Work out what your home uses, what it costs and what it needs

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How much do you save with solar panels?

Enter how many kWp you want to install, where you live, what you pay for electricity and what the installation costs. We’ll tell you how much you save per year, how many years to pay it back and what you save over 30 years.

Not sure how many? Work it out with the solar panel calculator.

Filled in when you pick a city (World Bank’s Global Solar Atlas).

Check your bill: the total divided by the kWh. €0.27 is Spain’s 2025 average (Eurostat); the US average was $0.173 (EIA).

Ideally, your quote. 1,200 is the middle of Fraunhofer ISE’s range for Germany (€900 to €1,500); the US benchmark was $2,680 (NLR).

🔒 The maths runs on your own phone or computer. We don’t store or send your data.

What you save

Produced in year one
—
dropping 0.7% a year
Installation cost
—
If you use it allIf you use half
Savings in year one——
Years to pay back the investment——
Savings over 30 years, after paying for it——

“Using it” means consuming the power while the panels produce it, or your power company paying you the same price it charges you. What you don’t use is paid at a lower rate or not at all: ask how it works in your country. Based on today’s electricity prices; if they rise, you save more.

How it’s worked out

  1. What the panels produce in year one = kWp × what 1 kWp gives per year in your city, according to the World Bank’s Global Solar Atlas, and 4% less on a roof (as in the Atlas’s own examples).
  2. Each year they produce a little less: the U.S. national energy laboratory (NLR, formerly NREL) assumes they lose 0.7% a year and that the system lasts 30 years.
  3. Maintenance (cleaning, insurance, the odd repair) costs about 1% of the installation price each year, using the ratio the same laboratory uses.
  4. Each year’s savings = power produced × what you pay per kWh × the share you use − maintenance.
  5. Years to pay back: when those savings add up to what the installation cost.

With what the calculator loads when you open it (3 kWp on a roof in Madrid, 0.27 per kWh and 1,200 per kWp): the panels produce 3 × 1,655 × 0.96 = 4,766 kWh in year one, which at 0.27 is 1,287. The installation costs 3 × 1,200 = 3,600, plus about 37 a year for maintenance. If you use all that power, you save 1,250 in year one and pay it back in 3 years; if you only use half, you save 607 and pay it back in 7, because the panels produce a little less each year.

Why we give two figures

Panels produce during the day, mostly around midday. The power you use at that moment saves you the full price. The surplus that goes to the grid, depending on the country and the company, is paid at a lower rate, credited on your bill or not paid at all. So real savings usually fall between the two columns. Ask your power company how it works where you live.

What it doesn’t account for

  • Batteries. They add a lot to the cost and don’t last as long as the panels: 3 to 15 years, according to Australia’s CSIRO. People mainly add them to have power during outages.
  • Incentives and taxes in each country, which can lower the cost.
  • Electricity price changes. In the US, for example, homes paid an average of 12.55 cents per kWh in 2016 and 17.30 in 2025, according to the EIA.
  • Shade and your roof’s direction: see how much solar panels produce.

Sources