System frequency performance of the Hawaii Electric Light System

Hawaii Electric Light operates an autonomous power system on the island of Hawaii with a diverse mix of generating resources. Although the system is small, with an annual peak in 2009 of less than 200 MW, the power system balancing and frequency control is provided through a conventional centralized Automatic Generation Control system. The mix of generation resources on the Hawaii Electric Light System has changed significantly in recent years to accommodate a large amount of wind and, more recently, a significant amount distributed solar photovoltaic generation. In addition to the variable wind and solar resources, the system incorporates run of river hydroelectric facilities and a geothermal facility which provide a significant portion of the system energy. The operation of the island power system provides an opportunity to observe, through actual operating experience, issues relating to power system frequency control and response under various levels of variable generation and changes in the mix of thermal generation. The change in generation mix has had a marked and measureable impact on the system frequency performance during normal and disturbance conditions, as well as on the generators providing system frequency response and control capabilities. This report will describe system and generation impacts found from studies and through actual operational experiences. These impacts will include system performance data collected during normal operation and disturbances, with some specific event analysis. This paper will also describe mitigation measures taken to improve the power system frequency performance including modification of the power system operation and control, changes to the conventional generators, and requirements for existing and anticipated generation facilities.