Solar Panel Calculator (2026): System Size, Cost, Savings, And Payback All In One

I built a 6 kW array on my own house in 2024 and have been logging production every day since. The math below — and the calculator that runs it — is the same math I used to size my own system, plus the same datasets every U.S. installer references. There is no lead capture, no email signup, no sales referral, and no AI-generated content. Just NREL, EIA, EPA, and LBNL data run through the public PVWatts API.

The Single Biggest Change In Solar Economics Since 2010

Before we walk through how to use the calculator, you need to understand the most important fact about U.S. residential solar in 2026 — one that nearly every other solar calculator on the web has not yet updated for:

The 30% federal solar tax credit ended on January 1, 2026.

Section 25D of the U.S. tax code — the Residential Clean Energy Credit — expired on December 31, 2025 under the One Big Beautiful Bill Act (Public Law 119-21, signed July 4, 2025), nearly a decade earlier than the Inflation Reduction Act's original schedule (which had it running through 2032 at 30%, then phasing down through 2034). For homeowners buying solar systems in 2026 or later, there is no federal tax credit to claim.

What this means in practical numbers: a 7 kW system that cost $21,000 gross would have netted $14,700 in 2025 (30% credit applied). That same system in 2026 nets the full $21,000. The cost of going solar increased by 43% overnight for a typical homeowner, with no transition period and no phase-down. This is the largest single-day price increase in U.S. residential solar in over a decade.

There is one workaround: Section 48E (the commercial solar credit) is still active through 2027 for third-party-owned systems — solar leases, Power Purchase Agreements (PPAs), and prepaid solar products. The installer or financing company claims the 30% credit at the corporate level and passes part of the savings through to you in the form of a lower lease rate or PPA price. You don't own the panels, you don't get the salvage value at end of life, and the lease typically has an escalator clause that erodes your savings over time — but in 2026 it's the only path to capturing federal solar tax dollars on a residential installation.

The calculator above defaults to 0% credit to reflect direct purchase under current law. If you're considering a TPO lease, the installer's quote will already factor the credit into their pricing — don't double-count it.

How To Use This Calculator

The calculator above is a guided 5-step form. You can fill it in top-to-bottom, or skip to whichever input you want to change — results update live.

Step 1: Enter your location

Click Use my location for one-click geolocation, or type your ZIP code and click Look up. The calculator hits NREL PVWatts v8 directly via our peak-sun-hours API and returns your annual peak sun hours per day plus the kWh-per-year-per-kW for your exact coordinates. Without a location, the calculator uses the U.S. average (4.98 PSH/day, 1,367 kWh/year per 1 kW). For deeper PSH analysis at your address, use the dedicated peak sun hours calculator.

Step 2: Enter your electricity use

Look at your most recent electric bill. The two numbers you need:

• Monthly kWh: how much electricity you used last month (or the 12-month average — your utility's online portal usually shows this).
• Electricity rate ($/kWh): what you pay per kilowatt-hour. This is on every bill, usually labeled "supply rate" or "energy charge per kWh."

Don't have a bill handy? The U.S. average is 875 kWh/month at $0.18/kWh (EIA, April 2026). Click the "875 kWh" link in the helper text to load it instantly. Range: $0.12/kWh in Louisiana to $0.40/kWh in Hawaii — the spread is more than 3×, and it's the single largest factor in your payback period.

Step 3: Pick your panel size

Default is 400 W (the U.S. residential standard in 2026). You can pick a preset (100W, 200W, 300W, 400W, 440W premium TOPCon, 580W commercial) or type any wattage from 50 to 750. Higher wattage panels mean fewer panels needed and slightly less roof area, but the total kW (and total cost and total kWh produced) is roughly the same. For details on real 2026 panels in each size class, see standard solar panel sizes and wattages.

Step 4: Set your coverage goal

Default is 100% of your bill — the most common target. Increase to 120–150% if you have an EV (~3,000–4,000 kWh/year extra), an electric heat pump (~5,000–8,000 kWh/year extra), or are planning to electrify more of your home in the next few years. Decrease to 50–80% if you have a small roof or a tight budget and want to cover the bulk of your bill without going for full offset.

Step 5: Set your install cost assumption

Default is $3.00/W, which is the middle of the U.S. residential median range for 2026 ($2.58–$3.25/W per Lawrence Berkeley National Laboratory's Tracking the Sun 2024 report and current trends). Lower in low-cost states (Texas, Arizona, Florida — closer to $2.50/W). Higher in California, New York, Massachusetts, Hawaii, and other high-soft-cost states ($3.25–$4.00/W). When you get an actual installer quote, plug their $/W in here for an apples-to-apples comparison.

What The Results Mean

The calculator returns five result panels, all updating live as you change inputs.

