Independent Source-cited No lead capture Static snapshot · May 2025

What will solar actually save you?

An independent payback calculator built on EIA utility rates, NREL solar data, and the IRS §25D federal tax credit. Four inputs, no email required.

Run the calculator See the math

30%

Federal tax credit

IRS §25D, through 2032

$2.90

National avg. $/W

EnergySage · SEIA · NREL

25 yrs

Production warranty

Industry standard

0.5%

Annual panel degradation

Tier-1 manufacturer median

Data from U.S. EIA · NREL · IRS §25D · DSIRE® · EnergySage · SEIA

Calculator

Your four-input estimate.

Every field is explained inline. Inputs are processed in memory and discarded.

1 ZIP

2 Bill

3 Roof

4 Sun

ZIP Code * Required

Used only to look up your state's average residential rate and peak sun hours.

Monthly electricity bill * 12-month avg.

We divide this by your state rate to estimate annual kWh.

Roof type

Shingle Asphalt Metal +5% labor Tile +15% labor

Sunlight exposure

Low Shaded −15% Average Typical ±0% High Open S. +10%

I understand this is an estimate, not professional advice. The numbers shown are derived from national averages and disclosed assumptions; actual costs and savings depend on installer pricing, your utility's tariff, roof geometry, and other factors outside this calculator's scope. Before any purchase decision I will consult a licensed installer, CPA, and my utility. Full terms · limitations.

No login. No email. Inputs discarded after the response is returned.

Your numbers will appear here.

Fill in the four fields on the left and we'll show payback, net cost, and a 25-year savings curve.

Will show

Payback period (years)

Will show

25-year net profit

The math

No black box. The full calculation in four steps.

Every formula and constant is published, sourced, and re-derivable in a spreadsheet.

Convert your bill to energy use

monthly_bill ÷ state_rate × 12 = annual kWh

A $180 bill at California's $0.31/kWh implies ~6,968 kWh/year — consistent with EIA's 6,500 kWh CA average.

Size the system from sun hours

annual_kWh ÷ (sun × 365 × 0.80)

The 0.80 is the industry "performance ratio" — losses from inverter, wiring, temperature, and soiling, per NREL PVWatts.

Apply national install cost

system_kW × $2,900 × roof_factor

Midpoint of EnergySage, Wood Mackenzie/SEIA, and NREL's 2024 benchmarks for residential cash-purchase systems.

Subtract the federal credit

gross_cost × 30%

IRS §25D Residential Clean Energy Credit, codified at 30% through 2032 under the Inflation Reduction Act.

Read the full methodology, with every constant and citation

Why us

A reference, not a sales pitch.

Most "free solar calculators" exist to capture your contact details for installer leads. This one doesn't.

Editorial principle

No leads. No commissions. No "best installer" rankings.

We don't capture your email or sell anything you type. The only future revenue source is non-targeted display advertising via Google AdSense — and only after we earn a real audience.

Lead forms

Trackers

Inputs

Every number cited.

EIA, NREL, IRS, DSIRE. No proprietary "secret sauce".

Code is public.

Audit our math line by line. CC BY-SA 4.0 license.

25-year projection, year by year.

Most calculators give you a single payback number. Ours shows the full cumulative-savings curve, with electricity inflation and panel degradation modeled explicitly, so you can see what year three actually looks like.

Versioned changelog.

Every constant change is dated and explained.

Transparency

What we collect — and what we don't.

A complete inventory of every data point that touches our server when you run a calculation.

We collect

ZIP code — Used only to look up state-level rate & sun-hour averages, then discarded.
Monthly bill (USD) — Used to compute annual kWh, then discarded.
Roof type — Cost multiplier (shingle, metal, tile).
Sunlight exposure — Modifier on sun hours (low, average, high).
Standard server logs — IP, user-agent, timestamp — 30-day retention, abuse prevention only.

Never collected

Name, email, phone, street address — no field exists.
Account creation, login, or persistent identifier.
Third-party tracking cookies or marketing pixels.
Geolocation beyond the ZIP you voluntarily type.
Lead sales or installer referral arrangements.

Audience

Built for the homeowner doing real due diligence.

Sanity-checking an installer quote

You've received one or more bids and want a defensible independent baseline for cost-per-watt and payback.

Comparing financing scenarios

Cash, solar loan, or PPA — the 25-year cumulative curve is the right denominator. We show it explicitly.

Researchers and students

Energy-economics students, policy analysts, and journalists who want a source-cited baseline for US residential solar.

FAQ

Common questions, taken seriously.

The questions a knowledgeable reader actually asks.

Why does this estimate differ from my installer's quote?

Quotes reflect a specific equipment package (panel and inverter brand, racking, monitoring, warranties), permitting fees, sales commissions, and financing markup. Our number is a market-average baseline — not a quote. A reasonable rule of thumb: if a quote is more than 20% above our estimate, ask for an itemized breakdown of why.

How accurate is the payback period?

For a household with steady consumption and an unshaded, south-facing roof in a state with stable electricity policy, our estimate is typically within ±15% of reality. Accuracy degrades for tiered or TOU rate structures, shaded sites, and DIY installs.

Is the 30% federal tax credit guaranteed?

It's statutory law through 2032, stepping down to 26% in 2033 and 22% in 2034 under the Inflation Reduction Act. It is non-refundable — you can only use it against tax you actually owe — though unused credit carries forward. Confirm eligibility with a CPA, especially if you have low taxable income or AMT exposure.

Why don't you include state and utility rebates?

They vary wildly by utility, change frequently, and frequently have capped budgets that exhaust mid-year. We show state-level incentives separately on each state page (drawn from DSIRE) so you can read program details and contact administering agencies directly. Bundling them into a single number gives false precision.

Does the projection assume net metering?

It assumes 1-for-1 retail-rate offset — the economic equivalent of traditional NEM 1.0/2.0 in most states. Under newer "net billing" regimes (notably California NEM 3.0), exported energy is compensated at avoided-cost rates 60–80% lower. In those markets, treat our payback as a best case and add roughly 2–3 years.

What about batteries?

Storage materially changes the economics — especially under NEM 3.0 and in markets with TOU rates or frequent outages. We deliberately exclude storage from the base calculator because the decision is highly location- and use-case-specific. A future release will add an optional battery module.

Intellectual honesty

What this calculator is not.

A generalised, four-input model cannot reproduce the precision of a site-specific engineering study. These are explicitly outside our scope:

Roof orientation, tilt, and per-module shading

Time-of-use, tiered, and demand-charge rates

Battery storage sizing and arbitrage value

Specific equipment selection (panel make / inverter)

Local permitting, interconnection, and HOA fees

State-specific NEM 3.0 export compensation

Financing terms (loan APR, dealer fees, PPA escalators)

Insurance and re-roof timing implications

For any of these, the right next step is a licensed installer's site assessment plus an independent review against tools like NREL PVWatts and your utility's tariff sheet.