Challenges and Mitigation Measures in Power Systems with High Share of Renewables—The Australian Experience

Global investment in large-scale renewable energy generation has exceeded 60% of new power generation in recent years, driven by emissions reduction goals and cost reductions. However, renewable energy zones (REZs), often located remotely, present challenges due to their lack of synchronous generation and strong transmission connections, resulting in low fault current and system strength. The integration of REZs, primarily through power electronic converters, further weakens the grid, leading to challenges in traditional stability (rotor angle, frequency, voltage), resonance, converter-driven stability, power system protection, and black-start capabilities. Grid reinforcement is a solution but is time-consuming. Alternative solutions include FACTS, synchronous condensers (SynCons), BESS, or combinations thereof. The Australian National Electricity Market (NEM) is a leading example of large-scale renewable integration, with significant installed solar and wind capacity. The NEM aims to operate securely with up to 75% variable renewable generation by 2025 and near 90% by 2035, requiring flexible devices like SynCons and BESSs to manage power system requirements. This paper aims to summarize challenges and mitigation measures in power systems with high renewable energy penetration, using the Australian experience to illustrate secure, low-cost, clean energy integration.

The paper references various studies and reports from organizations like the IEA, IRENA, and NREL, highlighting the global trend towards renewable energy and the associated challenges. It mentions previous work on optimal allocation and sizing of synchronous condensers and large-scale batteries in transmission grids. The Australian Energy Market Operator's (AEMO) reports and studies on renewable integration and system planning are also referenced. The literature review supports the context of the paper by showcasing the global significance of renewable integration and the challenges Australia faces, particularly in system strength and inertia.

The paper employs a descriptive and analytical methodology. It defines key concepts like short-circuit ratio (SCR) and system strength, using equations to illustrate their calculation and variations (CSCR, WSCR). It categorizes challenges into traditional stability (rotor angle, frequency, voltage), resonance and converter-driven stability, power system protection and coordination, and black-start capabilities. Mitigation measures are similarly categorized into operational constraints, transmission upgrades, special protection schemes, and inverter control (grid-following vs. grid-forming). The paper then presents case studies from the Australian NEM, including specific examples of challenges and solutions, such as voltage oscillations, resonance overvoltages, and the impact of IBR integration. Finally, it details the roles of synchronous condensers and battery energy storage systems in Australia's transition, drawing on specific projects and their impact. The methodology is primarily based on reviewing existing data, reports, and case studies to analyze the Australian experience.

The paper highlights that integrating high shares of inverter-based resources (IBRs) in power systems leads to decreased system strength and inertia, impacting traditional stability, causing resonance and converter-driven instability, affecting power system protection and black-start capabilities. The Australian NEM, with its high renewable penetration, serves as a case study showcasing these issues and their mitigation. The paper finds that operational constraints, while providing short-term solutions, come with economic consequences. Transmission upgrades, including synchronous condensers (SynCons) and battery energy storage systems (BESSs), are more sustainable solutions. Special protection schemes and advanced inverter control strategies are also necessary. In South Australia, SynCons have proven critical in enabling high levels of renewable energy integration, supporting over 2500 MW of IBRs and achieving minimum operational demands. BESSs, particularly the Hornsdale Power Reserve and Dalrymple BESS, have demonstrated significant market benefits and system security support during contingencies by providing fast frequency response, and the Dalrymple BESS being the first grid-forming battery in the NEM, showcasing its capabilities in synthetic inertia and island operation. The paper concludes that the combination of SynCons and BESSs has made a substantial contribution to Australia's energy transition, significantly reducing costs for consumers and paving the way for even higher penetration of renewable generation. However, it also notes the continuing need for traditional generation to address power variability and unforeseen events.

The findings of this paper address the research question by demonstrating the challenges and solutions involved in integrating high shares of renewable energy into power systems. The Australian NEM serves as a compelling real-world example of these challenges and solutions. The success of SynCons and BESSs in South Australia, highlighted by the achievement of unprecedented minimum operational demands, showcases the effectiveness of these technologies. The discussion emphasizes that these technologies are not mutually exclusive; rather, they complement each other, forming a portfolio of solutions to ensure grid stability and reliability. The results are relevant to the field by offering practical insights into the transition towards high-renewable penetration power systems, addressing technical issues with specific examples and quantifiable results. The findings are relevant globally, showcasing a successful model for other countries transitioning to more clean energy sources.

This paper provides a valuable overview of challenges and solutions involved in integrating high shares of renewables into power systems, using Australia as a case study. The successful deployment of synchronous condensers and battery energy storage systems highlights the importance of a portfolio approach, combining technologies to overcome system strength, inertia, and other limitations. Future research should explore the optimal integration of different energy storage technologies and the development of more sophisticated control strategies for seamless grid operation with high renewable penetration. Additionally, further research into regulatory frameworks that incentivize the deployment of these technologies is crucial.

The paper primarily focuses on the Australian experience, which might limit the generalizability of some findings to other power systems with different grid structures, renewable resource profiles, and regulatory environments. While the paper presents several case studies, a more in-depth quantitative analysis of the cost-benefit of different mitigation measures could strengthen its conclusions. Furthermore, the rapid evolution of technology means that some of the specific solutions and challenges discussed might change in the near future.