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Smart Reconfigurable photovoltaic modules for Building Integrated PhotoVoltaic applications

Periodic Reporting for period 1 - SRec BIPV (Smart Reconfigurable photovoltaic modules for Building Integrated PhotoVoltaic applications)

Período documentado: 2018-03-01 hasta 2020-02-29

One of the main limitations affecting the PhotoVoltaic (PV) energy production of a PV module is related to current mismatch. In applications such as Building Integrated PV (BIPV), the PV modules cannot always be placed under ideal circumstances due to restrictions arising from the building profile, so that both non-ideal orientation and inhomogeneous irradiation resulting from shadowing from obstacles will often create non-uniform illumination. This, in turn, creates current mismatch not only among different modules belonging to the same array, but also within each PV module. Unfortunately, performance of conventional PV modules is strongly degraded in conditions of partial shading, with dramatic losses even if only one cell is shaded. Thus, shade tolerant modules are needed to facilitate exploitation of PV in the urban environment. Such modules will thus enable net zero energy buildings, or even net positive energy buildings. As a consequence, shade-tolerant PV modules will also speed up the energy transition from fossil-based to zero-carbon, that is necessary to limit climate change. The main objective of this project is to design and demonstrate novel energy efficient, shade tolerant and cost-effective PV modules, with optimal performance in BIPV applications, thanks to the implementation of reconfiguration strategies
WP1 focused on the design of the different components of Reconfigurable Smart PV (RSPV) modules. First of all, the module layout has been investigated, to select few promising topologies able to significantly increase the energy yield under operating scenarios representative of BIPV applications. This investigation has been performed through accurate simulations, in which the irradiation profile over every cell of the PV module is calculated throughout the year. A methodology for the selection of candidate topologies has been developed based on practical manufacturing and financial considerations, then the resulting energy yield of different topologies has evaluated using an accurate and fast simulation framework (further discussed later). The best layout, allowing for highest net financial gain in 20 years (and also for highest energy generation in the simulated shading scenarios) has been selected for demonstration and fabricated. It is made of 120 6-inch half-cut cells, organized in 10 U-shaped strings that can be connected in series-parallel configuration under uniform operating conditions, or in parallel to 4 different local converters. Design of these local converters and realization of a first prototype on PCB has been also part of WP1. With the long-term goal of integration of the converters in the PV module laminate, the space of inductor-less converter topologies has been explored, and a cost-benefit analysis has led to the selection of two best candidates: Dickson topology with conversion ratio 3 and Dickson topology with conversion ratio 4. A fully controllable demo board that can implement both converter topologies has been designed and realized on PCB.
The focus of WP2 has been the development of the control algorithm for the RSPV module. This is based on a digital twin of the module itself that must run on a low-cost controller. Such a digital twin must ensure accuracy, to allow proper selection of the best configuration at run-time, and have limited execution time, to enable real-time reconfiguration. For this reason, the first part of WP2 has been devoted to the adaptation of the imec PV energy yield simulation framework for faster execution. Speed-up of ~190 times has been reached thanks to proper digitalization of the thermal network model and transformation of the electrical network model to remove implicit equations. This new simulation platform, implemented in both MATLAB and Python, is an essential part of current imec PV energy yield simulation framework and it has paved the way towards a collaboration (currently in place) between imec and the Lithuanian company PVcase to develop next-generation yield-simulation software for solar parks. The second task of WP2, to finalize the control algorithm, is to identify the PV module operating conditions with limited number of sensors, in order to use these identified parameters as input for the digital twin. In collaboration with University of Salerno and Tampere University, an identification algorithm has been developed that allows evaluation of irradiation and temperature based only on converter-level electrical measurements, that are also necessary to run the Maximum Power Point Tracking (MPPT) algorithm, and datasheet values.
WP3 and WP4 focused on the validation of the control algorithm and the RSPV module demonstrator. The algorithms developed in WP2 are both implemented in MATLAB, so that MATLAB itself could be used to port the algorithm on a digital device straightforwardly. Also, the different components of the RSPV module have been realized and indoor testing of the RSPV module layout have been performed, that demonstrates the feasibility of the proposed approach. Assembly of the full RSPV module for outdoor validation of its performance is work in progress at the moment this report is being written.
The idea of reconfiguration applied to PV system has been around for many years, with few researchers trying to apply this concept also to PV modules rather than systems. However, a thorough study of its applicability to the urban environment, with a procedure for the design of RSPV modules that takes into account also financial and fabrication constraints was missing. Furthermore, previous art focused usually only on one aspect of the problem. Some researchers/engineers focused on the algorithmic part, without considering the limitations of real fabrication of the electronics that is necessary to implement their reconfiguration strategies, coming up with e.g. extremely complex reconfiguration boards. Others only focus on the electronics part, proposing different levels of distribution of the power converters, that end up in expensive solutions or underestimate the complexity of the control algorithm. Some others only studied reconfigurable layouts, without taking into account the practical limitations related to the cells’ interconnection schemes they propose. The holistic design approach developed during this project is applicable to the design of other reconfigurable topologies, that goes beyond the one that has been developed during the project itself. Also, the algorithms that have been developed do not only find their application in the field of reconfigurable PV modules, but can be used for the control of both static and reconfigurable systems, as well as for the identification of PV systems’ state of health. This latter aspect is of utmost importance for early and automatic detection of faults and degradation, with positive consequences on the PV system lifetime (longer), operation and maintenance cost (reduced) and energy production (increased and preserved).