How to Your Solar Panels Need Repair or Replacement | 3 Signs

There are three key points to determine if a panel needs repair or replacement: a sudden drop in energy production exceeding 20% (after excluding shading);

visible physical damage such as cracks or burn spots on the surface; and usage exceeding 25 years. Regular testing ensures the system operates safely and efficiently.

Significant Drop in Energy Production

Comparing Energy Output

Common monocrystalline silicon modules experience an initial degradation (LID) of 2.5% to 3% in the first year of use, after which the annual linear degradation rate should remain around 0.4% to 0.6%.

If you check the monitoring system's history curve and find that the average daily power generation in July has dropped from 35 kWh last year to 28 kWh this year, a 20% decrease, this clearly exceeds the normal physical loss range of 0.5%.

By comparing with neighboring power stations installed in the same area and at the same tilt angle (e.g., 30 degrees), if your system's power generation per kilowatt (kW) is more than 15% lower than theirs, it indicates that at least 2 panels in your string array of 10 or 20 panels have a power mismatch.

· The rated power output of monocrystalline silicon modules after 10 years of operation should not be lower than 90.5% of the factory nominal value.

· If the measured power of a 500W panel is below 420W under a standard light intensity of 1,000W/㎡, the efficiency loss has reached 16%.

· Comparing the monthly peak power points (Pmax) over 12 months, if the fluctuation deviation exceeds 8.5%, the DC wiring terminals need to be checked.

· In the total power generation benefit model over a 25-year cycle, an additional 1% annual degradation will lead to a 12% to 18% shrinkage in net profit.

· The sampling frequency of the monitoring APP should be set to 5 minutes/time to capture transient voltage drops within 300 milliseconds.

Calculating Aging Loss

Potential Induced Degradation (PID) is the main cause of significant power drops in the middle and late stages. It can cause the conversion efficiency of the entire string of panels to plummet from 21% to 11.5% or even lower within 2 to 3 years.

When the leakage current between the module frame and the silicon wafer escapes through the tempered glass surface, the accumulation of charge causes the parallel resistance of a single cell to drop from 500 ohms to below 50 ohms.

High humidity environments (RH > 80%) and high DC operating voltages (> 600V) accelerate this process, resulting in a power deficit of 15% to 25% after 5 years of service.

· Power loss caused by the PID effect is usually not obvious in the first 12 months of the system, but it will break out intensively in the 36th month.

· Using a PID repair device can allow damaged panels to recover approximately 95% of their original output within 48 hours.

· If the insulation resistance of the module backsheet is lower than 40 megohms (MΩ), leakage loss will account for 2% to 4% of the total output.

· If 10% of the anti-reflective coating (ARC) on the silicon wafer surface peels off, the photon absorption rate will decrease by 7.5%, directly lowering the short-circuit current.

· Due to the yellowing of the encapsulation material EVA, the light transmittance of a 20-year panel will drop by 5% to 8%, corresponding to a power loss of about 25 W.

Checking for Shadow Shading

Even if only 3% of the panel area is covered by tree shadows or dust, if this part of the shadow happens to block a string of cells, the bypass diode will activate and force the current to bypass, causing 33% of the module's voltage to disappear instantly.

In a system with 10 panels connected in series, the conduction of one panel's diode will reduce the total system voltage from 400V to about 367V, which will cause the inverter's Maximum Power Point Tracking (MPPT) efficiency to drop by 2% to 5%.

Long-term partial shading produces high-temperature spots exceeding 85 degrees Celsius. This thermal stress causes micro-cracks of 5 to 10 microns in the silicon wafer.

· A 0.5 square meter shadow formed by a rooftop chimney can cause a 5 kW system to reduce production by 2.5 kWh of electricity per day.

· If dust 1 mm thick accumulates on the panel surface, the light transmittance will decrease by 12% to 15%. After cleaning, the power generation can be instantly increased by 10%.

· The turn-on threshold of a bypass diode is usually between 0.5V and 0.7V. Excessive action frequency will shorten its 15-year design life.

· The sweep area of the bracket shadow on the winter solstice is 3.5 times larger than on the summer solstice, so a 20% seasonal power loss in December must be accounted for.