Recommended system

• System size in kW — the smallest system that meets your coverage goal
• Panel count — system_kw × 1000 ÷ panel_watts, rounded up
• Roof area — panel_count × 21 sq ft (the average for a modern 400W residential panel), plus a "with setbacks" number that adds the ~33% overhead for NFPA 1 fire-code clearances
• Bill coverage — what % of your annual electricity use this system actually covers (often slightly above your target because panels are discrete)

Annual production

• Annual kWh — system_kw × kwh_per_kw_per_year for your location (PVWatts v8 default derate of 14% system loss + ~4% inverter loss already baked in)
• Daily and monthly averages — annual ÷ 365 and ÷ 12
• Monthly bar chart — the actual seasonal curve from PVWatts (June peak, December trough), so you can see how production varies through the year for your specific location

Cost & savings

• Gross install cost — system_kw × 1000 × cost_per_watt
• Federal tax credit — $0 in 2026 (per Section 25D expiration). The calculator also shows what the credit would have been worth in 2025 for comparison
• Net cost to you — gross minus credit
• Annual electricity savings — annual_kwh × your_rate
• Payback period — net_cost ÷ annual_savings, in years
• 25-year lifetime production, savings, and net profit — using a 0.92 degradation factor (the average of year-1 100% and year-25 85% for tier-1 panels)

Environmental impact

• Annual CO₂ offset — annual_kwh × 0.823 lbs/kWh (EPA eGRID 2022 U.S. average)
• 25-year lifetime CO₂ offset in pounds and metric tons
• Equivalencies — gallons of gasoline not burned and tree-equivalent absorption, both per the EPA Greenhouse Gas Equivalencies calculator

Bottom-line interpretation

A short narrative paragraph that ties all the numbers together: which system size makes sense for your specific location, what your payback verdict is, whether your 25-year lifetime profit is positive or negative, and what your environmental contribution looks like in plain English.

Worked Examples For 5 Cities

To make the calculator concrete, here are five complete worked examples — one each for a sunny, average, and cloudy U.S. location, plus a high-electricity-rate state and a hot-climate state. All assume a 400W panel, 100% coverage, $0.18/kWh rate (national average), $3.00/W install cost, and the EIA average household use of 10,500 kWh/year.

Example 1: Phoenix, AZ (sunniest U.S. city)

• PSH: 6.54 (1,755 kWh/year per 1 kW)
• System needed: 5.99 kW → 15 × 400 W panels
• Roof area: 315 sq ft (420 sq ft with setbacks)
• Annual production: 10,530 kWh (100% offset)
• Gross cost: $18,000 · Net (no credit): $18,000
• Annual savings: $1,895
• Payback: 9.5 years
• 25-year profit: $25,635

Example 2: Boston, MA (average sun, very high electricity rate)

• PSH: 4.70 (1,302 kWh/year per 1 kW)
• Boston rate: ~$0.32/kWh (Eversource, 2026)
• System needed: 8.07 kW → 21 × 400 W panels
• Roof area: 441 sq ft (588 sq ft with setbacks)
• Annual production: 10,937 kWh (104% offset)
• Gross cost: $25,200 · Net (no credit): $25,200
• Annual savings: $3,500 (huge because of the rate)
• Payback: 7.2 years — fastest of the five examples
• 25-year profit: $55,300

The Boston example shows the dominance of electricity rate in the payback math: even with worse sun than Phoenix, the much higher rate makes Boston a faster-paying investment.

Example 3: Chicago, IL (cloudy continental average)

• PSH: 4.27 (1,308 kWh/year per 1 kW)
• Rate: $0.17/kWh (ComEd, 2026)
• System needed: 8.03 kW → 21 × 400 W panels
• Roof area: 441 sq ft (588 sq ft with setbacks)
• Annual production: 10,987 kWh (105% offset)
• Gross cost: $25,200 · Net (no credit): $25,200
• Annual savings: $1,868
• Payback: 13.5 years — slow but still under the 25-year warranty
• 25-year profit: $17,750

Example 4: Austin, TX (average sun, low electricity rate)

• PSH: 5.30 (1,421 kWh/year per 1 kW)
• Rate: $0.14/kWh (Austin Energy, 2026)
• System needed: 7.39 kW → 19 × 400 W panels
• Roof area: 399 sq ft (532 sq ft with setbacks)
• Annual production: 10,800 kWh (103% offset)
• Gross cost: $22,800 · Net (no credit): $22,800
• Annual savings: $1,512
• Payback: 15.1 years — slow because Texas electricity is cheap
• 25-year profit: $11,950

Texas is a paradox: lots of sun but also some of the cheapest electricity in the country, so the payback is slower than New England states with worse sun. Cheap electricity is the silent killer of solar economics.

Example 5: Honolulu, HI (sunny, highest electricity rate in the country)

• PSH: 5.82 (1,622 kWh/year per 1 kW)
• Rate: $0.40/kWh (Hawaiian Electric, 2026)
• System needed: 6.47 kW → 17 × 400 W panels
• Roof area: 357 sq ft (476 sq ft with setbacks)
• Annual production: 11,034 kWh (105% offset)
• Gross cost: $20,400 · Net (no credit): $20,400
• Annual savings: $4,414
• Payback: 4.6 years — fastest in the U.S.
• 25-year profit: $81,180

Hawaii is the strongest residential solar market in the country by a wide margin — even after the federal tax credit eliminated. The combination of strong sun, very high electricity rates, and zero state-level competition (no natural gas grid means electricity is the option) makes Hawaii the only U.S. state where residential solar still pays back in under 5 years on a direct-purchase basis.

