Search

28th European Photovoltaic Solar Energy Conference and Exhibition; 2832-2837, We investigate the composition of ethylene-vinyl acetate (EVA) PV-module encapsulation materials with different degrees of crosslinking and its influence on the module performance degradation. To do so, 0%, 50% and 90% cured samples consisting out of 5 EVA compounds are prepared and the volatile additives they contain are extracted and characterized. The stability towards oxidation of each material and each curing state is evaluated and is shown to be depending on the material composition, with lower stabilities found for materials with high amounts of curing agents such as peroxides and coactivators. In a second step, 0%, 50% and 90% cured laboratory scale laminates with 2 solar cells each are prepared with 4 different EVA materials. These modules are then tested under damp-heat conditions (85°C, 85% humidity) up to 2000 h or under UV irradiation at 60°C and their electrical performances are periodically measured. The degradation of the material is monitored by measuring its fluorescence intensity over time and the chemical composition of materials samples extracted during and after ageing is investigated. These experiments show that the 0% cured material is faster degraded than the 50% and 90% cured ones. Nevertheless, the decrease of the module performance over testing time does not differ from a curing state to the other.

27th European Photovoltaic Solar Energy Conference and Exhibition; 3033-3040, We use the fluorescence effect of the lamination material of PV modules to detect cracks in waferbased solar cells in a power plant. For this purpose the PV modules are irradiated by UV light and the fluorescence light is measured by a camera. The measurement is realized in the dark. This new application of the fluorescence method allows new insight to cracks of a huge amount of PV modules during service life without remounting or touching the PV modules. We found that the frequency distribution of so-called “cross cracks” are almost homogenous in the PV modules. These cracks are frequently induced by crumbs or needle-shaped production equipment and not introduced after production. We show that the measured distribution of “cross cracks” in the PV modules fits to the binominal frequency distribution, as it is expected for production induced cell failures. The measured crack frequency distribution for other crack types is compared to a finite element simulation of a simplified PV module. We find that the lateral crack distribution correlates with the simulated strain distribution induced by module vibrations. In total we found that 4.1% of the solar cells in the PV modules show at least one crack.

26th European Photovoltaic Solar Energy Conference and Exhibition; 3290-3294, Solar cell cracks in wafer based silicon solar modules are a well-known problem. In order to identify the origin of cracks and thus lay the foundation for the inhibition of crack formation, we provide for the first time a statistic crack distribution in photovoltaic (PV) modules. We evaluate electroluminescence images of PV modules tested at the ISFH with respect to cracks. The results of the static load test and the “as delivered” PV modules are compared. Additionally we perform a simulation of the strain distribution on a glass plate subjected to a uniform mechanical load and supported at the edges, which is used as a measure for the relative mechanical load on the individual cells. The measured crack distribution correlates well with the stress distribution calculated by the simulation. “As delivered” PV modules show an average of 6% of broken cells per PV module. The analysis of the spatial distribution and orientation of micro cracks in PV modules offers valuable insight into the causes of micro cracks if the PV module is subject to a uniform mechanical load. It lays the foundation for PV module developments that reduce the risk of cracks, as well as for statistical power loss assessment.

25th European Photovoltaic Solar Energy Conference and Exhibition / 5th World Conference on Photovoltaic Energy Conversion, 6-10 September 2010, Valencia, Spain; 3745-3752, Micro cracks in wafer based silicon solar cell modules are nowadays identified by a human observer with the electroluminescence (EL) method. However, the essential question of how the micro cracks affect the PV module performance has yet to be answered. We experimentally analyze the direct impact of micro cracks on the module power and the consequences after artificial aging. We show that the immediate effect of micro cracks on the module power is small, whereas the presence of micro cracks is potentially crucial for the performance of the module after artificial ageing. This confirms the necessity to develop the means of quantifying the risk of power loss in PV modules with cracked solar cells in their lifetime, in order to enable manufacturers to discard defective modules with high risk of failure while keeping modules with uncritical micro cracks. As a first step towards a risk estimation we develop an upper bound for the potential power loss of PV modules due to micro cracks in the solar cells. This is done by simulating the impact of inactive solar cell fragments on the power of a common PV module type and PV array. We show that the largest inactive cell area of a double string protected by a bypass diode is most relevant for the power loss of the PV module. A solar cell with micro cracks, which separate a part of less than 8% of the cell area, results in no power loss in a PV module or a PV module array for all practical cases. In between approximately 12% to 50% of inactive area of a single cell in the PV module the power loss increases nearly linearly from zero to the power of one double string.