Why Choose Poly Solar Modules | Attenuation Rate, Effective Power Generation Duration
Choose Poly Solar modules for their industry-leading 0.55% annual attenuation rate, ensuring over 84.8% output after 30 years for a significantly longer effective power generation duration with only routine maintenance.
Attenuation Rate
In the life cycle of a photovoltaic power plant exceeding 25 years, the gap in initial peak power is far less critical than the annual power attenuation rate of the modules.
Conventional industry modules typically experience about 2% first-year attenuation, followed by 0.45% annual attenuation.
This means a module with an initial power of 550W might only output about 78% after 25 years.
Modules utilizing leading technologies (such as Poly Solar's N-type TOPCon cell technology) can suppress first-year attenuation to within 1%, and optimize the linear attenuation rate to 0.4% or even lower, ensuring an end-of-life power retention rate exceeding 85% after 25 years.
Definition and Calculation
Measurements must be conducted under standard conditions
To obtain comparable attenuation rate data, all measurements must be completed in a strictly controlled laboratory environment, known as Standard Test Conditions:
l Irradiance: 1000 watts per square meter
l Cell Temperature: 25 degrees Celsius
l Solar Spectrum: AM 1.5
Power tolerance defines the benchmark for calculation
l A module with a nominal power of 550W and a tolerance of "0 to +3%" may have an actual initial power between 550W and 566.5W when it leaves the factory.
l If a module starts operation at 566.5W and its measured power drops to 558W after one year, its actual power decrease is 8.5W. However, using the nominal value 550W as the denominator for calculation would yield an inaccurate attenuation rate.
Calculation Models for Attenuation Rate: Linear and Non-linear
Attenuation is not a simple, constant annual decrease; it is typically divided into two stages:
1. First-year Attenuation: This is a relatively large, one-time power drop, primarily caused by Light-Induced Degradation. The calculation formula is:
2. First-year Attenuation Rate = [(Initial Power - Power at End of Year 1) / Initial Power] × 100%
3. Subsequent Annual Attenuation: From the second year onwards, attenuation enters a relatively stable linear phase. The formula for calculating the attenuation rate in year N is:
4. Year N Attenuation Rate = [(Power at Year N-1 - Power at Year N) / Initial Power] × 100%
5. The industry often uses a linear model to simplify long-term attenuation representation: End-of-Period Power = Initial Power × (1 - First-year Attenuation Rate) × (1 - Annual Attenuation Rate)^(Operating Years - 1)
A Specific Calculation Example
Assume an N-type TOPCon module with a nominal power of 580W and a power tolerance of +3W, so the initial power is 583W.
The warranty promises first-year attenuation of 1%, and annual attenuation of 0.4% thereafter.
l Power at End of Year 1: 583W × (1 - 1%) = 577.2W
l Power at End of Year 2: 577.2W × (1 - 0.4%) = 574.9W
l Power at End of Year 10: 577.2W × (1 - 0.4%)^9 ≈ 557.5W. At this point, the actual retention rate relative to the initial power 583W is 557.5 / 583 ≈ 95.6%.
l Power at End of Year 25: 577.2W × (1 - 0.4%)^24 ≈ 523.9W. The power retention rate is 523.9 / 583 ≈ 89.9%.
This example shows that although the power decreases to 577.2W after the first year, due to the extremely low subsequent linear attenuation rate, the power retention rate after 25 years remains very high.
Main Mechanisms
Light-Induced Degradation (LID):
LID occurs within the first few hours to months of a module's operation and is the most significant initial power drop.
Atomic-level Mechanism
l In P-type boron-doped monocrystalline silicon, the silicon material introduces trace amounts of oxygen during manufacturing.
l When the module is first exposed to light, photon energy causes boron and oxygen atoms to form "boron-oxygen complexes."
l These complexes act as charge traps, capturing free electrons generated by light, significantly reducing charge mobility, leading to a short-term, irreversible drop in module efficiency.
l This is the main reason for the 1.5% to 2% first-year attenuation in traditional P-type PERC modules.
