US residential solar · 2026 data

Solar Panels for 400 kWh/Month

Q: How much does a solar system for 400 kWh per month cost in 2026?

A 3.6 kW system typically costs about $9,900 to $12,600 before incentives, based on installed prices of roughly $2.75 to $3.50 per watt reported by EnergySage marketplace data and the Lawrence Berkeley National Laboratory. The federal 30% residential clean energy credit (Section 25D) expired on December 31, 2025, so homeowners who buy a system in 2026 with cash or a loan generally receive no federal credit. Some states, such as New York (25% up to $5,000), Massachusetts (15% up to $1,000) and Arizona (25% up to $1,000), still offer tax credits.

Q: How long does it take a 400 kWh/month solar system to pay for itself?

At the 2025 US average residential electricity price of 17.3 cents per kWh, 400 kWh per month is worth about $830 per year, so a $10,800 system pays back in roughly 13 years at flat rates, or about 11 years if electricity prices rise 3% annually. In states with rates near 27 cents per kWh, payback drops to roughly 8 to 9 years before any state incentives. These are simple-payback estimates that include 0.5% annual panel degradation and exclude financing costs.

Q: Does roof direction or shade change how many panels I need?

Yes. The panel counts above assume an unshaded roof with a good orientation. East- or west-facing roofs, low or steep tilt, and shade all reduce output, so you may need one or two extra panels to reach 400 kWh per month. The size of the loss depends on your location and roof, so model your exact address in NREL's PVWatts calculator instead of relying on a rule of thumb. Microinverters or optimizers can limit the impact of partial shade.

Q: Is a small solar system worth it, and does net metering matter?

It depends mostly on your electricity rate and your utility's export policy. Small systems have higher fixed costs per watt, and lower usage means lower annual savings, so payback is longer where rates are low. Net metering matters because solar produces more in summer than winter: with full retail net metering, surplus is credited at the retail rate, while in states or utilities that pay a lower export rate (such as California's net billing tariff), you save the most by using solar power as it is produced. Check your utility's current export rules before you sign.

Est. net savings

$8,800

Net over 25 Years (flat rates) · no federal credit

$10,800 Typical cost (no federal credit)

11–13 yrs Payback

3.6 kW System size

Typical result:

7–12 panels (400W each)
3.6 kW at 5 sun hours
≈$10,800 before state incentives
11–13 year payback

✓ EIA rates & NREL sun data ✓ 2026 federal policy applied ✓ Open methodology

Updated September 29, 2026 · 10 min read ·By Green Energy Calculators Editorial Team

Calculate My System Size View State Data

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

$19,600

Rates rise ~3% per year

With solar

System cost + remaining bills

$10,800

Installed cost, no federal credit

Difference

Estimated 25-year net

+$8,800

Before any state or utility incentives

Author Green Energy Calculators Editorial Team

Editorial policy No paid placements

Last updated Sep 29, 2026

Data approach EIA rates · NREL sun hours · 2026 federal policy · methodology

To offset 400 kWh per month, most US homes need 7 to 12 solar panels rated 400W each, which is a 2.8 to 4.8 kW system, depending on local sunshine. At about 5 peak sun hours per day, roughly the national average, that is 9 panels (3.6 kW). Since the federal 30% residential credit ended on December 31, 2025, a 3.6 kW system in 2026 typically costs about $9,900 to $12,600 before state incentives, and pays for itself in roughly 11 to 13 years at the national average electricity rate.

Last updated: September 29, 2026. Figures are estimates for planning; your quote and utility rates will differ.

Key takeaways

Panel count: 7 (very sunny) to 12 (cloudier) panels of 400W; 9 is the national-average case.
Cost: about $2.75–$3.50 per watt installed, so roughly $9,900–$12,600 for 3.6 kW.
Federal credit: not available for systems you buy in 2026; state credits and utility programs may still apply.
Payback: about 13 years at flat 17.3¢/kWh, about 11 years if rates rise 3% a year, and 8–9 years where electricity costs about 27¢/kWh.
Reality check: 400 kWh/month is below the typical US home’s roughly 860–900 kWh, so annual savings (about $830 at average rates) are modest.

