system to today’s usage and then adding a major load next year is one of the most common planning mistakes homeowners make, so settle your consumption baseline before you move on.

Step 5: Understand Tax Credits and Verify Your Installer’s Quote

Once you’ve run your own panel count, use it as a benchmark when comparing installer proposals. A reputable installer should land within two or three panels of your calculation. A proposal that runs 30% higher deserves a direct question: “What consumption figure and production estimate are you using?” If the installer can’t answer clearly, treat it as a red flag.

The federal credit has ended for homeowner-owned systems

The 30% federal Residential Clean Energy Credit (Section 25D) was originally scheduled to run through 2032. The One Big Beautiful Bill Act (Public Law 119-21), signed July 4, 2025, ended it for expenditures after December 31, 2025. A system placed in service in 2026 or later does not qualify for 25D, so any quote that still assumes a 30% federal credit for a purchased system should be questioned. Third-party-owned systems (leases and power purchase agreements) are treated differently, and the provider may still claim a commercial credit under tighter deadlines, so ask each provider how its pricing is built and how long its terms and escalators run. Confirm current rules with the IRS or a tax professional.

State incentives still exist and now matter more. New York offers a state tax credit of 25% of system cost, up to $5,000, which is non-refundable but can be carried forward for up to five years. Massachusetts offers a 15% state tax credit capped at $1,000, along with the SMART program’s per-kWh payments. Programs change often, so verify the current terms on your state’s energy office or utility website before relying on them.

What does it cost, and how long is the payback?

Residential solar costs roughly $2.50 to $3.50 per watt installed in 2026 before incentives, with a national average of about $2.75 to $2.80 in industry price surveys. Here is an illustrative example, with every assumption stated:

• System: 7.5 kW, at $2.75 per watt = about $20,600
• Production: about 1,400 kWh per kW per year = about 10,500 kWh per year (a roughly average US location)
• Electricity value: 16.5 cents per kWh, with full retail net metering = about $1,730 per year, or about $144 per month
• Simple payback: $20,625 ÷ $1,732 = about 12 years
• 25-year bill savings, assuming 0.5% annual panel degradation and no electricity price increases: about $40,800, or about $20,200 net of the system cost

The chart below plots the same example year by year, once with flat electricity prices and once with a 3% annual rate increase.

Chart summary: With flat electricity prices, cumulative savings cross zero between year 12 and year 13 (about 12.2 years) and reach roughly $20,200 by year 25. If rates rise 3% per year, break-even comes at about 10.6 years and the 25-year total grows to roughly $38,400. The 3% case is an assumption, not a forecast, so test your own rate trend in the calculator.

Your results will differ. Payback is shorter in states with high electricity rates and strong net metering, and longer where export credits are low or rates are cheap. Run your own numbers through our solar payback calculator before committing to a contract. For state-by-state data, see our guide to Solar Panel Payback Period by State.

Common, legitimate reasons an installer’s panel count runs higher than yours: they are sizing for a planned EV or heat pump, they use a more conservative loss assumption, or your roof’s tilt or shading lowers production. Understand each reason before signing.