High-power UV-LED degradation: Continuous and cycled working condition influence

High-power (HP) UV-LEDs can replace UV lamps for real-time fluoro-sensing applications by allowing portable and autonomous systems. However, HP UV-LEDs are not a mature technology, and there are still open issues regarding their performance evolution over time. This paper presents a reliability study of 3W UV-LEDs, with special focus on LED degradation for two working conditions: continuous and cycled (30 s ON and 30 s OFF). Accelerated life tests are developed to evaluate the influence of temperature and electrical working conditions in high-power LEDs degradation, being the predominant failure mechanism the degradation of the package. An analysis that includes dynamic thermal and optical HP UV-LED measurements has been performed. Static thermal and stress simulation analysis with the finite element method (FEM) identifies the causes of package degradation. Accelerated life test results prove that HP UV-LEDs working in cycled condition have a better performance than those working in continuous condition

Functional analysis in long-term operation of high power UV-LEDs in continuous fluoro-sensing systems for hydrocarbon pollution

This work analyzes the long-term functionality of HP (High-power) UV-LEDs (Ultraviolet Light Emitting Diodes) as the exciting light source in non-contact, continuous 24/7 real-time fluoro-sensing pollutant identification in inland water. Fluorescence is an effective alternative in the detection and identification of hydrocarbons. The HP UV-LEDs are more advantageous than classical light sources (xenon and mercury lamps) and helps in the development of a low cost, non-contact, and compact system for continuous real-time fieldwork. This work analyzes the wavelength, output optical power, and the effects of viscosity, temperature of the water pollutants, and the functional consistency for long-term HP UV-LED working operation. To accomplish the latter, an analysis of the influence of two types 365 nm HP UV-LEDs degradation under two continuous real-system working mode conditions was done, by temperature Accelerated Life Tests (ALTs). These tests estimate the mean life under continuous working conditions of 6200 h and for cycled working conditions (30 s ON & 30 s OFF) of 66,000 h, over 7 years of 24/7 operating life of hydrocarbon pollution monitoring. In addition, the durability in the face of the internal and external parameter system variations is evaluated

Warranty Assessment of Photovoltaic Modules based on a Degradation Probabilistic Model

Evaluating the probability of failure of a product during the warranty is key to estimating the cost of its entire life cycle. PV modules are the most reliable elements of a PV system and their high reliability translates into long warranty periods (typically 25 to 30 years). The number of photovoltaic modules that fail during warranty and when they failed is an important issue to estimate Life Cycle Cost of photovoltaic modules. In this paper we pro-pose a coupled degradation-warranty model for PV modules. The proposed model is aimed to assess the probability of failure over time covered by warranty based on degradation data. This allows us to estimate the time of PV modules failure covered by the warranty. Alt-hough the warranty model has been applied to some forms of degradation and sales func-tions, our method can be applied to any real application. This allows the key parameters of the warranty to be obtained in a simple way. The required degradation parameters to fulfill warranty depends on the allowable ratio of warranted elements. However, as main conclu-sion of the influence of degradation rates on warranty is that it is not possible to fulfill 25 years of warranty if degradation rates are larger than 0,8%/year. The required degradation rates values, for 25 years of warranty, will be lower than 0,5%/year if the allowed warranted elements is in the range of 1%

Present status and main guidelines of IEC 62787: “Concentrator photovoltaic (CPV) solar cells and cell-on-carrier (CoC) assemblies – qualification”

Qualification standards are one the driving forces for the commercialization and production of the Concentrator Photovoltaic (CPV) technology. After several years of preparation the Committee Draft of IEC 62787 has been finally submitted. The new standard IEC 62787 (Concentrator photovoltaic (CPV) solar cells and cell-on-carrier (CoC) assemblies – Qualification) fills the gap between the IEC TS 62789:2014 (Photovoltaic concentrator cell documentation) and the IEC 62108 Ed 2 (Concentrator photovoltaic (CPV) modules and assemblies - Design qualification and type approval). In the present article, apart from analyzing the objective, main guidelines, the innovative characteristics, and the life estimation from several tests of the qualification standard is also explained

Reliability of commercial triple junction concentrator solar cells under real climatic conditions and its influence on electricity cost

This paper proposes a methodology for assessing the concentrator solar cell reliability in a real application for a given location provided the results from accelerated life tests. We have applied this methodology for the evaluation of warranty times of commercial triple junction solar cells operating inside real concentrator modules in Golden (Colorado, USA), Madrid (Spain) and Tucson (Arizona, USA) for the period 2012–2015. Warranty times in Golden and Madrid, namely, 68 and 31 years, respectively, for the analysed period, indicate the robustness of commercial triple junction solar cells. Nevertheless, the warranty time of 15 years for Tucson suggests the need of improvement in the heat extraction of the solar cell within the concentrator module. Therefore, the influence of the location on the reliability of concentrator solar cells is huge, and it has no sense to supply general reliability values for a given concentrator product. The influence of these warranty times for the three locations on the levelised cost of electricity has been analysed. Cost of €c10–12/kWh can be achieved nowadays, while after 1 GWp cumulative installed power, a dramatic reduction to levels of €c2–3/kWh is achievable

Innovative Temperature Accelerated Life Test for the determination of the activation energy of space solar cells

Space solar cells have been subjected to an innovative temperature Accelerated Life Test (ALT) to get information on their degradation and their activation energy. Our procedure emulates the thermal stress that solar cells suffer working under space conditions. Solar cells were kept in a climatic chamber under nitrogen atmosphere at three different temperatures for few months. After degradation, results have been fitted to a temperature Arrhenius model, in order to obtain the activation energy and acceleration factor of space GaInP/Ga(In)As/Ge triple junction solar cells