Advantage of N-type Technology
l N-type silicon wafers use phosphorus as the dopant, and the material itself is insensitive to boron-oxygen complexes.
l Simultaneously, N-type silicon wafers have extremely high purity, and the oxygen content introduced during manufacturing is an order of magnitude lower than in P-type wafers.
Therefore, for modules based on N-type technology (such as TOPCon or HJT), light-induced degradation can be controlled within 1%, with first-year attenuation for many high-quality models even below 0.5%.
Potential Induced Degradation (PID):
1. Occurrence Conditions and Process
l PID typically becomes significant when three conditions are simultaneously present: high temperature, high ambient humidity, and the module itself having a high negative voltage relative to the grounded frame.
l Under these conditions, a strong electric field forms. Sodium ions from the glass and encapsulant (typically EVA) migrate from the glass surface towards the interior of the cell under the drive of this electric field.
l These ions penetrate the cell's anti-reflection coating and accumulate in the passivation layer region of the cell.
l This ion accumulation degrades the passivation effect, increasing surface recombination, significantly reducing short-circuit current and fill factor, thereby causing power attenuation of the entire module, which can exceed 30% in severe cases.
2. Technical Solutions to Suppress PID
l Anti-PID Cells: Optimize the passivation layer and anti-reflection coating structure on the cell surface to enhance its resistance to ion intrusion.
l Changing Encapsulation Materials: Use POE or EPE film with superior insulation properties instead of traditional EVA film, fundamentally reducing the pathways for ion migration.
l System-side Measures: At night, applying a brief positive voltage to the string via the inverter can partially neutralize or disperse accumulated ions, allowing partial recovery of module performance.
Material Aging and Environmental Degradation:
1. Encapsulation System Performance Degradation
EVA Film Yellowing and Delamination: Long-term UV exposure causes EVA (Ethylene-Vinyl Acetate Copolymer) to undergo photo-oxidation reactions, leading to yellowing and decreased light transmittance. EVA with lower Vinyl Acetate (VA) content or inferior quality EVA is more prone to this issue. A 1% decrease in transmittance roughly proportionally reduces the module's short-circuit current output.
Back sheet Aging: Common back sheets like TPT, KPE, etc., degrade under UV light, heat, and moisture, leading to:
l Decreased mechanical strength, becoming brittle and prone to cracking.
l Reduced water vapor barrier properties, allowing more moisture to enter the module and corrode the circuitry.
l Decreased insulation performance, increasing leakage current and safety risks.
2. Cell and Interconnection Technology Reliability
l Cell Micro-cracks: Tiny cracks may occur during transportation, improper installation, or from long-term stress from snow, wind load, etc. Micro-cracks can interrupt the current conduction path collected by the fine gridlines, causing partial cell failure or reduced efficiency.
l Ribbon Aging and Corrosion: The ribbon (typically tinned copper tape) interconnecting cells may undergo electrochemical corrosion due to residual flux or corrosive substances from the environment, increasing series resistance, leading to a drop in Fill Factor (FF), and affecting maximum power output.
l Increase in Contact Resistance: At contact points between cell gridlines and ribbons, and connections between the junction box and cables, contact resistance may slowly increase under long-term thermal cycling stress, causing additional power loss.
Product Warranty
Specific Definition of Warranty Coverage
l Typically Covered Items:
l Material Defects: Such as back sheet delamination, rapid yellowing of EVA film, junction box seal failure leading to water ingress, frame corrosion, etc.
l Workmanship Flaws: Such as pre-existing cell micro-cracks (before installation), poor soldering, internal circuit connection failures.
l Extreme Output Power Loss: When the module power falls below the minimum tolerance range of the nominal power (e.g., -0% or -3%), it is covered by the warranty, even in the initial warranty period.
l Explicitly Not Covered Items:
l Force Majeure: Damage caused by events like earthquakes, tornadoes, war, etc.
l Improper Handling: Mechanical damage caused by human error during transportation, installation, or maintenance, e.g., stepping on modules, installation stress causing micro-cracks.
l Environmental Factors: Hail, sandstorms, bird droppings corrosion, etc., unless it can be proven that the product's inherent quality issue exacerbated the damage.
l Unauthorized Modifications: Any repairs or alterations to the module or junction box not authorized by the manufacturer.