400 kWh per month is a realistic target for small homes, efficient townhomes, apartments with rooftop access, or households that have cut usage with LED lighting and a smart thermostat. Three variables drive the range: your local peak sun hours, the panel wattage you choose (most residential panels today are 400W–440W), and whether your utility credits excess generation at the full retail rate.

How Many Panels Does 400 kWh per Month Actually Require?

The core formula divides your monthly target by what one panel produces where you live. One 400W panel at 5 peak sun hours per day, with an 80% system efficiency factor, generates:

0.4 kW × 5 h × 30 days × 0.80 = 48 kWh/month

Dividing 400 kWh by 48 kWh gives 8.3 panels, so round up to 9. The 80% factor is a conservative allowance for inverter, wiring, temperature and soiling losses; NREL’s PVWatts uses a default loss of about 14%, so real systems can perform slightly better.

Panels needed for 400 kWh/month (400W panels, 80% system efficiency)

Peak sun hours/day (illustrative)	Monthly output per panel	Required system size	Panels needed
3.5 (cloudier regions)	33.6 kWh	4.76 kW	12
4.0	38.4 kWh	4.17 kW	11
4.5	43.2 kWh	3.70 kW	10
5.0 (national-average case)	48.0 kWh	3.33 kW	9
5.5	52.8 kWh	3.03 kW	8
6.0 (sunniest Southwest locations)	57.6 kWh	2.78 kW	7

Sun-hour values are illustrative annual averages. Look up your own location with NREL PVWatts or our solar system size calculator.

Panels needed for 400 kWh/month by peak sun hours. Calculated as 400 ÷ (0.4 kW × sun hours × 30 × 0.80), rounded up. Assumes 400W panels and 80% system efficiency.

Chart summary: Sunshine is the biggest driver of panel count. Going from 3.5 to 6.0 peak sun hours cuts the requirement from 12 panels to 7, so a home in a cloudier region needs about 70% more panels than one in the sunny Southwest to produce the same 400 kWh.

Run the numbers for your state

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What System Size Produces 400 kWh per Month — and Does Roof Tilt Matter?

Installers quote system size in kilowatts (kW). For 400 kWh per month at the national-average 5 peak sun hours and 80% efficiency:

Required system size = 400 ÷ (5 × 30 × 0.80) = 3.33 kW

Installers usually round to a standard 3.2 kW, 3.6 kW or similar package. Expected output scales linearly with panel count (at 5 sun hours, each 400W panel adds about 48 kWh per month):

Panels (400W)	System size	Estimated monthly output at 5 sun hours
8	3.2 kW	≈384 kWh (about 4% short)
9	3.6 kW	≈432 kWh
10	4.0 kW	≈480 kWh
12	4.8 kW	≈576 kWh

Output also depends on your roof. South-facing roofs in the Northern Hemisphere generally produce the most, and tilt close to your latitude tends to maximize annual production. East- and west-facing roofs, very flat or very steep pitches, and shade from trees or chimneys reduce output, so you may need one or two extra panels to hit 400 kWh. Because losses vary by location and roof geometry, enter your exact address, tilt and azimuth in PVWatts rather than relying on a rule of thumb. For more on this topic, see our guide to How Many Solar Panels for 600 kWh/Month? 2026 Guide. For more on this topic, see our guide to How Many Solar Panels for 1,400 kWh a Month?.

Two more sizing notes:

Seasons: Production is highest in summer and lowest in winter. A system sized for a 400 kWh annual monthly average will overproduce in summer and underproduce in winter, which is where net metering or bill credits matter.
Degradation: Panels typically lose about 0.5% of output per year, according to NREL’s review of degradation studies, so output after 25 years is roughly 11–12% lower than in year one.

How Much Does a Solar System for 400 kWh per Month Cost in 2026?

