The 100-foot-high, 1-megawatt turbine, lowered into position during winter storms off the Orkney Islands, is powering homes and businesses on the island of Eday, officials with Scottish Power Renewables said.
The test is part of a plan to create a 10-megawatt tidal power array in the Sound of Islay, they said.
The test, which began in December, is part of a larger project for the Islay project that intends to install more turbines "as early as feasible" between 2013 and 2015, the energy company said.
"The performance of the first HS1000 device has given us great confidence so far," SPR Chief Executive Keith Anderson said in a company release Thursday. "Engineers were able install the device during atrocious weather conditions, and it has been operating to a very high standard ever since."