Link Between Warranty Period and Attenuation Curve
l A typical warranty clause might be: "10-year product warranty for materials and workmanship defects, providing repair or replacement; from year 11 to year 30, providing repair or pro-rata compensation."
l This stepped clause reflects the expected aging pattern of the module: the first 10 years have a higher failure rate, followed by a period of stable but slow performance degradation.
Specific Calculation Method for Compensation Mechanism
l Repair or Replacement: In the initial warranty period (e.g., first 10 years), if major quality issues occur, the manufacturer typically prefers to repair or directly replace with new or refurbished modules.
l Pro-rata Compensation: In the mid-to-late warranty period, economic compensation is more common. The calculation formula is typically:
l Compensation Amount = (Current market price of a comparable new product) × (Years of module use when fault is discovered / Total product warranty years)
For example, for a module that fails in year 15, with a total product warranty of 30 years, the compensation might be about 50% of the new product price (15/30=0.5).
Warranty Transferability and Inheritance
l Transferable Warranty: Warranties from most high-quality manufacturers can be transferred along with the module ownership to a new owner, usually requiring a simple online registration process at no extra cost.
l Non-transferable or Limited Transfer Warranty: Some warranties may stipulate that terms or duration are reduced after transfer.
Actual Warranty Validity and Manufacturer Strength
l A 30-year warranty is essentially a long-term credit commitment. If the manufacturer goes bankrupt after 10 years, the warranty becomes void.
l Therefore, choosing a financially healthy manufacturer with a long history and stable global operations carries much higher warranty credibility compared to new or financially unstable companies.
Effective Power Generation Duration
The commonly advertised 25-30 year lifespan in the PV industry actually has a key cognitive blind spot: theoretical lifespan is not equal to the high-efficiency output cycle.
If a module's power degrades by more than 15% after 10 years of operation, its power generation efficiency in the remaining years will be significantly reduced.
The core difference lies in the first-year attenuation and the linear attenuation rate—the former averages about 2% in the industry, while high-quality products can control it within 1%; the latter shows clear differentiation, ranging from 0.55% to 0.4%.
Definition
1. The 80% Power Line is the Economic Watershed
l Change in Balance of System Cost Proportion: Costs for inverters, mounting systems, cables, and annual O&M are relatively fixed. When the total module output decreases by 20%, the fixed cost allocated per kilowatt-hour increases significantly, leading to a higher Levelized Cost of Energy (LCOE).
l Calculation of the Profitability Threshold: In mature markets like Germany or California, USA, detailed calculations show that when module power degrades below 80%, the value of the electricity generated often barely covers the system's O&M, insurance, and management costs, contributing minimally to the return on the initial investment.
l Practical Case: The financial model for a 1MW PV plant in Spain over its 25-year operational period shows that the project's Internal Rate of Return meets investment requirements only when the module efficiency remains above 80%.
2. Time Scale:
The commonly used 25-year warranty period can easily be misinterpreted as the module's lifespan being only 25 years. In reality, the physical lifespan of many high-quality modules may exceed 30 or even 35 years.
l Value after 25 Years: A module that still maintains 85% output power at year 25 has significantly higher remaining value than a module with only 79% power. The former can continue to operate as a high-efficiency asset for many more years after 25 years, significantly increasing the total lifetime energy generation.
l Impact of the Degradation Path: Two modules might both reach the 80% threshold at year 25, but their degradation paths could be completely different.
