Solar Panel Estimate Calculator

Estimate your 2026 solar system size, installed cost, payback period, and 25-year savings using current EnergySage and EIA benchmarks.

The federal residential solar tax credit (Section 25D) expired for systems placed in service after December 31, 2025. The 0% default reflects that — enter a state or utility rebate percentage here if one applies to you.

System assumptions

Performance ratio (77% by default) is a standard PVWatts-style derate covering inverter conversion, wiring, soiling, and temperature losses. Annual degradation (0.5% by default) is the typical rate at which crystalline-silicon panel output declines each year, per NREL and manufacturer warranty data.

By · Energy analysts and engineers documenting every formula, source, and limitation behind our calculators.

Published Updated Formula, sources & limitations

Share this calculatorFree to use and free to embed — no sign-up and no attribution required.

Share Solar Panel Estimate Calculator

Page link

Share to

Embed on your site

Paste this iframe into any page, blog post, or app. It renders the calculator on its own, with no header or footer.

<iframe src="https://solarcalculator4u.com/embed/solar-panel-estimate-calculator/" title="Solar Panel Estimate Calculator" width="100%" height="820" style="border:0;max-width:720px" loading="lazy"></iframe>
HOW IT WORKS

How does the solar panel estimate calculator work?

The calculator sizes a system to hit your target electricity offset, prices it out at your cost per watt, then projects 25 years of savings against your local rate and its expected annual escalation.

1

Enter your usage & sun hours

Set your monthly electricity use, target offset, and local peak sun hours.

2

Add cost & rate assumptions

Enter your cost per watt, any tax credit or rebate, your electricity rate, and its expected annual increase.

3

View size, cost & savings

See your system size, installed cost, payback period, and 25-year savings.

Why system size is solved from your offset target

Rather than asking you to guess a system size, this calculator works backward from what you actually want: a chosen share of your annual electricity use covered by solar. It converts your monthly use to an annual figure, applies your offset target, then divides by how much energy a single kW of panels produces at your location — your peak sun hours times 365 days, discounted by a performance ratio that accounts for inverter conversion, wiring, soiling, and temperature losses between a panel's rated output and what it actually delivers.

THE CALCULATIONSystem size (kW) = (annual use × offset %) ÷ (peak sun hours × 365 × performance ratio)

Gross cost = system size (W) × cost per watt. Net cost = gross cost × (1 − tax credit / rebate %). Each projected year's savings = that year's production × that year's electricity rate, compounding degradation and rate escalation forward from year 1.

Worked example: a typical home at full offset

EXAMPLE 1

900 kWh/month, 100% offset, 4.8 peak sun hours, $2.49/W, no rebate

Say your home uses 900 kWh a month, your area averages 4.8 peak sun hours, and you want solar to fully offset your annual use. Installers in your area quote around $2.49 per watt, you don't have a state or utility rebate, your rate is $0.165/kWh with 3% expected annual escalation, and you're using the default 77% performance ratio and 0.5% annual degradation.

  1. Annual use: 900 kWh × 12 = 10,800 kWh.
  2. System size: (10,800 × 100%) ÷ (4.8 × 365 × 0.77) ≈ 8.0 kW.
  3. Annual production: 8.0 kW × 4.8 h × 365 × 0.77 ≈ 10,800 kWh.
  4. Gross cost: 8,006 W × $2.49 ≈ $19,934. With no rebate, net cost is the same.
  5. Year 1 savings: 10,800 kWh × $0.165 ≈ $1,782.

Projected forward 25 years with 3% rate escalation and 0.5% annual panel degradation, cumulative savings cross the $19,934 net cost around year 10.

Result: about an 8.0 kW system, $19,934 net cost, a roughly 10-year payback, and about $40,800 in net savings over 25 years.

Worked example: a smaller system with a state rebate

EXAMPLE 2

500 kWh/month, 80% offset, 5.5 peak sun hours, $2.75/W, 20% rebate

Now suppose a smaller household uses 500 kWh a month in a sunnier location averaging 5.5 peak sun hours, and only wants an 80% offset to keep the system smaller. Installers there quote a higher $2.75/W, but a 20% state rebate applies, the local rate is $0.22/kWh with a milder 2.5% escalation, and the performance ratio is set to 75% for a more shaded roof.

  1. Annual use: 500 kWh × 12 = 6,000 kWh.
  2. System size: (6,000 × 80%) ÷ (5.5 × 365 × 0.75) ≈ 3.2 kW.
  3. Annual production: 3.2 kW × 5.5 h × 365 × 0.75 ≈ 4,800 kWh.
  4. Gross cost: 3,188 W × $2.75 ≈ $8,767. Net cost after the 20% rebate ≈ $7,014.
  5. Year 1 savings: 4,800 kWh × $0.22 ≈ $1,056.

Result: about a 3.2 kW system, $7,014 net cost, a roughly 6.3-year payback, and about $26,800 in net savings over 25 years.

Understanding each result

System size (kW DC) is the panel nameplate capacity needed to hit your offset target, given your sun hours and performance ratio.