Summary of the 5 examples

The pattern is clear: electricity rate is more important than peak sun hours for residential solar economics. Boston has worse sun than Austin but pays back twice as fast because Boston's electricity costs 2.3× more.

Where Each Number Comes From

Every constant in the calculator is sourced from a public dataset. No estimates, no guesses, no industry self-reporting.

For the full math behind each number, see how to calculate solar panel output.

Is It Still Worth It In 2026?

Short answer: yes, for most U.S. homeowners — but the math is much tighter than it was in 2025, and certain marginal cases (low-rate states with cheap electricity, or cloudy locations with average rates) may now be break-even or slightly negative on a flat-rate-assumption basis.

Here's the rough decision framework based on the 5 worked examples and our state-by-state data:

Three things tilt the math toward "buy" even in the marginal cases:

1. Electricity rate inflation. U.S. residential rates have risen ~3% per year on average since 2020, and the 2024–2026 stretch saw 5–10% annual increases in the Northeast and West Coast as utilities pass through grid modernization costs. A 3% annual increase turns a 14-year payback into a 12-year payback and adds roughly 40% to your 25-year savings.
2. State and utility rebates. DSIRE tracks every state, county, and utility incentive in the U.S. Many states (NY, MA, CA, NJ, MD) still have state-level tax credits, SREC markets, or upfront rebates that can knock $2,000–$8,000 off the install cost.
3. TPO leases. If your math doesn't work for direct purchase, a third-party-owned lease that captures the still-active Section 48E credit can move the needle. You give up ownership and the salvage value, but you avoid the upfront cost entirely. Get quotes from Sunrun, Sunnova, or Palmetto for 2026 lease pricing.

Common Mistakes When Using A Solar Calculator

Five things people get wrong:

1. Using your summer electric bill as your monthly average

Summer bills run 30–50% higher than winter bills (in most of the U.S.) because of air conditioning. Use the 12-month average from your utility's online portal, not the highest-month bill, or you'll oversize your system and overpay.

2. Forgetting that the 30% federal credit is gone

Most solar calculators on the web — including some installer quote tools — still apply a 30% federal credit by default. For purchases on or after January 1, 2026, this is wrong. Always ask your installer to show you the breakdown line by line and confirm what credit they're assuming.

3. Comparing nameplate watts across different installer quotes

A "7 kW system" from one installer may be 18 × 390 W panels and a "7 kW system" from another may be 17 × 410 W panels. The kW number is what matters, not the panel count. Use the standard solar panel sizes article to verify you're comparing apples to apples.

4. Ignoring electricity rate variation across the U.S.

Hawaii's $0.40/kWh and Louisiana's $0.12/kWh produce wildly different paybacks for the same physical system. Look up your specific utility's residential rate (not the state average), because in many states there are 2× rate differences between urban and rural utilities.

5. Comparing a 2025 quote to a 2026 quote and not accounting for the credit change

A 2025 quote for $14,700 net (with credit) is the same as a 2026 quote for $21,000 net (no credit). Many homeowners are still anchored to the 2025 numbers and think 2026 quotes are much higher than they actually are.

State-By-State Cost Variation

Median residential install cost varies significantly by state, even for the same size system. Per Lawrence Berkeley Tracking the Sun 2024:

These are gross prices before any state, county, utility, or property tax incentives. A $3.40/W install in Massachusetts may be cheaper net than a $2.50/W install in Texas after applying the Massachusetts state credit, the SREC market, and the property tax exemption. Always check DSIRE for state-specific incentives.

Bottom Line

The math for U.S. residential solar in 2026 is harder than it was in 2025 — but for most homeowners, it still pencils out. Use the calculator at the top of this page with your real ZIP, your real electricity bill, and your real installer quote (not the defaults). If your payback comes out under 12 years, it's a strong buy. Between 12 and 16 years, marginal — let rate inflation and state incentives decide. Above 16 years on a direct-purchase basis, look at TPO leases or wait for state-level policy changes.

The single biggest variable is your electricity rate, not your peak sun hours. A homeowner in Boston pays back faster than one in Phoenix, despite having much worse sun, because Massachusetts electricity costs nearly 2× the U.S. average. Look at your bill before you look at the weather.

Keep Reading

• Peak Sun Hours Calculator — Find PSH At Your Location — the location input above lives here
• How To Calculate Solar Panel Output — the formula breakdown and PVWatts methodology
• How Many kWh Does A Solar Panel Produce Per Day — daily output lookup tables
• Standard Solar Panel Sizes And Wattages (100W–600W)
• Solar Panel Watts Per Square Foot
• Average Peak Sun Hours By State
• Rooftop Solar Calculator — How Many Panels Fit On Your Roof
• How Much Power A 5 kW Solar System Produces
• How Much Power A 10 kW Solar System Produces