Marine Current Turbines, the developer of SeaGen, demonstrated its first prototype of a tidal stream generator in 1994 with a 15 kilowatt system in Loch Linnhe, off the west coast of Scotland.

[3][13] It consisted of twin axial-flow rotors, each driving a generator through a gearbox like a hydro-electric or wind turbine.

[14] The SeaGen turbines had a patented feature by which the rotor blades can be pitched through 180 degrees allowing them to operate in both flow directions – on ebb and flood tides.

The power units of each system were mounted on arm-like extensions either side of a tubular steel monopile some 3 metres (9.8 ft) in diameter and the arms with the power units could be raised above the surface for safe and easy maintenance access.

[15] SeaGen had been licensed to operate over a period of 5 years, during which it was accompanied by an environmental monitoring programme to determine the precise impact on the marine environment.

Seals appeared to avoid the device, or transit passed at slack water when the turbine was not generating (i.e. not turning).