Solar Panel Degradation Tracker

Understanding Solar Panel Degradation

Solar panels are among the most durable electricity-generating technologies available today, routinely operating for three decades or more with minimal maintenance. However, no energy technology is immune to the passage of time. Every photovoltaic module gradually loses a small fraction of its power output each year through a process known as degradation. Understanding this process is essential for homeowners, commercial operators, and project financiers who need to forecast long-term energy production and financial returns.

Degradation does not mean that a solar panel suddenly stops working. Instead, the cells within each module produce slightly less electricity with each passing year. The widely cited industry average is roughly 0.5% per year, meaning a panel retains about 87.5% of its original capacity after 25 years. High-performance modules from premium manufacturers can hold that figure above 90%, while lower-cost panels may dip to around 80% over the same period. This tracker lets you model your own system using the actual degradation rate appropriate for your panels.

What Causes Solar Panels to Degrade?

Several physical and environmental mechanisms contribute to the gradual loss of output in photovoltaic modules. Light-induced degradation (LID) occurs during the first hours of sun exposure and typically accounts for a 1-3% drop in power. After that initial period, the ongoing mechanisms include:

• UV exposure: Ultraviolet light slowly breaks down the encapsulant material that protects solar cells, leading to discoloration and reduced light transmission over many years.
• Thermal cycling: Daily temperature swings cause repeated expansion and contraction of cell materials, solder joints, and interconnects, eventually producing micro-cracks that increase electrical resistance.
• Humidity and moisture ingress: Even with sealed edges, tiny amounts of moisture can penetrate the module laminate over decades, corroding metallization and reducing cell performance.
• Potential-induced degradation (PID): High system voltages can drive ion migration within cells, causing significant power loss if panels are improperly grounded or lack PID-resistant design.
• Mechanical stress: Snow loads, wind uplift, and hail impacts can create micro-fractures that slowly worsen over time, particularly if mounting structures allow excessive flexing.

Degradation Rates by Panel Technology

Different photovoltaic technologies exhibit different degradation profiles. Monocrystalline silicon panels, the most common residential technology, typically degrade at 0.3-0.5% per year. Their high purity silicon and advanced cell architectures, such as PERC and heterojunction (HJT), provide excellent long-term stability. Polycrystalline (multicrystalline) panels generally degrade slightly faster, at 0.4-0.7% per year, due to the grain boundaries within their silicon structure that can act as recombination sites. Thin-film technologies like cadmium telluride (CdTe) and copper indium gallium selenide (CIGS) have historically shown higher degradation rates of 0.5-1.0% per year, although modern formulations have narrowed this gap considerably. Amorphous silicon thin-film panels experience an initial rapid degradation phase called the Staebler-Wronski effect, where output can drop 10-15% in the first year before stabilizing at a lower but relatively steady output level.

How Manufacturer Warranties Work

Solar panel warranties come in two forms: a product (or materials) warranty and a performance (or power output) warranty. The product warranty covers manufacturing defects and premature failure, typically lasting 10 to 25 years depending on the manufacturer. The performance warranty guarantees that the panels will still produce a minimum percentage of their rated power at the end of the warranty period.

For example, SunPower offers a 40-year warranty guaranteeing 92% of original output, one of the longest and strongest in the industry. Most tier-one manufacturers provide 25-year performance warranties guaranteeing between 80% and 92% of rated power. If independent testing demonstrates that a panel has degraded faster than the warranty allows, the manufacturer is obligated to repair, replace, or refund the affected modules. It is important to retain your purchase documentation and have your system professionally tested if you suspect excessive degradation.

Signs Your Panels Are Underperforming

While gradual degradation is normal, sudden or excessive drops in production may indicate a problem beyond ordinary aging. Key warning signs include a month-over-month decline in production that exceeds what seasonal changes can explain, visible hot spots or browning of the encapsulant, cracked glass or delamination along panel edges, inverter error codes or frequent tripping, and a noticeable discrepancy between your monitoring data and the expected output predicted by tools such as PVWatts. If your monitoring system shows a year-over-year decline greater than 1-2% after accounting for weather variability, it is worth scheduling a professional inspection. Infrared thermography can reveal hidden hot spots and micro-cracks that are invisible to the naked eye.

Extending Your Solar Panel Lifespan

Although some degradation is inevitable, homeowners can take proactive steps to maximize the productive life of their solar panels. Keeping panels clean is one of the simplest and most effective measures. Dust, pollen, bird droppings, and leaf debris reduce light reaching the cells and can cause localized heating that accelerates wear. In most climates, rain provides adequate cleaning, but panels in arid or dusty regions benefit from an annual rinse with plain water and a soft brush.

Ensuring adequate ventilation beneath the panels is equally important. Solar cells lose efficiency at elevated temperatures, and poor airflow can cause panels to run 10-20 degrees Celsius hotter than well-ventilated installations. Roof-mounted systems should maintain the manufacturer-recommended gap between the panel and the roof surface. Trimming overhanging tree branches prevents physical damage from falling limbs and reduces shading, which can trigger bypass diode activation and create uneven wear patterns across the array.

Scheduling an annual inspection by a certified solar technician helps catch problems early. Technicians check electrical connections for corrosion, verify that racking hardware is secure, inspect for cracked cells or delamination, and confirm that the inverter and monitoring system are functioning correctly. Many installers offer maintenance plans that include annual inspections, cleaning, and priority service if issues arise.

When to Consider Panel Replacement

The decision to replace aging solar panels involves balancing remaining output against the cost and performance gains offered by newer technology. A common rule of thumb is to begin evaluating replacement options once panels drop below 80% of their original rated capacity. At that point, the loss in annual production may justify investing in modern modules that offer significantly higher efficiency and better degradation characteristics.

For a typical 8 kW system with a 0.5% annual degradation rate, the 80% threshold is reached around year 45, well beyond the standard 25-year warranty period. However, panels with higher degradation rates, such as 1% per year, may reach this threshold in as few as 22 years. Replacement becomes especially attractive when new panels offer meaningful efficiency improvements. If your original panels were rated at 15-17% efficiency, modern modules offering 22-24% efficiency could produce 30-50% more power from the same roof area, dramatically improving your energy economics.

Other factors that may trigger earlier replacement include physical damage from a severe weather event, the need to reroof (since panels must be removed and reinstalled anyway), or the desire to add battery storage that integrates better with newer inverter technology. In all cases, a cost-benefit analysis comparing the remaining value of existing panels against the projected returns from a new system will guide the decision.

Monitoring Your System Performance

Effective monitoring is the foundation of long-term solar system management. Most modern inverters include built-in monitoring portals that report daily, monthly, and annual production data. Microinverter and power optimizer systems provide panel-level monitoring, making it easy to identify individual underperformers. Comparing your actual production against expected values from the NREL PVWatts calculator gives you an objective benchmark. Track your system's performance ratio (actual production divided by theoretical maximum) over time. A healthy system typically maintains a performance ratio between 75% and 85%. If this ratio drops below 70% after accounting for seasonal and weather variations, further investigation is warranted.

For systems without built-in monitoring, aftermarket energy monitors can be installed at the main electrical panel to track solar production independently. Some utility companies also provide production data through their smart meter portals. Regardless of the monitoring method, the key is consistent tracking. Recording monthly production figures in a spreadsheet or dedicated app creates a valuable historical record that makes it easy to spot trends and anomalies over the life of the system.

By understanding degradation, choosing quality equipment, and maintaining your system properly, you can ensure that your solar investment continues to deliver strong returns for decades. Use the tracker above to model your own system and see exactly how your panels are projected to perform over time.