Large-scale BTU study shows: solar panels last longer than previously thought

The study “From shine to decline: Degradation of over 1 million solar photovoltaic systems in Germany”, published in *Energy Economics*, is based on data collected over 16 years from more than 1.25 million PV systems with a total installed capacity of 34 GW – a dataset that is unprecedented in terms of scope, quality and duration.

Key findings:

• Annual power decline: PV systems lose 0.52–0.61 per cent of their power per year, roughly half of previous estimates.
• Slower power loss with age: Older systems lose less power per year than newer ones.
• Environmental factors influence performance: Extreme heat, frost and air pollution reduce electricity production. Rain has little effect.
• Smaller systems last longer: Smaller systems lose output more slowly than large, complex systems – an important consideration when planning large-scale solar projects.

BTU Professor Felix Müsgens, chair of Energy Economics, explains: “Our study shows that solar installations supply electricity reliably for longer than previously assumed. For investors, planners and the energy transition, this means: PV is an economically attractive technology that generates electricity reliably for decades.”

Why the results are important

• Higher returns: Less power loss means greater electricity production over the system’s lifetime and lower levelised cost of electricity – around 4.8 per cent cheaper than previous estimates.
• Better planning: The data helps planners to calculate modernisations, replacement cycles and investments more accurately.
• Environment and climate: Reduced air pollution increases energy yield. At the same time, the study shows that more frequent hot days have a greater impact on the performance of older systems.

What the researchers did

Research group leader Dr Christin Hoffmann explains: “We compared the actual electricity production of the annexes with theoretical values based on actual solar radiation and the characteristics of the annexes (size, tilt, orientation). Thanks to the excellent data available and with the help of statistical methods, we were then able to show how much performance loss is caused by ageing itself and how much by environmental conditions.

“Solar energy is expanding rapidly and has a longer lifespan than expected,” says BTU scientist Diego Alejandro Prieto Melo. “An analysis of over a million real-world PV systems shows that the annual power loss is only around 0.59 per cent – significantly less than many earlier assumptions. This is good news for homeowners, investors and the solar industry as a whole, as it also means that the ageing costs of solar installations will be approximately €638 million per year lower than previously thought by 2040.”

Conclusion

The results show that solar installations are reliable, profitable and durable. Even after 20 years, they still deliver around 90 per cent of their output compared to the first year, which simplifies modernisation cycles and investment decisions. The results thus strengthen confidence in the solar-driven energy transition in Germany.