· Although micro-cracks are invisible to the naked eye, if the broken grid area shown under EL testing exceeds 10%, the loss is extremely high.

Monitoring Conversion Efficiency

The weighted efficiency (Euro Efficiency) of an inverter is usually between 97.5% and 98.3%. However, if the DC input voltage is lower than the MPPT startup threshold (e.g., lower than 150 V), the inverter will not be able to work in the optimal efficiency range, causing 5% to 10% of the energy to be lost as heat.

When the ambient temperature exceeds 35 degrees Celsius, due to the negative temperature coefficient of the silicon wafer (usually -0.35%/℃), the panel's operating temperature will rise to 65 degrees Celsius, causing the output of a 500W panel to drop to 447.5W.

If the inverter's cooling fan speed is lower than 2500 RPM at this time, the internal capacitor life will be shortened by 50%, and the conversion loss will increase by another 3%.

· If the contact resistance of the circuit breaker in the DC distribution box is greater than 10 milliohms, it will produce a power loss of 1 watt per hour at 10A current.

· If the MPPT tracking accuracy of the inverter is lower than 99.8%, it will cause the system to lose 3.5% of power generation revenue in cloudy weather.

· If the DC/AC ratio exceeds 1.4, a clipping loss of 5% to 15% will occur at noon.

· If a 4 square millimeter AC cable is selected instead of 6 square millimeters, the voltage drop loss over a 30-meter length is about 1.2%.

· For every 1 degree Celsius rise in ambient temperature, the Performance Ratio (PR value) of the PV system usually drops by 0.4%.

Visible Physical Damage

Fracture Cracks

The outermost layer of a solar panel usually uses 3.2 mm thick ultra-white tempered glass, which is designed to withstand the impact of hailstones with a diameter of 25 mm and a speed of 23 m/s.

However, when encountering snow loads exceeding 5400 Pa or extreme wind pressures of 2400 Pa, visible spider-web-like cracks may appear on the glass surface.

Even if the cracks are as thin as a hair, moisture will penetrate the EVA encapsulation material through the siphon effect within 48 hours, causing the system's insulation resistance to drop rapidly from a normal 1,000 megohms (MΩ) to below 50 megohms (MΩ).

This damage not only causes an increase in leakage current but also triggers a "low insulation impedance" alarm at the inverter, causing the entire 5 kW system to shut down completely on rainy days.

Large Yellow Spots

If yellow, brown, or even black spots appear on the surface of the panel, it is usually due to high-temperature hot spots caused by the failure of internal cells turning into "loads."

Under Standard Test Conditions (STC), the panel operating temperature is about 45 degrees Celsius, but the instantaneous temperature in the hot spot area will soar to 120 or even 150 degrees Celsius.

This violent temperature difference causes the chemical decomposition of the EVA encapsulation material, producing acetic acid and corroding the silver paste grid lines, reducing the Fill Factor (FF) of a single module from 0.78 to below 0.55.

If 3 out of 72 cells in a module show severe yellowing, the output voltage of the entire panel will drop by about 4.5 volts (V), directly dragging down the power generation revenue of the entire string by 15%.

Bubbling

Delamination manifests as white or transparent bubbles between the glass and the cells, meaning the encapsulation adhesion has fallen below the industry standard of 40 N/cm.

Bubbles change the refraction path of light entering the silicon wafer, causing the absorption rate of effective photons to drop by 8% to 12%.

More seriously, the air trapped inside the bubbles will produce condensation due to temperature differences, expanding continuously during the freeze-thaw cycles of winter and summer, causing the bubble area to expand at a rate of 15% per year.

When the delaminated area covers more than 10% of the total cell area, the rated life of the module will be shortened from 25 years to less than 12 years, entering the failure cycle early.

Corroded Frames

The aluminum alloy frame of a solar panel is usually anodized with a thickness of over 15 microns (μm) to resist acid rain and salt spray.

If you find obvious white oxidation spots, deformation, or even sealant peeling on the frame, it means the mechanical strength of the frame can no longer be guaranteed.

In a level 12 gale (wind speed about 33 m/s), the pull-out resistance of a damaged frame will drop by more than 25%, making it very easy for the panel to fall off the bracket and fly away.

