Enrichment · Passion Projects · Energy

When does the roof
start paying you?

Solar costs a lot up front and saves a little every month. Put an installer’s quote beside your power bill and see the year the savings catch up.

Find my payback yearWhat you get

The home solar payback calculator

The worked example is a 6.5 kW system on a south-facing roof, with a $1,000 utility rebate. Nothing you type leaves this browser.

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What you get

Enrichment · Passion ProjectsFree

What you finish with
Year-by-year output, savings and the running total, the payback year to a tenth, the savings over the period net of the cost and the cost per watt. It prints as a page to set beside each installer’s quote.
Who it is for
Homeowners and families thinking about rooftop solar, adults comparing two or three installer quotes, and students studying energy, prices and payback.
Format
Browser calculator for a phone, tablet or computer, by touch or keyboard. Prints a summary; downloads a spreadsheet (.csv); export and import a file.
Access
Free. No account, no sign-in and nothing to install. Everything you type stays in this browser; nothing is sent to Caveat.
Where it lives
The Passion Projects space in Caveat Enrichment.
Support
Questions, a correction or a request: team@caveatacademic.com.

How to use it

  1. Copy the size and cost.
  2. Look up output in PVWatts.
  3. Type your price per kWh.
  4. Set the share at full price.
  5. Read the payback year.

Find my payback year

How the payback year is found

Output, valued at your price, added up until it covers the cost.

The worked example: a 6.5 kW system on a south-facing roofOutput, year one8,775 kWh6.5 kW × 1,350Savings, year one$1,26890% at $0.17, less $75Cost to recover$17,500$18,500 − $1,000Paid back12.2 yearsprices up 2.5% a yearThe worked example: a 6.5 kW system on a south-facing roofOutput, year one8,775 kWh6.5 kW × 1,350Savings, year one$1,26890% at $0.17, less $75Cost to recover$17,500$18,500 − $1,000Paid back12.2 yearsprices up 2.5% a year
Each year’s output, valued at your electricity price, is a saving. The running total of savings, as prices rise and panels slowly age, pays back the cost after incentives.

Output and its value

A kilowatt of panels makes roughly 1,000 to 1,700 kWh a year in most of the country, depending on sun, tilt and shade; NREL’s free PVWatts calculator estimates it for your address. As a check: 6 kW × 1,300 kWh is 7,800 kWh; at $0.16 a kWh that is $1,248 off the bills in year one.

Rules that change the answer

Under net metering, power you send to the grid earns about the retail price. Under net billing it earns less, so the share of output you use at home matters. Incentives and tax credits change over time and by place; type only the ones you have confirmed apply to your installation date.

Sources

  1. National Renewable Energy Laboratory. PVWatts Calculator (pvwatts.nrel.gov).
  2. U.S. Department of Energy. Homeowner’s Guide to Going Solar (energy.gov/eere/solar).
  3. U.S. Energy Information Administration. Electricity data: average retail prices by state (eia.gov).
  4. Database of State Incentives for Renewables and Efficiency, NC Clean Energy Technology Center (dsireusa.org).

A cash-payback estimate from figures you type, not financial or tax advice; weather, shading, rate design and future prices change the result. Your entries stay in this browser. Support: team@caveatacademic.com.