Dynamic modelling and simulation of the all-vanadium redox flow battery

With the increasing need for large energy storage in renewable energy applications, the all-vanadium redox flow battery has received the most attention to date as the energy storage technology most likely to meet the required energy efficiency, cycle life and cost structure. The widespread commercialization of the vanadium redox flow battery will only be realized however, if battery operation can be optimised to achieve the necessary cycle life and cost reduction of key components are properly addressed. This thesis aims to explore first-principle dynamic models that can be subsequently utilized in model-based control system development for the safe and efficient operation of the VFB under a range of temperatures and cycling conditions. The work begins with modelling of the effects of vanadium ion diffusion across the membrane and gassing side reactions on the basis of mass balance and Fick's law, followed by employing energy balance to investigate the variation in electrolyte temperature as a function of time under different operating conditions and battery structure design. The energy balance is subsequently coupled with the mass balance by means of considering the temperature dependence of vanadium ion diffusion and the thermal effect of self-discharge reactions, providing a more accurate prediction of electrolyte temperatures during both continuous charge-discharge cycling and standby periods. n addition to self-discharge, the shunt currents arising from the potential gradient across the stack are also modelled in an electric resistance circuit that is combined into the mass and energy balances. The upgrade in the model not only accounts for the heat generation from shunt currents during battery cycling and standby, but contributes to a more accurate prediction of stack round-trip efficiency in the presence of the parasitic loss of energy as a result of shunt currents. Last but not the least, the pressure drop in the flow frame along with the pressure losses in the porous electrode and the pipes is calculated and incorporated into the model. With the knowledge of total pressure losses in the vanadium redox flow battery system, the overall system efficiencies under different constant or variable flow conditions are compared in an effort to explore the optimal flow rate for certain stack and flow-frame design. Simulations of a 40-cell stack showed that overall energy efficiencies of over 79% can be achieved by using a flow factor of 7 along with the variable flow rate.

Grantor dc:publisher

UNSW, Sydney

Year dc:date

2014

Author dc:creator

• Tang, Ao

• Simulation analysis
• Vanadium redox flow battery
• Dynamic modelling

Statement dc:rights

• open access
• CC BY-NC-ND 3.0
• free_to_read

Licence

• https://purl.org/coar/access_right/c_abf2
• https://creativecommons.org/licenses/by-nc-nd/3.0/au/

Language dc:language

EN

Identifier

https://doi.org/10.26190/unsworks/16601

OAI identifier oai:identifier

oai:unsworks.library.unsw.edu.au:1959.4/53204