Investigation of the reliability of the encapsulation system of photovoltaic modules

Good reliability of the encapsulation system of Photovoltaic (PV) modules is crucial to ensure the long-term performance of PV modules. A carefully controlled lamination process is required to produce a reliable encapsulation system. To date, the influences of different lamination conditions on the reliability of the encapsulation system are poorly understood. To predict the performance of the encapsulation system, the correlation of the reliability of the encapsulation system with various stress levels is required, which is poorly developed. This thesis improves the understanding of these issues by investigating the correlation of different lamination conditions with the reliability of the encapsulation system and the degradation of adhesion strength under variable damp-heat conditions. The influence of the curing temperature and curing time on the long-term reliability of the encapsulation system is investigated from various viewpoints such as curing level of EVA, chemical and optical stability of EVA and adhesion strength within the encapsulation system. The correlation of curing level and lamination quality has been identified. The effects of over-curing are demonstrated. Results show that the chemical stability, optical stability and the adhesion strength between encapsulant and backsheet increases with the increasing curing level. However, the best long-term adhesion performance at the glass-encapsulant interface is obtained at lower gel content. Too high curing can cause problems of bubble generation, discoloration and unstable interfaces. Among those identified degradation phenomena, interfacial adhesion strength demonstrates the fastest and the largest degradation. The reliability of the adhesion strength is further examined under different stress levels. Among different environmental stress factors, moisture is considered to cause the greatest problems of adhesive interfacial stability. Therefore, the adhesion strength is investigated under different damp-heat conditions. A methodology is developed that can be used to model the adhesion degradation induced by moisture at different humidity and temperature conditions. To do so, a stress model is established which enables quantitative description of the moisture related stresses on PV modules. Based on this model, an exponential correlation is established between the adhesion strength and the humidity and temperature levels. This enables the comparison of adhesion strength of PV modules operating at different humid environments

Electricity generation and bivalent copper reduction as a function of operation time and cathode electrode material in microbial fuel cells

The performance of carbon rod (CR), titanium sheet (TS), stainless steel woven mesh (SSM) and copper sheet (CS) cathode materials are investigated in microbial fuel cells (MFCs) for simultaneous electricity generation and Cu(II) reduction, in multiple batch cycle operations. After 12 cycles, the MFC with CR exhibits 55% reduction in the maximum power density and 76% increase in Cu(II) removal. In contrast, the TS and SSM cathodes at cycle 12 show maximum power densities of 1.7 (TS) and 3.4 (SSM) times, and Cu(II) removal of 1.2 (TS) and 1.3 (SSM) times higher than those observed during the first cycle. Diffusional resistance in the TS and SSM cathodes is found to appreciably decrease over time due to the copper deposition. In contrast to CR, TS and SSM, the cathode made with CS is heavily corroded in the first cycle, exhibiting significant reduction in both the maximum power density and Cu(II) removal at cycle 2, after which the performance stabilizes. These results demonstrate that the initial deposition of copper on the cathodes of MFCs is crucial for efficient and continuous Cu(II) reduction and electricity generation over prolonged time. This effect is closely associated with the nature of the cathode material. Among the materials examined, the SSM is the most effective and inexpensive cathode for practical use in MFCs

Realistic adhesion test for photovoltaic modules qualification

Adhesion requirements for photovoltaic modules to ensure reliability are often discussed but not well defined, neither in terms of tests nor actual requirements. This paper presents a new approach for realistic assessment of the adhesion strength, which shows the conventional peel test may not ensure reliability. The test presented reproduces the actual adhesion requirements for fielded modules much more closely than the commonly used peel testing. The test is conducted in-situ during standard damp-heat test at a temperature of 85°C and 85% relative humidity, with the modules installed at an angle to give an appropriate force vector perpendicular to the backsheet. This is achieved by attaching weights to the back of the tested samples which are mounted with a 45° angle on a testing rack in the environmental cabinet. With an appropriate weight holder, this could be done as part of the standard damp-heat cycle during certification and would not involve additional testing time nor significant changes in the commonly used racking. This approach will identify the weakest interface of the multilayer encapsulation system. A number of test-to-fail bespoke samples are tested to set realistic fail criteria. It is shown that the test allows discrimination between different samples and can identify unsuitable production processes

Adhesion testing for photovoltaic laminates

An adhesion test allowing for the realistic assessment of adhesion needs for PV modules has been developed. The difference is that the test is conducted in-situ during ageing experiments. Weights were attached to the backsheet of tested PV mini-modules in order to test stability of lamination and adhesion. All samples were tested at standard test conditions of module temperature of 85ºC and 85% relative humidity. It is shown that appropriately laminated samples were able to withstand the force of 20g/cm for 1000 hours

Adhesion requirements for photovoltaic modules of polymeric encapsulation

Adhesion requirements for PV are often discussed but a detailed quantification based on scientific principles is outstanding. A test for the realistic assessment of requirements is presented. The difference between this test and the conventional peel test is that the test is conducted in-situ during ageing experiments in the climatic cabinet at realistic operating temperatures. Weights are attached to the backsheet of tested PV mini-modules to test stability of adhesion as devices being aged. This test is designed to identify the weakest interface of the multilayer encapsulation system and investigate the difference between field tests and failures (not) observed in certification testing. A series of samples was prepared under a wide range of lamination conditions. Different failure modes and ageing characteristics were observed. Some samples suffered quick failure of the adhesive bonds in the encapsulation system while others withstood forces of 20g/cm for 1000 hours. The test allows a clear discrimination between different samples and links closely to operational requirements

