Solar Panels for a Duplex: How Many Do You Need? (2026)
Est. net savings
$32,000
Over 25 Years (Estimate) · no federal credit
Typical result:
- ~39 panels (400W)
- 15.6 kW system
- $39K–$55K before incentives
- ~14 year simple payback
25 years without solar vs with solar
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
Without solar
25-year utility bills
$79,500
Rates rise ~3% per year
With solar
System cost + remaining bills
$46,800
Installed cost, no federal credit
Difference
Estimated 25-year net
+$32,700
Before any state or utility incentives
How Much Energy Does a Duplex Actually Use?
A duplex uses roughly 1,400 to 2,000 kWh per month across both units, or about twice a single home. The U.S. Energy Information Administration reports that the average U.S. residential customer used 865 kWh per month in 2024 at an average price of 16.5 cents per kWh. Two average households therefore land near 1,700 kWh per month, which this guide uses as its reference load.
Actual usage swings with climate and unit size. Smaller two-bedroom units often run 600–750 kWh per month, while larger units with central air conditioning can exceed 1,000 kWh. Electric vehicle charging at home can add a few hundred kWh per month.
Pull 12 months of utility bills for both units (or ask both tenants for statements) to get a reliable baseline. Avoid sizing from a single summer month, because cooling loads can inflate usage and push your system size too high. NREL’s PVWatts calculator uses location-specific solar data and is a free way to cross-check an installer’s production estimate.
A single solar array can serve both units if it is sized to the combined load and the metering arrangement allows it (see the metering section below). To turn your kWh figure into a panel count, use our Solar System Size Calculator.
Duplex Solar Panel Count by System Size (2026 Reference Table)
Panel count equals system size divided by panel wattage, and most residential installs in 2026 use 400W to 430W modules. The table below shows panel counts, estimated monthly output and installed cost for common duplex system sizes.
Duplex Solar Panel Count by System Size (2026)
| System Size | Est. Monthly Output* | Panels (400W) | Panels (430W) | Installed Cost at $2.50–$3.50/W** |
|---|---|---|---|---|
| 7 kW | 670–840 kWh | 18 | 17 | $17,500–$24,500 |
| 10 kW | 960–1,200 kWh | 25 | 24 | $25,000–$35,000 |
| 12 kW | 1,150–1,440 kWh | 30 | 28 | $30,000–$42,000 |
| 14 kW | 1,340–1,680 kWh | 35 | 33 | $35,000–$49,000 |
| 16 kW | 1,540–1,920 kWh | 40 | 38 | $40,000–$56,000 |
| 18 kW | 1,730–2,160 kWh | 45 | 42 | $45,000–$63,000 |
*Output assumes 4.0–5.0 peak sun hours per day and 80% overall system efficiency (inverter, wiring, temperature and soiling losses). **Price per watt typically falls as systems get larger, so the upper end is conservative for big arrays. Panel counts are rounded up.
Chart summary: Moving from a 7 kW to an 18 kW system takes you from 18 to 45 panels at 400W. Higher-wattage 430W modules save about 1 to 3 panels at each size, which matters if roof space is tight. For a 1,700 kWh/month duplex, the 16 kW (40-panel) row is the closest match for a full offset.
Chart summary: At 4.5 peak sun hours, a 16 kW system produces about 1,730 kWh per month, which meets a 1,700 kWh load. A 12 kW system produces about 1,300 kWh, covering roughly three-quarters of that load. Sun hours range from roughly 3.5 in the Pacific Northwest to 6 or more in the Desert Southwest, so the same building can need up to about 40% fewer panels in the sunniest regions.
Before you commit, confirm usable roof area. Each panel covers roughly 18 to 22 square feet, so a 39-panel array needs about 700 to 860 square feet of unshaded roof. Panels also degrade about 0.5% per year according to NREL research, so a system producing 14,000 kWh in year one will produce roughly 12,300 kWh in year 25.
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What Does a Duplex Solar System Cost in 2026?
Residential solar typically costs about $2.50 to $3.50 per watt installed in 2026, so a 12 kW duplex system runs roughly $30,000 to $42,000 and a 16 kW system $40,000 to $56,000. Published averages differ by source and quote mix, so treat this as a planning range and compare itemized quotes in dollars per watt.
