Data approachEIA rates · NREL sun hours · 2026 federal policy · methodology
Last updated: October 3, 2026. Prices, rates, and incentives change often. Figures below are calculations from the assumptions stated in each section, not measurements from a specific installation.
A home using 70 kWh per day needs about a 19.4 kW solar system at the U.S. average of 4.5 peak sun hours, roughly 49 panels of 400 W. Depending on where you live, the range runs from about 13.5 kW in Phoenix to 25 kW in Seattle. At published 2026 prices of $2.50–$3.50 per watt, a 19.4 kW system costs about $48,500–$67,900 before state incentives. The 30% federal credit for homeowners no longer applies to systems installed in 2026.
Key takeaways
Size = daily kWh ÷ peak sun hours ÷ 0.80. For 70 kWh/day at 4.5 sun hours, that is 19.4 kW.
70 kWh/day is about 25,550 kWh per year, or roughly 2,130 kWh per month.
The federal Section 25D homeowner credit expired December 31, 2025.
Your electricity rate moves payback more than almost any other variable.
⚡ System Size
How Many Solar Panels Does a 70 kWh/Day Home Need?
At 70 kWh per day, you use roughly 2.4 times the typical U.S. home, which averages about 10,500 kWh per year (around 29 kWh per day). That load is common in large homes with electric heating or cooling, a pool, or EV charging.
Sizing starts with peak sun hours, not panel count. One peak sun hour equals 1 kWh of sunlight per square meter, and it varies by location.
Formula: Daily kWh ÷ Peak Sun Hours ÷ System Efficiency = Required System Size (kW)
We use a 0.80 system efficiency factor, which already accounts for inverter, wiring, soiling, and temperature losses. Do not add a second buffer on top of it. Panel count is then system size divided by module wattage.
System size by city for a 70 kWh/day target
City
Peak sun hours (approx. annual avg.)
System size
Panels (400 W)
Panels (450 W)
Phoenix, AZ
6.5
13.5 kW
34
30
Dallas, TX
5.2
16.8 kW
43
38
Atlanta, GA
4.8
18.2 kW
46
41
Chicago, IL
4.1
21.3 kW
54
48
Seattle, WA
3.5
25.0 kW
63
56
U.S. average
4.5
19.4 kW
49
44
Peak sun hours are rounded planning values consistent with NREL solar resource data; published city figures differ slightly by tilt and data set. Enter your address in NREL’s PVWatts Calculator for a location-specific value.
Data visualization
Required solar system size for 70 kWh/day by city (kW). Seattle needs 25.0 kW versus 13.5 kW in Phoenix. Calculated as 70 ÷ peak sun hours ÷ 0.80. Source: NREL-consistent peak sun hours.
Chart summary: Sunnier cities need much smaller systems for the same 70 kWh/day. Seattle needs about 85% more capacity than Phoenix (25.0 kW vs. 13.5 kW), which means more panels, more roof area, and a higher upfront cost. The U.S. average of 4.5 sun hours sits between Atlanta and Chicago at 19.4 kW. Use our solar system size calculator for a location-specific panel count.
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💰 System Cost
What Does a 70 kWh/Day Solar System Cost in 2026?
Published 2026 estimates of installed residential solar cost range from about $2.50 to $3.50 per watt before incentives. One widely cited national benchmark is $3.36 per watt from SEIA and Wood Mackenzie, while marketplace averages are lower. Prices vary by state, installer, equipment, and roof complexity.
Applying that range to a 19.4 kW system:
Price per watt
19.4 kW system
$2.50
$48,500
$3.00
$58,200
$3.50
$67,900
These are gross costs. There is no federal homeowner credit to subtract in 2026 (see the incentives section below).
Data visualization
Installed cost by system size at $2.50 and $3.50 per watt ($). A 19.4 kW system costs $48,500–$67,900 before incentives. Calculated as system watts × price per watt; price range from 2026 SEIA/Wood Mackenzie and marketplace estimates.
