Photovoltaic (PV) module manufacturers, installers, and system owners share common interests in the long-term reliability of PV modules. When assessing the reliability of a PV system, you cannot focus solely on the performance of the PV module. What is more important is to control the overall system performance. The installed PV system can only reach the expected level when all its components from the PV system in the PV system to the grid connection can achieve the expected performance and the entire PV system is reliably maintained.
Environmental conditions, equipment temperatures, pollution levels, and other specific characteristics of PV system installation sites will have a direct impact on the performance and expected service life of a given installation, and will accelerate different aging rates at specific sites. In addition, the continued integration of the PV industry may lead to the closure of some manufacturers, so that manufacturers' warranty commitments are not guaranteed. In order to avoid these problems, PV manufacturers should adopt a comprehensive quality control program to solve the main problems such as sample sampling qualification rate, reliability test plan and test equivalent time.
The UL White Paper discusses various test methods that help manufacturers and customers evaluate the reliability of PV modules under real-world conditions. The white paper first elaborated on the durability and reliability of components in PV system performance, and explored the shortcomings of the theoretical model of average life when evaluating component reliability. Second, the white paper also introduced the framework for the reliability assessment of PV modules and demonstrated how three different tests can provide meaningful component reliability data in a continuous QC environment.
Theoretical estimation of service life
Lifetime or life cycle modeling of PV modules is based on a set of preconditions. These prerequisites are combined with laboratory measurement data and, in some cases, are related to information obtained through field practice and products returned on-site. However, the photovoltaic industry is a relatively new and rapidly changing industry that focuses on improving efficiency (ie, more efficient batteries, new materials, new designs, etc.). In contrast, PV's life expectancy can reach 20 to 30 years. These factors severely limit the availability and value of data currently available to predict the expected lifespan of the PV.
In order to answer major problems related to the service life of PV modules, accelerated aging test programs are usually used. Through these tests, the activation energy (Ea) can be determined using the Arrhenius method. Typically, Ea measurements for temperature, humidity, and ultraviolet (UV) are used in the first life prediction calculation after they are determined. The combination of *1,*2,*3,*4 with local weather data can provide a basis for the calculation of the expected service life.
However, the basic problem with this approach is that it depends only on the triggering of a single failure mechanism. In fact, with the almost unpredictable random and regionally relevant weather events (wind, wind, storm, snow, ice, and hail), different mechanisms of concurrent degradation occur.
Figure 1 shows the different power loss curves (dotted lines) observed for a certain class of PV modules, as well as phase warranty curves (blue and orange lines) that may occur. The green and red curves show any combination of degenerative curves, and each curve is the result of a combination of three different factors. The main problem revealed in this figure is which of the two-stage warranty curves (orange or blue) is more closely related to actual life performance.
To improve the theoretical estimation method of PV life, it is necessary to understand the interaction between various environmental conditions and the observed impact of these specific conditions on PV modules. Therefore, performance data must be collected from different locations, and data analysis must be conducted to determine the root cause of the failure. Table 1 lists the various environmental parameters and shows some of the observed effects of causing PV module failures.
Figure 1: Comparison of different degradation rates and warranty commitments over any time frame
Table 1: Environmental Factors and List of Observed PV Component Phenomenon
Realize reliability
The durability of PV modules depends on their design. On the other hand, the reliability of a PV module depends on the quality and integrity of the component manufacturing process. Even small changes in material quality or manufacturing processes can affect part reliability.
Testing and certification of PV modules in accordance with established standards often focuses on verifying that the basic design requirements have been met. It is proposed to adopt a component durability program that verifies the long-term stress test and end-of-life measurement for different batteries. *5,*6,*7 It is generally assumed that such long-term tests can also evaluate the reliability of PV modules, but the purpose of reliability testing is to verify whether a product is always produced within the original design parameters. Reliability testing increases people's confidence in the quality of production, and it consumes less time and costs than durability testing.
To ensure the test results, the reliability test must detect multiple samples. ISO2859-1, and other industry standards can provide guidance on how to select and evaluate production samples, and the standard can be used to determine whether a batch of test products is qualified. According to the sample acceptance and determination of the actual situation of the sample unqualified, a more rigorous or looser sampling plan can be adopted.
However, considering its importance in the reliable operation of the PV system, when it comes to PV components, it is necessary to carry out more complex quality inspections. Table 2 shows the scope of the ISO 2859-1 test, including:
· Number of samples required for different detection levels (S1-S4 and G1-G3) and plant size
· Acceptance Quality Level (AQL)
Permissible percentage of failed samples
The number of samples to be evaluated will implement statistical product differentiation. AQL determines the credibility of acceptance or determination of a given batch of samples that are not qualified. For some key tests such as security, a lower AQL (eg, 0.1) is considered an intolerable failure (zero failure tolerance). High levels of AQL are also acceptable in other tests designed to assess apparent defects such as mismatched batteries. Industry standards often specify benchmarks for determining the conformity of a product.
