The role of inertia for grid flexibility under high penetration of variable renewables - A review of challenges and solutions

Several studies show that grid-integrated renewable energy (RE) sources have the potential to replace conventional synchronous generators in the network. This means the grid will experience low conventional inertia that is currently provided by synchronous generators. Low, unpredictable and time-changing inertia in the power system, as a result of high penetration of non-synchronous RE sources, can cause rapid frequency oscillations. The rapid and unpredictable frequency oscillations are the major source of stability challenges in the power system. Therefore, this research presents a comprehensive literature survey on the role of inertia for grid flexibility under high penetration of non-synchronous RE sources to the power system. As inertia is becoming a time-changing quantity, inertia estimation techniques have been gaining popularity as solutions to stability challenges faced by the power system. Related to time-changing inertia, the following are discussed in this survey research. First, synthetic inertia provision in the network and the need for inertia estimation are intensively discussed. Second, the importance of prior knowledge of the system inertia, which will help operators to apply suitable control strategies to mitigate stability challenges, is also addressed. Third, the significance of co-existence, coordination and optimization of both conventional synchronous generator's inertia and synthetic inertia, as a key feature towards reliable and flexible grid in low inertia environment, are also emphasized. Finally, technical challenges, key issues, and further research needs are highlighted. •Discussed challenges of low and time-varying inertia on the grid's frequency stability.•Explained significance of synthetic inertia to the grid's frequency stability.•Reviewed inertia estimation techniques in power systems extensively.•Highlighted the need for coordination and optimization of inertia for grid flexibility.•Emphasized the need for inertia monitoring for planning and operation of the grid.