[2] The first phase of the project uses four 1.5 MW turbines with 18 m (59 ft) rotor diameter which were installed submerged on the seabed in winter 2016/17.

The high speed of currents in the area, reaching up to 5 m/s (11 mph), made the chosen site in the Pentland Firth well suited to this type of energy generation.

[7] A consent was granted in 2013, under Section 36 of the Electricity Act, to construct up to 61 two or three-bladed turbines with a total installed capacity of 86 MW.

This initially only lasted until the end of 2020, but was extended in July 2016 to cover the period until 1 January 2041 or 25 years after completion of phase 1a.

[11] TTG1 was supplied by Andritz Hydro Hammerfest, and was joined by three further AR1500 turbines developed by Atlantis Resources with design support from Lockheed Martin.

These would be up to 24 m in diameter, remove the limit on the rated power per turbine, and increase the maximum voltage of the underwater cables to 33 kV.

[22] The project received £1.5 million Scottish Government grant from the Saltire Tidal Energy Challenge Fund in 2020, to develop a sub-sea hub to connect multiple turbines.

[23] Phase 1 of the project comprises four 1.5 MW turbines, three Andritz Hydro Hammerfest AH1000 MK1 and one Atlantis Resources AR1500 developed in conjunction with Lockheed Martin.

[14][17] These are all three-bladed horizontal-axis turbines with an 18 m rotor diameter, that reach the 1.5 MW rated power at a current speed of 3 m/s.