Comparative Analysis of Energy-Based and Revenue-Based Availability Metrics of Wind Turbines

Sammanfattning: Different key performance indicators are used to assess various aspects of a wind turbine (performance, reliability, financial aspects…). Availability metrics mainly, time-based and energy-based availability are the main indicators used to monitor and evaluate turbine’s availability performance today. However, due to significant growth of the share of energy sold into the electricity market as well as different selling structures, a new indicator has been established in order to assess availability performance in terms of revenues rather than time or energy.  This thesis compares energy and revenue-based availabilities of two turbines during 12 months of operational production. A methodology of calculation is suggested based on the International Electrotechnical Commission (IEC) information model for availability calculation. Time-based availability is calculated first, followed by energy-based, and finally revenue-based availability is derived from revenues as a result of combining energy production and electricity prices and revenue losses from energy losses and electricity prices. Availability metrics are calculated for three different scenarios, pure-market, mix of market and fixed price purchase agreement (PPA), and finally a PPA with a minimum monthly baseload to simulate the impact of volume risk. Results indicate a significant impact caused by the electricity price as well as the specifics of the selling agreement on revenue-based availability. Finding that in such cases, a significant divergence between energy and revenue-based indicators is possible. Limitations associated with the suggested methodology and case studies are presented and discussed.