On the Costs of Grid Inertia

Inertia plays an important role in the function of electrical grid stability. When there is a difference between supply and demand grid frequency will change. Inertia resists this change and limits the rate of change of frequency (RoCoF) giving time for power stations to change their supply to match demand. Traditional thermal power stations have significant amounts of inertia in their generators and steam turbines. Renewable energy sources such as wind and solar tend to have little or no inertia and as a result grid inertia has reduced and will continue to do so in the future, causing issues of grid stability. There are various ways to address this problem including: replacing grid inertia, increasing the maximum level of RoCoF allowed, or minimising the largest generator or load on the grid. Inertia hasn't traditionally been a traded commodity as it has been a by-product of large thermal power generation. This is likely to change in the future with the increase in non-synchronous generation. The costs and methods of creating grid inertia are somewhat novel fields. This paper surveys some of the options of creating grid inertia. It also presents SHyKESS which is a flywheel based method of creating grid inertia and primary frequency control.