Panels do not stop working at a certain age. They gradually produce a little less each year. The practical answer is decades, and the part that will need replacing sooner is the inverter.
What degradation means
A panel’s output falls slightly each year. Manufacturers state this as an annual degradation rate on the datasheet, and back it with a performance warranty guaranteeing a minimum output after a given number of years.
Two things to understand:
- The loss is gradual and small annually. It only becomes noticeable over a long period.
- Panels often see a slightly larger drop in the first year, then settle into a slower steady rate. The datasheet usually distinguishes the two.
What that means in practice
A panel still producing the large majority of its original output after 25 years is doing what it was sold to do. It has not failed and it does not need replacing. It simply produces a little less than it did.
Most systems installed today will still be generating usefully well beyond their warranty period. The panels are generally the most reliable part of the installation.
What actually fails first
The inverter It contains electronics working hard every day, and its warranty is typically shorter than the panels’ for that reason. Budget for replacing it at some point during the system’s life and ask what one costs. See choosing an inverter.
Connectors and cabling, occasionally, particularly where the original work was rushed. This is a workmanship issue rather than a product one, which is why the workmanship warranty matters. See warranties.
Battery capacity, if you have one. Batteries lose usable capacity with use and their warranties are often stated in cycles or throughput rather than years. See solar batteries.
Mounting and flashings, if not done well. The failure you notice is water coming through the roof, not a drop in generation.
What accelerates degradation
- Heat. Less of a problem in Britain than almost anywhere.
- Poor ventilation behind the panels. In-roof mounting runs hotter than standard mounting on rails.
- Physical damage. Storm debris, or somebody walking on them.
- Manufacturing defects, which show up early and are what the product warranty is for.
Not much of this is within your control, which is the point. Panels are mostly a fit-and-forget item.
How to spot a problem
Look at your monitoring occasionally. Compare a year against the previous year rather than a month against last month, because month-to-month variation is weather rather than degradation.
A sudden drop is a fault, not degradation. Degradation is slow. A step change means something has broken, usually the inverter or a connection, and it is worth chasing rather than accepting.
The most expensive failure mode in domestic solar is a system that quietly stops producing and nobody notices for a year.
What happens at the end
Panels reaching the end of their useful life can be recycled. There is a growing UK recycling route for photovoltaic panels, and manufacturers and importers carry obligations for end-of-life handling under electrical waste rules.
It is not something you need to plan for now, but it is worth knowing the answer is not landfill.