IEC 61400-26-1:2019 defines an information model from which time-based, and production-based availability indicators for services can be derived and reported. The purpose is to provide standardised metrics that can be used to create and organise methods for availability calculation and reporting according to the user's needs. The document provides information categories, which unambiguously describe how data is used to characterise and categorise the operation. The information model specifies category priority for discrimination between possible concurrent categories. Further, the model defines entry and exit criteria to allocate fractions of time and production values to the proper information category. A full overview of all information categories, exit and entry criteria is given in Annex. The document can be applied to any number of WTGSs, whether represented by an individual turbine, a fleet of wind turbines, a wind power station or a portfolio of wind power stations. A wind power station is typically made up of all WTGSs, functional services and balance of plant elements as seen from the point of common coupling. This first edition cancels and replaces IEC TS 61400-26-1:2011, IEC TS 61400-26-2:2014 and IEC TS 61400-26-3:2016.