Structure and Functional Principle of Conventional Crystalline Silicon PV Modules

As the core energy conversion unit of photovoltaic power generation systems, PV modules play a crucial role in directly converting solar energy into electrical energy. Conventional crystalline silicon PV modules adopt a laminated packaging structure, mainly consisting of six core components: solar cells, high-transmittance tempered glass, EVA encapsulation film, insulating backsheet, aluminum alloy frame, and junction box. Each component performs its own functions in photoelectric conversion, mechanical protection, electrical connection, and environmental resistance, collectively determining the conversion efficiency, mechanical strength, insulation performance, and long-term operational reliability of the modules. This paper systematically elaborates on the core composition structure of conventional PV modules, and analyzes the material characteristics, working mechanism, and core functions of each component in detail, providing a theoretical reference for PV module design, production and manufacturing, quality inspection, and engineering application.

1. Introduction​

Against the backdrop of the global energy structure transitioning towards cleanliness and low carbonization, photovoltaic power generation has become one of the most widely used and rapidly developing technologies in the renewable energy field. PV modules are the core power generation equipment of photovoltaic power plants, and their performance and service life directly affect the power generation capacity and investment return of the entire system. Conventional PV modules take crystalline silicon cells as the core and form a modular whole through lamination and encapsulation of multi-layer functional materials, featuring strong weather resistance, stable structure, and easy large-scale installation.​

During long-term outdoor operation, modules must withstand complex environmental tests such as alternating high and low temperatures, ultraviolet radiation, wet-heat freezing-thawing, wind and sand, and hail. Therefore, their structural design must balance high light transmittance, high insulation, high bonding strength, and high environmental stability. In-depth analysis of the composition and functions of conventional PV modules is an important foundation for optimizing module performance, improving reliability, and reducing attenuation rate.

2. Core Composition and Functional Analysis of Conventional PV Modules​

Conventional PV modules adopt a typical "sandwich" laminated structure, which is, from top to bottom: tempered glass, upper EVA layer, cell string, lower EVA layer, backsheet, with aluminum alloy frame and junction box attached externally to achieve mechanical fixation and electrical output. The functions of each part are highly coordinated and indispensable.​

(1) Solar Cells: Core Devices for Photoelectric Conversion​

Solar cells are the core components of PV modules for energy conversion. The mainstream products are crystalline silicon cells, including P-type PERC cells and N-type high-efficiency cell technology routes such as TOPCon and HJT.​

Their core function is to directly convert incident solar radiation into DC electrical energy based on the photovoltaic effect. Through the diffusion process, a PN junction is formed in the cell. Under photon excitation, electron-hole pairs are generated, which are separated and move directionally to form current under the action of the built-in electric field. Parameters such as the conversion efficiency, series resistance, leakage current, and low-light response of the cells directly determine the nominal power and actual power generation performance of the modules.​

Inside the module, the cells are connected in series through interconnectors to form cell strings, which are then connected in parallel through bus bars to achieve reasonable configuration of voltage and current, ultimately meeting the electrical design requirements of the system.

(2) High-Transmittance Low-Iron Tempered Glass: Outer Protection and High-Transmittance Light Collection​

The surface layer of PV modules adopts high-transmittance low-iron ultra-white tempered glass, which is the first protective and light-collecting structure of the module.​

Its main functions include:​

1. High Light Transmittance: The low-iron formula can significantly reduce iron content, reduce light absorption and reflection, improve solar transmittance, ensure that the cells receive sufficient radiation, and enhance photoelectric conversion efficiency.​

2. Mechanical Protection: Tempering treatment endows the glass with high strength and impact resistance, which can resist external impacts such as hail, gravel, and wind pressure, avoiding damage to the internal cells.​

3. Environmental Weather Resistance: It has excellent UV resistance, moisture-heat resistance, and aging resistance, and is not easy to yellow, crack, or corrode during long-term outdoor use.​

4. Insulation and Support: As a rigid carrier on the surface of the module, it provides flat support for the internal structure and has basic electrical insulation function.