In addition, frame sealing failure allows moisture to directly enter the junction box, accelerating the corrosion of internal triodes by 10 times, and causing the contact resistance to surge from 0.2 milliohms (mΩ) to 5 ohms (Ω), resulting in severe Joule heat loss.

Burned Connectors

Due to long-term exposure to UV light, the outer skin of inferior cables will become brittle and crack, exposing the internal 4 or 6 square millimeter copper core.

If the plastic shell of the connector is found to be yellowed, deformed, or melted, it means the resistance at the contact point is already too high.

Under a 10 A DC current, if the contact resistance increases from 0.5 milliohms to 1 ohm due to oxidation, the connector will generate 100 watts (W) of heat, which is enough to ignite the backsheet material within 15 minutes.

According to statistics, 70% of fires in PV systems originate from these visible damaged electrical connection points.

Severe Discoloration or Corrosion

Discolored

The encapsulation material EVA (ethylene-vinyl acetate) inside the solar panel undergoes chemical degradation and produces acetic acid under long-term UV radiation and high temperatures exceeding 60 degrees Celsius.

This chemical reaction causes the originally transparent encapsulation layer to gradually turn yellow or brown, a phenomenon known as "yellowing" or "browning."

When the Yellowing Index (YI) exceeds 20, the light transmittance of the glass will drop rapidly from 92% to below 80%, meaning more than 120 watts of light energy capture per square meter is lost.

Since photons cannot penetrate the dark brown encapsulation layer to reach the silicon wafer surface, the short-circuit current (Isc) will experience a cliff-like drop of 10% to 15%.

In a 10 kW system, if 30% of the panels show this color difference, the annual power generation loss will reach more than 1,200 kWh. Calculated over a 20-year operation period, the cumulative economic loss exceeds 15,000 CNY.

Numerous Rust Spots

Grid line corrosion usually manifests as white "snail trails" or dark brown oxidation marks on the cell surface, which are caused by electrochemical reactions between the silver paste electrode and moisture penetrating the panel.

In environments with humidity exceeding 85%, the rate of moisture penetration through backsheet molecular gaps increases by 4 times.

Once the silver paste grid lines are oxidized into silver oxide or silver acetate, the contact resistance will surge from 0.1 ohms (Ω) to more than 5 ohms (Ω).

This increase in resistivity causes the Fill Factor (FF) of the cell to drop from 0.80 to below 0.65.

At noon, when working at high current, the Joule heat generated by corrosion points will cause local temperatures to exceed 85 degrees Celsius, further inducing micro-cracks in the silicon wafer and forming a vicious cycle.

This power mismatch caused by corrosion will "lock" the output current of the entire string to the worst-performing cell, causing systematic production reduction.

Corroded Edges

Frame corrosion and sealant failure are the culprits behind Potential Induced Degradation (PID). When the anodized layer of the aluminum alloy frame is thinner than 15 microns (μm), salt spray will cause pitting corrosion on the frame within 5 years in coastal or industrial environments.

These pits break the panel's insulation barrier, leading to an increase in leakage current to ground on the DC side of the system.

When the leakage current exceeds 50 milliamperes (mA), the inverter will frequently report a "Low Riso" fault and automatically shut down, shortening the daily power generation time by 2 to 4 hours.

More seriously, the PID effect will drive sodium ions inside the silicon wafer to the surface under high voltage (1000V or 1500V systems), causing the parallel resistance of a single cell to plummet from 500 ohms to 50 ohms. The entire string of panels will lose 30% of peak power output in just 12 months.

Burned Black Spots

Discoloration or burn marks on the busbar usually mean the tin layer at the connection has undergone severe metal migration or oxidation.

A normal busbar solder joint should be able to withstand a current intensity of more than 5 amperes (A) per square millimeter without significant temperature rise.

Once an oxidation layer appears at the welding interface due to corrosion, the effective contact area will decrease by more than 60%.

When a 400W panel is working at full load, this high-impedance connection point will generate more than 10 watts (W) of local heat power, raising the backsheet temperature to over 100 degrees Celsius.

The black spots observed with the naked eye are actually carbonized backsheet material.

This physical damage is irreversible. The insulation strength of the carbonized area will drop by 90%, making it very easy to cause arc fires in thunderstorms, even burning through tiles or bracket structures.