What is the failure rate of solar panels

According to NREL data, the annual failure rate of photovoltaic modules is only about 0.05%, and although there is a linear degradation of 0.5% per year, their lifespan typically exceeds 25 years.

Degradation vs. Failure

Slow Power Loss

According to the definition by the International Electrotechnical Commission (IEC), it is considered normal physiological degradation for standard crystalline silicon modules to experience a decrease in power output of 0.5% to 0.8% annually over a 25-year lifecycle.

A monocrystalline module with a factory nominal rating of 400 watts will immediately undergo a one-time Light Induced Degradation (LID) within the first hour of installation.

This is due to the reaction of boron-oxygen complexes under sunlight, causing an instant power loss of 2% to 3%, causing the output to drop directly to around 390 watts.

In each subsequent year, because ultraviolet rays cause the EVA film to slowly turn yellow, light transmittance decreases by 0.1% to 0.2% annually.

Additionally, the Fill Factor (FF) of the solar cells will drop from roughly 80% to 78% due to minute oxidation of the soldering ribbons.

By the 20th year, if the actual output power of this panel can still maintain above 330 watts (i.e., 82.5% of the initial value), it is a very healthy panel that fully complies with the linear power warranty terms.

During this process, the Open Circuit Voltage (Voc) may only decrease by 0.1 volts per year, and the Short Circuit Current (Isc) remains almost unchanged.

The system continues to work at full load, it simply produces 15% fewer kilowatt-hours (kWh) than when it was new.

Only when the annual power attenuation rate exceeds a threshold of 1%, or if the power has already fallen below 90% by the 10th year, does it need to be judged as abnormal degradation, but this still does not necessarily constitute a "fault" in the sense of electrical safety.

Immediate Scrapping

If your monitoring system shows that the voltage of a certain panel instantly drops to zero, or the voltage of an entire string is 40 volts lower than that of the neighboring string (equivalent to the open circuit voltage of one panel), then this is a fault.

According to field test reports by TÜV Rheinland, true module failure is usually caused by a diode short circuit.

At this point, the bypass diode not only fails to conduct current but turns into a resistor, rapidly heating up to over 150 degrees Celsius under a 10-ampere operating current, directly burning through the back sheet.

Another common hard fault is water ingress in the junction box.

When the protection rating fails and drops from IP68 to below IP65, internal metal contacts will undergo electrochemical corrosion under high DC voltages of 600 to 1,000 volts.

This causes contact resistance to surge from 0.5 milliohms to over 1 ohm, ultimately triggering a DC arc.

In this case, the module's output power does not decrease slowly but plummets 100% in a cliff-like drop, potentially even causing a fire.

Voltage Leakage

When a photovoltaic system operates at a high voltage of 1000 volts or 1500 volts, the module's aluminum frame is grounded while the solar cells are at a high potential. Driven by the electric field, sodium ions in the glass will migrate to the surface of the cell.

This causes the shunt resistance (Rsh) of the cell to drop sharply from a normal 1000 ohms or more to below 100 ohms.

In severe cases, this causes the module power to plummet by 30% or even 50% within a few months.

Although the panel looks intact from the outside—the glass isn't broken, and the back sheet isn't cracked—its actual power generation efficiency has dropped from 21% to around 10%.

Localized High Fever

Under Standard Test Conditions (STC), if the current flowing through the module is 12 amperes, a shaded cell cell needs to consume the power generated by the other 60 cells.

According to Joule's Law, this generates tremendous heat on an area of only 156 mm x 156 mm. The local temperature can soar to 120 degrees Celsius or even 160 degrees Celsius within 10 minutes.

This high temperature will melt the EVA film on the back, leading to back sheet bulging and scorching.

Although the bypass diode is designed to conduct and bypass this string of cells when the reverse bias reaches 12 volts, if the resistance value of the hot spot happens to be stuck just below the critical point for diode conduction, this localized high fever will persist.

While the entire module still seems to be generating electricity and power might only be lost by 30%, the fire risk coefficient has increased tenfold.

Under an infrared thermal imager, the surface temperature difference of a normally operating module is usually within 3 degrees Celsius. Once a temperature difference at a certain point is found to exceed 20 degrees Celsius, the panel must be marked as a "high-risk fault" and listed in the replacement plan.

Invisible Cracks

Hidden cracks (micro-cracks) are micrometer-level cracks that are completely invisible to the naked eye. Their width is usually only 10 to 30 microns, thinner than a strand of hair, but their impact on module life is fatal.

