Assumes 3%/yr rate increases, 0.5%/yr panel degradation and no federal tax credit (the 30% §25D credit ended for systems installed after Dec 31, 2025). How we calculate
Data approachEIA rates · NREL sun hours · 2026 federal policy · methodology
A typical US 1-story house needs about 8 kW of solar (roughly 20 panels) to cover its electricity use, but the right size for your home depends on three things: how many kWh you use, how many peak sun hours your location gets, and how much usable roof you have. This guide gives you the sizing formula, location examples, and 2026 cost and payback figures built from public data from the U.S. Energy Information Administration (EIA) and Lawrence Berkeley National Laboratory (LBNL).
Important 2026 update: The 30% federal tax credit for homeowner-owned solar (Section 25D) ended for expenditures after December 31, 2025. Every cost and payback figure below is calculated without it. Some states and utilities still offer incentives — check DSIRE.
⚡ System Size
What Size Solar System Does a 1-Story House Need?
Short answer: about 8 kW for a home using roughly 10,400 kWh a year at 4.5 peak sun hours.
EIA data show the average US residential customer used about 865 kWh per month in 2024, or roughly 10,400 kWh a year. EIA does not break usage out by number of stories, so treat this as a national benchmark rather than a 1-story average. Your own bills are the better input.
Use this formula:
System size (kW) = annual kWh ÷ (peak sun hours × 365 × 0.80)
The 0.80 factor is a planning allowance for inverter, wiring, temperature, and soiling losses (the same as multiplying by 1.25). For the national benchmark: 10,380 ÷ (4.5 × 365 × 0.80) = ≈7.9 kW.
For context, LBNL reports that the median US residential system installed in 2024 was 7.2 kW, with most systems between about 4 and 11 kW. Systems are usually sized to a home’s usage and its roof, so both matter.
Three practical steps:
Add up the kWh on your last 12 utility bills.
Divide by your location’s peak sun hours × 365 × 0.80.
Add 15–30% if you expect an EV charger, heat pump, or electric water heater.
HVAC load is usually the biggest driver of usage, so square footage alone is a weak predictor. Use our solar system size calculator to enter your actual kWh.
Data visualization
System size needed by annual electricity use (calculated). Formula: kWh ÷ (4.5 sun hours × 365 × 0.80), rounded to 0.1 kW. Calculated by Green Energy Calculators; 4.5 sun hours is a national-average planning value.
Chart summary: System size rises in a straight line with usage: every extra 1,000 kWh a year adds about 0.76 kW at 4.5 sun hours. A home at the US-average 10,380 kWh needs about 7.9 kW, while a 15,000 kWh home (for example, with electric heat or an EV) needs about 11.4 kW. Your own local sun hours will shift these numbers up or down.
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🌎 State Comparison
How Does Your Location Change the kW You Need?
Short answer: the same house needs about 40% less solar in Phoenix than in Seattle, because peak sun hours differ so much.
Peak sun hours are the number of hours per day of full-strength (1,000 W/m²) sunlight your location receives on average. The table applies the formula above to the same 10,380 kWh/year home in four cities. The sun-hour values are rounded planning figures based on NREL solar-resource data; published sources vary by a few tenths of an hour, so confirm your address in NREL’s PVWatts calculator.
City
Approx. peak sun hours
System size for 10,380 kWh/yr
Phoenix, AZ
≈6.5
≈5.5 kW
Denver, CO
≈5.5
≈6.5 kW
Miami, FL
≈5.3
≈6.7 kW
Seattle, WA
≈3.8
≈9.4 kW
Calculated with kW = kWh ÷ (sun hours × 365 × 0.80). Approximate values; verify in PVWatts.
Location also affects the value of each kWh you generate. Residential electricity prices vary widely by state, which is a major reason solar pays back faster in some states than others.
Data visualization
Average residential electricity price by state, 2024 (cents per kWh). Source: U.S. Energy Information Administration, Average Retail Price of Electricity to Ultimate Customers by End-Use Sector (EIA-861), 2024. U.S. average: 16.48¢.
Chart summary: California, Massachusetts, and New York pay roughly 1.5–2 times the national average per kWh, so each kWh of solar output saves them more. Washington pays about 28% below the national average and also has low sun, which is why solar there has the longest payback. In 2025, EIA’s preliminary US residential average rose to 17.30¢/kWh, so these 2024 state figures are likely a bit higher today.
In low-sun or low-rate areas, sizing to about 70–80% of your usage instead of 100% can be more cost-effective, especially if your utility pays less than the retail rate for exported power. Net metering rules vary by state and change often; for example, LBNL notes that battery attachment on new California systems jumped from 14% to 57% in 2024 following net metering changes. For more on this topic, see our guide to What Size Solar System for a 2-Story House?.
