Cost and performance estimates in the Base Year are intended to represent a commercial-scale project of 600 MW in capacity. The ATB Base Year offshore wind plant technology reflects a machine rating of 6 MW with a rotor diameter of 155 m and hub height of 100 m, which is typical of European projects installed in 2016 and 2017 and the turbine rating installed at the Block Island Wind Farm (GE Haliade 150-6MW). For the 2020 ATB cost projections, this representative technology changes to a 15-MW turbine (Moderate case), 12-MW (Conservative case), and 18-MW (Advanced case) turbine rating by 2030. Four substructure types are represented in the cost estimates, namely jacket and monopile (fixed-bottom) and semi-submersible and spar (floating technology). See below for details on changes to parameters in ATB projections.