Optimization of battery energy storage systems for PV grid integration based on sizing strategy.

摘要

The market for solar energy has been expanding rapidly worldwide. However, due to the weather conditions, photovoltaic (PV) systems generally have considerable power variations, which include voltage fluctuations and frequency variations. As a result, the connected power systems may experience adverse effects from the fluctuating power generated by the PV system. The intermittent power generation of a solar farm can perturb the supply and demand balance of the whole power system. For stability, a power network requires a spinning reserve, which increases with the growth of PV installations and inevitably degrades the efficiency of power generation. Therefore, mitigating the adverse effects on the grid from an intermittent PV source is expected to be essential for increasing the penetration level of PV systems. Recently, battery energy storage system (BESS) has been seen as a promising solution to help PV integration, due to the flexible real power control of the batteries. Unfortunately, this technique has not been applied extensively due to the high cost of batteries. If chosen, battery storage needs to be designed methodically, which is critical for the owners of PV.;Firstly in this dissertation, an original sizing strategy is proposed for a dispersed BESS in distribution feeders with distributed PV systems. The main functions of the dispersed BESS are overvoltage reduction and peak-load shaving. The benefits and cost analysis of the installed dispersed BESS are conducted. Under high penetration level of PV systems, to assess the effect of the dispersed BESS on overvoltage reduction, the proposed cost--benefit analysis uses the work stress of voltage regulation devices as a reference. The factors of load shifting, peaking power generation, as well as dispersed BESS costs and an estimation of lifetime are considered in the annual cost calculation. In particular, lithium iron phosphate (LiFePO4) batteries and lead-acid batteries have been selected to demonstrate the proposed method on the modified GE distribution feeders. The economic analysis of these two types of battery can determine the lower cost battery type and the cost-effective size design for the dispersed BESS on different locations in the distribution system under high PV penetration level.;Secondly, this dissertation proposed a method to optimize the design of a centralized BESS capacity and the energy management system (EMS) based on a utility revenue analysis for a large-scale PV plant application. The battery storage, which is controlled by the EMS, aims to enhance the integration into the grid of a large PV plant by shaping the fluctuating PV plant output into a relatively constant power and supporting the peak load. LiFePO4 batteries and lead-acid batteries are used to demonstrate the proposed method in a utility model. The lifetime and the systematic performance of these two types of battery are compared. Furthermore, the change in utility revenue caused by the installed battery storage can be calculated and maximized based on the proposed method to determine the optimal design of BESS capacity and EMS for a large PV power plant application.;These two proposed methods can offer insights into the performance and economic analysis of a BESS in PV applications for project designers and business stakeholders. With the help of the developed methods, BESS designs can be optimized for any PV application with the necessary changes according to practical application. Finally, the scope of future work is discussed.