Degradation rate
The gradual annual loss of a PV module power output over its life, typically around 0.5% per year for crystalline silicon.
PV modules lose output slowly because of material changes in cells, encapsulant, backsheet and interconnects. Degradation is expressed as a percentage of initial rated power lost per year.
where d1 is first-year degradation and d the annual rate thereafter. A meta-analysis of about 2,000 field measurements by NREL (Jordan and Kurtz, 2013) found a median of 0.5%/yr for crystalline silicon; newer studies of modern fleets report 0.5–0.8%/yr, with hot climates at the upper end.
Typical warranty terms (2025):
- p-type PERC: 2% in year one, then about 0.55%/yr, 84–85% after 25 years.
- n-type TOPCon: 1% then 0.4%/yr, about 87–89% after 30 years.
- HJT: 1% then 0.25–0.4%/yr.
Main mechanisms:
- Light-induced degradation (LID) and LeTID in p-type cells.
- Potential-induced degradation (PID) from high system voltage.
- UV-induced degradation in some n-type cell designs.
- Encapsulant browning, delamination, backsheet cracking, solder fatigue and cell microcracks.
Degradation reduces lifetime energy by roughly 6–10% versus a no-loss case over 25–30 years and is a standard input to LCOE and yield models.
Related terms
All terms →- PERC (Passivated Emitter and Rear Cell)
A silicon cell design that adds a passivating dielectric layer to the rear surface, reducing recombination and reflecting light back into the cell.
- TOPCon
Tunnel Oxide Passivated Contact: an n-type silicon cell whose rear uses an ultra-thin oxide and doped polysilicon layer to extract current with minimal recombination.
- Heterojunction (HJT) solar cell
A cell that sandwiches an n-type crystalline silicon wafer between ultra-thin amorphous silicon layers, giving very high voltage and a low temperature coefficient.
- LCOE (Levelized Cost of Electricity)
The constant price per MWh that recovers all lifetime costs of a power plant, discounted to present value, divided by its discounted lifetime output.
- Performance ratio
Ratio of actual AC energy output to the theoretical output implied by plane-of-array irradiation and nameplate capacity; a location-independent quality metric for PV plants.