Table 2: Selected tests for reliability testing
Note: The above table shows the level of testing to be used, the number of samples required for each test, and the number of component failures allowed according to the ISO 2859-1 standard. Among them, "a)" refers to a power plant with a generating capacity of 1 MW, "b)" refers to a power plant with a generating capacity of 10 MW, and "c)" refers to a generating capacity of 50 MW with 240 W components. A power plant). *15
Table 3: Testing Services Provided by UL for Quality and Durability Requirements
At a Glance The above criteria can also be based on the requirements of customers, using more stringent or relaxed conditions. However, before the project and its testing begin, specific criteria for determining eligibility need to be specified. UL's own test programs include short-term quality tests as described above, as well as continuity testing of each test to assess the range of long-term durability or failure tests. Table 3 gives a brief overview of the various tests and the PV process technologies that are applicable to each test.
Selected test details
The following sections explore selected reliability tests for PV modules and demonstrate their potential value in assessing the reliability of PV modules. It is important to note that although these tests are not time-consuming or costly, it is important that the minimum number of necessary samples be evaluated to obtain statistically significant test results.
Electrical performance test
The electrical performance test is an effective way to verify the output power of a PV module within a defined uncertainty range. This uncertainty mainly comes from the spectral sensitivity of a given PV module, the old light source, and the general measurement uncertainty on the calibration chain.
The last uncertainty is usually constant, but the first two may have a significant impact on absolute measurements, especially for thin-film technology.
In addition to these limitations, electrical performance tests can also be used to examine the following aspects related to component reliability:
Determine the initial power loss due to preprocessing
· Verification of production electrical performance list
· Nameplate rating verification
These three factors are crucial for any effective estimation of production. To achieve a higher degree of confidence in estimating production, it is best to use the measurement data obtained from the actual PV modules that will be used for installation. This objective can be achieved by selecting test samples on site.
According to the shock absorber technology used in a given PV module, there is an initial power loss in the solar cell. The average initial degradation of polycrystalline cells is generally less than 1%, while single crystal cells may be as high as 5%. Figure 2a shows the potential distribution of the actual initial power loss value. However, when thousands of components are installed, this distribution appears on all components on average.
Verification of the production of electrical performance lists is an important first step for selecting PV module manufacturers. Verification of the list of production electrical properties is used to compare with the measured power loss parameters produced by tagged values ​​and the data obtained from third-party measurements. This verification work validated the PV manufacturer's calibration chain. Electrical performance verification is usually performed on at least 20 individual components to ensure proper distribution of defects and reduce uncertainty. In general, if there are fewer components tested, higher measurement uncertainty should be considered.
PV modules are generally sold on the PV module nameplate rating. The rated power on the PV module nameplate is used to simulate the energy output, ie accurate nameplate information is a key factor in achieving the energy output of a given installation. In accordance with the requirements of standards such as EN50380 and UL4730, *9, *10, the rating on the nameplate must take into account the effects of all initial degradation or light irradiation. Therefore, the PV module must be stabilized before measuring, and the ratio measurement value and rating on the nameplate should be handled.
Figure 2: Example of verification of electrical performance test.
a) Component power loss after pretreatment.
b) Power deviation and rated power on the nameplate.
An example of nameplate rating is shown in Figure 2b. In this case, the actual measured power is about 2.2% smaller than the specified nameplate rating. This inconsistency is likely to result in a difference between expected and actual power output.
Electroluminescence: Failure Detection and Mapping
The second method of evaluation, electroluminescence (EL) imaging, is mainly used for crystalline silicon PV modules, because if this method is adopted, it is generally believed that there will be obvious various component defects. *11,*12 Through EL imaging, various types of defects can be identified, each with its own root cause and performance impact. Evaluating EL images according to conventional methods can provide useful information about the reliability of PV modules.
Figure 3 shows two components, each with different numbers of cracks of varying severity. Components similar to those described in Part Number 1 are generally acceptable and can generate electricity in a reliable manner. A component that is similar to the one described in component number 2 will typically show a failed area after a short period of time, which can result in severe power loss.
Figure 3: EL image of two components; component number 1 shows some less severe cracks, and component number 2 shows some very serious defects.
