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 3-bedroom house in the US needs about 20 solar panels rated at 420 watts (roughly 8.4 kW) to offset average electricity use. The count ranges from about 14 panels in very sunny Arizona to about 25 in cloudy Washington. The US Energy Information Administration (EIA) reports that the average US residential customer uses about 10,800 kWh per year, or roughly 899 kWh per month. That is about 30 kWh per day, and it is the benchmark we use below. Your own bills matter more than any average. For more on this topic, see our guide to How Many Solar Panels for a 3-Bedroom House?.
Three variables decide your panel count: your annual kWh use, your local peak sun hours (roughly 3.5 in the Pacific Northwest to 6.5 in Phoenix), and system losses from heat, wiring, inverter conversion, soiling and shading. This guide shows the math, so you can check it against your own numbers.
⚡ System Size
How Many 420W Solar Panels Does a 3-Bedroom House Need?
The sizing formula is: daily kWh ÷ (panel kW × peak sun hours × 0.80) = panels needed. The 0.80 factor is a conservative allowance for real-world losses. For a home using 30 kWh per day at 4.5 peak sun hours: 30 ÷ (0.42 × 4.5 × 0.80) = 19.8, rounded up to 20 panels (8.4 kW).
The table applies the same formula to a household using 10,800 kWh per year (29.6 kWh per day) in six climates. Sun-hour values are rounded annual averages for a representative city in each state (based on NREL solar resource data); use PVWatts for your exact ZIP code.
State (representative city)
Peak sun hours (approx.)
420W panels needed
System size (kW)
Modeled annual output (kWh)
Arizona (Phoenix)
6.5
14
5.88
~11,160
Florida
5.3
17
7.14
~11,050
Texas
5.2
17
7.14
~10,840
Illinois (Chicago)
4.2
21
8.82
~10,820
Michigan
4.0
23
9.66
~11,280
Washington (Seattle)
3.6
25
10.50
~11,040
Panel counts are rounded up to whole panels, so output slightly exceeds 10,800 kWh in some rows. If your home has an EV, a heat pump or electric resistance heating, or a pool pump, expect to need more. An EV driven about 12,000 miles per year typically adds roughly 3,000–4,000 kWh per year, which can mean 4–8 additional panels depending on your location. Use our solar system size calculator to size from your actual bill.
Data visualization
Modeled number of 420W panels needed to offset 10,800 kWh per year, by climate. Calculated with panels = daily kWh ÷ (0.42 kW × sun hours × 0.80). Sun hours are rounded NREL-based averages for a representative city. Source: EIA (consumption), NREL (solar resource); calculation by our editorial team.
Chart takeaway: The same house needs about 80% more panels in Washington (25) than in Arizona (14). Sunlight, not house size, is the main reason panel counts differ so much between states.
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⚡ System Size
How Much Electricity Does One 420W Panel Produce?
A panel’s daily output is 420 W × peak sun hours × 0.80. That gives roughly 1.2 kWh per day at 3.5 sun hours and 2.2 kWh per day at 6.5 sun hours.
Peak sun hours
kWh per day (one 420W panel)
kWh per year
3.5
1.18
~429
4.5
1.51
~552
5.5
1.85
~675
6.5
2.18
~797
These are estimates using a conservative 0.80 loss factor. NREL’s PVWatts calculator uses a default 14% system loss and hourly weather data for your location, so it gives a more precise result for your roof. Roof tilt and direction matter, but for most pitched roofs the effect is modest compared with shading and local climate.
Panel output also declines slowly over time. Manufacturers commonly warrant roughly 0.4–0.55% degradation per year, and our payback model below uses 0.5%.
💰 System Cost
How Much Does Solar Cost for a 3-Bedroom House in 2026?
Installed residential solar quotes commonly fall around $2.50–$3.50 per watt before incentives, although prices vary by installer, equipment, roof complexity and location. EnergySage’s marketplace data is a good live benchmark for your state. For the typical 8.4 kW system:
Price per watt
Estimated system cost (8.4 kW)
$2.50
$21,000
$3.00
$25,200
$3.50
$29,400
The 30% federal residential credit (Section 25D) is not available for systems completed after December 31, 2025, so a system you buy in 2026 does not get it. Older articles and some quotes still show a 30% reduction, which is out of date for purchases today. See the incentives section below for what remains. Use our solar payback calculator to test your own quote.
Data visualization
Estimated cost of an 8.4 kW system before incentives at three price levels. Calculated as 8,400 W × price per watt. Actual quotes vary; compare at least three. Source: calculation using the $2.50–$3.50/W range described above.
Chart takeaway: A $1.00-per-watt spread in price is worth $8,400 on this system, more than the difference between many mid-range equipment choices. Quote comparison is one of the most valuable steps you can take.
Solar vs utility company · 25-year comparison
25-year totals: 3%/yr rate increases, 0.5%/yr degradation, no federal credit. Methodology
How Long Does Solar Take to Pay Back Without the Federal Credit?
This model assumes an 8.4 kW system costing $25,200 that offsets 10,800 kWh per year, priced at the recent national average residential rate of about 16.5 cents per kWh (EIA). Year-1 savings are about $1,780. It also assumes electricity prices rise 3% per year, panel output falls 0.5% per year, and exported power is credited at roughly the retail rate. It excludes financing costs, maintenance and inverter replacement.
