Trovò, Andrea (2019) Industrializing Vanadium Redox Flow Battery. [Ph.D. thesis]
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Abstract (italian or english)
Redox flow batteries (RFBs) have strong potential for providing future stationary energy storage, in view of the rapid expansion of renewable energy sources and smart grids. Their development and future success largely depend on the research on new materials mainly electrolytic solutions, membranes, and electrodes that are typically conduced on small single cells. Technological development plays a fundamental role in view of the successful application of RFBs in large plants, and while a quite vast literature on these topics already exists, very little research has been reported on the technology of large RFB systems. This thesis presents the design, construction, and extensive experimental campaigns of a vanadium redox flow battery (VRFB) test facility of industrial size, referred to as IS-VRFB, where such technologies have been developed and tested.
The heart of the IS-VRFB is a 9 kW/27 kW h 40-cell 600 cm2 stack, which is one of the very few VRFB plants of this size in the world. The polarization curve during charge and discharge has been performed showing superior performances in comparison to those normally reported in the literature for this type of battery, and a procedure for qualifying such performance has been developed, and is presented in this study.
Extensive numerical modeling has been carried out to gain a full understanding of the experimental data. Accordingly, this thesis reports on an original model capable of simulating the thermal behavior of a VRFB stack both in standby (i.e. without power and reactants flow), and in charge/discharge conditions, capable of computing the evolution of the temperature distribution in the cells (taking into account ions crossover through the membrane, and Joule loss due to shunt currents and inherent self-discharge effects). For the first time, a model is presented that is capable of simulating the cell temperature distribution in the stack and its time evolution considering all above effects, providing new results that can constitute the basis for advanced cooling strategies in future industrial RFB systems.
An analysis is also presented of the losses occurring in the system due to species crossover, shunt current, hydraulic pressure drops, and pumping, in addition to cell over potentials. Fast response analyses have been developed, achieving important information with regard to the dynamic response of the battery when connected to a grid. Preliminary impedance spectroscopy tests in a multichannel configuration are also reported showing the electrical behavior of such a VRFB system.
This study enables important drivelines to aid the designers of a compact VRFB stack to increase the battery efficiency. Similar analyses have been performed to obtain the optimal flow for each operating condition on such an industrial VRFB system. To the best of the autor's knowledge, studies that offer detailed scrutiny of all major loss causes that are experimentally validated on a kW-class system are missing in the literature. In general, the results presented are new and aim to cover the lack of studies on IS-VRFB in view of widespread commercialization.
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