📋 Key Insights
How Many Panels and How Much Roof Does a 1-Story Home Need?
Divide system size by panel wattage. An 8 kW system is 8,000 W ÷ 400 W = 20 panels; a range of 18–22 panels gives 7.2–8.8 kW. A modern 400 W panel covers roughly 18–21 sq ft, so 20 panels take about 360–420 sq ft. LBNL reports a median module efficiency of about 21% for residential systems installed in 2024, which is why 400 W-class panels are now standard.
Do 1-story homes have enough roof? Usually yes. LBNL estimated that single-story homes covered a median of 22% of roof area with panels in 2024, compared with 32% for multi-story homes, meaning many single-story roofs still have unused space. Two practical points:
Orientation: About 54% of 2024 residential arrays faced south and 23% faced west, according to LBNL, so a west- or east-facing roof plane is common and workable. Output is somewhat lower than due south; model your exact roof in PVWatts rather than relying on a rule of thumb. North-facing planes are generally avoided.
Roof age: If your roof is near the end of its life, replace it before installing solar, since removing and reinstalling panels later adds labor cost.
💰 System Cost
How Much Does Solar Cost for a 1-Story House in 2026?
Short answer: about $24,000–$41,600 for an 8 kW system before incentives, with a median around $28,000–$32,000, and no federal credit for homeowner-owned systems installed in 2026.
LBNL’s October 2025 data update covers systems installed in 2024 and reports gross prices (before incentives) in 2024 dollars:
Measure (host-owned residential, 2024)
Price per watt
Cost of 8 kW
20th percentile
$3.0/W
$24,000
Cash-purchase median
$3.5/W
$28,000
Median (all financing types)
$4.0/W
$32,000
Loan-financed median
$4.7/W
$37,600
80th percentile
$5.2/W
$41,600
Source: LBNL, Tracking the Sun 2025 Data Update. 8 kW costs calculated as price per watt × 8,000 W. Prices are gross, exclude third-party-owned systems, and include loan fees rolled into price for loan-financed systems.
Data visualization
Estimated gross cost of an 8 kW system at 2024 US price points (before incentives). Source: Lawrence Berkeley National Laboratory, Tracking the Sun 2025 Data Update (2024 installs); costs calculated as $/W × 8,000 W.
Chart summary: The price of the same 8 kW system varies by about $17,600 between the 20th and 80th percentiles. Loan-financed systems cost about $9,600 more at the median than cash purchases ($37,600 vs. $28,000), partly because dealer fees are built into the price. LBNL also found top-100 installer medians ranging from about $2.7 to $6.5 per watt, so getting at least three quotes matters more than almost any other decision.
About incentives in 2026. The Section 25D credit ended for expenditures made after December 31, 2025, with no phase-down; the IRS treats the expenditure as made when installation is complete. Systems finished and operating by that date can still claim 30% on their 2025 return (IRS Form 5695), and unused credit from an eligible project can carry forward. Third-party-owned systems (leases and PPAs) are owned by a company that may claim a separate commercial credit (Section 48E) if it meets construction or placed-in-service deadlines; ask the installer how, or whether, that benefit reaches you. LBNL reports that third-party ownership rose from 26% to 43% of residential installs in 2024. Also check state, local, and utility incentives on DSIRE, since programs change frequently.
Solar vs utility company · 25-year comparison
25-year totals: 3%/yr rate increases, 0.5%/yr degradation, no federal credit. Methodology
Is Solar Worth It for a 1-Story House Without the Federal Credit?
Short answer: often yes in high-rate states, more marginal in low-rate states, and highly dependent on the price per watt you negotiate.
Here is a transparent base case you can rebuild yourself:
System: 8 kW, producing 8 × 4.5 × 365 × 0.80 ≈ 10,512 kWh in year 1
Electricity price: 17.3¢/kWh (EIA 2025 US residential average), so year-1 savings are about $1,819
Panel output declines 0.5% per year (a common planning assumption)
Purchase price: $28,000 (LBNL cash-purchase median), no incentives
Two rate scenarios: flat 17.3¢, or 2.5% per year growth (roughly the nominal average annual rise in US retail prices over the past decade, per LBNL’s 2024 retail price trends update)
Scenario
Simple payback
Bill savings over 25 years
Net of $28,000 cost
Flat electricity price
≈16 years
≈$42,800
≈$14,800
2.5%/yr price growth
≈14 years
≈$58,200
≈$30,200
Changing the purchase price moves these results a lot. At the 20th-percentile price ($24,000), the payback ranges from about 12 to 14 years; at the all-financing median ($32,000), about 16 to 19 years. These figures exclude financing costs, maintenance, inverter replacement, and any battery.
