1,720,971 research outputs found
Fracture Mechanics of Silicon: From durability of photovoltaic modules to the production of thin film solar cells
Full text linkNowadays the photovoltaic research is focused on increasing the performances, the durability and reducing the cost of production of solar cells, such as PV modules. These are the paromount fields to make photovoltaics more attractive for the energetic market. In this dissertation two of these aspects are investigated: the durability and the cost reduction issues. The fracture mechanics of the Silicon, the standard material used for the solar cells, is the main subject of the presented study. In the recent and next years the relevance of the durability studies is expected to increase more and more because of the developing of a new segment of PV, the building integrated Photovoltaic (BIPV). These new products incorporating PV modules in the building materials are curtains, walls, windows, sloped roofs, flat roofs, facades, shading systems and roofing shingles. In the new generation of BIPV systems, PV modules replace parts of the building structure, providing functional considerations and lowering costs. In this market the thin-film PV is the most promising technology because of its superior flexibility, minimal weight, and the ability to perform in variable lighting conditions. The issues of this particular PV market are not only the energy production but also the structural safety and performance in addition to architectural specifics as the shadowing. In this framework the durability, the degradation and new technology to achieve a cost reduction are of fundamental importance. In this thesis, experimental diagnostic techniques and interpretative models based on linear and nonlinear fracture mechanics for studying the phenomena of fracture in Silicon are presented. In particular the development and the use of techniques for the quantitative analysis of electroluminescence signals, for the detection of cracks in Silicon caused by thermo-elastic stresses, have been developed. The experimental results have been obtained during an extensive experimental campaign conducted at Politecnico di Torino. For the interpretation of the experimental evidence it has been proposed an original onedimensional electrical model for predicting the eect of cracks on the distribution of electric current. Subsequently, the electric field has been coupled to the mechanical, introducing an electric resistance located at the level of the crack and dependent on the crack itself. In parallel, a numerical analysis has been carried out, using the finite element codes FRANC2D and FEAP, on the phenomenon of peeling in mono-crystalline Silicon induced by thermoelastic stresses. This study, which can be very important in applications because it may allow the production of ultra-thin solar cells with a significant saving of material, is carried out in collaboration with the Institute for Solar Energy Research (ISFH), Hamelin, Germany. This process exploits the thermo-mechanical stresses due to the contrast between the elastic proviii perties of Silicon and Aluminium in line with earlier studies of the school of Harvard. It has been proposed a broad campaign experimental and numerical in order to optimize the proces
A generalized electric model for mono and polycrystalline silicon in the presence of cracks and random defects
No full textDamage, micro-cracks, grain boundaries and other defects in solar cells are impacting on the electric power-loss of photovoltaic modules, their actual solar conversion efficiency and also their lifetime. In the present contribution, a one-dimensional model for simulating the electric current distribution in solar cells accounting for a distributed series resistance is generalized to the presence of partially conductive cracks. The proposed model is used to perform a quantitative analysis of electroluminescence (EL) images of cracked monocrystalline silicon solar cells. A further generalization in a stochastic direction is also proposed in order to take into account randomly distributed defects typical of polycrystalline silicon
Electro-mechanical coupling in cracked Silicon solar cells embedded in photovoltaic modules: experiments and simulations
No full textQuantitative EL image analysis towards thermo-electro-mechanical simulations in solar cells
No full textNumerical model for the prediction of the electric response of Solar Cells in presence of cracks
No full textA coupled thermo-electro-mechanical model for fracture in solar cells
No full textDamage, micro-cracks, grain boundaries and other defects in solar cells are impacting on the electric power-loss and lifetime of photovoltaic modules, a complex example of a laminate structure. In the present contribution, a one-dimensional model for simulating the electric current distribution in solar cells accounting for a distributed series resistance is generalized to the presence of partially conductive cracks. The proposed model is used to perform a quantitative analysis of electroluminescence (EL) images of cracked monocrystalline silicon solar cells. A further generalization in a stochastic direction is also proposed in order to take into account randomly distributed defects typical of polycrystalline silicon. These developments represent a fundamental step towards the realization of an innovative fully coupled thermo-electro-mechanical numerical method for the study of fracture in solar cells and assessing the durability of photovoltaics
Fatigue degradation and electric recovery in Silicon solar cells embedded in photovoltaic modules
Full text linkCracking in Silicon solar cells is an important factor for the electrical power-loss of photovoltaic modules. Simple geometrical criteria identifying the amount of inactive cell areas depending on the position of cracks with respect to the main electric conductors have been proposed in the literature to predict worst case scenarios. Here we present an experimental study based on the electroluminescence (EL) technique showing that crack propagation in monocrystalline Silicon cells embedded in photovoltaic (PV) modules is a much more complex phenomenon. In spite of the very brittle nature of Silicon, due to the action of the encapsulating polymer and residual thermo-elastic stresses, cracked regions can recover the electric conductivity during mechanical unloading due to crack closure. During cyclic bending, fatigue degradation is reported. This pinpoints the importance of reducing cyclic stresses caused by vibrations due to transportation and use, in order to limit the effect of cracking in Silicon cells
A global/local approach for the prediction of the electric response of cracked solar cells in photovoltaic modules under the action of mechanical loads
No full textAbstractA numerical approach based on the finite element method to assess the impact of cracks in Silicon solar cells on the electric response of photovoltaic modules is proposed. A global coarse-scale finite element model of the composite laminate is used for carrying out the structural analysis. The computed displacements at the edges of each solar cell are passed via a projection scheme as boundary conditions to a 3D local fine-scale finite element model of the cells which accounts for cohesive cracks. The evaluated crack opening displacements along the crack faces are finally used as input to an electric model characterizing the grid line/solar cell ensemble. The identification of the relation between the localized electric resistance due to cracks and the crack opening, to be used as a constitutive model of cracks, is finally discussed in reference to experimental tests performed in the laboratory
Electrical recovery and fatigue degradation phenomena in cracked silicon cells
No full textAn experimental study based on the electroluminescence technique is herein proposed to demonstrate the existence of coupling between mechanical deformations and the intensity of the electric field due to cracks in monocrystalline Silicon cells embedded in photovoltaic modules. In spite of the very brittle nature of Silicon, due to the action of the encapsulating polymer and residual compressive stresses resulting from the lamination stage, cracks experience crack closure and contact during mechanical unloading, partially recovering their original electric response. Crack propagation in case of cyclic loading, as, e.g., in case of vibrations due to transportation and use, have also been reported for the very first time. The research results pinpoint the need of improving electric predictions based on the estimation of inactive cell areas, since worst case scenarios not accounting for electro-mechanical coupling are too conservative
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