3. Correlation with Reliability Indicators:
l Potential Induced Degradation Suppression Capability: PID can cause severe power loss in modules in the short term. A module with excellent anti-PID performance (e.g., power degradation less than 2% after harsh testing at 85°C/85% relative humidity for 96 hours) ensures long-term output stability under complex climatic conditions.
l Stability of Light-Induced Degradation: Especially for P-type mono-crystalline modules, the LID caused by boron-oxygen complexes typically occurs in the first few months. High-quality modules stabilize LID loss within 1% through optimized cell processes and ensure no further periodic large fluctuations after the first year.
l Material Aging Rate: The yellowing of EVA encapsulant and the weather resistance of the back sheet directly affect the module's light transmittance and insulation, thereby influencing the annual 0.x% linear degradation rate. Using more aging-resistant encapsulation materials (like POE, co-extruded POE) is the physical key to extending the effective duration.
4. Quantitative Assessment:
l Interpretation of Warranty Data: A typical warranty for a high-quality module states: "First-year degradation not more than 1%, then linear degradation not more than 0.45% per year from year 2 to year 25". Using this model, the guaranteed minimum power for any year N can be calculated: Power at Year N ≥ 1 - (First-year % + Linear % × (N-1)).
l Example Calculation: According to the above model, the guaranteed power at the end of year 10 is: 1 - (1% + 0.45% × 9) = 95.95%. The guaranteed power at the end of year 25 is: 1 - (1% + 0.45% × 24) = 84.8%. This 84.8% is the key figure for assessing whether its 25-year "Effective Power Generation Duration" meets the standard.
Determining Factors
Cell Technology Path is the Starting Point of Degradation
The type of PV cell technology fundamentally determines its initial efficiency and degradation characteristics.
P-type mono-crystalline cells, represented by PERC, exhibit relatively noticeable Light-Induced Degradation caused by boron-oxygen complexes.
In the initial operation period, efficiency drops after light exposure, with typical LID degradation ranging from 1% to 2%.
Although this degradation can be partially recovered under certain conditions, it constitutes the main part of the first-year power loss.
Cells using an N-type substrate (such as TOPCon, HJT), however, essentially eliminate boron-oxygen complexes by using phosphorus doping, significantly reducing their LID rate.
Substantial empirical data shows that the median first-year degradation of N-type TOPCon modules can be stably controlled within 1%, and their annual linear degradation rate after the first year is generally lower than that of P-type products.
Stability of Encapsulation Materials is like the Module's Immune System
Cells need to be protected by encapsulation materials. The durability of these materials directly determines the rate at which environmental stress erodes the cells.
l Encapsulant: Moisture Barrier. EVA is the traditional material, but it is prone to hydrolysis and aging in damp heat environments, leading to decreased transmittance and cell corrosion. High-performance co-extruded POE or EPE films provide superior moisture barrier properties and anti-PID performance. In accelerated laboratory aging tests (e.g., 1000 hours DH test), the power degradation of PV modules using POE encapsulation is typically more than 0.5 percentage points lower than those with conventional EVA encapsulation.
l Back sheet: External Defense Line. The back sheet must withstand up to 25 years of UV exposure, temperature variations, and weather erosion. Multi-layer composite structure back sheets (e.g., TPT, KPK) offer more reliable insulation and mechanical strength than single-layer or coated back sheets. A key indicator is the Water Vapor Transmission Rate; high-quality back sheets typically have values below 2 g/m²/day, effectively preventing moisture ingress into the module interior.
l Glass: Light Transmission Window. The transmittance of PV glass directly affects energy yield. The anti-reflective coating is key to maintaining high transmittance, and its durability varies significantly. The coating on high-quality glass is optimized to ensure minimal decrease in transmittance after long-term outdoor exposure.
Environmental Stress is the External Driver Accelerating Degradation
The same module installed in different climatic regions will exhibit different degradation rates. Environmental stress is the real-world test for module durability.
l High Temperature and Humidity: Catalysts for Chemical Aging. In tropical and subtropical coastal areas, sustained high temperatures and humidity significantly accelerate the aging of encapsulation materials, corrosion of cell gridlines, and PID effects. Research shows that for every 10°C increase in ambient temperature, the rate of chemical reactions within materials approximately doubles.
l UV Radiation: The Molecular Chain Breaker. UV photons have high energy and can break polymer molecular chains, causing encapsulant yellowing and back sheet embrittlement. High-altitude, low-latitude regions have stronger UV radiation, demanding higher weather resistance from materials.
l Thermal Cycling: Source of Mechanical Stress: Daily and seasonal temperature variations cause alternating stress due to the different coefficients of thermal expansion of different materials (glass, silicon wafer, metal ribbons). Under long-term effects, this can lead to cell micro-cracks, ribbon fatigue fracture, causing power loss.
