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
Short answer: Most 2-story US homes need about 7–12 kW of solar, depending on how much electricity the household uses and how many peak sun hours the location gets. A 9.5 kW system typically means around 24 panels and costs roughly $24,700 before incentives at the 2026 marketplace average. One important 2026 change: the 30% federal tax credit no longer applies to solar systems homeowners buy after December 31, 2025. This guide shows the sizing formula, updated cost and payback math, and the assumptions behind every number so you can check them against your own utility bill.
Three variables drive the answer more than anything else: your annual kWh consumption (from your utility bill), your local peak sun hours (roughly 3.5 in Seattle to 6.5 in Phoenix), and how much unshaded roof you have. Each extra 1 kW of capacity adds roughly $2,600–$3,500 to the upfront price at current per-watt costs, so oversizing or undersizing by 2 kW moves your cost by about $5,000–$7,000.
⚡ System Size
How Many kW Does a 2-Story House Actually Need?
A 2-story house typically needs 7–12 kW of solar for a full electricity offset, depending mostly on local sun and household usage. The EIA reports that the average US residential customer used about 10,800 kWh in 2022 (roughly 900 kWh per month). Larger two-story homes, electric heating, EVs, and pools push that higher, so use your own bills rather than a national average.
Here is the core sizing formula:
System size (kW) = Annual kWh ÷ (Peak Sun Hours × 365 × 0.80)
The 0.80 factor covers real-world losses such as inverter efficiency, wiring, heat, and soiling. NREL’s PVWatts tool defaults to 14% system losses, which combined with typical inverter efficiency lands near 0.82, so 0.80 is a slightly conservative planning factor. Panel degradation of roughly 0.5% per year (the median reported in NREL’s degradation review) is a separate factor for long-term modeling.
Required system size by annual usage and location (kW):
Annual Usage (kWh)
Phoenix (6.5 PSH)
Denver (5.5 PSH)
Chicago (4.3 PSH)
Seattle (3.6 PSH)
10,000
5.3 kW
6.2 kW
8.0 kW
9.5 kW
13,000
6.8 kW
8.1 kW
10.4 kW
12.4 kW
16,000
8.4 kW
10.0 kW
12.7 kW
15.2 kW
19,000
10.0 kW
11.8 kW
15.1 kW
18.1 kW
PSH = peak sun hours per day, rounded annual averages for a fixed south-facing array. Published NREL-derived values differ by roughly ±10% depending on dataset and exact address, so confirm yours in PVWatts.
Installers often quote very different system sizes for the same home because they start from different consumption assumptions or sun-hour figures. Run your own numbers with our solar system size calculator before requesting quotes.
Data visualization
Required solar system size for a 2-story home using 13,000 kWh/year, by climate. Calculated with the sizing formula above (0.80 loss factor) using rounded annual peak sun hours (PSH) from NREL-derived data.
Chart summary: For the same 13,000 kWh of annual use, a Seattle home needs about 12.4 kW while a Phoenix home needs about 6.8 kW, roughly 80% more capacity. Sun hours, not home size, explain most of the difference, so always size from your own kWh and your own location.
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💰 System Cost
How Much Does a Solar System Cost for a 2-Story Home in 2026?
A 9.5 kW system costs roughly $24,700 before incentives at the 2026 EnergySage marketplace average of about $2.60 per watt, and closer to $33,250 at the $3.50 per watt that Lawrence Berkeley National Laboratory’s installed-price data has reported for cash purchases (2024 installs). The gap exists because marketplace quotes and broader installed-price datasets measure different samples, so use both as a range and compare it against real local quotes.
System cost by size, before any incentives:
System Size
Cost at $2.60/W (marketplace average)
Cost at $3.50/W (higher-cost case)
6 kW
$15,600
$21,000
8 kW
$20,800
$28,000
9.5 kW
$24,700
$33,250
10 kW
$26,000
$35,000
12 kW
$31,200
$42,000
Calculated as system watts × price per watt. EnergySage reported an average 12 kW system near $31,135 in 2026, consistent with the first column. Your quote will vary with equipment, roof complexity, and location.
Installers price by the watt, so always ask for itemized quotes (equipment, labor, permits) from at least three companies and compare the price per watt rather than the total. Also confirm the inverter type, the panel warranty, and how the installer handles interconnection with your utility. For related sizing, see our guides for a 1-story house and a 2,100 sq ft house.
Data visualization
Installed cost of a home solar system by size at two per-watt price points (before incentives). Calculated as kW × 1,000 × price per watt. $2.60/W reflects the 2026 EnergySage marketplace average; $3.50/W reflects the higher cash-purchase median reported by LBNL for 2024 installs.
Chart summary: Cost scales in a straight line with system size, adding roughly $2,600–$3,500 per kW. The price-per-watt gap between quotes can matter as much as adding 3 kW of capacity: a 9.5 kW system ranges from about $24,700 to $33,250, an $8,550 spread for the same equipment size.
Solar vs utility company · 25-year comparison
25-year totals: 3%/yr rate increases, 0.5%/yr degradation, no federal credit. Methodology
Is There Still a Federal Solar Tax Credit in 2026?
