In short
- In the short term, your bill drops from the first month, and with batteries you have power during outages.
- In the long term, panels last about 30 years: once the investment is paid back, the energy they produce is almost free.
- With 3 kWp on a roof in Madrid and 2025 prices, the investment pays back in 3 to 7 years. In Miami, with US costs, in 12 to 28.
- What changes the result most is how much of that power you use yourself, your electricity price and what the installation costs.
Short-term benefits
- Your bill drops from the first month. Every kWh the panels produce that you use at that moment is a kWh you don’t buy.
- With batteries, you have power during outages. For the fridge, lights, chargers or a medical device. Work out how much battery you need with the power outage battery calculator, and see how long food lasts without power.
Long-term benefits
- They last a long time. The U.S. national energy laboratory (NLR, formerly NREL) assumes home solar systems last 30 years, producing 0.7% less each year.
- Once paid back, the power is almost free. Only maintenance remains: the same laboratory puts it at about 1% of the installation cost per year.
- They protect you from price rises. In the US, homes paid an average of 12.55 cents per kWh in 2016 and 17.30 in 2025, 38% more, according to the Energy Information Administration (EIA). The energy you produce yourself doesn’t go up in price.
Two examples with numbers
Both cases use the same maths as our solar savings calculator, with panels on a roof:
| Madrid, 3 kWp | Miami, 5 kWp | |
|---|---|---|
| Produced in year one | 4,766 kWh | 7,939 kWh |
| Electricity price (2025) | €0.27 per kWh | $0.173 per kWh |
| Installation cost | €3,600 (€1,200 per kWp) | $13,400 ($2,680 per kWp) |
| Savings in year one | €607 to €1,250 | $550 to $1,237 |
| Years to pay back | 3 to 7 | 12 to 28 |
| Savings over 30 years, after paying for it | €12,765 to €30,232 | $1,141 to $19,783 |
The higher figure is if you use all the power produced; the lower one, if you only use half. Where each figure comes from:
- Production: what 1 kWp gives per year according to the World Bank’s Global Solar Atlas (1,655 kWh in Madrid, 1,654 in Miami), 4% less for being on a roof. For example, in Madrid: 3 × 1,655 × 0.96 = 4,766 kWh.
- Electricity price: the 2025 average including taxes, from Eurostat for Spain (€0.27, for a home using 2,500 to 5,000 kWh a year; the EU average was €0.29) and from the EIA for the United States.
- Cost: in Europe, the Fraunhofer ISE research institute gives €900 to €1,500 per kWp for a 10 kWp rooftop system in Germany in 2024; we took 1,200, the midpoint. In the US, NLR estimates $2.68 per watt in 2023, and notes its figure tends toward the low end of what people pay.
Most importantly: these are examples. Get a quote and do the maths with your own figure.
What makes you save more or less
- How much of the power you use. Panels produce during the day, mostly around midday. What you use at that moment saves you the full price; the surplus that goes to the grid is paid at a lower rate, credited or not paid at all, depending on the country. Running the washing machine or dishwasher around midday helps you use more of it. Ask your power company how it works where you live.
- Your electricity price. The more expensive, the sooner it pays back. Where electricity is cheap or subsidised, it takes longer.
- Your city’s sunshine. The table of 24 cities shows 1 kWp gives from about 1,000 kWh a year in London to almost 1,900 in Guadalajara, Mexico.
- What the installation costs, and any incentives or tax breaks in your country.
- 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 for power during outages, not to save more.
- Shade on the roof, which can cut production a lot.
Before you decide
- Check your bill for how much you use per year and what you pay per kWh.
- Work out how many panels you need with the solar panel calculator.
- Get at least one quote from a qualified installer, and ask how you’ll be paid for surplus power.
- Run your own figures in the solar savings calculator.
To understand what the installation includes, see what’s in a solar kit.
Sources and references
- National Laboratory of the Rockies (NLR, formerly NREL), Annual Technology Baseline 2024. Residential PV.
- Eurostat. Electricity prices for household consumers (nrg_pc_204), second half of 2025, retrieved October 3, 2026.
- U.S. Energy Information Administration (EIA). Electric Power Monthly, Table 5.3, retrieved October 3, 2026.
- Fraunhofer ISE, July 14, 2026. Photovoltaics Report.
- Global Solar Atlas 2.0 (World Bank and ESMAP, data by Solargis). globalsolaratlas.info.
- CSIRO (Australian Government), 2021. Batteries for Homes.
Frequently asked questions
How many years do solar panels take to pay back?
It depends mainly on your electricity price, what the installation costs and how much of the power you use. With 3 kWp in Madrid, at €0.27 per kWh and €1,200 per kWp, 3 to 7 years. With 5 kWp in Miami and US costs, 12 to 28.
How long do solar panels last?
The U.S. national energy laboratory assumes home systems last 30 years, losing 0.7% of production per year. Batteries last less: 3 to 15 years, according to Australia’s CSIRO.
Is it worth adding batteries to save more?
Batteries add a lot to the cost and don’t last as long as the panels. People mainly add them for power during outages. To save, the first step is using power at the time the panels produce it: what you use at that moment saves you the full price.
