Effects of lamination condition on durability of PV module packaging and performance

Ten mini-modules of glass /encapsulant /backsheet structure were laminated under the condition of the same curing time and pressure, but different curing temperatures and aged in damp-heat accelerated ageing test in order to investigate the effect of temperature on the durability of PV module packaging and performance. Results show that the mini-modules using EVA as encapsulant were affected more by the laminating temperature compared to the mini-modules using modified ionomer. For EVA modules, samples with relatively low curing temperatures at 135-140ºC appeared to have higher adhesion between EVA and glass, lower moisture permeability into module and better dielectric of cells than those with high curing temperatures

Degradation of interfacial adhesion strength within photovoltaic mini-modules during damp-heat exposure

The degradation of adhesion strength between the back sheet and encapsulant due to moisture penetration has been investigated for commercial crystalline silicon photovoltaic mini-modules. The damp-heat tests originating from the International Electrotechnical Commission qualification test were carried out at five different temperature and relative humidity (RH) conditions (95 °C/85% RH, 85 °C/85% RH, 65 °C/85% RH, 85 °C/65% RH and 85 °C/45% RH). The adhesion strength was measured by 90° peel tests, carried out at specified time intervals during degradation. Several visible defects were observed, including delamination, moisture ingress and bubble formation. The adhesion strength showed a stretched exponential decay with time, and significant influence of test conditions was demonstrated. A humidity dose model was proposed by assuming micro-climates seen by the modules, that is, surface relative humidity of the back sheet as the driving factor for an Arrhenius-based model using temperature as accelerating factor. The correlation between adhesion strength degradation and humidity dose was investigated through linear and exponential models. Results showed that the conventional linear model failed to represent the relationship while the exponential model fitted to this correlation with extracted activation energy (Ea) of around 63 kJ/mol. This provides a model for the estimation of adhesion strength decay in dependence of the humidity conditions

Ageing of amorphous silicon devices in dependence of irradiance dose

The ageing behaviour of amorphous silicon (a-Si) devices is investigated in dependence of different light and temperature conditions. Eight a-Si mini-modules are illuminated and kept at constant temperature in an environmental chamber. The ageing behaviour is characterised in terms of a temperature-dependent irradiance dose rather than the exposure time or irradiance dependence in order to investigate possible ageing dependencies of environmental strains and to develop models for device long-term degradation

Modelling of realistic annealing behaviour of amorphous silicon photovoltaic devices

Long-term degradation and annealing behaviour of a-Si mini-modules is investigated in this paper. Four devices were firstly degraded by light and then annealed in the dark at temperatures ranging from 65-85°C. Dark annealing rates were obtained for each temperature. Further annealing with light bias was carried out for two of the devices in order to study the interaction between the light-induced degradation and thermal annealing process. Results demonstrate that the annealing in the dark is strongly influenced by the operating temperature but also dependent on the history of the devices. Annealing is a self-limiting process and is significantly influenced by the light intensity in the short-term exposure, giving rise for a balance-equation for modelling purposes

Evaluation of uncertainty sources and propagation from irradiance sensors to PV energy production

This work quantifies the uncertainties of a pyranometer. Sensitivity to errors is analysed regarding the effects generated by adopting different time resolutions. Estimation of irradiance measurand and error is extended throughout an annual data set. This study represents an attempt to provide a more exhaustive overview of both systematic (i.e. physical) and random uncertainties in the evaluation of pyranometer measurements. Starting from expanded uncertainty in a monitored pyranometer, the study concludes with an evaluation of its impact on the estimation uncertainty in the performance of a photovoltaics (PV) solar farm

Performance of an amorphous silicon mini module in the initial, light-induced degraded and annealed states

This work analyses the performance of single junction amorphous silicon (a-Si) mini modules in three main states: the initial non-degraded state, degraded state after light soaking and recovered state after thermal annealing. The applied methods of controlled indoor light-soaking and thermal annealing are detailed. Performance measurements are carried out under varying spectrum (E), light intensity (G) and temperature (T). Results show a reduction in STC power of up to 27.5% during the first 250h light soaking and a recovery of 56% after annealing for 250h at 80°C in the dark. After light soaking, devices also showed a reduction in low light performance and an increase in temperature coefficients, which was partly re-versed after annealing

Modeling A-Si module ageing using the concept of environmental dose

This paper investigates ageing of a-Si devices using indoor controlled irradiance and temperature stresses testing. Device maximum power degradation is analyzed against the proposed environmental dose, which is derived from the microscopic model of defects generation and annealing of a-Si material. This dose model well describes the ageing behavior for the devices degraded at different conditions of irradiances from 130-500W/m2 and temperatures from 25-85°C. This, thus, enables the comparison study of device ageing under different environmental conditions and allows the attempt to correlate the outdoor environment to indoor performance

Effect of module degradation on inverter sizing

The effect of amorphous Silicon (a-Si) module degradation on inverter sizing is investigated in this paper to identify appropriate sizing ratios even if only undegraded data-sheet values are available. The seasonal degradation and annealing pattern of a-Si modules requires special attention to the sizing of inverters for these devices, as is demonstrated in this paper for three types of modules with different degradation rates. The efficiency of the inverters depends on the sizing ratio as well as the DC input voltage. Here data of an inverter with relatively dependence on operating voltage is used. As modules degrade, the optimum ratio of system rated power with respect to inverter nominal power increases by 10 to 15% for the specific inverter. Considering the module life-time, the inverter size chosen to be matched to the degraded power and voltage rating achieves high efficiency over the life-time of the modules, while the inverter chosen to match initial values, as given by some manufacturers on their datasheets, can add about ten percent losses to the operation

Performance of amorphous silicon in the initial, degraded and annealed states under varying spectrum, irradiance and temperature

This work analyses and discusses the performance of amorphous silicon (a-Si) single junction mini modules in three main states: in the initial non-degraded, as purchased state, in the degraded state after light-soaking and in the recovered state after thermal annealing. The experimental set-up and applied methods of controlled indoor light-soaking and thermal annealing are detailed. Device performance measurements are carried out indoors under varying spectrum (E), light intensity (G) and temperature (T). Measurement results have shown a reduction in STC power of up to 27.5% during the first 250h light soaking and a recovery of 56% of the performance losses after annealing for 250h at 80°C in the dark. After light soaking, devices also showed a reduction in low light performance and an increase in temperature coefficients, which to some extent reversed during the annealing process

Thermo-mechanical stresses of silicon photovoltaic modules

Modelling and analysis of the thermomechanical behaviour of silicon photovoltaic (PV) modules has been conducted using finite-element numerical methods (FEM). Experimentally determined material properties have been implemented in the model to represent the 6-cell mini-modules fabricated at the Centre for Renewable Energy Systems Technology (CREST). The stresses generated during indoor accelerated ageing tests and real outdoor conditions have been compared. It is found that the thermo-mechanical stresses are highest at the extreme temperatures during indoor testing. The outdoor accumulated stress generated within the interconnecting ribbons is greater than the stress generated during indoor thermal cycling programs for the same amount of temperature travelled. The results shed light on the relevance of indoor accelerated ageing programs to real outdoor conditions