No, not for homeowners who buy a system with cash or a loan in 2026. The 30% Residential Clean Energy Credit (Section 25D) ended for expenditures made after December 31, 2025, under the One Big Beautiful Bill Act signed on July 4, 2025. The IRS Residential Clean Energy Credit page confirms the credit is not available for property placed in service after that date.
What still exists in 2026:
Systems completed by December 31, 2025: the 30% credit can still be claimed on the 2025 return, and unused credit can generally carry forward to later tax years.
Leased or power-purchase-agreement (PPA) systems: the third-party owner may claim the commercial Section 48E credit, generally requiring the system to be placed in service by December 31, 2027 unless construction began by July 4, 2026. Any savings passed to you depend on the contract terms.
State, local, and utility incentives: these vary widely. Search your state on DSIRE for current rebates, property tax exemptions, and net metering rules.
Because the federal credit no longer reduces the price, the payback figures in this guide use the full before-incentive cost. Tax rules can change, so confirm your situation with a qualified tax professional before signing.
📋 Key Insights
Worked Example: Sizing a 2-Story Home in Denver
This is a calculation, not a measured install, showing how the formula turns bills into a system design. Assume a 2,500 sq ft, 2-story home in the Denver area using 13,000 kWh per year, with a south-facing roof and no shading.
Step
Value
Basis
Annual electricity use
13,000 kWh
Example household; use your own bills
Peak sun hours
5.5 per day
Rounded annual average for Denver
Required size
8.1 kW
13,000 ÷ (5.5 × 365 × 0.80)
Panels
20 × 400 W = 8.0 kW
Nearest whole panel count
Estimated output
~12,850 kWh/yr (~99% offset)
8.0 kW × 5.5 × 292
Roof area needed
~420 sq ft
20 panels × ~21 sq ft
Cost before incentives
~$20,800
8,000 W × $2.60/W
Electricity rate
17.13¢/kWh
EIA Electric Power Monthly, Colorado residential, June 2026
Estimated year-one savings
~$2,200
12,848 kWh × $0.1713
Simple payback
~9.5 years
$20,800 ÷ $2,200
Two cautions apply. First, the output figure is a planning estimate, so request a PVWatts run for your exact address, roof tilt, and orientation. Second, the savings assume every kWh is valued at the retail rate, which holds under full retail net metering or when you use the power yourself, but not under low export-compensation rules. Use our solar savings calculator to test your own inputs.
📈 Payback Period
What Solar Payback Period Should a 2-Story Homeowner Expect?
In our model, a correctly sized system on a 2-story home pays back in roughly 9–11 years in most mid-sun, mid-rate metros, and can exceed 16 years where sun hours and electricity rates are both low. This assumes no federal credit, a $2.60 per watt installed cost, and full retail-rate value for all solar output.
The formula behind the table is simple: payback = installed cost per kW ÷ (annual kWh per kW × electricity rate). Because the system is sized to the same 13,000 kWh in every city, the differences come entirely from local sun and local rates.
Modeled simple payback for a 2-story home using 13,000 kWh/year (no federal credit, $2.60/W):
Location
Residential Rate (June 2026)
Peak Sun Hours
System Size
Cost
Year-1 Savings
Payback
Phoenix, AZ
15.18¢/kWh
6.5
6.8 kW
$17,800
$1,973
9.0 yrs
Denver, CO
17.13¢/kWh
5.5
8.1 kW
$21,000
$2,227
9.5 yrs
Chicago, IL
19.89¢/kWh
4.3
10.4 kW
$26,900
$2,586
10.4 yrs
Atlanta, GA
16.36¢/kWh
5.0
8.9 kW
$23,200
$2,127
10.9 yrs
Seattle, WA
14.91¢/kWh
3.6
12.4 kW
$32,200
$1,938
16.6 yrs
Rates: state residential averages from EIA Electric Power Monthly Table 5.6.A, June 2026. The US average that month was 18.34¢/kWh. Excludes financing costs, state incentives, rate increases, panel degradation, and inverter replacement. At $3.50/W, each payback figure is about 35% longer.
Net metering policy matters a great deal. Under full retail net metering, excess summer production offsets winter usage one-for-one. Where the utility pays a lower export rate, the value of each exported kWh falls and payback lengthens, so check your utility’s current rules on DSIRE before committing.
Data visualization
Modeled simple payback for a 2-story home using 13,000 kWh/year, by location (no federal credit, $2.60/W installed). Calculated from June 2026 EIA state residential rates and rounded annual peak sun hours; assumes full retail-rate value for all solar output.
Chart summary: Four of the five locations pay back in about 9–11 years, while Seattle takes roughly 16.6 years because it combines the lowest sun hours with a below-average electricity rate. Higher rates shorten payback (Chicago’s 19.89¢ offsets its weaker sun), which is why both numbers matter.
For a national baseline, consider the 9.5 kW example: at 4.5 peak sun hours it produces about 12,480 kWh in year one, worth roughly $2,290 at the 18.34¢ national average rate. Against a $24,700 cost, simple payback is about 10.8 years, and about 11 years once 0.5% annual degradation is included.
