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How Long Do Solar Panels Last on a Roof?
Solar panels usually lose output gradually. The roof, inverter and panels can need attention at different times, so useful life is a maintenance decision as well as a warranty question.
How long can a rooftop solar system keep working?
DOE describes a 20–30-year PV system lifespan in its longevity guidance. This is a planning horizon, not a fixed retirement date. Roof condition, damage, equipment support and useful generation all affect the decision to keep operating or replace parts.
Model output over time
Start with measured first-year generation and the degradation assumption in your module documents. The sample 0.5% annual decline illustrates the gradual-loss approach used in published PV research; real systems vary.
What does panel degradation mean?
This model uses year-N generation = first-year generation × (1 − degradation rate)^(N − 1). With 10,000 kWh in year 1 and a 0.5% annual decline, year 25 is about 8,867 kWh. Weather variation and shading can obscure small annual changes. This model does not diagnose equipment faults or include a separate first-year loss.
Panel warranty, inverter and roof: three different clocks
- Panel warranty: read the product and performance warranties separately, including remedy, labour coverage and exclusions.
- Inverter: check its warranty, failure alerts and replacement availability. A panel life assumption does not guarantee the inverter lasts as long.
- Roof: ask whether roof repairs or replacement are likely during the project life, and get a removal/reinstallation allowance in writing.
Investigate a drop before replacing panels
Compare production over similar seasons and check monitoring alerts. New shade, a disconnected string, inverter downtime or dirt can look like aging. Ask an appropriately qualified solar professional to investigate unexpected losses; do not access rooftop electrical equipment yourself.
When does replacement make financial sense?
Compare the cost to repair the existing system against the additional useful energy and roof work involved in replacement. An older panel that still produces useful electricity is not automatically worthless. Use your utility's import/export prices and allow for inverter replacement and maintenance when reviewing payback.