The federal credit changed. The 30% Residential Clean Energy Credit (Section 25D) ended for expenditures made after December 31, 2025, with no phase-down, according to SEIA’s summary of the 2025 budget law. Older articles that show a 30% credit “through 2032” are out of date. Third-party-owned systems and some business-owned systems may still qualify for the Section 48E credit under deadlines that generally require being placed in service by the end of 2027 unless construction began by July 4, 2026, and subject to foreign-entity sourcing rules. If you own the duplex as a rental, ask a CPA whether any business credit or depreciation applies to you.
State and utility incentives still matter. Verify each program in the DSIRE database before relying on it, because funding and rules change.
Examples of State Incentives to Verify (2026)
| State | Incentive Examples | What to Check |
|---|---|---|
| New York | State income tax credit of 25%, up to $5,000 | Eligibility for owner-occupied vs. rental use |
| Arizona | State income tax credit of 25%, up to $1,000 | Annual cap and filing rules |
| Florida | Sales tax and property tax exemptions for solar | Net metering terms with your utility |
| California | Battery incentives (SGIP) when funded | Export credits under the Net Billing Tariff are below retail rates |
| Massachusetts | SMART production incentive program | Current block availability |
| Texas | No statewide tax credit | Utility and city rebates, retail-plan buyback rates |
Financing check. A $20,000 solar loan at 6.99% over 15 years costs about $180 per month. Scaled to a $46,800 system (15.6 kW at $3.00 per watt), the same loan costs about $420 per month, which is more than the roughly $280 per month of electricity a 1,700 kWh duplex would avoid at 16.5 cents per kWh. At this size, a loan is not cash-flow positive from day one at average rates, so compare loan terms against your actual bills with our Solar Savings Calculator.
Solar vs utility company · 25-year comparison
25-year totals: 3%/yr rate increases, 0.5%/yr degradation, no federal credit. Methodology
Total utility payments
$79,500
Total solar cost (installed + remaining bills)
$46,800
Net savings
+$32,700
Avg. monthly difference
+$109/mo
One Meter vs. Two Meters: Which Solar Setup Works for a Duplex?
Match the system design to your meters: one meter usually means one system, while two meters usually mean two systems or a shared array with utility-approved credit sharing. Metering is the step most duplex owners skip, and it determines permitting, billing and tenant fairness.
Single shared meter (owner pays utilities): One array, one inverter and one interconnection agreement. All net metering credits flow to one account. This is the simplest setup and fits owner-occupied duplexes where the owner pays both electric bills.
Two separate meters (tenants pay their own bills): You have two options. Install two smaller systems, one per meter, each with its own interconnection agreement. This is cleaner legally and avoids tenant disputes. Or install one larger shared array and allocate production across the two meters. That can lower equipment and permitting costs, but it needs utility approval and a program that allows credits to move between meters.
Virtual net metering: Some utilities and states let multi-tenant buildings share solar credits across separate meters without physical sub-metering. California’s virtual net metering tariffs for multi-tenant properties are one example. Availability varies by utility, so confirm eligibility with your utility and check DSIRE before signing a contract.
Export credits matter. How your utility values excess solar sent to the grid can change payback by years. Some states credit exports at retail rates, while others, such as California under its Net Billing Tariff, credit them at lower avoided-cost rates. Ask every installer to model your savings using your utility’s current export-credit rules, and compare against our net metering calculator.
Is Solar Worth It for a Duplex Owner in 2026?
Solar can still be worth it for a duplex, mainly where electricity rates are high, but simple payback now runs roughly 8 to 19 years depending on your rate. The table and chart below use one consistent scenario: 4.5 peak sun hours, a system price of $3.00 per watt, 80% system efficiency, full retail-rate credit for every kWh, no rate increases and no incentives.
Illustrative Simple Payback by Electricity Rate
| Electricity Rate | Annual Savings per kW | Simple Payback |
|---|---|---|
| 12¢/kWh | ~$158 | ~19.0 years |
| 16.5¢/kWh (U.S. average, 2024) | ~$217 | ~13.8 years |
| 20¢/kWh | ~$263 | ~11.4 years |
| 25¢/kWh | ~$329 | ~9.1 years |
| 29¢/kWh | ~$381 | ~7.9 years |
Residential rates vary widely. According to EIA’s 2024 state data, average rates ran about 29 cents per kWh in Massachusetts and Connecticut, versus roughly 11 to 13 cents in Nebraska, North Dakota and Iowa.
