  The increasing penetration of renewable energy in recent years has led to
more uncertainties in power systems. These uncertainties have to be
accommodated by flexible re- sources (i.e. upward and downward generation
reserves). In this paper, a novel concept, Uncertainty Marginal Price (UMP), is
proposed to price both the uncertainty and reserve. At the same time, the
energy is priced at Locational Marginal Price (LMP). A novel market clearing
mechanism is proposed to credit the gener- ation and reserve and to charge the
load and uncertainty within the Robust Unit Commitment (RUC) in the Day-ahead
market. We derive the UMPs and LMPs in the robust optimization framework. UMP
helps allocate the cost of generation reserves to uncertainty sources. We prove
that the proposed market clearing mechanism leads to partial market
equilibrium. We find that transmission reserves must be kept explicitly in
addition to generation reserves for uncertainty accommodation. We prove that
transmission reserves for ramping delivery may lead to Financial Transmission
Right (FTR) underfunding in existing markets. The FTR underfunding can be
covered by congestion fund collected from uncertainty payment in the proposed
market clearing mechanism. Simulations on a six-bus system and the IEEE 118-bus
system are performed to illustrate the new concepts and the market clearing
mechanism.