Recent marketplace and industry data put residential solar at roughly $2.50–$3.50 per watt installed. EnergySage marketplace quotes have averaged about $2.6 per watt in 2026, while installed-price data from the Lawrence Berkeley National Laboratory has shown higher cash-purchase medians. Small systems often sit toward the higher end because permitting, design and crew costs are spread over fewer panels. For a 3.6 kW system, we use $2.75 to $3.50 per watt:

Price per watt	3.6 kW system cost (before incentives)
$2.75	$9,900
$3.00 (midpoint used in this guide)	$10,800
$3.50	$12,600

Estimated cost of a 3.6 kW system at different installed prices (before any incentives). Calculated as 3,600 W × price per watt. Price range based on EnergySage marketplace data and LBNL installed-price data.

Chart summary: Installed price per watt moves the total by about $2,700 across the range. The gap between a competitive quote and a high one is often bigger than any single incentive, so compare at least three local quotes on a per-watt basis. Sources: EnergySage and LBNL Tracking the Sun.

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

$19,600

Total solar cost (installed + remaining bills)

$10,800

Net savings

+$8,800

Avg. monthly difference

+$69/mo

See my savings →

Is There Still a Federal Solar Tax Credit in 2026?

For most homeowners buying a system in 2026, no. The One Big Beautiful Bill Act, signed July 4, 2025, ended the 30% Residential Clean Energy Credit (Section 25D) for expenditures made after December 31, 2025. Key points:

Installed and operating by December 31, 2025: you can still claim the credit on your 2025 federal return.
Purchased with cash or a loan in 2026: no federal residential credit.
Leases and power purchase agreements: the solar company owns the system and may still be able to claim a federal commercial credit under current rules, which can influence pricing. You do not receive the credit yourself, and terms vary, so compare offers carefully.

Confirm current rules on the IRS Residential Clean Energy Credit page or with a tax professional. This guide is not tax or financial advice.

How Long Until a 400 kWh/Month Solar System Pays for Itself?

Payback depends on system cost, the value of the electricity you offset, and how prices change over time. At the 2025 US average residential price of 17.3¢/kWh (EIA), 400 kWh per month is worth about $830 per year.

Assumptions used for every payback figure in this guide: 3.6 kW system at $10,800, no incentives, 400 kWh/month of solar production offsetting purchases at the retail rate, 0.5% annual panel degradation, no financing cost, no maintenance or inverter replacement.

Electricity price	Example region	Payback, flat rates	Payback, rates +3%/yr
13¢/kWh	Lowest-rate states (Nevada was about 13.1¢ in June 2026)	18.1 years	14.6 years
17.3¢/kWh	US average, 2025 (EIA)	13.4 years	11.4 years
27¢/kWh	High-rate states (New York averaged about 27.4¢ in Dec 2025)	8.5 years	7.7 years
32¢/kWh	California-level rates	7.1 years	6.6 years

Simple payback for a 3.6 kW, $10,800 system at different electricity prices. Assumes 400 kWh/month offset, 0.5% annual degradation, no incentives or financing costs. Rate scenarios based on EIA price data.

Chart summary: Your electricity price matters more than almost any other input. At the national average, payback is about 11 to 13 years; at roughly 27¢/kWh it falls to 8 to 9 years, and at about 13¢/kWh it stretches past 14 to 18 years. In California, exports to the grid are credited at lower rates than retail, so the 32¢ scenario assumes you use most of the power on-site.

Cumulative net cash flow for a 3.6 kW, $10,800 system at the 17.3¢/kWh US average. Assumes 400 kWh/month in year one, 0.5% annual degradation, no incentives, no financing cost.

Chart summary: At flat 17.3¢ rates the system breaks even between years 13 and 14 and finishes 25 years about $8,800 ahead. If rates rise 3% a year, break-even moves to about year 11 and the 25-year net gain grows to roughly $17,500. Either way, a first-year outlay of about $10,800 buys around $830 of annual savings, so this is a long-term investment rather than a quick win.

Financing note: A solar loan adds interest, which lengthens payback compared with the cash figures above. Model your own loan terms in our solar payback calculator.

