Thermal modelling and cost analysis for large-scale battery energy storage system (BESS) in grid-connected PV plant

Abstract

With the growing renewable energy capacity at an exponential rate every year, energy storage system has become popular. Among available energy storage systems, battery energy storage system (BESS) is widely used technology for its high-power density and fast response in renewable plants such as photovoltaic (PV) farm. The indispensable operation of battery system is to store excess PV generation and utilise it effectively. Fluctuation in PV generation output is a usual incident due to the unpredictable nature of PV generation. Therefore, a storage system is required to smooth its output generation prior to export it to the grid. Despite a lot of advancement in electrochemical storage technology and cost reduction, battery degradation remains a big obstacle for its wider acceptance in large-scale PV plant. Battery degrades because of charging/discharging operation as well as during idle condition. Elevated temperature of battery cell accelerates battery degradation, which indicates an imminent loss of expensive investment on BESS. In addition, elevated temperature is responsible for adding to the cost of battery system operation in the plant by accelerating cooling system operation.A number of research studies have been carried out to model thermal characteristics and behaviour of battery. However, the majority of studies reported in the literature are conducted on the small-scale battery thermal management where thermal behaviour is investigated using complicated thermo-dynamical models. However, a detailed thermo-dynamical model is not feasible for a large-scale BESS, where thousands of battery cells are installed and thermally interacting with each other. To consider battery degradation cost in the EMS, a solution is required to estimate battery thermal behaviour for any given profile without following any complex computational methods. An accurate battery cell temperature estimation can play a significant role in ensuring BESS optimal operation considering its degradation.In this thesis, the work starts with investigating the thermal behaviour of the battery with respect to its charging/discharging operation along with other possible effective parameters. Identifying the most dominant factors for battery cell temperature is one of the primary steps. A comprehensive thermal model will be developed to estimate battery cell temperature with 24 hours horizon in advance with high accuracy. Finally, an effective cost function will be developed considering dominant parameters. Different simulation strategies are implemented to assess the proposed models. This thesis will consider all pertinent matters and undergo rigorous assessments using real field data to ensure practicality. Scalability of the solution will be kept in mind for future development along with the aforementioned features. Power industries and academia will be benefited from the studies on thermal behaviour of battery, battery cell temperature estimation, and cost functions for effective BESS operations in a PV plant.