These cracks usually occur due to mechanical vibrations during module transportation, or because installation workers violated regulations by stepping on the panels, causing the cells to be subjected to a local pressure exceeding 5400 Pascals.

Initially, hidden cracks do not affect power generation, and voltage and current readings are completely normal.

However, as the diurnal temperature difference causes the module to undergo thermal expansion and contraction cycles from -40 degrees Celsius to +85 degrees Celsius, these micro-cracks will gradually expand, eventually cutting off the fine grid lines (Fingers) on the cell surface.

Once the conductive path is broken, that area becomes a "dead zone" and no longer contributes any current.

According to EL (Electroluminescence) test image statistics, if the area of hidden cracks exceeds 15% of the cell, the power attenuation amplitude of the module after 3 years of operation will be 5% to 10% higher than that of normal modules.

Damage to the Wallet

If it is just normal degradation, such as the power generation in the 15th year being only 88% of the 1st year, your Levelized Cost of Electricity (LCOE) rises slightly from the initially calculated $0.05/kWh.

But if it is a failure, such as a panel breaking in the 5th year, what you need to pay is not just the hardware cost of a new panel of about $150, but the more expensive labor cost.

In the United States or Australia, the minimum call-out fee (Truck Roll) for a licensed electrician to come and replace a panel is usually between $250 and $400.

If the fault is not discovered in time, causing a DC arc to burn out the inverter's MPPT input terminal, the loss starts at $2,000.

Therefore, for a linear degradation of 0.7% per year, we can "turn a blind eye," but for any sudden power dive exceeding 3%, we must immediately take out a multimeter to troubleshoot, because behind that often lies a loss of real money.

Types of Failures

Cracked but Invisible

The width of this type of crack is usually only 10 to 30 microns, much thinner than a human hair (about 70 microns).

They usually originate from the solar cells withstanding mechanical stress exceeding 2400 Pascals during production, transportation, or installation, or are caused by installation workers violating regulations by stepping on them.

Although these cracks do not cut off the current initially and Open Circuit Voltage (Voc) readings may be completely normal, in the subsequent 3 to 5 years, as the module experiences daily thermal expansion and contraction cycles from 15 degrees Celsius in the morning to 65 degrees Celsius in the afternoon, the cracks will gradually expand like cracks on a windshield.

Once the crack sever the silver paste fine grid lines (fingers) on the cell surface, that area becomes a "dead zone" and no longer outputs any power.

According to Electroluminescence (EL) test data, if the hidden crack area of a cell exceeds 20%, the module's power output will immediately drop by 3% to 5%, and the contact resistance at the crack will rise sharply, generating local heat and further accelerating aging.

In extreme cases, severe hidden cracks will limit the output current of the entire string of cells, causing the actual output power of a 400-watt module to be stuck below 300 watts, permanently losing 25% of its capacity.

Local Burn Hole

When a cell is shaded by bird droppings or fallen leaves, or its resistance increases due to internal cracks, it no longer generates current.

Instead, it turns into a load resistor, consuming the energy generated by the other 19 to 23 cells in the same series circuit.

Under a standard 10-ampere operating current, this shaded cell will withstand reverse bias. According to the formula P=I²R, huge heat is generated locally.

· Temperature Soaring: Within just 5 to 10 minutes, the temperature at the center of the hot spot can soar from a normal 45 degrees Celsius to 150 degrees Celsius or even 200 degrees Celsius.

· Material Melting: This high temperature will directly melt the EVA film encapsulating the cell (melting point approx. 70-80°C) and the back sheet (melting point approx. 120-150°C), causing the back sheet to bulge, char, or even burn through.

· Diode Failure: Although bypass diodes are designed to conduct and protect the cell when the reverse voltage reaches 12 to 15 volts, if the shading only causes partial shadowing and the voltage is insufficient to trigger the diode, heat will continue to accumulate. Once the glass shatters because the local temperature difference exceeds 40 degrees Celsius, oxygen enters, and a fire is just a matter of minutes.

Voltage Being Stolen

In large commercial or ground-mounted power stations, modules are usually connected in series to high-voltage DC systems of 1000 volts or even 1500 volts.

If the module frame is grounded and the solar cells are in a negative high voltage state (e.g., -600 volts), sodium ions (Na+) in the glass will migrate through the EVA film to the cell surface driven by the strong electric field.

This is like sprinkling a layer of conductive salt on the cell surface, causing the cell's parallel resistance (Rsh) to drop drastically from thousands of ohms to a few hundred ohms or even tens of ohms.

· Power Plunge: This is like having countless small holes punched in the bottom of a bucket; the current is consumed by internal short circuits before it even flows out of the module. For modules severely affected by PID, power output can drop by 30% to 70% within just six months.