(3) EVA Film: Laminated Encapsulation, Bonding and Insulation​

EVA (Ethylene-Vinyl Acetate Copolymer) film is a key encapsulation material for PV modules, which is laid on both upper and lower sides of the cells and cured by high-temperature lamination.​

Its core roles are reflected in:​

1. Bonding and Fixing: Firmly bond tempered glass, cells, and backsheet into a whole, eliminate interlayer gaps, and improve the structural integrity of the module.​

2. Optical Coupling: High light transmittance can reduce interface light reflection, improve light utilization rate, and assist in improving power generation efficiency.​

3. Insulation Protection: It has excellent electrical insulation performance, preventing cell leakage and short circuit, and ensuring system safety.​

4. Buffering and Sealing: Buffer external stress, block the intrusion of water vapor, oxygen, and dust, and avoid cell oxidation, corrosion, and PID attenuation.​

5. Environmental Aging Resistance: UV absorbers and crosslinking agents are added to ensure no yellowing, delamination, or failure during long-term outdoor use.

(4) Backsheet: Back Insulation and Environmental Barrier

The backsheet is located at the bottom layer of the PV module, which is a composite polymer material. Common types include TPT, KPE, KPK and other structures.

Its main functions are:

1. Back Insulation: High volume resistivity and surface resistivity prevent electrical leakage, meeting safety regulations and system insulation requirements.

2. Water and Oxygen Barrier: Excellent water vapor barrier performance, forming a fully enclosed structure with EVA to delay internal aging of the module.

3. UV Resistance and Weather Resistance: Effectively block UV penetration, protect internal EVA and cells, and adapt to high temperature, high humidity, and low temperature environments.

4. Mechanical Protection: Improve the scratch and puncture resistance of the module's back, and protect the internal structure during transportation and installation.

(5) Aluminum Alloy Frame: Mechanical Reinforcement and Installation Adaptation

The frame of PV modules generally adopts anodized aluminum alloy profiles, which form a rigid outer frame through corner code connection.

Its core functions include:

1. Structural Enhancement: Improve the overall bending strength and wind pressure resistance of the module, preventing deformation and breakage of the laminated part.

2. Edge Protection: Protect the glass edge of the module, reduce the risk of collision and chipping, and improve the safety of transportation and construction.

3. Easy Installation: The standardized frame design can adapt to installation methods such as pressing blocks and fixtures, realizing rapid fixation of the module on the bracket system.

4. Grounding and Current Conduction: It can realize module grounding, reduce damage to the module caused by lightning strikes and static electricity, and improve system safety.

(6) Junction Box: Electrical Lead-Out and Bypass Protection

The junction box is installed outside the backsheet of the module, which is the electrical output interface and protection device of the PV module, integrating bypass diodes inside.

Its main functions are:

1. Electrical Energy Lead-Out: Collect the DC electrical energy generated by the cell string and output it to the inverter through cables to realize electrical connection.

2. Bypass Protection: When the module is partially shaded, damaged, or mismatched, the bypass diode conducts, avoiding local overheating and burning caused by the "hot spot effect" and ensuring the safety of the module.

3. Sealing and Insulation: It has a high protection level (usually IP67 and above), which is waterproof, dustproof, and anti-leakage, adapting to harsh outdoor environments.

4. Electrical Connection Expansion: Support series connection of multiple modules, facilitating the formation of PV strings and meeting the voltage design requirements of the power station system.

3. Impact of Component Synergy on Module Performance

The overall performance of PV modules is not determined by a single component, but by the synergy of all components:

• Tempered glass and EVA together determine the optical utilization rate, directly affecting the power generation performance under low and strong light;

• Cell efficiency and encapsulation loss determine the nominal power of the module;

• The sealing of EVA, backsheet, and frame determines the long-term weather resistance and anti-attenuation ability;

• Junction box and insulation design determine the electrical safety and reliability;

• The overall structural design determines the mechanical strength, installation adaptability, and environmental adaptability.

Material defects or process out of control in any single link may lead to problems such as delamination, yellowing, hidden cracks, hot spots, and PID attenuation of the module, greatly shortening its service life.

4. Conclusion​

Conventional PV modules take crystalline silicon cells as the core and form a complete functional system consisting of tempered glass, EVA film, backsheet, aluminum alloy frame, and junction box. Each component has a clear division of labor: solar cells realize photoelectric conversion, tempered glass and backsheet provide environmental protection, EVA completes encapsulation, bonding and insulation, the frame achieves mechanical reinforcement, and the junction box undertakes electrical output and safety protection.​

This structural design not only ensures efficient power generation but also achieves excellent mechanical strength, insulation performance, and long-term outdoor reliability, making it the mainstream technical solution for current photovoltaic power generation applications. With the continuous iteration of high-efficiency cell technology and encapsulation materials, the module structure will be continuously optimized, but the core composition and basic functional logic will remain stable for a long time, which plays an important supporting role in promoting the large-scale and standardized development of the photovoltaic industry.