Simple payback (no rate increases): 25,200 ÷ 1,780 ≈ 14.2 years
With 3% annual rate growth and 0.5% degradation: about 12 years
Modeled 25-year net savings: about $35,500
Export credits matter. Many utilities now pay less than the retail rate for exported solar power (California’s NEM 3.0 rules, in effect since 2023, are one example), which lengthens payback unless you use more of your solar power yourself or add a battery.
Data visualization
Modeled cumulative net cash flow for an 8.4 kW system costing $25,200. Assumes $1,780 year-1 savings, 3% annual electricity price growth, 0.5% annual degradation, no incentives, no financing. Source: calculation by our editorial team using EIA rate data.
Chart takeaway: In this scenario the system breaks even between years 12 and 13 and reaches roughly $35,500 in net savings by year 25. Lower-cost quotes, state incentives, or higher local electricity rates move break-even earlier.
Electricity price is the biggest lever. The next chart holds the system cost at $25,200 and varies only the rate (simple payback, no rate growth).
Data visualization
Simple payback (years) for a $25,200 system offsetting 10,800 kWh per year, by electricity rate. Calculated as $25,200 ÷ (10,800 kWh × rate). Assumes full retail-rate credit for solar output and no rate growth. Source: calculation by our editorial team.
Chart takeaway: Payback falls from about 23 years at 10 cents per kWh to under 8 years at 30 cents. Check your own utility rate, and any time-of-use or fixed charges, before judging whether solar fits your budget.
🏛️ Incentives
What Solar Incentives Are Still Available in 2026?
Federal. The Residential Clean Energy Credit (Section 25D) let homeowners claim 30% of solar costs, but the One Big Beautiful Bill Act, signed July 4, 2025, ended it for expenditures after December 31, 2025. See the IRS residential clean energy credit page for the current rules and for claims on systems finished in 2025. In 2026, companies that own leased or PPA systems can still claim the commercial Section 48E credit under current law, and some pass part of the value to homeowners through lower prices. Terms vary widely, so compare the full cost over the contract.
State and local. Programs change often. Examples that were available at the time of this update include:
State
Incentive
Typical value
New York
State residential solar tax credit
25% of cost, up to $5,000
Massachusetts
State residential solar tax credit
15% of cost, up to $1,000
Arizona
State solar energy credit
25% of cost, up to $1,000
Texas
Property tax exemption for added home value from solar
Varies by county
Confirm eligibility, caps and funding for your address in the DSIRE database and with your installer and tax professional before signing. This is general information, not tax advice. Our solar tax credit calculator and solar savings calculator help you model your own numbers.
Methodology and Sources
Consumption: EIA’s average US residential use of about 10,800 kWh per year (899 kWh per month). EIA FAQ.
Electricity price: about 16.5 cents per kWh national residential average. EIA Electric Power Monthly, Table 5.6.A. Check the latest release, since rates change.
Solar resource and output: NREL solar resource data and the PVWatts calculator. Sun-hour figures in this article are rounded approximations.
Costs: $2.50–$3.50 per watt is an illustrative range. Compare with EnergySage local data and your own quotes.
Direct answers for US homeowners — sized for a $150/month electric bill.
A 3-bedroom house using the US average of about 10,800 kWh per year (roughly 30 kWh per day) needs about 20 panels rated at 420W (8.4 kW) at 4.5 peak sun hours. That ranges from about 14 panels in Arizona to about 25 in Washington. Homes with an EV, electric heating or a pool need more. Start with your last 12 months of utility bills, then run your ZIP code through NREL's PVWatts.
An 8.4 kW system typically costs about $21,000–$29,400 before incentives at $2.50–$3.50 per watt, with $25,200 as a mid-range estimate. The 30% federal homeowner credit (Section 25D) ended for systems completed after December 31, 2025, so there is no federal credit on a system you buy and own in 2026. State and local incentives may still reduce the price, so compare at least three quotes.
For an 8.4 kW system costing $25,200 that offsets 10,800 kWh per year at 16.5 cents per kWh, simple payback is about 14 years. With 3% annual electricity price increases and 0.5% annual panel degradation, break-even falls near year 12. Payback is shorter where electricity is expensive, for example about 8 years at 30 cents per kWh, and longer where it is cheap. Actual results depend on your rate plan and export credits.
Buying with cash or a loan gives you ownership and the lowest long-term cost in most cases, but no federal tax credit in 2026. Leases and power purchase agreements (PPAs) are owned by a company that can still claim the commercial Section 48E credit and may pass part of that value to you as lower monthly payments. Compare the total 25-year cost, the payment escalator, and what happens if you sell your home before choosing.
Usually yes. East- and west-facing roofs typically produce somewhat less than an ideal south-facing roof, often in the range of 10–20% less, and heavy shading matters more than direction. Model your exact roof with NREL's PVWatts (tilt, azimuth, shading losses) and ask installers for a shade analysis before deciding.
Same usage, bill-based guide
Your 3-Bedroom 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.