· Environmental Factors: The PID effect is most severe in environments with relative humidity exceeding 85% and temperatures exceeding 30 degrees Celsius.

· Irreversibility: Although installing a PID recovery box at the inverter end to apply reverse positive voltage at night can "push" some sodium ions back and recover 5% to 10% of the power, if the PN junction of the cell has been physically broken down, this damage is permanent.

The Box is Burnt

The standard junction box protection rating is usually IP67 or IP68, theoretically dustproof and waterproof.

However, in reality, after more than five years of ultraviolet irradiation and thermal expansion and contraction, the sealing ring of the junction box will age and become brittle, leading to sealing failure.

Once water vapor penetrates, the internal copper connectors will rapidly undergo electrochemical corrosion under the action of 600-volt DC electricity, and contact resistance will surge from 0.5 milliohms at the factory to over 1 ohm.

· Diode Thermal Breakdown: The junction box usually contains 3 bypass diodes, which generate heat when high current passes through. If heat dissipation is poor and the junction temperature exceeds 150 degrees Celsius, the diode will undergo thermal breakdown and short circuit.

· Arcing Risk: Once the diode shorts or the connector corrodes and breaks, a DC arc (Arcing) will instantly generate high temperatures of over 3,000 degrees Celsius, directly igniting the plastic casing of the junction box.

· Data Statistics: According to TÜV Rheinland's failure analysis report, about 15% of module failures are attributed to junction box and connector issues, with a large proportion caused by burning due to loose interconnection of MC4 connectors.

Glass Delamination

Delamination refers to the separation of the bonding layers between the glass, EVA film, solar cells, and back sheet, much like a layer cake falling apart.

Qualified module peel strength should be greater than 40 Newtons/cm, but under long-term high humidity (humidity >80%) or strong UV irradiation, inferior EVA film will degrade and release acetic acid.

· Chemical Corrosion: Acetic acid will not only corrode the silver grid lines on the cell surface, increasing series resistance, but also generate gas, causing visible bubbles on the module surface.

· Optical Blocking: Once delamination occurs, air enters the gap, changing the refractive index of light. This leads to increased light reflection and fewer photons reaching the cell, directly causing a current drop of more than 10%.

· Moisture Channel: Bubbles and delaminated areas will accumulate condensation, becoming a fast channel for leakage current, causing the module Insulation Resistance Test (Megger Test) to fail. The inverter will refuse to start because it detects that the insulation impedance to ground is lower than 50 megohms.

Backsheet Peeling

Between 2010 and 2015, some manufacturers used immature Polyamide back sheets, leading to large-scale early failures. These back sheets would start to show chalking and severe cracking after 4 to 5 years of operation.

· Insulation Failure: Once the back sheet cracks, internal live parts are directly exposed to the air. If someone touches it or the metal mounting structure contacts the crack, an electric shock accident will occur.

· Water Absorption and Leakage: Cracked back sheets absorb rainwater like a sponge, causing the module's wet leakage current to exceed 300 milliamps on rainy days, triggering the inverter's Residual Current Device (RCD) to trip.

· Replacement Cost: Back sheet cracking cannot be repaired; applying sealant only works for a few months. In this situation, the modules of the entire power station need to be replaced in batches. This is one of the most expensive types of material failure, with losses usually counted in millions of dollars.

Service Life

Really Lasts a Long Time

According to long-term validation data from the International Energy Agency (IEA) and the U.S. National Renewable Energy Laboratory (NREL), the design physical life of Tier 1 monocrystalline silicon modules is usually over 30 years.

Even when the 25-year warranty period promised by the manufacturer ends, they are not broken, but their power generation efficiency has dropped to about 80% to 84% of the initial value.

· Actual Cases: The world's first batches of grid-connected solar panels, such as ARCO Solar modules installed in Europe or the United States in the 1980s, still maintain an output capacity of over 80% of their rated power after 40 years of operation.

· Aging Speed: Although the silicon wafer itself hardly ages, the packaging materials (EVA film, back sheet, glass) will degrade over time. For standard glass-back sheet modules, the annual average power degradation rate is between 0.5% and 0.8%.

· New Technology Performance: Double-glass modules use two layers of 2.0 mm or 2.5 mm tempered glass for encapsulation because they eliminate the organic back sheet. Their resistance to water vapor penetration is stronger, and the expected life is even calibrated by many manufacturers to 40 years, with an annual attenuation rate as low as 0.4%.

