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
Quick answer: A home using 15 kWh per day needs about a 4 kW solar system, or 8 to 13 panels of 400 W, depending on local sunshine. At typical 2026 prices of $2.50–$3.50 per watt, that costs about $10,000–$14,000. The 30% federal tax credit for homeowner-owned systems ended on December 31, 2025, so payback is now typically about 11–12 years at average U.S. electricity rates.
A household using 15 kWh per day (about 450 kWh per month) is well below the typical U.S. home, which uses roughly 29 kWh per day. A modest rooftop array can therefore cover most or all of its annual electricity use. Three variables decide your actual numbers: your location’s peak sun hours, your electricity rate, and how your utility credits power you send back to the grid.
This guide shows the calculation behind each figure. All dollar projections are modeled estimates built from the assumptions listed under each chart and in the methodology section at the end. They are not measurements from a specific installation.
⚡ System Size
How Many Solar Panels Does a 15 kWh/Day Home Need?
Most homes need between 8 and 13 panels of 400 W each. To size a system, divide your daily usage by your location’s average peak sun hours, then apply a system efficiency factor of 0.80 to account for inverter, temperature and wiring losses:
System size (kW) = Daily kWh ÷ (Peak sun hours × 0.80)
For example, with 4.7 peak sun hours: 15 ÷ (4.7 × 0.80) = 4.0 kW, which is 10 panels at 400 W. Across a year, that system produces about 5,500 kWh, matching 15 kWh × 365 = 5,475 kWh of use.
Solar panel count by location, 15 kWh/day home (rounded estimates)
City
Peak sun hours (approx.)
System size
Panels (400 W)
Panels (350 W)
Phoenix, AZ
6.5
2.9 kW
8
9
Denver, CO
5.5
3.4 kW
9
10
Dallas, TX
5.3
3.5 kW
9
11
Atlanta, GA
4.7
4.0 kW
10
12
Chicago, IL
4.1
4.6 kW
12
14
Seattle, WA
3.7
5.1 kW
13
15
Peak sun hours are rounded approximations of annual averages; use NREL’s PVWatts Calculator for your exact ZIP code, tilt and shading.
Data visualization
Panels needed for 15 kWh/day by city. A 4.0 kW system in Atlanta needs 10 panels at 400 W. Source: NREL PVWatts peak sun hours, 2026.
Chart summary: Sunnier cities need fewer panels for the same 15 kWh/day. Phoenix needs about 8, while Seattle needs about 13, roughly 60% more, because it gets about 40% less usable sunlight. Roof orientation and shading shift these counts further: east- and west-facing roofs generally produce less than south-facing ones, so installers often add a panel or two to compensate.
Some homeowners add 10–15% extra capacity to offset panel degradation (typically around 0.5% per year) and cloudy-day shortfalls. Whether that is worthwhile depends on how your utility values exported power. Use our solar system size calculator for a panel count tailored to your ZIP code and roof.
Run the numbers for your state
The savings calculator loads your state's average electricity rate, sun hours and net-metering rule. Then enter your own bill and installer quote.
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💲 Cost
What Does a 15 kWh/Day Solar System Cost in 2026?
A 4 kW system for a 15 kWh/day home typically costs about $10,000 to $14,000 before state and local incentives. Residential solar prices in 2026 generally fall between $2.50 and $3.50 per watt depending on the data source, state, installer and equipment, so this guide uses $3.00 per watt (about $12,000) as its central case.
Federal tax credit update: The 30% residential clean energy credit (Section 25D) no longer applies to homeowner-owned systems with expenditures after December 31, 2025, under the One Big Beautiful Bill Act signed July 4, 2025. Older articles that show a “net cost after ITC” for a 2026 purchase are out of date. Two exceptions remain: systems completed by the end of 2025 can claim the credit (including carryforward of unused amounts), and leased or PPA systems owned by a company may still qualify for the business credit under Section 48E, subject to its deadlines. See the IRS residential clean energy credit page and our solar tax credit calculator for details.