Manufacturing Process and Quality Control Ensure Consistency
Excellent design must be realized through refined and stable manufacturing processes. Any deviation during production can become a hidden risk to long-term reliability.
l Lamination Process: The temperature, pressure, vacuum, and time profile during lamination must be precisely controlled to ensure full cross-linking of the encapsulant, no internal bubbles, and avoidance of delamination and cell displacement.
l Frame Sealing: The adhesion between the frame and the laminate must be sealed using continuous, bubble-free silicone sealant. Any gap can become a pathway for moisture ingress.
l Raw Material Batch Stability: The specifications of bus bars, ribbons, tabbing wires, and the chemical composition of silver paste must remain highly consistent between batches.
Economic Impact
Energy Yield Loss Creates a Revenue Gap
Taking a 1 Megawatt (MW) PV power plant as an example, assume its first-year equivalent full-load hours are 1300 hours (applicable to most of Europe). Assuming linear power degradation of modules, the cumulative energy yield difference under different degradation rate models is as follows:
l Model A (High-quality Module): First-year degradation 1%, subsequent annual degradation 0.45%
l Model B (Industry Average): First-year degradation 2%, subsequent annual degradation 0.55%
Simulating the 25-year energy yield, the total yield of Model A is about 4% to 6% higher than Model B.
For a 1MW plant, this means generating over 1,300,000 kilowatt-hours (kWh) more electricity over its lifetime.
Calculated at an industrial/commercial electricity price of 0.12 EUR/kWh, this difference in energy yield translates to a difference in electricity revenue exceeding 150,000 EUR.
In regions with better solar resources (over 1500 equivalent full-load hours per year), this revenue gap widens further.
Levelized Cost of Energy is Redefined
LCOE is the core metric for assessing the economics of a PV project, calculated as the total project cost over its life cycle divided by the total energy yield.
The module degradation rate directly affects the LCOE by influencing the denominator (total energy yield) in the formula.
A project's total cost includes initial investment, O&M costs, insurance, etc.
Assuming the total costs of two projects are identical, but the project installed with low-degradation modules (Model A) will have a lower LCOE than the project using standard modules (Model B) because its total energy yield is higher.
Specifically, if the total project cost is 700,000 EUR, the total yield for Model A is 29,500,000 kWh, its LCOE is approximately 0.0237 EUR/kWh.
The total yield for Model B is 28,200,000 kWh, its LCOE rises to about 0.0248 EUR/kWh.
This difference of 0.0011 EUR/kWh, multiplied by millions of kilowatt-hours, will have a long-term impact on the project's competitiveness.
Declining Utilization of Balance of System Modules Incurs Hidden Costs
The capacity of Balance of System modules like inverters, cables, and mounting structures is sized based on the initial power of the modules.
When the module output power decreases due to degradation, these modules will operate below full capacity for some of the time.
For example, inverters typically have an optimal operating range.
When the array output power consistently falls below the inverter's optimal start-up voltage or fails to reach the rated power for extended periods due to degradation, the inverter's conversion efficiency decreases, further amplifying the energy yield loss.
Differentiation in Return on Investment and Asset Value
PV projects typically have clear Internal Rate of Return targets. Modules with lower degradation rates directly improve the project's cash flow by increasing energy revenue, thereby enhancing the project's actual IRR.
During the mid-life of the project (e.g., year 10), when project financing or equity transfer is considered, the asset valuation of the power plant is closely linked to its future energy yield expectations.
A plant with good historical yield data and slow degradation will have a significantly higher valuation than a plant with persistently lower-than-expected yield and rapid degradation.
Asset appraisal firms will scrutinize historical yield data and use more conservative degradation models to assess underperforming assets, leading to a discount in asset valuation.