Empirical observations of bidding patterns in Australia's National Electricity Market

For more than a decade, electricity industries have been undergoing reform worldwide. However, there are various, sometimes contradictory, conclusions about the performance of these restructured electricity markets. Market performance depends largely on how each market participant responds to the market design — including market rules, market operational procedures, and information revelation. In this paper, we identify and examine the strategies adopted by generators in Australia's National Electricity Market, based on publicly available data for the period from May 1, 2002 to May 31, 2003. We try to understand and answer some basic questions like how generators respond collectively or individually to changes in market conditions (e.g. load changes) and why they behave in this way. The statistics calculated from the data show that wide variations in the frequency of strategic bidding and rebidding exist; that generators more frequently use capacity offers as a strategic tool than price offers; that large generating units are more likely to use capacity strategies to control market prices; and that generators are capable of responding to changes in market conditions.