Data visualization
Estimated cost of a 4 kW system by price per watt. At $3.00/W the system costs about $12,000 before incentives. Source: SEIA and LBNL price ranges, 2026.
Chart summary: Every $0.25 per watt changes the price of a 4 kW system by $1,000. The gap between a low quote ($2.50/W) and a high one ($3.50/W) is $4,000, which is why comparing at least three itemized bids matters. With no federal credit for purchased systems, state, utility and local incentives become the main way to lower the price; check DSIRE’s incentive database for your area.
Solar vs utility company · 25-year comparison
25-year totals: 3%/yr rate increases, 0.5%/yr degradation, no federal credit. Methodology
At the U.S. average residential electricity rate of about 18.8¢/kWh (EIA, spring 2026), a 4 kW system producing 5,475 kWh a year saves about $1,030 in the first year. On a $12,000 system, that is a simple payback of about 11.7 years. If electricity prices rise 2% per year and panel output declines 0.5% per year, payback improves to about 10.8 years. To see how your state compares, our guide to Solar Panel Payback Period by State has the full data.
Your electricity rate matters more than almost anything else:
Simple payback by electricity rate ($12,000 system, 5,475 kWh/year, full retail credit)
Electricity rate
Year-1 savings
Simple payback
12¢/kWh
$657
18.3 years
15¢/kWh
$821
14.6 years
18.8¢/kWh (U.S. average)
$1,029
11.7 years
25¢/kWh
$1,369
8.8 years
30¢/kWh
$1,643
7.3 years
35¢/kWh
$1,916
6.3 years
Data visualization
Simple payback by electricity rate. A $12,000 system pays back in 11.7 years at the 18.8 cent U.S. average. Source: EIA 2026 rates, formula cost divided by 5,475 kWh times rate.
Chart summary: Payback shrinks quickly as rates rise. At 12¢/kWh it takes more than 18 years, longer than most panel warranties, while at 30¢/kWh it is about 7 years. Rates near or above 30¢/kWh occur in states such as California, Massachusetts and Hawaii. Those states also have export rules and incentives that change the result, so check your own utility’s terms.
Payback by rate is a snapshot. To see how the same system performs over its full life, the next chart tracks cumulative cash flow year by year under two electricity price scenarios.
Data visualization
Cumulative cash flow over 25 years. A $12,000 system reaches about $18,900 net gain with 2% yearly rate growth. Source: EIA 2026 rate, 0.5% degradation, no financing.
Chart summary: Cumulative cash flow crosses zero around year 11 with 2% annual rate increases (about 10.8 years) and around year 12 with flat rates (about 12.0 years). By year 25, the modeled net gain is about $18,900 with rising rates and about $12,200 with flat rates. An inverter replacement would lower these totals, so run your own figures with our solar payback calculator.
📋 Key Insights
How Do Net Metering and Usage Patterns Change Your Savings?
Savings depend on when you use power and how your utility credits what you export. A home that runs appliances during the day consumes more of its own solar output directly, which is worth the full retail rate. A home that uses most power in the evening relies on its utility to credit daytime exports.
Policies vary by state and utility. Under full retail net metering, exported kWh offset your bill one-for-one. California moved most new solar customers to a net billing structure in April 2023, under which exported power earns a fraction of the retail rate. As a result, California households often pair solar with a battery to shift use into the evening. Other states, including Florida, Texas and Arizona, have their own utility-specific export rules, and some utilities add demand or fixed charges that limit savings. Policies change frequently, so confirm your utility’s current rules before signing, and ask your installer to model both a full-retail and a reduced-export scenario.
Roof direction also matters. South-facing roofs generally produce the most, while east- and west-facing roofs typically produce somewhat less, often in the range of 10–20%. PVWatts lets you model your exact orientation and tilt. For state-specific context, see Massachusetts and New York and our state data hub.
