Hydroelectric power comes from water driving a water turbine connected to a generator. Experimental wind farms consisting of a single wind turbine for testing purposes have been built. SeaTwirl develops a floating vertical axis wind turbine (VAWT). Materials commonly used in wind turbine blades are described below. Power electronics are also at the heart of the variable speed wind turbine. The variability of production from a single wind turbine can be high. There are rotating wind socks which spin like a turbine. The aerodynamics of a horizontal-axis wind turbine are not straightforward. The aerodynamics of a wind turbine are not straightforward. This makes compressor speed independent of turbine speed. Heligoland was the site of a trial of GROWIAN, a large wind turbine testing project. Heat storage enables better utilization of the steam turbine. Some of the power generated by the turbine is used to drive the compressor. A limited number of steam turbine railroad locomotives were manufactured. The Rankine cycle is a model used to predict the performance of steam turbine systems.