Solar Panel Degradation and Warranty Guide: How to Check Whether Your System Is Performing Normally

Overview

Solar panel degradation is the gradual reduction in a panel’s ability to produce electricity. It is measured against the panel’s rated output under laboratory conditions, not against the amount of energy your home receives on a particular day. A hot, cloudy, smoky, dusty, or shaded day can produce less energy without indicating permanent damage.

Most manufacturers publish two separate warranties: a product warranty and a performance warranty. The product warranty addresses defects in materials or workmanship. The performance warranty describes the minimum output the panel is expected to retain after specified periods. These terms differ by manufacturer and model, so the document supplied with your system is more useful than a generic industry assumption.

As a planning reference, many modern panels are sold with a first-year output allowance followed by a smaller annual reduction. A simple illustrative schedule using an assumed 1% first-year reduction and 0.4% annual reduction afterward would look like this:

This table is not a prediction or a warranty promise. It demonstrates why a modest, steady decline can be normal while a sudden drop deserves investigation. For a broader comparison of efficiency, warranty language, and real-world value, see the Solar Panel Comparison Guide.

What to track

Production data

Record monthly and annual energy production from your monitoring portal. If the system has multiple orientations, string-level monitoring, or module-level monitoring, save those figures separately. A system-wide total can hide one underperforming string or panel.

Do not compare a short cloudy month with a clear month from another year and call the difference degradation. Compare the same calendar month across multiple years, or compare production with a weather-adjusted expectation supplied by your installer or monitoring platform.

System conditions

Keep a simple log of events that may affect output:

• New or growing shade from trees, buildings, antennas, or seasonal foliage.
• Dust, pollen, bird droppings, snow, leaves, or other soiling.
• Storms, hail, nearby construction, or visible panel damage.
• Inverter alerts, communications failures, tripped breakers, and periods of grid outage.
• Changes to roof equipment or nearby structures.
• Cleaning, repairs, firmware updates, or electrical work.

Also record whether the monitoring app reports energy produced on the DC side of the system or energy delivered after inverter conversion. Those are different measurements. A battery may add further differences between solar production, battery charging, and energy delivered to the home.

Warranty information

Store the panel model, serial numbers, installation date, installer details, invoices, commissioning report, monitoring screenshots, and warranty documents in one folder. Check whether the performance warranty is measured per panel or across the system, and whether the manufacturer requires testing by an approved technician.

Useful questions include:

• What output level is guaranteed at each warranty milestone?
• Does the warranty cover labor, shipping, removal, or reinstallation?
• What evidence is required for a solar panel warranty claim?
• Are claims submitted to the manufacturer, installer, distributor, or another party?
• Are exclusions listed for shading, improper installation, unauthorized repairs, or environmental damage?

Cadence and checkpoints

A recurring review is more reliable than a single inspection. Use this schedule as a practical baseline:

• Monthly: Check for alerts, missing data, unusual zero-production periods, and obvious changes in daily production.
• Quarterly: Review the previous quarter against the same period in earlier years. Inspect from the ground for visible soiling, cracked glass, loose components, or new shade. Do not climb onto the roof unless you are qualified and the work can be done safely.
• Annually: Export a full-year production report, record the system’s cumulative energy, and compare the result with the installer’s original estimate after accounting for weather and system changes.
• After a severe event: Check monitoring alerts and arrange a professional inspection after hail, wind, flooding, fire, or other potentially damaging events.
• At warranty milestones: Re-read the performance warranty and confirm that your records are sufficient if output is approaching the stated threshold.

Monitoring portals can help, but they are not infallible. A communications failure may look like a production failure. If the app shows no data, check whether the inverter itself is operating and whether other household or utility systems are online. The Solar Monitoring Explained guide provides a useful framework for reading alerts and production graphs.

How to interpret changes

A gradual decline across the whole array

A small, consistent decline may align with the panel’s performance warranty, particularly when weather and shading are stable. Compare the trend with the exact warranty document before concluding that panels need replacement.

A sudden system-wide drop

A sharp change is more likely to involve an inverter fault, disconnected equipment, a tripped protective device, monitoring error, new shade, or a grid-related issue than ordinary panel degradation. Review alerts and ask a qualified solar professional to test the system.

One string or section underperforming

Localized underperformance can point to shading, a failed optimizer, a loose connection, a damaged panel, or a string-level issue. Module-level monitoring can narrow the location, but electrical diagnosis should be performed by a qualified technician.

Lower output after hot weather

Solar panels generally produce less power when operating at higher temperatures, even in strong sunlight. A hot spell can reduce short-term output without permanently accelerating degradation. Compare multiple periods and use weather-adjusted data rather than one day’s result.

Soiling and cleaning decisions

Cleaning may help when dirt or biological material is visibly blocking the panel surface, but it is not always necessary. Consider local rainfall, roof access, water quality, safety, and the likely production benefit. Never use abrasive tools or harsh chemicals without confirming that they are compatible with the panel manufacturer’s instructions.

Before filing a solar panel warranty claim, document the issue, avoid unauthorized repairs, and ask the installer what diagnostic evidence is required. A professional test may measure voltage, current, insulation, or panel performance under defined conditions. Monitoring data alone can identify a problem, but it may not prove that a panel has failed.

When to revisit

Revisit this guide each month or quarter when you review monitoring data, and complete a more detailed annual check after the year’s production report is available. Update your records whenever panels are cleaned, trees are trimmed, an inverter is replaced, a battery is added, or the roof is modified. Recheck warranty terms before contacting a manufacturer because claim procedures and covered components are specific to the product and installation documents.

Start with these actions:

1. Download the last 12 months of production data.
2. Write down the panel and inverter models, installation date, and warranty thresholds.
3. Compare the same months across years, noting weather, shade, outages, and soiling.
4. Check the monitoring portal and inverter for alerts or missing data.
5. Photograph visible issues from a safe location and save relevant reports.
6. Contact the installer or a qualified technician if the decline is sudden, localized, or persistent.
7. File a warranty claim only after confirming the required evidence, testing method, and responsible party.

Keeping a consistent record makes it easier to distinguish normal solar panel output over time from a repairable fault. It also gives you better information when comparing maintenance costs, inverter replacement, future storage, or the long-term value of your home solar system.