State Incentives That Reduce the Cost of a Small Solar System

With the federal credit gone, state and local programs matter more. Programs change often, so verify details in the DSIRE database before you buy.

Selected state incentives for owned residential solar (2026)

State	Incentive	What it means for a $10,800 system
New York	25% state income tax credit, up to $5,000, plus sales and property tax exemptions	Up to $2,700 credit
Massachusetts	15% state tax credit, up to $1,000, plus SMART production payments	Up to $1,000 credit plus per-kWh payments
Arizona	25% state tax credit, up to $1,000, plus property tax exemption	Up to $1,000 credit
Hawaii	35% state tax credit, up to $5,000	About $3,780 credit (35% of cost, under the cap)
Texas	No state income tax credit; solar value is exempt from property tax assessment	No credit, but no property tax increase

For a 400 kWh/month system in a high-rate state, a state credit shortens payback meaningfully. For example, in New York a $2,700 credit lowers a $10,800 system to about $8,100 net; at 27.4¢/kWh that is a simple payback of roughly 6 years, versus about 8.5 without the credit (same assumptions as above).

Net metering matters as much as rebates. Where utilities credit exports at the full retail rate, summer surplus offsets winter shortfalls one-for-one. Where export credits are lower, as in California’s current net billing tariff, a smaller system sized to your own daytime use is usually the better fit. Check your utility’s current export rules with our solar net metering calculator.

Small systems generally qualify for the same state programs as large ones, but some utility rebates have minimum size requirements, so confirm eligibility with your installer.

Assumptions and Sources

Formulas: Panels = monthly kWh ÷ (panel kW × peak sun hours × 30 × 0.80). Payback figures use the assumptions listed in the payback section.
Electricity prices: U.S. Energy Information Administration, Electric Power Monthly, average price by sector (2025 US residential average: 17.30¢/kWh). State examples reflect EIA-derived monthly averages and change over time.
Sun hours and site estimates: NREL PVWatts Calculator.
Installed cost: EnergySage marketplace data and LBNL Tracking the Sun.
Panel degradation: NREL, Photovoltaic Degradation Rates — An Analytical Review (median about 0.5% per year).
Federal credit status: IRS Residential Clean Energy Credit and the One Big Beautiful Bill Act (Public Law 119-21).
State incentives: DSIRE and state program pages.

This guide provides general estimates, not financial, tax or engineering advice. Get multiple written quotes and confirm current incentives with your installer and tax professional before purchasing.

Frequently asked questions

Direct answers for US homeowners — sized for a $69/month electric bill.

How many solar panels do I need to produce 400 kWh per month?

Most US homes need 7 to 12 solar panels rated 400W each, or a 2.8 to 4.8 kW system. The exact number depends on peak sun hours. At about 5 peak sun hours per day (a common national average), 9 panels (3.6 kW) produce roughly 430 kWh per month with an 80% system efficiency factor. In very sunny areas with about 6 sun hours, 7 panels are enough; in cloudier regions with about 3.5 sun hours, you need about 12. Use NREL's free PVWatts calculator with your ZIP code for a site-specific estimate.

How much does a solar system for 400 kWh per month cost in 2026?

How long does it take a 400 kWh/month solar system to pay for itself?

Does roof direction or shade change how many panels I need?

Is a small solar system worth it, and does net metering matter?

Same usage, bill-based guide

Your 400 kWh/Month target maps to roughly a $75/month electric bill nationally.

$75 $75/month electric bill guide Panels · cost · payback · by state →

Popular state solar guides

Electricity rates and incentives vary — see data for your state.

CA California 33.25¢/kWh · 5.8h sun TX Texas 16.06¢/kWh · 5.6h sun FL Florida 15.3¢/kWh · 5.7h sun AZ Arizona 15.44¢/kWh · 6.5h sun NC North Carolina 14.94¢/kWh · 5.2h sun NY New York 29.38¢/kWh · 4.3h sun MA Massachusetts 30.14¢/kWh · 4.2h sun CO Colorado 16.72¢/kWh · 5.5h sun

View all 50 states →

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: September 29, 2026 · 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.