Compared to other Pv equipment (such as inverters and grid-tie cabinets), Pv modules have fewer technical parameters. However, these parameters conceal deeper Pv knowledge, which we will explore in detail below.

1. Pv Module Power

Definition: Refers to the maximum output power of a Pv module under Standard Test Conditions (STC). STC conditions are: irradiance of 1000 W/m², cell temperature of 25°C, and air mass AM1.5.

Analysis:

The power rating marked on the PV module nameplate represents the peak power under specific test conditions. Actual operating power is influenced by factors such as weather conditions and load characteristics.

The unit for peak power is Wp, where W is the base unit of power in the International System of Units (SI). It is used to describe the power of any electrical device, including PV modules.

2. Conversion Efficiency

Definition: The ratio of the maximum output power (i.e., peak power) of a Pv module under Standard Test Conditions (STC) to the total solar power incident on the module's light-receiving surface, typically expressed as a percentage (%).

Analysis:

Conversion efficiency refers to the peak power conversion efficiency under specific test conditions. Actual operating efficiency is also influenced by factors such as weather conditions and load characteristics.

The conversion efficiency of most modules decreases as light intensity diminishes, with the rate of decline varying significantly depending on module materials and manufacturing processes.

3. Low-Light Performance of Pv Modules

Definition: Refers to the variation characteristics of a module's power generation performance (conversion efficiency, output power, voltage, current, etc.) under low light intensity. It is a key indicator for evaluating a module's power generation capability under non-intense light conditions.

Analysis:

Measuring a Pv module's performance under low-light conditions (typically defined as irradiance below 200 W/m², far below the standard test condition of 1000 W/m²) is a crucial metric for evaluating the module's suitability in complex lighting environments.

The strength of a module's low-light effect is primarily influenced by factors such as cell material, cell manufacturing process, and module encapsulation. With technological advancements, the low-light performance of modules has significantly improved.

The low-light effect directly impacts a module's total daily power generation. In regions where sunlight is not consistently intense—such as high-latitude areas or regions with frequent overcast and rainy conditions—modules with superior low-light performance can more efficiently utilize light during dawn, dusk, and cloudy/rainy days, thereby increasing overall electricity generation.

4. Pv Modules as Current Sources

Definition: The output current of a module remains constant under fixed illumination conditions (affected solely by light intensity), while the output voltage varies according to load characteristics.

Analysis:

Vmp (maximum power point operating voltage) describes the output voltage at which a module delivers maximum power under STC conditions. During actual operation, the module's real-world voltage ranges between 0 and Voc (open-circuit voltage).

In practical applications, inverters or controllers employ Maximum Power Point Tracking (MPPT) technology to automatically adjust load characteristics, ensuring the module operates at its maximum power point. At this point, the voltage is determined by the corresponding Vmp of the MPPT system.

Combining the above points: When a module is connected to an MPPT controller, the MPPT detects the module's open-circuit voltage (Voc). Once the module voltage exceeds the MPPT activation voltage, the MPPT begins operation, maintaining the module at its optimal power point voltage (Vmp).

5. Fill Factor

Definition: The ratio of the maximum power point (Pm) to the product of open-circuit voltage (Voc) and short-circuit current (Isc) under Standard Test Conditions (STC), typically expressed as a percentage (%).

Analysis:

Voc × Isc represents the theoretically maximum possible output power for a given Pv module, determined by the upper limit of the Pv characteristics of the cell material.

The fill factor expresses the ability to convert this “theoretically maximum possible output power” into the actual maximum power (Pm) available. Generally, high-quality Pv modules have fill factors typically ranging between 70% and 85%, influenced by factors such as cell material, manufacturing process, and temperature.

6. Bifacial Efficiency

Definition: The ratio of rear-side power generation to front-side power generation, typically expressed as a percentage. This ratio is also referred to as the bifaciality ratio.

Analysis:

Currently, TOPCon Pv modules demonstrate outstanding bifaciality performance, with mass-produced modules typically achieving bifaciality rates exceeding 80%. The ultra-high bifaciality solar module based on TOPCon technology showcased by Tongwei's Global Innovation R&D Center, certified by Germany's TÜV Rheinland, achieved a cell bifaciality rate exceeding 94.3% and a module bifaciality rate of 91.7%.

Back-side efficiency does not equate to back-side power gain. Back-side power gain depends not only on the module's back-side efficiency but also on multiple factors such as ground reflectance in the installation environment, module mounting height, array spacing, and tilt angle.