Chart summary: Payback falls from about 19 years at 12¢/kWh to about 8 years at 29¢/kWh. At the 16.5¢ national average, a $46,800 system pays back in roughly 14 years and, with 0.5% annual degradation, produces about $79,000 of avoided electricity over 25 years. That is roughly $32,000 net before inverter replacement, maintenance and financing costs. Rising utility rates would improve these figures, while weak export credits would worsen them.
Resale value. A multi-state Lawrence Berkeley National Laboratory study, Selling Into the Sun, found that homes with owned solar sold at a premium of about $4 per watt. That study covers single-family homes and dates from 2015, so do not assume a duplex appraisal will follow it. Income-producing property is often valued on rental income, so ask a local appraiser or agent how buyers in your market value solar.
Use our Solar Payback Calculator to model your break-even year with your own rate, system price and incentives.
How to Size a Duplex Solar System Step by Step
To size a duplex system, divide combined monthly kWh by 30 days, peak sun hours and 0.80 system efficiency to get kilowatts, then divide system watts by panel watts. These four steps give you an independent benchmark, and quotes that land far from your result deserve a direct question to the installer.
Step 1: Calculate combined monthly kWh. Add 12 months of bills for both units and divide by 12. Example: 18,000 kWh per year ÷ 12 = 1,500 kWh per month.
Step 2: Find your peak sun hours. Look up your address in NREL’s PVWatts. Most of the continental U.S. falls between roughly 3.5 and 6.5 peak sun hours per day, with the Pacific Northwest at the low end and the Desert Southwest at the high end. This guide uses 4.5.
Step 3: Calculate system size. Formula: monthly kWh ÷ (30 × sun hours × 0.80). Example: 1,500 ÷ (30 × 4.5 × 0.80) = 1,500 ÷ 108 = 13.9 kW.
Step 4: Convert to panel count. Divide system watts by panel watts and round up. 13,900 W ÷ 400 W = 35 panels. At 430W: 13,900 ÷ 430 = 33 panels.
At $2.50 to $3.50 per watt, a 13.9 kW system costs roughly $34,750 to $48,650 before any state or utility incentives. Shading can reduce output and raise the panel count you need, and microinverters or power optimizers can reduce shading losses at extra cost, so ask for an itemized quote and a shade analysis on complex roofs. If panels face east and west rather than south, output per panel is lower, but the production curve spreads across the day. Have the installer model each roof plane in PVWatts and show the annual kWh difference.
Finally, run your numbers through our Solar System Size Calculator and Solar Tax Credit Calculator to check your eligibility under current rules.
Sources and Methodology
Last reviewed October 1, 2026. Figures are estimates for planning, not quotes or tax advice.
- Usage and rates: U.S. Energy Information Administration, Today in Energy, 2024 residential electricity prices and consumption (865 kWh per month; 16.5 cents per kWh) and EIA 2024 state average residential price and consumption data.
- Federal tax credit status: SEIA summary of the 2025 budget law (Section 25D terminated after December 31, 2025; Section 48E deadlines). Confirm your situation with a tax professional.
- Installed cost: Planning range of $2.50 to $3.50 per watt reflects published 2026 industry figures, including marketplace quote data and SEIA/Wood Mackenzie market insight reporting. Your local quotes will differ.
- Production and degradation: NREL PVWatts; NREL, Photovoltaic Degradation Rates: An Analytical Review (median about 0.5% per year).
- State incentives and metering: DSIRE, plus state tax agency and utility tariff pages. Programs change; verify before relying on them.
- Resale value: Lawrence Berkeley National Laboratory, Selling Into the Sun (2015).
- Our assumptions: 400W and 430W panels; 4.0–5.0 peak sun hours (4.5 for reference scenarios); 80% overall system efficiency; 1,700 kWh/month reference load; simple payback ignores rate increases, financing, maintenance and inverter replacement.
Frequently asked questions
Direct answers for US homeowners — sized for a $280/month electric bill.
Popular state solar guides
Electricity rates and incentives vary — see data for your state.
How these numbers were calculated
- Electricity rate
- 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).
- Model
- Version 2026.10 · 3%/yr electricity price escalation · 0.5%/yr panel degradation · simple payback = installed cost ÷ year-1 savings
- Policy checked
- · Full methodology · Report an error
Estimates only — not tax, legal or financial advice. Get at least three installer quotes and confirm incentives with your utility and a tax professional.