Solar Panel Payback Calculator

Solar panel payback period is the time it takes for the energy savings generated by a solar system to equal its installation cost. After payback, the system generates essentially free electricity for the remainder of its 25–30 year lifespan.

There are two paybacks and they run on different clocks. The financial one is what most people mean, and on a typical US system it lands somewhere between eight and twelve years. The carbon payback, the time it takes for avoided grid emissions to cover the emissions from making and shipping the panels, is usually a small fraction of that, often one to three years. This page reports both, because a system can look like a mediocre investment and still be a good piece of decarbonisation.
For the four-field financial version on its own, without the rate escalation or the carbon figures, use the solar panel payback period calculator. Set the rate increase here to zero and the two agree to the dollar.

Output falls about 0.5% a year, which is what a 25-year 80%-output warranty implies. Year 25 makes roughly 89% of year 1, and holding output flat overstates the lifetime total by about 6%. Every figure on this page applies the decline, including the payback date itself.

Simple payback formula: Payback Period (years) = Net Installation Cost ÷ Annual Electricity Savings

Net installation cost: Net Cost = Gross System Cost − Federal Tax Credit − State/Local Incentives − Utility Rebates

Federal Investment Tax Credit (ITC, 2024): 30% of system cost (applies to US homeowners; direct reduction in federal income tax owed)

Annual savings formula: Annual Savings = Annual kWh Production × Electricity Rate ($/kWh)

System production formula: Annual kWh = System Size (kW) × Peak Sun Hours per Day × 365 × System Efficiency Factor

System efficiency factor accounts for inverter losses, shading, temperature, and soiling: typically 0.75–0.85.

What each variable means:

• Peak Sun Hours (PSH) - the equivalent number of hours per day at 1,000 W/m² irradiance:
  • Arizona/Nevada: 5.5–6.5 hours/day
  • California: 4.5–5.5 hours/day
  • Midwest: 4.0–4.5 hours/day
  • Northeast US: 3.5–4.5 hours/day
  • Pacific Northwest: 3.0–3.5 hours/day
• Electricity rate - US average: $0.14–$0.17/kWh (2024); utilities vary widely from $0.10 (Southeast) to $0.30+ (Hawaii, California)
• Net metering - allows you to sell excess solar energy back to the grid at the retail rate; significantly improves economics in states that offer full retail net metering

Reference: typical US solar installation costs (2024)

• 6 kW system: $15,000–$20,000 gross ($10,500–$14,000 after 30% ITC)
• 8 kW system: $18,000–$25,000 gross ($12,600–$17,500 after ITC)
• 10 kW system: $22,000–$30,000 gross ($15,400–$21,000 after ITC)

Worked example: 8 kW system. Gross cost: $22,000. After 30% federal ITC: $22,000 × 0.70 = $15,400 net cost Location: Texas (5.0 peak sun hours/day). System efficiency: 0.80.

Annual production = 8 kW × 5.0 × 365 × 0.80 = 11,680 kWh/year Electricity rate: $0.13/kWh Year 1 savings = 11,680 × $0.13 = $1,518

The simple division gives $15,400 ÷ $1,518 = 10.1 years, and that is the figure most calculators stop at. Feed the same numbers into the one above and it says 10.4 years, because output falls half a percent a year and each year saves slightly less than the one before it. Three months is not a large difference, but it is a real one, and it grows with the term.

Over 25 years the system saves $35,767, which is $20,367 more than it cost. Free electricity years = 25 − 10.4 = 14.6.

None of that adjusts for rising electricity rates, which push the other way. Put 3% in the rate-increase box and the payback drops to about 9.2 years.