Annual production (kWh) is what the sized system is expected to generate in its first year — by construction, this tracks your usage and offset target directly, since that's exactly what the system was sized to hit.

Gross cost and net cost price the system at your entered cost per watt, then apply your tax credit or rebate percentage. For 2026, that's most often a state or utility program, since the federal residential credit has expired.

Payback period is when cumulative electricity savings first equal your net cost, projected with your entered degradation and rate-escalation assumptions rather than a flat first-year savings figure. For a deeper look at break-even — including your state's current electricity rate and incentives, ROI, internal rate of return, and a year-by-year cash flow — use the solar payback period & ROI calculator.

Year 1 savings and 25-year savings show the near-term and lifetime value: year 1 uses your current rate and full production, while the 25-year figure compounds rising rates against slowly declining production, net of your system cost.

Common ways to use this calculator

Budgeting before you request quotes

Get a starting system size and cost range before installers visit your home.

Comparing offset targets

See how sizing for 80%, 100%, or 120% offset changes cost and payback.

Sanity-checking an installer's quote

Enter their quoted cost per watt and rebate to compare against your own benchmark.

Planning around rate increases

Adjust annual rate escalation to see how utility price trends affect your payback.

Privacy and appropriate use

Your inputs are processed directly in your browser and are not sent to a database. This is a planning-stage budgeting estimate, not an engineering, permitting, or financing document — get a formal site assessment and quote from a licensed solar installer before making a purchase decision.

Estimate your solar system ↑Browse all calculators →
FREQUENTLY ASKED QUESTIONS

Questions about the solar panel estimate calculator.

Clear answers about accuracy, the 2026 tax credit, sun hours, and how payback is calculated.

How accurate is this estimate?

It's a planning-stage estimate built from the same formulas EnergySage and NREL's PVWatts use to size residential systems — accurate enough to budget and compare quotes. Your actual system size and cost will shift based on your roof's usable area, shading, panel and inverter model, and installer pricing, which only a site visit and a formal quote can pin down.

Why is the federal tax credit set to 0% by default?

The federal residential Clean Energy Credit (Section 25D), which covered 30% of system cost, expired for systems placed in service after December 31, 2025 under the One Big Beautiful Bill Act. The 0% default reflects that as of 2026 — enter a percentage here only if a state, utility, or other local rebate applies in your area.

What does "target offset" mean?

It's the share of your annual electricity use you want the system to generate, as a percentage. 100% sizes the array to produce roughly as much energy over a year as you consume. Setting it above 100% builds in headroom for an EV or home addition you're planning; setting it below 100% sizes a smaller, cheaper system that only offsets part of your bill.

Where do I find my peak sun hours?

Peak sun hours measure your location's average daily solar resource, not daylight hours — a value of 4.8 means your site gets the equivalent of 4.8 hours of full, direct sun per day. NREL's PVWatts Calculator and most solar quote tools report this figure for your ZIP code; sunnier states like Arizona and California typically run 5.5–6.5, while the Pacific Northwest and Northeast often run 3.5–4.5.

Why does annual production track my usage and offset target, not my sun hours?

This calculator solves for the system size needed to hit your offset target, given your sun hours and performance ratio — so those two figures cancel out of the final production number by construction. Fewer sun hours or a lower performance ratio produce a physically larger, more expensive system, not a lower annual output; the array just needs more panels to reach the same energy target under weaker conditions.

What's the difference between gross cost and net cost?

Gross cost is the full installed price before any incentive: system size in watts × your cost per watt. Net cost subtracts your entered tax credit or rebate percentage. If you don't have a rebate, gross and net cost will be the same, matching the 0% federal credit default for 2026.

How is the payback period calculated?

The calculator projects your annual electricity savings for 25 years, reducing production each year by your panel degradation rate and increasing your electricity rate by your annual rate escalation, then finds the year your cumulative savings first cover your net system cost. A higher electricity rate, a higher escalation rate, or a lower net cost all shorten payback; a larger, more expensive system lengthens it.

What is annual rate escalation, and why does it matter?

It's the yearly percentage increase you expect in your electricity rate. Utility rates have historically risen a few percent a year on average, so even a modest escalation assumption meaningfully shortens payback and raises 25-year savings, since the energy your system produces later in its life is worth more per kWh than what it produces today. EnergySage and most solar quote tools default to 2–4%; check your utility's recent rate history if you want a more site-specific figure.

Why 25 years for the savings projection?

25 years is the standard manufacturer performance warranty period for crystalline-silicon solar panels, and the convention most solar quote tools use for lifetime savings figures, which is why this calculator uses it too. Panels typically keep producing well past 25 years, just at a further-reduced output.

Is this a substitute for an installer's quote?

No. This is a starting estimate to help you budget and sanity-check quotes before you talk to installers. A formal quote will measure your actual roof area, shading, and orientation, price specific equipment, and account for your utility's interconnection and net-metering rules — all of which can shift the final numbers from this estimate.

Is my data stored?

No. All inputs and calculations run directly in your browser and are not sent to a server or saved in an account. General site usage may be measured through Google Analytics as described in our Privacy Policy.