Module Type	Expected Physical Life	First Year Degradation	Average Annual Degradation	Remaining Power after 25 Years
Standard Mono PERC	25-30 Years	2.0% - 2.5%	0.55%	~84.8%
N-type TOPCon	30+ Years	1.0%	0.40%	~87.4%
HJT Heterojunction	30-35 Years	1.0%	0.30% - 0.35%	~90.0%
Flexible Thin Film	10-15 Years	3.0% - 5.0%	1.0% - 2.0%	<70%

Manufacturer's Warranty

Claiming on a warranty is not as easy as imagined because manufacturers divide the warranty into two completely different concepts: "Product Warranty" and "Performance Warranty." The word game in between determines whether you can get compensation.

· Product Warranty: Usually only 10 or 12 years. This covers "workmanship," such as the frame rusting, the junction box lid falling off, the glass shattering for no reason, or the back sheet peeling. If the junction box breaks in the 13th year, causing no power generation, this is not covered by the product warranty, and you have to pay for a new panel out of your own pocket.

· Performance Warranty: Usually as long as 25 or 30 years. This covers "output power." The manufacturer promises that the power will not be lower than 98% in the 1st year, and the attenuation will not exceed 0.55% annually thereafter, and not lower than 84.8% in the 25th year. If you feel that generation is low in the 10th year, you must provide a Flash Test data report for that module under Standard Test Conditions (STC, 1000 W/m², 25°C).

· Hidden Costs: Almost all module warranty terms clearly state "Labor and Shipping Costs Not Included." In the United States, the labor cost to hire a worker to go up to the roof, remove a panel, and install a new one is usually between $200 and $400, while the price of a new panel might only be $150.

Inverters are Short-Lived

Although solar panels can last for 30 years, the inverter, which acts as the system's brain, usually does not live past 15 years.

· Electrolytic Capacitors: Large-capacity electrolytic capacitors inside string inverters work at high temperatures, and the electrolyte will gradually evaporate. Usually, after 10 to 12 years of operation, the capacitance decreases, leading to excessive ripple voltage, and the inverter will report an error and stop working.

· Replacement Cost: For a 10 kW residential system, the hardware cost of replacing a high-quality inverter is between $1,500 and $2,500, which is equivalent to 10% to 15% of the initial installation cost.

· Microinverters: Although microinverters like Enphase claim a 25-year warranty, this is usually limited to core functions. Since they are installed under the roof modules and endure high temperatures above 60 degrees Celsius for a long time, the failure rate of actual electronic modules increases exponentially with time. Once a microinverter in the middle of the roof breaks, the labor cost to remove surrounding modules for replacement can be as high as $300.

When Exactly to Replace

When the maintenance cost exceeds the power generation revenue, this system is economically dead, even if the panels can still generate electricity.

· Generation Threshold: It is generally believed that when the module power degrades to below 70% of the initial value, the opportunity cost of keeping it is too high. Because with the same roof area, switching to current high-efficiency modules (e.g., from 250 watts to 450 watts) can directly double the power generation.

· Payback Period Calculation: Assume your electricity price is $0.15/kWh. An old 5 kW system produces 6,000 kWh per year, worth $900. If it requires repairs twice a year due to aging wiring or oxidized connectors, costing $600, then the net profit is only $300.

· BOS Cost: Besides the panels, the insulation layer (XLPE/PVC) of DC cables will become brittle and crack after 20 years of outdoor exposure, triggering a Ground Fault.

The Climate is Too Torturous

Environmental factors directly determine whether your panel can be used for 30 years or 15 years.

The same brand of modules will have vastly different lifespans when installed in the desert of Arizona versus the seaside of Florida.

· Damp Heat Test: In the IEC 61,215 standard test, modules must persist for 1,000 hours in an environment of 85 degrees Celsius and 85% humidity. But in tropical coastal areas, this kind of "sauna weather" is the norm. Salt mist will corrode aluminum alloy frames and grounding wires. If you do not choose modules that pass IEC 61701 Salt Mist Corrosion level 6, the frames may crumble within five years.

· UV Bombardment: Strong ultraviolet rays in high-altitude areas (such as Colorado) will accelerate the yellowing (browning) of EVA film. Once the film turns yellow, light transmittance decreases, and the current (Isc) will permanently decrease.

· Mechanical Load: In snowy regions, modules must withstand a snow load of 5400 Pascals (about 550 kg) per square meter for months every winter. This repeated heavy pressure will cause invisible hidden cracks in the solar cells. If the frame thickness is only 30 mm instead of the reinforced 35 mm or 40 mm, frame deformation under long-term heavy pressure will cause the glass to burst, directly ending the service life.