Accelerated aging tests vs field performance of PV modules

Abstract

The solar conversion market with photovoltaic (PV) systems has experienced and is experiencing an enormous growth worldwide and - according to the agreed goals of many countries to protect the climate - will further grow over the coming decades. Investments related to PV became an important financial product with the special feature of very long contract durations. A typical setting is an operation of more than 20 years, during which the generation of electricity and also revenues are expected. Sometimes Power Purchase Agreements with durations of up to 50 years have been reported. Taking these long operational times into account, quality, durability, reliability, and degradation rates become a crucial topic for the investment and for all stakeholders. PV modules are the dominating components in this regard since they prevail the investment and - due to their sheer quantity - are in most cases hard to replace if a system has PV module immanent issues. Accelerated ageing tests are in general used to ensure the quality of PV components. These tests are partly standardized, for PV mainly by the International Electrotechnical Commission IEC and related national committees. These standards are used for type approval testing or safety testing, which can also address legal issues. Accelerated ageing tests are also adapted to specific needs and for example used for quality assurance (QA) of manufacturers or service life prediction (SLP) by manufacturers or research institutes. All the efforts are taken to gain more knowledge about the behavior of PV modules in operation and thus the accelerated tests have to be related to normal operation. Since PV is used around the globe, the conditions vary significantly depending on the location of installation, from dry and sunny deserts to mountain climates to tropical or maritime climates. In addition, the type of installation has severe influence on the operational conditions of PV modules i.e. mounted on a roof, roof integrated, open rack - or even in upcoming applications like floating PV. The papers attempt is to give an overview on the state of the art of accelerated testing and field performance analysis of PV modules with focus on the developments over the last five to ten years. Developments are described and the status is analyzed regarding the significance of tests including the latest developments and open scientific gaps related to the envisaged correlation of accelerated tests with field performance. In the end the reader is enabled to differentiate between reliability testing and service life prediction. The understanding for a comprehensive approach of reliability testing including field evaluation data will be developed.