LAUSR

This letter investigates the fundamental differences between how California Independent System Operator (ISO) and Midcontinent ISO calculate performance accuracy scores in their performance-based regulation markets. Both ISOs tend to follow the Federal Energy Regulatory Commission order 755 to pay regulation resources—whether conventional generators or distributed and demand side resources—based on their actual performance. The advantages and disadvantages of each method are systematically explained. First, real-world ISO data are used to show that there may exist major differences between these two methods in scoring accuracy under similar regulation performance scenarios. Next, the root causes for the observed differences are studied mathematically. Finally, some suggestions are made to improve these scoring methods; should these or other ISOs seek to refine their scoring formulas.