Chart summary: The gap between low and high pricing is $13,500 for a 13.5 kW system and $25,000 for a 25.0 kW system, so the price per watt matters more as the system grows. Moving from Phoenix-level to Seattle-level sun adds $28,750 at $2.50/W and $40,250 at $3.50/W. Compare written quotes in dollars per watt to spot an overpriced bid.
Equipment choices matter at this size. Microinverters and panel-level optimizers cost more than a basic string inverter but add panel-level monitoring and better performance on partly shaded or multi-orientation roofs. Ask installers to itemize inverter type, panel brand, warranty terms, and any electrical panel upgrade, because large systems often need one.
📋 Key Insights
Worked Example: Sizing a 70 kWh/Day System at U.S. Average Sun
This is a calculation, not a case study of a specific installation.
Daily load: 70 kWh (about 25,550 kWh per year).
Sun resource: 4.5 peak sun hours (U.S. planning average).
System size: 70 ÷ 4.5 ÷ 0.80 = 19.4 kW.
Panel count: 19,400 W ÷ 400 W = 49 panels (44 panels at 450 W).
Roof area: a typical 400 W panel covers about 20 square feet, so 49 panels need roughly 1,000 square feet of usable, unshaded roof.
Real production differs month to month. Summer output runs well above the annual average and winter output well below it, which is why net metering or net billing rules matter. For a design-grade estimate, run your address, tilt, and azimuth through PVWatts.
📈 Payback Period
What Is the Payback Period for a 19–25 kW System?
Simple payback is the system cost divided by the annual electric bill it avoids. For a 70 kWh/day home, annual use is 25,550 kWh. At the 2026 U.S. average residential price of roughly 18.3¢ per kWh, that is about $4,676 per year. To see how your state compares, our guide to Solar Panel Payback Period by State has the full data.
With a $58,200 system ($3.00 per watt), payback is about 12.4 years. Across the $2.50–$3.50 price range it is about 10–15 years.
These estimates assume the system offsets 100% of use at the retail rate and ignore financing, rate increases, panel degradation, and maintenance. Several factors shift the result:
Electricity rate: the biggest driver, as the table below shows.
Net metering policy: states that credit exported power at full retail rates pay back faster than those using lower export rates. California, for example, moved new customers to a net billing tariff with lower export credits.
Financing: interest raises total cost, so a loan lengthens payback compared with paying cash.
Production: a system in Phoenix produces far more per kW than the same system in Seattle.
Simple payback by electricity rate (system cost $58,200; 25,550 kWh per year; 100% offset; no incentives):
Electricity rate
Annual bill avoided
Simple payback
13¢/kWh
$3,322
17.5 years
16¢/kWh
$4,088
14.2 years
18.3¢/kWh (U.S. average)
$4,676
12.4 years
25¢/kWh
$6,388
9.1 years
30¢/kWh
$7,665
7.6 years
33¢/kWh
$8,432
6.9 years
Data visualization
Cumulative cash flow of a $58,200 system over 25 years ($). Breaks even in year 13 at flat rates and year 11 at 3% annual rate growth. Based on 25,550 kWh per year at 18.3¢/kWh. Source: EIA 2026 average residential rate.
Chart summary: At today’s flat 18.3¢/kWh, the system recovers its $58,200 cost in about 12.4 years (the first positive year is 13) and ends year 25 about $58,700 ahead. If rates rise 3% per year, break-even moves to about 10.7 years and the 25-year gain grows to about $112,000. Both lines ignore financing, panel degradation, maintenance, and inverter replacement, which lower the real result. Use our solar payback calculator with your own rate and quote.
NREL field studies report that panels typically lose about 0.5% of output per year, so a system still produces roughly 88% of its original output after 25 years.
💰 System Cost
Which Incentives Still Reduce the Cost in 2026?
