The Impact on System Inertia and Frequency From High Penetration of Renewable Energy

Sammanfattning: For the last couple of years, there has been an upsurge in investment in renewable energy. Whenincreasing the share of renewables in the energy mix numerous conditions have to be considered.Wind and solar power are not synchronously connected to the power grid, with the consequencethat they do not contribute to the inertia in the power system. Inertia is of crucial importance forregulating frequency changes and prevent instability, which is the outcome when there is adifference between the amount of production and consumption of energy in the power system. Thepurpose of this study is to analyse the effect on inertia and frequency when an increasing amount ofrenewable energy is injected into the system. This is done through simulating the system's reactionwhen a disturbance in the form of a production loss occurs. Five different scenarios are studied, bothwith frequency dependent and frequency independent loads. Furthermore, a battery is constructedwith the purpose of injecting power in order to keep the frequency within approved limits. Theresults show that loss of inertia and frequency independent loads have a substantial negative impacton frequency stability. On the other hand, frequency dependent loads considerably help withstabilising the frequency. Furthermore, the battery was successful in keeping the frequency withinthe set requirements, given that it being able to inject 90-460 MW (dependent on the amount ofrenewables and loads) of power. This amount of battery capacity is currently somewhat greatercompared to what is installed in Sweden today, however it is not an unreasonable amount. Thisindicates that batteries are able to cope with the frequency instability caused by large scalerenewable penetration of the power system.