TOPCon Case Study : Glass/Backsheet vs. Dual Glass

Posted on: 25/02/2025

 

The evolution of photovoltaic module structures has been marked by the transition from glass-backsheet to dual-glass, largely driven by durability concerns and the rise of bifacial cells. While glass-backsheet design dominated until 2019 due to its ease of manufacturing, aging issues with certain polymer films led manufacturers to reconsider their choices. From 2022 onwards, the rapid growth of TOPCon modules, which are more sensitive to humidity and corrosion risks, further accelerated the adoption of dual-glass, already present on the market, to better protect the cells. This structural choice impacts several performance criteria: resistance to moisture penetration, mechanical stability under loads and impacts, and the overall long-term reliability of the module. However, trade-offs exist between durability and other factors such as weight, mechanical resistance, and energy performance.

The following comparative table highlights these different criteria to provide a clearer assessment of the advantages and limitations of current solutions in the context of TOPCon monofacial module aging :

Durability

Glass (3,2 mm) - Backsheet

Moisture Penetration : 
● Power loss during Damp-Heat test (2000 h): -1.9 % on average.
● 46 % of glass/backsheet modules had a power degradation below 2 % after DH2000.
 

Degradation Rate :
● Around 0.7 % annual degradation, with a residual performance of 80 % after 25 years. 
 

PID resistance :
● Sensitive to PID due to moisture infiltration.
 

Thermal Stability :
● Limited : polymer backsheet degrades at high temperatures.
 

Thermal Dissipation : 
● Dissipates heat better, improving efficiency in hot climates by maintaining a reasonable cell temperature.

Dual-glass (2 x 2,0 mm)

Moisture Penetration :
● Power loss during Damp-Heat test (2000 h): -1.0 % on average.
● 85 % of glass/glass modules had a power degradation below 2 % after DH2000.
 

Degradation Rate :
● Around 0.45 % annual degradation, with a residual performance of 87 % after 25 years.
 

PID resistance :
● PID resistance thanks to better moisture sealing.
 

Thermal Stability :
● Very good : glass has strong thermal resistance properties.
 

Thermal Dissipation :
● Retains more heat, which may reduce efficiency due to higher operating temperature.

Mechnanical Constraints

Glass (3,2 mm) - Backsheet

Resistance to Pressure/Depressions : 
● Prone to microcracks under wind/snow loads. 
● The asymmetric structure exposes cells to tensile forces, increasing the risk of cracking.
 

Hail resistance : 
● RG4 (Higher resistance).

Dual-glass (2 x 2,0 mm)

Resistance to Pressure/Depressions : 
● More rigid, less prone to microcracks. 
● The symmetrical structure places cells on a neutral line, reducing tensile-compression stress.
 

Hail resistance : 
● RG3 (Lower resistance).

Performance Indicators

Glass (3,2 mm) - Backsheet

Energy Yield : 
● Limited to monofacial, so no rear-side gain. 
● Due to backsheet aging, moisture resistance decreases, leading to accelerated encapsulant aging and metal contact corrosion, resulting in efficiency loss or panel failure.
 

Cost : 
● Lower initial cost, as polymer backsheet is cheaper.
 

Weight : 
● Lighter : ∼ 20 kg (per 1762 × 1134 mm module). 
 

Applications : 
● Standard PV installations, not suitable for bifacial or semi-transparent systems (AgriPV). 
● Low compatibility with 2000V systems.
 

Lifespan : 
● Expected lifespan of around 25 years.
 

Recyclability : 
● For panels in good condition, layer separation via delamination is offered by Soren.

Dual-glass (2 x 2,0 mm)

Energy Yield :
● Enables bifacial functionality for ground modules, providing up to 11 % production gain under ideal conditions (4-5 % in real-world conditions).
● Thanks to better resistance to degradation phenomena, long-term performance is improved.


Cost :
● Higher initial cost, as dual glass adds material costs.
 

Weight :
● Heavier : ∼ 25 kg (per 1762 × 1134 mm module).
 

Applications :
● Suitable for semi-transparent rooftops (AgriPV) and bifacial systems. 
● Better compatibility with 2000V systems.
 

Lifespan :
● Longer lifespan, exceeding 30 years. 
 

Recyclability :
● Currently, only shredding is possible, followed by material separation (hydraulic processes, Eddy currents, or density separation).

Dual-glass is more durable, offering better moisture resistance, a lower degradation rate, and a longer lifespan. It enhances efficiency through bifaciality  and reduces the risk of microcracks. However, it is heavier, more expensive, and requires more frequent maintenance. Glass-backsheet, being lighter and cheaper, degrades faster and is limited to monofacial applications, but its recycling process is more advanced. At Synapsun, we choose dual-glass to ensure optimal performance and long-term durability. 

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