Strategic interaction between wholesale and ancillary service markets

In electricity markets, ancillary services (AS) are vital to ensuring system reliability through the instantaneous balancing of supply and demand. An important current policy question is whether AS markets clear simultaneously or sequentially with wholesale markets. We develop a model to study the strategic implications of market timing. We demonstrate that a strategic incentive to reduce AS and, consequently, lower marginal cost in the wholesale market arises when markets clear sequentially. Using data from Alberta, we find that the strategic effect has a small impact on wholesale outcomes but a large impact on the AS market.