Market Power and Transmission Congestion in the Italian Electricity Market

Abstract

Analysis of market power in electricity markets is relevant for understanding the competitive development of the industry's restructuring and liberalization process. Because the existing literature lacks adequate consideration of line transmission congestion, this paper sets forth a new approach to measuring market power in the Italian Power Exchange (IPEX) by explicitly taking into account transmission line congestion. We construct the residual demand curve to disentangle the measure of unilateral market power from congestion rent for the main Italian generators during the period of April 2004 to December 2007. In Italy, this was a period of stable transmission network structure. Following the approach of Wolak (2003, 2009), we measure the unilateral market power with the Lerner Index (LI) computed as the inverse of the residual demand elasticity. In conclusion, the correct modeling of the residual demand curve including transmission congestions allows us to compute the zonal LI and therefore more accurately measure the market power when congestion occurs. Our results show that various generators exercise market power in only some zones, which provides us with a deeper understanding of the IPEX and better support for designing appropriate market surveillance and competition regulation.