How Many Solar Panels Does a Two-Story House Need?

How Much Does Solar Cost for a Two-Story House in 2026?

Wood Mackenzie and SEIA reported an average turnkey residential system price of $3.36 per watt in the second quarter of 2026, down 1.4% from a year earlier. Marketplace quote averages are often lower, and EnergySage-based figures cited in 2026 industry summaries run closer to $2.58 per watt. Quotes vary by state, installer, equipment, and roof complexity.

Gross cost = system watts × price per watt. The $3.36/W figure is the SEIA/Wood Mackenzie Q2 2026 national average; $2.60 and $3.00 are illustrative marketplace-range scenarios. No incentives are subtracted.

Financing changes cash flow but not the total price. Compare loan payments against your projected bill savings with our solar loan calculator. For help comparing offers, see our guide on how many solar panels you need.

How Do Peak Sun Hours Change the Number of Panels?

A peak sun hour is one hour of sunlight at 1,000 watts per square meter. It measures solar energy, not daylight hours. The NREL PVWatts calculator gives location-specific results for any U.S. address.

Sun-hour values are rounded city averages consistent with NREL National Solar Radiation Database figures; published sources differ by a few tenths. Use PVWatts for your address. Same 0.80 system-loss factor as above.

Chart summary: For the same electricity use, a Portland, Oregon home needs about 31 panels while a Phoenix home needs about 18, roughly 70% more. Cloudier or northern locations need a larger array, which matters more on a two-story roof with limited space. Net-metering and export-credit rules also differ by state and utility, so check your utility’s current tariff and our net-metering calculator.

What Is the Solar Payback Period in 2026?

Simple payback is net system cost divided by first-year savings. The reference system below is a 10 kW array with 25 panels producing about 13,140 kWh in year one (10 kW × 4.5 sun hours × 365 × 0.80). At the June 2026 U.S. average residential price of 18.34 cents per kWh from EIA’s Electric Power Monthly, year-one savings are about $2,410.

No federal credit, no state incentives, flat 18.34¢/kWh, all solar output credited at the retail rate. Rising utility prices would shorten payback; lower export credits would lengthen it.

Payback depends heavily on your local electricity rate. The chart below applies the same $30,000, 10 kW system to six June 2026 EIA residential rates.

Chart summary: Electricity price drives payback more than almost anything else. At roughly 30 cents per kWh (California, Massachusetts, New York), the reference system pays back in about 7–8 years. At the U.S. average it takes about 12 years, and in the lowest-rate states (Louisiana, Idaho) it takes about 16–17. California’s current export-credit rules pay less than the retail rate for exported power, so real payback there is longer than shown. Estimate yours with our solar payback calculator and solar savings calculator.

Over 25 years, with panel output declining about 0.5% per year (the median degradation rate NREL researchers have reported), the reference system produces roughly 309,500 kWh. At a flat 18.34¢/kWh that is about $56,800 of electricity, or about $26,800 more than the $30,000 cost. This is a model, not a guarantee, and it excludes inverter replacement, financing costs, and future rate changes.

Chart summary: Once 0.5% yearly degradation is included, the lower-cost system turns cash-positive around year 12 and the higher-cost system around year 15, slightly later than the simple payback figures above. By year 25 they are about $30,767 and $23,167 ahead, before inverter replacement, financing costs, or any change in utility rates. Rising rates would improve these results; lower export credits would reduce them.