This chapter addresses the economic theory of electricity markets, viewed from an idealized competitive equilibrium setting, taking into account volatility and the physical and operational constraints inherent to transmission and generation. In a general dynamic setting, we establish many of the standard conclusions of competitive equilibrium theory: Market equilibria are efficient, and average prices coincide with average marginal costs. However, these conclusions hold only on average. An important contribution of this chapter is the explanation of the exotic behavior of electricity prices. Through theory and examples, we explain why, in the competitive equilibrium, sample-paths of prices can range from negative values, to values far beyond the "choke-up" price-which is usually considered to be the maximum price consumers are willing to pay. We also find that the variance of prices may be very large, but this variance decreases with increasing demand response.
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