Photovoltaic Module Reliability - a Study on Cell Mismatch
Date
2020
Authors
Qian, Jiadong (Harry)
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This thesis is devoted to model and analyse the reliability of photovoltaic modules impacted by non-uniformity of cell performance. Both the short-term failure and the long-term degradation are discussed for a range of module technologies. This thesis is comprised of two main categories: simulating the hotspot effect in crystalline silicon solar modules with different configurations and the reliability of potential perovskite/silicon tandem modules.
First, an electrical-thermal simulation method is established to model the operating conditions and cell temperatures of crystalline silicon photovoltaic modules. Explicit solutions to the diode model for solar cells in the model allow for fast computation and easier implementation into other simulation models. Electroluminescence images of cells at reverse bias are used to characterize the distribution of reverse leakage current and verified to provide good simulation accuracy for ohmic-shunt-free cells. Applying the simulation to both a conventional full-cell module and a newer module design using half-cut cells and series-parallel mixed cell connections, the impact of the new module design on the hotspot risk is studied. Simulated and experimental results show a potential drop in the peak hotspot temperature by using the half-cell module design while also unveils a potential risk for certain cells to experience elevated temperatures even when fully-illuminated.
Next, the simulation method is applied to potential perovskite/silicon tandem modules to explore both the hotspot risks and long-term module degradation scenarios. Based on experimentally acquired current and voltage (I-V) characteristics of both perovskite and silicon sample cells, the module and cell operating conditions, as well as cell temperatures are modelled for tandem modules at non-ideal conditions using either two- or four-terminal designs. A unique effect by the reverse bias found at the tested perovskite sample cells that causes temporary short-circuit current reduction is studied. Its impact on module operation during dynamic shading conditions and the potential risk of prolonged hotspots are analysed and tested. Furthermore, this thesis presents a techno-economic analysis of the perovskite/silicon tandem modules accounting for potential perovskite cell degradation scenarios. Three perovskite cell degradation cases and an optical degradation coefficient are established including one representative case based on accelerated degradation experiments. The lifetime energy yield and economic viability of tandem modules using both two- and four-terminal designs are then simulated. The permissible perovskite cell degradation rates and additional cost for tandem technologies are estimated in comparison with reference main-stream crystalline silicon modules in 2025.
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