A comparative study between rotational and virtual inertia : role of liquid air energy storage as a source of inertia in future power systems

Abstract

Using power system frequency response simulations, this study develops understanding of the different factors that influence the capacity of fast energy storage systems and inverter capacity that can compensate for the reduction in synchronous rotational inertia. It is observed that the required virtual inertia (VI) capacity increases as the VI response time increases and, also with increases in the reference fault size. The required VI capacity also varies depending on the level of existing system inertia. The rate of increase in VI capacity increases as the system inertia decreases. This is also noted in the Nordic power system where the system inertia is at a high level and relatively small fast frequency response (FFR) capacity is suitable to sustain frequency nadir above desired limits. For example, at a particular simulation instant with relatively low inertia in the present Nordic grid, the FFR capacity of 62.4 MW suffices to improve the frequency nadir which would otherwise require almost 9.44 GWs of additional KE reserves. For the Cyprus power system, exploratory analysis looked at possible Liquid Air Energy Storage (LAES) scope and capacity to support a 100% renewable grid. Sources of synchronous rotational inertia (RI) such as LAES are believed to have a role in maintaining a minimum inertia base in the grid such that the RoCoF dynamics doesn’t become prominent. If high amounts of RI are maintained in the system, then further gaps in inertia requirements can be addressed with limited capacity of fast energy storage. This study contributes towards a long-term view on the competitiveness of synchronous RI, considering the fast energy storage capacity and inverter capacity needed for VI.