報告書番号

Y98008

タイトル（和文）

電力プール市場に関する経済分析の展望 -水平的市場支配力の問題を中心として-

タイトル（英文）

Economics Analysis of Horizontal Market Power in Electricity Wholesale Market: A Survey

概要 （図表や脚注は「報告書全文」に掲載しております）

本稿では、電力プール市場に関する経済分析、とりわけ水平的市場支配力の問題を分析した研究を中心にサーベイを行った。理論モデルに基づいたシミュレーション分析や英国を対象とした実証分析では、寡占的な電力プール市場における電力価格は限界費用を上回って、効率性が損なわれている可能性が指摘されている。実際には、新規参入圧力や規制当局の監視によって、平均では極端な価格の高騰は見られないものの、潜在的な市場支配力は過小評価できない。市場支配力を抑制するためには、各発電事業者のシェアを小さくすべきであるが、適切な市場構造は規模の経済とのバランスで考慮されなければならない。また、価格がどの程度上昇するかは、需要の価格弾力性といった前提条件にも依存している。さらに、市場支配力の行使は制度的要因によって助長される場合も有り、制度設計についても慎重な検討を要する。

概要 （英文）

An electricity pool for a wholesale market has been established in many countries or regions where competition has been introduced into electricity generation. The problem of horizontal market power is one of the central issues to be resolved in order to encourage effective competition in the pool and in recent years a number of studies have been done on the extent of market power exercised by dominant generators in various countries. Simulation analyses based on oligopoly models (Supply function equilibrium /Cournot equilibrium) suggest that, when the price elasticity of demand is low, pool prices would be significantly higher than marginal cost, resulting in huge losses to social welfare. The simulation results are sensitive to price elasticity of demand assumptions, though in the short-run these are unlikely to be high. Countermeasures to mitigate such market power include splitting or divestiture of dominant generators, encouraging new entrants, and integrating neighboring markets. While these policy measures would reduce the price-cost margin, policy makers need to make sure that the benefits from increasing competition outweigh the loss of company-level scale economies. An empirical analysis of pool price and bid data for the electricity pool in England and Wales indicate markups of 20-25%, which are not as high as the theoretical models might suggest. It appears that the two largest generators keep their price low in order to stave off action by the regulator, as well as to deter new entry. Other empirical analyses show how they exercised their market power: They may have strategically withdrawn their capacity at peak time, thereby earning extra revenue from higher system marginal prices and capacity charges. They also tend to bid strategically higher for a given capacity when they have more infra-marginal capacity. Such behavior is partly driven by the specific market rules of England and Wales, indicating the importance of the design of pool market.

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