Towards Equilibrium Offers in Unit Commitment Auctions with Nonconvex Costs

We compare two types of uniform-price auction formats commonly used in wholesale electricity markets—centrally committed and self-committed markets. Auctions in both markets are conducted by an independent system operator that collects generator bids and determines which generators will operate and how much electricity each will produce. In centrally committed markets, generators submit twopart bids consisting of a startup cost and a variable energy cost. Self-committed markets force generators to incorporate their startup costs into a one-part energy bid. The system operator in a centrally committed system ensures that each generator recovers the startup and energy costs stated in its two-part bid, while no such guarantees are made in self-committed markets. The energy cost ranking and incentive properties of these market designs remains an open question. While the system operator can determine the most efficient dispatch with a centralized market, the auction mechanism used to solicit generator data compels generators to overstate costs. Self commitment might involve less efficient dispatch but have better incentive properties. We derive Nash equilibria for both market designs in a symmetric duopoly setting. We also derive simple conditions under which the two market designs will be expected cost-equivalent.