How solar payback works
Solar panels save money in two ways. Electricity you use at home while the sun shines replaces power you would otherwise buy at your full retail rate. Electricity you export to the grid earns a credit, which may equal the retail rate (full net metering) or be much lower (as with many newer export tariffs, the UK Smart Export Guarantee or Australian feed-in tariffs). The payback period is the time until the savings add up to the net cost of the system.
Yearly savings = production × self-use share × electricity price + production × export share × export credit
Production falls each year by the degradation rate; prices rise by the price-increase rate
Payback = year when cumulative savings ≥ system cost − incentives
Worked example
A system costs $20,000 with no incentives and produces 10,000 kWh in its first year. The household uses 70% of it at home, buys electricity at $0.17 per kWh and gets $0.08 for each exported kWh. Prices rise 3% a year and output falls 0.5% a year.
- First-year savings: 7,000 kWh × $0.17 + 3,000 kWh × $0.08 = $1,430.
- Savings grow as electricity prices rise, from $1,430 to about $2,577 in year 25.
- Payback: about 12.2 years.
- After 25 years the system has returned about $28,751 more than it cost, 144% of the net cost, before any maintenance or inverter replacement.
With a $2,000 rebate and a lower $0.05 export credit, the first-year saving falls to $1,340 but the lower net cost brings payback to about 11.7 years.
What changes payback the most
- Your electricity price. The higher it is, the faster solar pays back. Use your full unit rate including delivery charges, not the fixed charge.
- Self-use versus export. When exports earn much less than imports cost, using more of your solar power at home, by running appliances, heating water or charging an EV in the daytime, shortens payback.
- Incentives. Rebates, tax credits and grants vary by country, state and year, and some have ended or changed recently. Enter only incentives you are sure you qualify for; check current rules with your tax authority and energy agency.
- Installed cost. Get several quotes and compare cost per watt (total cost ÷ system watts).
Costs not included
Inverters often need replacing once during a panel's life, and some systems need cleaning, monitoring or roof work. A battery adds cost and changes the self-use share. Financing adds interest. If you pay with a loan, compare the monthly saving with the loan payment rather than using the simple payback here.
Is a 10–15 year payback good?
Panels commonly carry 25-year performance warranties and often last longer, so a payback well inside that period means many years of savings afterwards. Another way to judge it is the return: savings divided by cost. In the example, first-year savings are about 7% of the cost, rising each year with electricity prices.
Testing the assumptions
Because the result depends on future prices, run a few scenarios. Set the price increase to 0% for a cautious view and 5% for a high-inflation view, lower the self-use share if you are out during the day, and raise the degradation rate to 0.8% for older or cheaper panels. If payback stays comfortably inside 25 years in the cautious case, the decision is robust; if it only works in the optimistic case, a smaller system or a better quote may be wiser.
Common mistakes
- Valuing every kWh at the retail rate when exports earn less.
- Assuming prices stay flat. Try 0% and 5% to see the range.
- Using a sales estimate of production without checking it. Compare it with PVWatts or PVGIS for your roof.
Estimates only, not financial advice. Incentive rules and tariffs change; check them for your location.
Frequently asked questions
How long do solar panels take to pay for themselves?
It depends on cost, sunshine and prices. A $20,000 system producing 10,000 kWh, with 70% used at $0.17 and exports at $0.08, pays back in about 12.2 years.
How do I calculate solar savings?
Self-used kWh × your electricity price + exported kWh × the export credit, adjusted each year for price rises and panel degradation.
Does exporting solar power save as much as using it?
Only under full net metering. Where export credits are lower than import prices, self-use is worth more.
Are solar panels worth it?
Often, when payback is well within the panels' 25-year-plus life. Test your own prices, production and incentives.
Sources
- National Renewable Energy Laboratory (nrel.gov). PVWatts Calculator.
- US Department of Energy, Solar Energy Technologies Office. Homeowner's guide to the federal tax credit for solar and solar financing.
- Ofgem (UK). Smart Export Guarantee (SEG).
- Energy Saving Trust (UK). Solar panels: costs and savings.
Last reviewed 27 October 2026. Results are estimates; see our disclaimer.