Utilities are charged with serving the public interest: They must keep the lights on. That means they need to have something in reserve for times when more electricity is needed than is usual for a given day and time or for those times when equipment is out of service. They need operating reserves, known in electric utility parlance as spinning reserves (obtaining more output from generators already operating) and non-spinning reserves (quickly bringing generators online to meet demand spikes).
Renewable generation poses several challenges to reliable operation of power systems thanks to its inherent variability: Wind speed and direction isn’t a constant for example. Operating reserves compensate for variability in both load and generation.
How much does adding renewables to the grid change what operating reserves are needed and how they are dispatched during spikes of demand? That’s what our part in the Full Cost of Electricity (FCe-) project by the University of Texas at Austin Energy Institute seeks to understand.