Photovoltaic power generation is a technology that directly converts light energy into electrical energy by using the photovoltaic effect at the semiconductor interface, mainly composed of solar panels (modules), controllers, and inverters. At present, the photovoltaic power generation market in China will shift from independent power generation systems to grid-connected power generation systems, including desert power stations and urban rooftop power generation systems.
Solar cell modules are composed of high-efficiency crystalline silicon solar cells, ultra-white textured tempered glass, EVA, transparent TPT backplane, and aluminum alloy frames. During processing, transportation, and installation, it is very easy to cause component splitting and hidden crack faults. The deterioration of the hidden crack and splitting of the components after the completion of the components will lead to thermal breakdown during the operation of the components, which will further cause damage to the components. Moreover, the splitting and hidden crack faults are not easy to detect, especially the hidden crack faults, which can hardly be distinguished by the naked eye. Combined with the desert photovoltaic project in Xinjiang, this paper specifically discusses the quality control of the splitting and hidden crack faults of the photovoltaic modules in the project to reduce the occurrence of splitting and hidden crack of the solar cell modules in the project.
1. Project Overview
The planned total capacity of a desert photovoltaic project in Xinjiang is 1000MW, of which the construction capacity of the photovoltaic project is 900MW fixed tilt photovoltaic system, and the construction capacity of the solar thermal project is 100MW tower-type solar thermal power generation unit, with a total of 208 photovoltaic sub-arrays. The project area has a continental arid – semi-arid climate, with the wind force generally being level 3 to 5, and the maximum being level 8.
2.Quality Control at the Source of Components
2.1 On-site Supervision
The project should entrust a third-party testing institution with corresponding qualifications for on-site supervision to comprehensively supervise the manufacturing process and manufacturing technology of the component manufacturer, the compliance of inspection and testing, and the inspection and testing of important links that affect the factory quality of the components, including the electroluminescence full inspection of the battery cells before lamination and packaging, the photoelectric conversion efficiency inspection of the components before leaving the factory, the performance inspection at low irradiance, the hot spot durability performance, the thermal cycle performance, the wet-freeze performance, and the resistance to potential-induced degradation performance [2]. These performances will directly affect the service life and power generation power of the components, and the relevant inspection and test results should comply with national standards.
2.2 Contractually Agreed Power Warranty
The contract with the component manufacturer should stipulate the power warranty, and the power attenuation rate should not be lower than that agreed in the owner’s main contract (determined according to the actual situation of the project): within 1 year from the start of the warranty period, the output power of the components under standard test conditions should not be lower than 97% of the STC (Standard Test Conditions) rated peak power indicated in the product specification or product nameplate; in the 2nd to 25th years, the annual output power decline of the components under standard test conditions should not exceed 0.7% of the STC rated peak power indicated in the product specification or product nameplate; after 25 years, the power output value of the components under standard test conditions should not be lower than 80.2% of the STC rated peak power indicated in the product specification or product nameplate.
3.Component Incoming Inspection Procedure Control
3.1 Joint Inspection
For each batch of components entering the site, the owner, supervisor, project materials department, engineering department, quality department, business department, labor service unit, and component supplier should conduct a joint inspection to jointly witness the EL characteristic detection and appearance inspection of the components entering the site.
3.1.1 EL Hidden Crack Detection
Sampling ratio: Different models and different production batches of components are sampled and inspected at a ratio of 2%. Instrument equipment and test environment: Single-chip EL tester, dark environment. Formed documents: EL hidden crack detection record, which needs to be signed and confirmed by the supplier and labor service unit.
3.1.2 Appearance Inspection
Inspection ratio: Visual full inspection (this inspection is for the outer packaging of the components, and the box has not been opened yet). Inspection focus: Check whether the outer packaging of the components is damaged, deformed, or has visible cracks. For components with obvious impacts on the box and visible cracks, the whole box will be returned. Formed documents: Component outbound list, which needs to be signed and confirmed by the labor service unit respectively. The labor service unit is responsible for the protection of the qualified components from unloading to installation and after installation. The labor service unit is responsible for the breakage and hidden crack of the components during the unloading, transfer, and installation of the components. Since the components are packed in boxes, it is difficult to transfer them after opening the box, and it is impossible to conduct 100% unpacking inspection when the components enter the site. Therefore, before the installation of the components, unpacking inspection is required, and the labor service unit witnesses the EL test, retains image data, and reports for approval and signs for confirmation on the same day.
3.2 100% EL Hidden Crack Characteristic Test
For components with poor packaging (box deformation, holes, soaked by rain), 100% EL hidden crack characteristic test should be conducted, which is implemented by the corresponding testing personnel arranged by the manufacturer under the joint witness of the project department and the component installation sub-labor service unit.
3.3 Sampling Inspection
Quantification of the sampling inspection ratio for component entry: In addition to the full inspection of components with poor packaging, the rest are sampled and inspected at a sampling ratio of 200 pieces / 10,000 pieces, that is, 2%. Each factory has a dedicated code. Taking a solar cell module manufacturer in a desert photovoltaic project in Xinjiang as an example, its factory codes include P, H, D, M, etc., which can be distinguished by the component outer box list.
3.4 Qualification Conditions for Component Sampling Inspection
Qualification conditions for each batch of component sampling inspection: The number of unqualified components is less than or equal to 5 pieces. If there are unqualified products in the sampling inspection, even if the number of unqualified components is < 5 pieces, the manufacturer should compensate or 补发 components according to the unqualified rate of the sampling inspection.