Effects of different lamination conditions on the reliability of encapsulation materials of pv modules: adhesion strength

Adhesion strength at different interfaces of the packaging materials of Photovoltaic (PV) modules is an important factor to ensure the long-term reliability and durability of PV modules. The performance of the encapsulation system is expected to be influenced by the lamination processes where temperature, pressure, time and cooling rate are to be controlled. This paper investigates the effects of different lamination temperatures and time on the durability of the packaging materials of PV modules from the viewpoint of adhesion and de-bonding behaviors through damp-heat tests

Influences of lamination condition on device durability for EVA-encapsulated PV modules

PV modules rely on their encapsulation to provide durability. The pottant is predominantly ethylene vinyl acetate (EVA). It is protected by foils and glass to minimise encapsulant related degradations such as delamination, decomposition and corrosion. Types of EVA and/or backsheet will influence overall durability, as has been reported frequently. The lamination process as well as material handling also contributes to overall durability, but the impact is not always obvious. This paper investigates the effect of lamination temperature on encapsulation quality and its impact on module durability in accelerated ageing tests. A series of laminations is carried out at different conditions within the typical window suggested by the manufacturer as well as slightly off specifications as could occur due to insufficient temperature control. The samples were exposed to prolonged standard ageing tests for up to 7000 hours. Use of subtractive electroluminescence (EL) images demonstrates a minimum of two different ageing mechanisms are active at different time constants and of different activation energies (Ea)

Adhesion requirements for photovoltaic modules of polymeric encapsulation

Adhesion requirements for PV are often discussed but a detailed quantification based on scientific principles is outstanding. A test for the realistic assessment of requirements is presented. The difference between this test and the conventional peel test is that the test is conducted in-situ during ageing experiments in the climatic cabinet at realistic operating temperatures. Weights are attached to the backsheet of tested PV mini-modules to test stability of adhesion as devices being aged. This test is designed to identify the weakest interface of the multilayer encapsulation system and investigate the difference between field tests and failures (not) observed in certification testing. A series of samples was prepared under a wide range of lamination conditions. Different failure modes and ageing characteristics were observed. Some samples suffered quick failure of the adhesive bonds in the encapsulation system while others withstood forces of 20g/cm for 1000 hours. The test allows a clear discrimination between different samples and links closely to operational requirements

DataSheet1.DOCX

<p>If the scalp potential signals, the electroencephalogram (EEG), are due to neural “singers” in the brain, how could we listen to them with less distortion? One crucial point is that the data recording on the scalp should be faithful and accurate, thus the choice of reference electrode is a vital factor determining the faithfulness of the data. In this study, music on the scalp derived from data in the brain using three different reference electrodes were compared, including approximate zero reference—reference electrode standardization technique (REST), average reference (AR), and linked mastoids reference (LM). The classic music pieces in waveform format were used as simulated sources inside a head model, and they were forward calculated to scalp as standard potential recordings, i.e., waveform format music from the brain with true zero reference. Then these scalp music was re-referenced into REST, AR, and LM based data, and compared with the original forward data (true zero reference). For real data, the EEG recorded in an orthodontic pain control experiment were utilized for music generation with the three references, and the scale free index (SFI) of these music pieces were compared. The results showed that in the simulation for only one source, different references do not change the music/waveform; for two sources or more, REST provide the most faithful music/waveform to the original ones inside the brain, and the distortions caused by AR and LM were spatial locations of both source and scalp electrode dependent. The brainwave music from the real EEG data showed that REST and AR make the differences of SFI between two states more recognized and found the frontal is the main region that producing the music. In conclusion, REST can reconstruct the true signals approximately, and it can be used to help to listen to the true voice of the neural singers in the brain.</p

Audio2.WAV

<p>If the scalp potential signals, the electroencephalogram (EEG), are due to neural “singers” in the brain, how could we listen to them with less distortion? One crucial point is that the data recording on the scalp should be faithful and accurate, thus the choice of reference electrode is a vital factor determining the faithfulness of the data. In this study, music on the scalp derived from data in the brain using three different reference electrodes were compared, including approximate zero reference—reference electrode standardization technique (REST), average reference (AR), and linked mastoids reference (LM). The classic music pieces in waveform format were used as simulated sources inside a head model, and they were forward calculated to scalp as standard potential recordings, i.e., waveform format music from the brain with true zero reference. Then these scalp music was re-referenced into REST, AR, and LM based data, and compared with the original forward data (true zero reference). For real data, the EEG recorded in an orthodontic pain control experiment were utilized for music generation with the three references, and the scale free index (SFI) of these music pieces were compared. The results showed that in the simulation for only one source, different references do not change the music/waveform; for two sources or more, REST provide the most faithful music/waveform to the original ones inside the brain, and the distortions caused by AR and LM were spatial locations of both source and scalp electrode dependent. The brainwave music from the real EEG data showed that REST and AR make the differences of SFI between two states more recognized and found the frontal is the main region that producing the music. In conclusion, REST can reconstruct the true signals approximately, and it can be used to help to listen to the true voice of the neural singers in the brain.</p