✅ Decision
Is Solar Worth It at 15 kWh/Day? Cash vs. Loan vs. Lease
For many homes using 15 kWh/day, solar pays for itself within the 25-year warranty period, but with no federal credit for purchased systems, the result is more sensitive to your rate and export policy than it used to be. As a rough guide, rates above about 15¢/kWh combined with fair export credits tend to produce a positive return. At 12¢/kWh, payback exceeds 18 years in the model above.
Ways to pay:
Cash: Highest lifetime return because you pay no interest. You own the system and capture all bill savings, though you no longer receive a federal credit on a 2026 purchase.
Loan: A 6%, 12-year loan on $12,000 costs about $117 per month, which is more than the roughly $86 per month of year-one bill savings in this model. Cash flow is therefore negative at first and improves as rates rise. Interest and loan fees also lengthen payback, so compare the loan’s APR and dealer fees carefully.
Lease or PPA: Usually $0 down. Because the installer owns the system, it may still be able to claim the federal business credit (Section 48E) and pass part of that value on through lower rates. Ask for the escalator, term, transfer terms and buyout price in writing, and compare against a cash or loan quote.
Whichever route you choose, get at least three quotes, ask for itemized pricing in dollars per watt, and model the system in PVWatts before you sign. Use our solar savings calculator to compare scenarios with your own rate.
Methodology and Sources
System size: kW = daily kWh ÷ (peak sun hours × 0.80). Peak sun hours are rounded approximations; use NREL PVWatts for your site.
Prices: $2.50–$3.50 per watt reflects the range of published 2026 residential estimates; $3.00 per watt is used for modeling. Actual quotes vary.
Electricity rate: about 18.8¢/kWh national average residential price from the EIA Electric Power Monthly, spring 2026. State and monthly rates differ.
Payback and 25-year figures: modeled estimates with the stated assumptions (0.5% annual degradation, 0% or 2% annual rate increase, full retail credit, no financing, no inverter replacement, no discounting). They are illustrations, not guarantees.
Federal tax credit status:IRS residential clean energy credit and the One Big Beautiful Bill Act (Public Law 119-21). This is general information, not tax advice; consult a tax professional.
Direct answers for US homeowners — sized for a $75/month electric bill.
Most homes need 8 to 13 panels of 400 W each, which is a system of roughly 3 to 5 kW. The exact number depends on peak sun hours: about 8 panels in Phoenix, 10 in Atlanta, 12 in Chicago and 13 in Seattle. The formula is system size (kW) = daily kWh ÷ (peak sun hours × 0.80). Confirm your number for your ZIP code and roof in NREL's PVWatts calculator.
A 4 kW system typically costs about $10,000 to $14,000 before incentives, based on $2.50 to $3.50 per watt. Pricing varies widely by state, installer and equipment. Get at least three itemized quotes and compare them on price per watt.
Not for homeowners who buy a system. The 30% residential clean energy credit (Section 25D) ended for expenditures made after December 31, 2025, under the One Big Beautiful Bill Act. If your system was completed in 2025, you can still claim it on your 2025 return, and unused credit can carry forward. Leases and PPAs owned by a company may still benefit from the business credit (Section 48E), which the installer may pass through as lower rates. Ask for the terms in writing. Some states and utilities still offer rebates, so check DSIRE.
At the U.S. average residential rate of about 18.8¢/kWh, a $12,000 4 kW system saves about $1,030 in year one, for a simple payback of about 11.7 years. With electricity prices rising 2% a year, payback falls to about 10.8 years. At 12¢/kWh it takes about 18 years; at 30¢/kWh about 7 years. These figures assume solar offsets 100% of use at the full retail rate and exclude financing costs and inverter replacement.
It can be, but it depends on three things: your electricity rate, your utility's net metering or export policy, and your upfront price. Solar tends to make the most sense where rates are above roughly 15¢/kWh and exported power earns close to the retail rate. Where exports earn only a fraction of retail, as in California under its newer net billing rules, self-consumption and batteries matter more. In low-rate areas, payback can stretch past 15 years, so get a quote and run your own numbers before deciding.
Same usage, bill-based guide
Your 15 kWh/Day target maps to roughly a $75/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.