Solar Module Degradation Rate: PERC, TOPCon, HJT 25-Year Performance

Definition

Module degradation rate is the annual percentage decline in PV module power output over its operating lifetime. Typical 0.4–0.7%/year for modern modules; cumulative loss 88–90% at year 25.

Degradation Rates by Technology (2024)

Technology	Annual Rate	Year 25
Standard PERC	0.55–0.70%	85%
Premium PERC	0.45–0.55%	88%
TOPCon	0.40–0.50%	89%
HJT	0.25–0.35%	92%
Premium HJT	0.20–0.25%	95%

Why Degradation Rate Matters in Design

Degradation is not a single event — it is a slow, cumulative decline driven by UV exposure, thermal cycling, microcracks, and encapsulant aging, compounding year over year for the life of the plant. Because it compounds, small differences in assumed rate translate into large differences in year-25 output. That is why degradation rate is never treated as an afterthought in the simulation software used to model a PV module’s output over time — the assumed rate is carried through the same run that produces P50 energy estimates and feeds directly into LCOE and kWh/kWp figures used to price a bid or size a loan.

Worked Example

Take a TOPCon module degrading at 0.45%/year, generating 100 units of energy in year 1. Using the standard model — Energy at year N equals year-1 energy multiplied by (1 − rate) raised to (N − 1) — year 25 output works out to roughly 90% of year 1, in line with the 89% shown in the table above for TOPCon technology. Run the same formula at 0.65%/year (standard PERC) and year-25 output drops closer to 86–87%. Over a 25-year PPA, that few-percentage-point gap in retained output is exactly what an EYA is built to catch before it becomes a financing problem.

Key Takeaways

Module degradation = annual power decline.
0.4–0.7%/yr modern modules; HJT lowest.
Year-25 cumulative: 85–95% of original.
Required input for LCOE and EYA calculations.
Premium HJT carries lower-degradation warranties.

Degradation rate only turns into a real number once it is run through a full energy yield model — the same modeling work that underpins the Complete Guide to Solar Design Services in India, where EYA and PVsyst deliverables are covered in more depth. On the financing side, degradation assumptions move project economics the same way engineering inputs move competitive bids, as shown in SECI Tariff Math — How Engineering Inputs Move Bids by 4 Paise/kWh. If you’re evaluating who builds these yield models for your portfolio, How to Choose a Solar Design Partner lays out the questions worth asking about degradation and warranty assumptions before signing off on a design partner.

Frequently Asked Questions

5 commonly searched questions about Degradation Rate.

What is degradation rate?

Annual fractional power decline of PV modules. Typical 0.4–0.7%/year. Result of UV exposure, thermal cycling, microcracks, encapsulant aging, cell degradation.

What's the warranty?

Linear power warranty: year 1 ≥ 98%, year 25 ≥ 80–85%. Premium TOPCon/HJT: year 25 ≥ 87%.

How is degradation modeled?

PVsyst applies cumulative annual rate. Energy_year_N = Energy_year_1 × (1 − rate)^(N-1). 0.5%/yr gives 89% at year 25.

Newer modules degrade slower?

Yes. PERC: 0.55–0.70%/yr. TOPCon: 0.40–0.50%/yr. HJT: 0.25–0.35%/yr.

Why does degradation rate matter for project financing?

Lenders and PPA counterparties size 25-year revenue off the energy yield forecast, and degradation rate is a direct input to that forecast. A module modeled at 0.7%/yr instead of 0.4%/yr produces meaningfully lower cumulative generation by year 25, which lowers LCOE-based bid competitiveness and can affect debt sizing in an EYA-backed financial model.