Federal. The 30% Residential Clean Energy Credit (Section 25D) does not apply to expenditures made after December 31, 2025, under the One Big Beautiful Bill Act, according to the IRS. A system installed in 2026 and owned by the homeowner receives no federal residential credit, and home batteries lost the same credit.
Third-party-owned systems (leases and power purchase agreements) are different: the owner can still claim commercial credits under Section 48E, subject to deadlines. Whether any savings reach you depends on the contract, so read the terms and escalator carefully.
State examples (verify before relying on them):
New York: a state income tax credit of 25% of qualified costs, up to $5,000.
Massachusetts: a 15% state income tax credit capped at $1,000, plus per-kWh SMART program payments.
On a large system, a capped credit covers a small share of the total. A $5,000 credit on a $58,200 system is about 9%.
For many high-usage homes, yes, because the avoided bill grows with every kWh you use. A larger system can also cost slightly less per watt than a small one. Whether the numbers work depends mostly on three things: your electricity rate, your utility’s net metering or net billing rules, and your roof’s sun exposure.
Audit your load before sizing. System size scales directly with consumption, so every 10 kWh per day you cut shrinks the system by about 14%. For example, an EV driven 1,000 miles per month at about 0.3 kWh per mile uses roughly 300 kWh per month, or 10 kWh per day. Cutting 10 kWh per day would lower the 19.4 kW system to about 16.7 kW (60 ÷ 70 × 19.4).
A system larger than your roof or net metering rules can credit may not pay off. Confirm how your utility values exported power before oversizing.
Before meeting installers, use our solar ROI calculator with your own rate and quotes.
SEIA / Wood Mackenzie Solar Market Insight, as reported by Solar.com (national price benchmark); other 2026 marketplace estimates range $2.50–$3.50/W
DSIRE: dsireusa.org (state and utility incentives)
All sizing, cost, and payback figures are calculated from the stated assumptions (0.80 system efficiency, rounded peak sun hours, $2.50–$3.50/W, 18.3¢/kWh, 100% retail offset). They are estimates for planning, not quotes, tax advice, or financial advice. Get written installer quotes and consult a tax professional.
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At the U.S. average of 4.5 peak sun hours, a 70 kWh/day home needs about a 19.4 kW system, which is roughly 49 panels of 400 W (44 panels of 450 W). The count changes with your location: about 34 panels in Phoenix and about 63 in Seattle with 400 W modules. Use the formula daily kWh ÷ peak sun hours ÷ 0.80, then divide by panel wattage.
Published 2026 estimates put installed residential solar at about $2.50–$3.50 per watt, so a 19.4 kW system costs roughly $48,500–$67,900 before state or local incentives. Low-sun states need larger systems, so a 25 kW system at the same prices would cost about $62,500–$87,500. Get at least three local quotes, since pricing varies by installer and state.
Not for homeowners who buy a system with cash or a loan. The 30% Residential Clean Energy Credit (Section 25D) does not apply to expenditures made after December 31, 2025, under the One Big Beautiful Bill Act, according to the IRS. Some state credits still apply, and third-party-owned lease or PPA systems may still benefit from commercial credits under separate deadlines, so confirm the terms before signing.
At the 2026 U.S. average residential rate of roughly 18¢/kWh and $3.00 per watt, simple payback is about 12 years, or 10–15 years across the $2.50–$3.50/W price range. In states with rates near 30¢/kWh, such as New York and Massachusetts, the same system pays back in roughly 7–8 years. At 13¢/kWh it takes about 17–18 years. These figures assume full retail credit for output and exclude financing, rate changes, and maintenance.
Yes. Panels facing east or west typically produce less than south-facing panels, and the loss depends on your tilt and location, so model your actual roof in NREL's PVWatts. As an illustration, if orientation cuts output by 15%, a 49-panel design becomes about 58 panels (49 ÷ 0.85) to deliver the same energy. Roof area matters too: 49 typical 400 W panels need roughly 1,000 square feet of usable roof.
Same usage, bill-based guide
Your 70 kWh/Day target maps to roughly a $350/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.