By evaluating multiple images in a single batch, it is possible to determine the approximate quality level by the number and distribution of defects. Figure 4 shows an example of such an assessment. Each batch includes the same number of components. In the first batch, only a small number of randomly distributed defects were found, indicating that the test passed. However, in the second batch, the number of defective components significantly increased, and the defects and battery cracks were mainly concentrated in regions I4 and J5.
In short, these observations all indicate that there are important issues in the manufacturing process or the finished product transportation process, or both. In any case, the second batch of test results is unacceptable, and through further investigation will be able to find the root cause. More measures can include performing EL testing or more frequent testing of all components prior to installation and testing the in-use PV system.
Potential induced degradation
At present, potential induced degradation (PID) is mainly related to crystalline silicon components. Although some c-Si component manufacturers currently offer PV components that are said to have PID resistance, PID is still a problem to be solved. Due to the use of different test procedures and comparable indicators, there is a lack of data on the correlation between PID and recovery effects, so the work done to solve PID issues becomes more complex.
Unfortunately, thin-film PV modules do not always withstand ground potentials. Early thin-film assemblies exhibited some problems associated with transparent conductive oxide (TCO) corrosion (also referred to as "bar graph corrosion"), which is a very significant defect. However, today's thin-film modules also exhibit severe PIDs, a problem that cannot be detected early in the standard test protocol. *13
The focus of PID testing may vary, depending on the expected result. However, some options include:
· Mapped PV components for PID susceptibility
Batch verification for PID susceptibility
· Screening of component materials (batteries and encapsulants)
Standard test conditions (STC) and low irradiance performance test after PID test
The first item on this list may seem obvious, but the additional options provide more evidence for the long-term reliability of the component, allowing PID issues to be identified and resolved through more rapid measures.
Figure 5 shows the PID screening test results for three components from three different manufacturers. Over time, the first component exhibited an approximately linear degradation with different magnetic susceptibilities.
Figure 5: Investigation of PID susceptibility for different components (with three different degradation rate types)
The second component shown is actually an extreme case of the first component because it can quickly achieve 100% degradation and no further degradation over time. The third component is generally stable during the first phase of the PID test, but once it reaches a certain threshold of potential application, it quickly begins to degrade. *14 It is essential that the general behavior under the continuous laboratory voltage stress test (type 1 or type 3) must be ascertained and that the recovery of the components and the possible system-related options be investigated. *16
Since PV components can produce such aerobic results, it is important to set reasonable test parameters. It may be necessary to select parameters based on previous understanding of the type of component or the actual scope of the test, such as quality checks or durability surveys. UL's own default test scheme is to generate a potential through the conductive foil so that the assembly is subjected to a system voltage test in two weeks, thereby uniformly screening the entire assembly and all its solar cells. This default set of parameters can be adjusted and customized according to the specific requirements of a given project.
Summary and conclusion
In an increasingly competitive market environment, manufacturers must provide customers with PV modules that meet the promised performance specifications. The consistent reliability of the components depends on the quality and integrity of the manufacturing process. Even minor changes can adversely affect the reliability of the components and jeopardize the performance of the PV system. An effective and statistically-reliable reliability test scheme helps identify components that do not meet the design specification, thereby providing customers with confidence that they will be able to achieve the desired PV system performance.
By consolidating the results of years of research in the PV industry, UL has developed a reliable scientific testing program that can select PV modules from reliability, performance, and safety aspects. UL's performance and reliability services for PV modules provide third-party evidence of industry-standard testing to assess consistency in manufacturing processes including technical inspection of PV component plant processes. Additional tests can be performed to demonstrate the effect of long-term stress on the performance and safety of PV modules.
Roofing Sheet :Corrugated Metal Sheet,Corrugated Galvanized Steel Roofing Sheet, Corrugated Galvalume Roofing Tile, Corrugated Aluminum Roofing Tile,
Corrugated Stainless Steel Sheet ,Corrugated Hot Dip Zinc-Aluminum Steel Sheet .
Specifications:
1) Thickness: 0.14-0.8mm
2) Width: 600mm-1250mm
3) Length: Less than 12m
4) Zinc coating: 40g/sqm-220g/sqm
5) Color: blue, red, green, yellow, purple, pink and any other colors on the RAL COLORS
6) Standard: EN, ASTM, DS51D, JIS
7) Used for roof/wall
8) Made from pre-painted galvanized steel
9) Other exchanging model: YX35-125-750(V-
Advantage:
1) Easy installation and cut
2) High strength and long span
3) Low in costs
4) Durable 15-20years
5) Nice appearance
6) Anti-rust
Roofing Sheet
Roofing Sheet,Corrugated Iron Roof ,Tin Roof Sheet,Commercial Sheet Metal
CSTAR WIRE MESH ENTERPRISES CO., LTD. ,