Tony Sample

Ensuring quality of PV modules

Photovoltaic (PV) customers need to have confidence in the PV modules they purchase. Currently, no test can quantify a modules lifetime with confidence, but stress tests are routinely used to differentiate PV product designs. We suggest that the industry would be strengthened by using the wisdom of the community to develop a single set of tests that will help customers quantify confidence in PV products. This paper evaluates the need for quality assurance (QA) standards and suggests a path for creating these. Two types of standards are needed: 1) QA of the module design and 2) QA of the manufacturing process.

Development of comparative tests of PV modules by the International PV Module QA Task Force

The International Photovoltaic (PV) Module Quality Assurance Task Force (PVQAT) was created in 2011 to develop a rating system that provides comparative information about the relative durability of PV modules. The identification of accelerated stress tests that can provide such comparative information is seen as a major step toward being able to predict PV module service life. This paper provides details of the ongoing effort to determine the format of such an overall module rating system.

A framework for a comparative accelerated testing standard for PV modules

As the photovoltaic industry has grown, the interest in comparative accelerated testing has also grown. Private test labs offer testing services that apply greater stress than the standard qualification tests as tools for differentiating products and for gaining increased confidence in long-term PV investments. While the value of a single international standard for comparative accelerated testing is widely acknowledged, the development of a consensus is difficult. This paper strives to identify a technical basis for a comparative standard.

Three-prong path to comprehensive technical standards for photovoltaic reliability

As the photovoltaic (PV) industry has grown, the long-term reliability of PV systems has become increasingly important. Many organizations are taking on the challenge of this multi-faceted issue. This paper describes three closely coordinated efforts that together will provide a comprehensive set of consensus standards and specifications for the technical aspects of verifying PV system quality and bankability. These three efforts are developing standards for 1) qualifying the design for the intended application (climate zone and mounting configuration), 2) quality management systems for PV module manufacturing, and 3) system-level inspections to ensure appropriate design, installation, commissioning, and operation of PV systems. A pathway has been identified for international implementation of these standards through the International Electrotechnical Commission.

Moving toward quantifying reliability - the next step in a rapidly maturing PV industry

Some may say that PV modules are moving toward being a simple commodity, but most major PV customers ask: “How can I minimize chances of a module recall?” Or, “How can I quantify the added value of a `premium module?” Or, “How can I assess the value of an old PV system that Im thinking of purchasing?” These are all questions that PVQAT (the International PV Quality Assurance Task Force) and partner organizations are working to answer. Defining standard methods for ensuring minimal acceptable quality of PV modules, differentiating modules that provide added value in the toughest of environments, and creating a process (e.g. through IECRE [1]) that can follow a PV system from design through installation and operation are tough tasks, but having standard approaches for these will increase confidence, reduce costs, and be a critical foundation of a mature PV industry. This paper summarizes current needs for new tests, some challenges for defining those tests, and some of the key efforts toward development of international standards, emphasizing that meaningful quantification of reliability (as in defining a service life prediction) must be done in the context of a specific product with design parameters defined through a quality management system.

Predicting PV module service life

The International PV Module Quality Assurance Task Force was created in 2011 to develop a rating system that provides comparative information about the relative durability of PV modules. The identification of accelerated stress tests that can provide such comparative information is seen as a major step toward being able to predict PV module service life. This paper will describe the methodology being employed by the Task Force as well as the efforts of the Ten Task Groups formed by the Task Force. Since this is an ongoing effort, this paper will serve as a progress report.

Assessment of ageing through periodic exposure to damp heat (85°c / 85 % RH) of seven different thin-film module types

In this paper we have investigated the accelerated ageing of seven different thin-film module types through the use of sequential damp heat (85°C/85% RH) tests. The module types [a-Si, tandem a-Si/a-Si micro-morph a-Si/μ-Si, triple junction a-Si, CIS (x2) and CdTe] were selected to cover a range of thin-film devices, materials and construction types. Sequential damp heat tests for cumulative exposure times of 250, 1000, 2000 and 3000h have been achieved to date, with the modules subjected to visual inspection, electrical insulation measurements and electrical performance measurements (IV curves). A wide range of performance losses (Pmax), from almost zero to −70%, were evident for the different technologies. Sequential damp heat exposure tests can be used to induce accelerated aging on thin-film modules. However, it is not possible to equate loss of power to a number of years of outdoor exposure due to the lack of knowledge of the acceleration factors for each PV module type.

Fill factor dependence of bilinear I–V curve translation accuracy

This paper presents an application of the bilinear interpolation/extrapolation I–V curve translation method [1–3] for the calculation of indoor curves of different photovoltaic devices at variable irradiance levels. Special attention was paid to modules exhibiting distorted I–V curves due to degradation provoked by 20 years outdoor exposure. The accuracy of the method was investigated for both interpolated and extrapolated curves at different levels of irradiance and compared to the IEC method. The accuracy of the bilinear curve translation is greater than the IEC method for devices with strongly distorted I–V characteristics (reduced FF) but similar for modules with high FF. Moreover, the bilinear method enables the translation of the I–V curves to irradiances varying by more than 30% from the recorded ones giving accurate results.