Data visualization
Cumulative cash flow of an 8 kW system bought for $28,000, no incentives (calculated). Assumes 10,512 kWh in year 1, 17.3¢/kWh (EIA 2025 US residential average), 0.5% annual output decline. Scenario prices: flat vs. 2.5% annual growth. Excludes financing, maintenance, and inverter replacement.
Chart summary: With flat electricity prices, the system breaks even in year 16 and finishes year 25 about $14,800 ahead. If prices rise 2.5% a year, break-even moves to about year 14 and the 25-year gain roughly doubles to about $30,200. Both curves are calculated from the stated assumptions, not measured results, so replace them with your own quote and utility rate using our solar payback calculator.
Resale value. A 2015 LBNL study of nearly 4,000 solar home sales in eight states found buyers paid about $4 per watt more for homes with owned solar, roughly $15,000 for an average 3.6 kW system. LBNL cautioned that premiums depend on the local market and are likely smaller now that installed prices have fallen. Treat resale value as a possible bonus, not a guaranteed return, and note that leased systems generally do not carry the same premium.
Methodology and Sources
Data in this article come from the U.S. Energy Information Administration (usage, electricity prices), Lawrence Berkeley National Laboratory (installed prices, system size, roof coverage, orientation, ownership, home-value premiums), and NREL’s PVWatts framework (sun-hour planning values). Charts labeled “calculated” apply the formulas shown in the text to those inputs; they are estimates, not measured results. Tax rules are summarized for general information and are not tax advice; confirm eligibility with a tax professional. Prices and incentives change often, so request current quotes and verify local programs. Last reviewed September 29, 2026.
Related calculators
Free tools for US homeowners — instant results, all 50 states.
Direct answers for US homeowners — sized for a $150/month electric bill.
Most 1-story homes need about 5 to 10 kW, and a home using the US average of roughly 10,400 kWh a year needs about 8 kW at 4.5 peak sun hours. Use this formula: system kW = annual kWh ÷ (peak sun hours × 365 × 0.80). Sunny states such as Arizona can need about 5.5 kW for the same usage, while cloudy states such as Washington can need more than 9 kW. Add 15–30% if you plan to add an EV charger or electric heating.
About 18 to 22 panels of 400 W each, which equals roughly 7.2 to 8.8 kW, covers an average-use home. Twenty panels take up roughly 360–420 sq ft of roof. Berkeley Lab data show single-story homes typically cover a median of 22% of their roof with panels, so most 1-story roofs have room. Fewer panels are needed in high-sun states, and more in low-sun states.
Not for homeowner-owned systems. The Section 25D Residential Clean Energy Credit ended for expenditures made after December 31, 2025, under the One Big Beautiful Bill Act, and installation date is what counts. Systems completed and operating by that date can still claim 30% on a 2025 return using IRS Form 5695. Leased or PPA systems are owned by a company that may claim a separate commercial credit, so ask installers how any savings are passed on. Check state and utility incentives on DSIRE.
Berkeley Lab reports a 2024 median installed price of about $4.0 per watt (middle 60% of systems: $3.0–$5.2/W), before incentives. For 8 kW, that is roughly $24,000 to $41,600, with about $28,000 at the $3.5/W cash-purchase median. At 17.3¢/kWh and 4.5 sun hours, an 8 kW system saves about $1,800 in year one, giving a simple payback near 16 years at flat rates or about 14 years if rates rise 2.5% a year. Your quote and utility rate can move this by several years.
Cash is usually cheapest up front: Berkeley Lab found 2024 median prices of $3.5/W for cash purchases versus $4.7/W for loan-financed systems, partly because loan fees are rolled into the price. Leases and power purchase agreements (about 43% of 2024 residential installs) avoid the upfront cost, but you don't own the system. Compare total 25-year cost, not just monthly payment, and ask each installer for price per watt, loan fees, and any rate escalator.
Same usage, bill-based guide
Your 1-Story House target maps to roughly a $150/month electric bill nationally.
18.19¢/kWh — US average residential price. Source: EIA Electric Power Monthly, Table 5.6.B (year-to-date through July 2026), residential average retail price (July 2026) (EIA)
Solar production
4.5 peak sun hours/day × 0.82 system derate. Approximate state-average daily solar resource (peak sun hours) based on NREL solar resource data (NSRDB); not location-specific — use NREL PVWatts for an address-level estimate. (NREL PVWatts)
Installed price
$3.00 per watt before incentives. Blended 2026 US residential installed price used by this site; EnergySage marketplace reported about $2.60/W (mid-2026); full-market medians are higher.
Federal tax credit
$0 for homeowner-owned systems installed in 2026 — the 30% §25D credit ended Dec 31, 2025 (IRS)
Net metering
National blend — solar assumed to offset 75% of the bill (87% in full-retail net-metering states, 55–70% elsewhere).
Estimates only — not tax, legal or financial advice. Get at least three installer quotes and confirm incentives with your utility and a tax professional.