In short
Remaining useful life is the time during which the system can still be operated sensibly, technically and economically. It ends at the first hard limit: roof renovation, end of lease, mounting structure or the year from which costs exceed revenue.
What limits remaining useful life
| Component or factor | What we look at |
|---|---|
| Modules | degradation from measured data, delamination, cell cracks, PID, hotspots |
| Inverters | age, fault history, spare parts; replacement usually after 10 to 15 years |
| Mounting structure | corrosion, clamps, statics, ballast |
| Roof | condition of covering, upcoming renovation, sealing at penetrations |
| Cabling, connectors | insulation values, connectors, UV damage, fire safety |
| Contracts | term of roof use or lease, removal obligations |
| Economics | year from which costs exceed revenue, usually after the tariff ends with full feed-in |
Technical and economic useful life
Many modules run for 30 years and longer. Economically, operation often ends earlier: after the tariff ends, 4 to 5 ct/kWh with full feed-in barely covers maintenance, insurance and metering. In our worked example a 250 kWp system only just covers its costs after 2031. With self-consumption the picture changes: the 10 kWp system from 2012 remains economic until the end of its technical life.
The 20-year depreciation period under German tax law has nothing to do with either. It only determines depreciation.
Effect on value
Five years less useful life cost considerably more value for systems with high self-consumption than for full-feed-in systems after the tariff ends. The evaluation from the calculator shows the effect of a useful life five years shorter in its sensitivity analysis.
Frequently asked questions
How long does a PV system last?
Modules often 30 years and more, inverters usually 10 to 15 years. The system as a whole runs as long as roof, mounting, contracts and economics allow.
How is remaining useful life determined?
By inspecting the individual components on site, analysing yield data, checking roof and contracts and an economic calculation that shows the year from which operation no longer pays.