Data visualization
Cumulative net cash flow for a 9.5 kW system bought for $24,700 (no federal credit). Model assumptions: 12,483 kWh in year one (4.5 peak sun hours, 0.80 loss factor), 18.34¢/kWh held flat, 0.5% annual panel degradation. Excludes financing, maintenance, and inverter replacement.
Chart summary: The system reaches break-even at about year 11 and builds to roughly $29,200 in net savings by year 25 under flat electricity prices. If retail rates rise over time, savings would be higher; if you finance the purchase or replace the inverter, they would be lower.
⚡ Panel Count
How Many Solar Panels Does a 2-Story House Need in 2026?
A 2-story house typically needs 18 to 30 panels for a 7–12 kW system, and a 9.5 kW system needs about 24 panels at 400 W each. Standard residential panels in 2026 commonly range from about 400 W to 430 W, so higher-wattage panels reduce the count. A decade ago the same 9 kW system needed about 36 panels at 250 W.
Each 400 W panel occupies roughly 21 sq ft, so panel count translates directly into required roof area.
Panel count and roof area by system size (400 W panels):
System Size
Panel Count
Roof Area Needed
Cost at $2.60/W (before incentives)
6 kW
15 panels
315 sq ft
$15,600
8 kW
20 panels
420 sq ft
$20,800
9.5 kW
24 panels
~504 sq ft
$24,700
10 kW
25 panels
525 sq ft
$26,000
12 kW
30 panels
630 sq ft
$31,200
Two-story homes stack their floors, so the roof is usually smaller relative to the home’s electricity use than on a single-story house of the same size. On a complex roofline or with heavy shading, the usable roof may cap the system below your full-offset target, which is worth confirming before you design around a specific kW figure.
If your south-facing roof cannot fit enough panels, split arrays across east and west faces. East- or west-facing planes typically produce about 10–20% less per panel than south, but they add usable area and can produce more of their power in the morning or late afternoon. Microinverters or DC power optimizers are worth considering on roofs with partial shading or several planes, because they limit the impact of a shaded panel to that panel rather than the whole string.
Use our solar payback calculator to test how panel count, roof orientation, and your local rate interact before you request quotes.
Sources and Methodology
All calculations use the formula shown above (annual kWh ÷ peak sun hours × 365 × 0.80), and every worked figure is labeled as a model or an example rather than a measured result. Inputs come from the following public sources, reviewed on September 29, 2026:
This guide is for general information and is not tax, legal, or financial advice. Prices, incentives, and net metering rules change, so confirm current terms with local installers, your utility, and a tax professional.
Related calculators
Free tools for US homeowners — instant results, all 50 states.
Direct answers for US homeowners — sized for a $191/month electric bill.
Most 2,500 sq ft, 2-story homes land between about 7 kW and 12 kW, but your electricity use and local sun hours set the number, not square footage. For an example home using 13,000 kWh a year, the formula (annual kWh ÷ peak sun hours × 365 × 0.80) gives about 6.8 kW in Phoenix, 8.1 kW in Denver, 10.4 kW in Chicago, and 12.4 kW in Seattle. Use the 12-month kWh total from your utility bill, and add expected load if you plan to buy an EV or a heat pump.
Roughly 18 to 30 panels for a 7–12 kW system. A 9.5 kW system uses about 24 panels rated at 400 W, and each panel takes up about 21 sq ft, so plan on roughly 500 sq ft of unshaded roof. Divide your target system size in watts by the wattage of the panel you are quoted (for example, 9,500 W ÷ 400 W ≈ 24).
Not for systems you buy with cash or a loan. The 30% Residential Clean Energy Credit (Section 25D) ended for expenditures made after December 31, 2025, under the One Big Beautiful Bill Act, so a system you own and place in service in 2026 receives no federal credit. Systems placed in service by the end of 2025 can still claim it, and unused credit can carry forward. Leased or power-purchase-agreement systems may still capture federal value because the provider can claim the commercial Section 48E credit, subject to deadlines. Check DSIRE for state and utility incentives and confirm your situation with a tax professional.
In our model, with no federal credit, an installed cost of $2.60 per watt, and full offset of 13,000 kWh at the state's June 2026 EIA residential rate, simple payback is about 9.0 years in Phoenix, 9.5 in Denver, 10.4 in Chicago, 10.9 in Atlanta, and 16.6 in Seattle. At $3.50 per watt, those figures are about 35% longer. Payback also depends on your utility's net metering or export rules, so treat these as planning estimates and get local quotes.
Yes. Southeast- and southwest-facing roofs typically produce about 5–10% less than due south, and east- or west-facing roofs about 10–20% less. North-facing roof planes are usually not viable on their own, so installers often place panels on the east, south, and west faces instead. West-facing panels can even be worth more under time-of-use rates because they produce later in the day. Get a PVWatts estimate for your exact address and roof angles before you decide.
Same usage, bill-based guide
Your 2-Story House target maps to roughly a $175/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.