Solar Two was a 10-MWe prototype central receiver plant east of Barstow, California. Solar Two, which was sponsored by a consortium of utilities and industry in partnership with the U.S. Department of Energy, began regular electricity production in February 1997 and completed its last day of regular electricity production in March 1999. This paper presents preliminary results from the most recent Solar Two performance evaluation.The primary aspect of the performance evaluation is the lost-electricity analysis. This analysis compares the actual generation with the generation predicted by the Solar Two model. (SOLERGY, a Sandia National Laboratories- developed computer program designed to simulate he operation and power output of a solar central receiver power plant, is the code used to model Solar Two.) The difference between the predicted and the actual generation (i.e., the lost electricity) is broken down into the different efficiency and availability categories responsible for the loss. Having the losses broken down by system and in terms of electricity is useful for understanding and improving the plant’s performance; it provides a tool for determining the best operating procedures for plant performance and for indicating where operation and maintenance resources should be focused for the best performance payback. This paper briefly describes the methodology behind the lost-electricity analysis.