Coordination of Storage Systems to reduce the Impact of high Penetration of Solar Energy in Distribution Network

Dongxiao Wang, Australian Energy Market Operator, Australia

Introduction

Smart grids and cities are about anticipating situations, with an efficient forecast of weather conditions (for example solar energy prediction) and the possibility of making decisions in almost real-time [1]-[4]. With high penetration of variable renewable sources and the lack of anticipatory capabilities will result in uneconomic choices (such as severe the curtailment of generation) or lack of resilience when facing faults and disturbances [5-6]. However, as an effective solution to a future energy crisis, renewable energy resources are playing a vital role in current power systems. Based on the electricity forecast of International Energy Agency (IEA), the share of renewable energy in meeting global power demand would reach almost 30% in 2023, up from 24% in 2017 [7]. During this period, more than 70% of global electricity generation growth is met by renewables, led by solar PV. The large-scale penetration of PV energy in the distribution network causes many power quality issues as well, such as harmonic pollution and voltage problem. Overvoltage problem usually occurs at the time of high PV penetration periods and light load periods while undervoltage happens at the time of low PV penetration periods and heavy load periods. Although the energy storage cost has dropped, customers still bear a financial burden on installing large energy storage systems [8].

Except for voltage regulation, loading management is another important issue in distribution network due to the increasing energy-hungry appliances [9]. Especially in recent years, air conditioners are rapidly making the way to households because of summer heat and falling upfront cost. In line with an investigation led by Ausgrid [10], air conditioners contribute more than half of the load in some of their substations in summer days. If such demand comes up to a certain ratio of feeder load, challenges would be imposed on system operation. Network infrastructure capacity needs to be upgraded by the system operator to maintain reliable electricity supply. Consequently, billions of dollars would be spent on network upgrading to deal with the short but sharp peak load period. Nevertheless, infrastructure upgrading is only used for short periods of the year to meet peak demand, which is not cost-effective for system operators.

How to address the noted issues (i.e. voltage regulation and loading management) in a technically and economically efficient manner needs to be considered by the researchers. With the popularity of demand response (DR) technologies, an alternative way to address peak load is through DR programs by shaping the load curve for optimal use of energy and improving asset investment overall efficiency [11,12]. The pressure on integrating large-scale PV resources into distribution network can be alleviated as well with the help of DR programs. Owing to rapid progress in control and communication techniques, thermostatically controlled loads (TCLs) in the end-user side can be equipped with control modules to be better involved in DR programs. Among various types of TCLs, air conditioners receive researchers’ increasing attention because they have relatively fast response time with least end-user disruptions and mainly contribute to the summer peak load. When air conditioners are turned on/off, the room temperature can maintain within a certain range by storing a large amount of heat/cold air. This phenomenon is referred to as thermal inertia, which is defined as a thermal mass is capable of resisting the change on its temperature faced with the fluctuation of ambient temperature[13]. Consequently, a household can shift its energy consumption over the planning horizon to help consume the peak PV generation amount or reduce the peak load periods. The thermal buffering capacity in an air-conditioned household can imitate the energy buffering characteristics of physical energy storage systems, such as batteries, and hence can be viewed as virtual energy storage systems (VESSs).  Meng et al. coordinated DR from the domestic refrigerator to form the VESS, aiming to provide frequency service for the system. Distribution utilities are encountering new opportunities in the situation of a growing number of air conditioners and increasing penetration of PV resources at customer side. By coordinating VESSs, network voltage regulation and overloading issues can be solved in an efficient and economical way.

References

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Author

Dongxiao Wang (M’18) received the B.Eng. degree in thermal energy and power engineering from North China Electric Power University, Beijing, China, and the Ph.D. degree in electrical engineering from University of Newcastle, Australia, in 2014 and 2018. He is current a forecasting analyst in Australia Energy Market Operator, Australia. His research interest includes demand side management, the utilization of thermostatically controlled loads, energy storage systems, and renewable energy integration.

18 March 2020