Module degradation: what a 25-year performance warranty really means

Solar module datasheets often advertise long performance warranties. Owners sometimes read these as guarantees that output will stay high for decades. The reality is more specific: modules do lose output over time, and the warranty defines how much loss is acceptable and what remedy applies if the loss is greater.

Why modules degrade

Modules are exposed to sunlight, heat, humidity, temperature cycling and mechanical stress for decades. Over time this causes:

• Gradual loss of cell efficiency
• Discolouration or delamination of encapsulants
• Cracks in cells (sometimes invisible to the eye)
• Corrosion of internal connections
• Degradation of backsheets

Some losses occur early in a module's life; others accumulate gradually. The rate depends on module technology, manufacturing quality, installation practice and climate — hot, humid conditions tend to be harder on modules.

Two different warranties

The performance warranty typically specifies a guaranteed output for the first year and a maximum annual decline after that. Check the exact figures and conditions in the manufacturer's warranty document — not just the datasheet summary.

What a performance warranty does not cover

Read the exclusions carefully. Common ones include:

• Damage from improper installation, handling or cleaning
• Soiling, shading or environmental factors
• Damage from extreme weather or force majeure
• Use outside the specified operating conditions
• Modules moved or modified after installation

Making a claim

A warranty is only as useful as your ability to prove a claim. That requires:

• Baseline data — flash test results and serial numbers from delivery
• Monitoring records showing performance over time (performance ratio and availability)
• Testing — field measurements or laboratory flash tests on sample modules
• Diagnostic imaging — thermal or electroluminescence imaging to find cracks and hot spots

The burden of proof usually sits with the owner. Without baseline data and good records, claims are hard to pursue.

The manufacturer behind the warranty

A long warranty is only as reliable as the company standing behind it. Owners and lenders consider the manufacturer's financial strength, track record, and whether the warranty is backed by insurance or a local entity.

Building degradation into planning

Energy yield models and financial models should include a realistic degradation assumption over the project life. Underestimating degradation overstates long-term revenue.

Common types of degradation

• Light-induced degradation — an initial drop in output when modules are first exposed to sunlight, typically stabilising afterwards.
• Potential-induced degradation (PID) — output loss linked to voltage differences between cells and the frame, more likely in hot, humid conditions; mitigated through design and module selection.
• Cell cracks and micro-cracks — caused by handling, transport, installation or weather; often invisible without imaging.
• Hot spots — localised heating from damaged cells, shading or soiling, which can accelerate damage.
• Encapsulant browning and delamination — material ageing that reduces light reaching the cells.
• Backsheet degradation — cracking or chalking that can compromise insulation and safety.

Inspection practices

Periodic inspections help catch problems early:

• Visual inspections for broken glass, discolouration, delamination and frame damage
• Thermal (infrared) imaging to find hot spots and faulty cells or connections
• Electroluminescence imaging to reveal micro-cracks
• I-V curve testing on sample strings to measure performance against specification

Inspections at delivery, after installation and periodically during operation build the evidence needed for warranty claims.

Questions to ask before buying modules

• What exactly does the performance warranty guarantee, year by year?
• What are the exclusions?
• Who stands behind the warranty locally, and how are claims made?
• What testing and certification do the modules have?
• What do independent test results show for this model?
• Do the modules meet current procurement requirements for the project?

Handling and installation

Many problems that later appear as "degradation" are actually caused during transport and installation. Careful handling, correct storage on site, proper installation and avoiding foot traffic on modules all protect long-term performance.

Keeping the evidence

Keep delivery documents, flash test reports, serial number lists, commissioning test results and every inspection report in one place for the whole warranty period. Warranty claims may arise many years after construction, often after the people involved have moved on. A well-kept project documentation file is what makes a claim possible.

How we help

Through O&M coordination and project advisory, we help owners keep the records and testing data needed to protect warranty rights, and to separate true degradation from fixable losses like soiling or faults.