Capacity payments in imperfect electricity markets: Need and design

This paper argues that a variety of imperfections in wholesale energy-only electricity markets lead to generators earning net revenues that are inadequate to support investment in a least cost portfolio of generating capacity and to satisfy consumer preferences for reliability. Theoretical and numerical examples are used to illustrate the sources of this missing money problem. Improvements in energy-only wholesale electricity markets, especially those that improve pricing when capacity is fully utilized, can reduce the magnitude of the missing money problem. However, these improvements are unlikely to fully ameliorate it. Forward capacity obligations and associated auction mechanisms to determine capacity prices are necessary to restore appropriate wholesale market prices and associated investment incentives to support the optimal portfolio of generating investments. The deficiencies of the original capacity payment mechanisms adopted in the US are discussed and the necessary improvements identified. © 2008 Elsevier Ltd. All rights reserved.