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Tidal power for all of Southcentral AK? Anchorage company says tidal fence structures in Turnagain Arm could meet the whole of the Alaska Railbelt’s electricity needs Alan Bailey Petroleum News
Anchorage-based Little Susitna Construction Co. says that it wants to partner with Blue Energy Canada Inc. to build a tidal power system in Turnagain Arm, the sea inlet off Alaska’s Cook Inlet, to generate sufficient electricity to meet the needs of the entire Alaska Railbelt.
In a preliminary permit application to the Federal Energy Regulatory Commission, dated July 28, the company described a system in which structures called tidal fences, built near the entrance to the arm, would harness the famous 30-foot tides of the region to drive what are known as Davis turbines — turbines that use vertical hydrofoils to turn shafts coupled to generators, rather like a system of slowly revolving hotel doors, without any glass.
Blue Energy Canada is a renewable energy company that specialized in the use of the Davis turbine.
There have been several successful tests of prototype Davis turbine systems and a 200-megawatt Davis turbine tidal fence under construction in the Orkney Islands, north of the mainland of Scotland, is expected to come on line in 2011, the permit application says.
Tidal power potential For several years Cook Inlet has been viewed as a possible location for a tidal power system and since 2007 another renewable energy company, Ocean Renewable Power Co., has been investigating a modest-scaled tidal power option, involving the placement of some subsea turbines in the entrance to Knik Arm or near Fire Island, offshore Anchorage. ORPC hopes to install a single turbine in 2010, as an initial test of the concept, although the National Marine Fisheries Service has raised questions over the possible impact of the power system on marine wildlife, including the Cook Inlet Beluga whale, a listed species under the Endangered Species Act.
Dominic Lee, president and CEO of Little Susitna Construction, has told Petroleum News that Asian investors are willing to fund the $2.5 billion Turnagain Arm project that Little Susitna Construction and Blue Energy Canada have proposed, and that the project would be viable at an electricity price of 6 to 8 cents per kilowatt hour. CH2M Hill would do the engineering design, and Fluor would carry out the construction, Lee said.
A tidal fence of the type envisaged in Turnagain Arm consists of a line of Davis turbines strung across the path of a tidal current. In the Turnagain Arm application, each turbine would occupy a 30-foot-diameter caisson, topped by a generator structure that would be situated above the water surface at high tide. The turbine itself would extend from the channel bottom to a height of about 9 feet below the low tide water level. A service road would run along the top of the fence, a design arrangement that could be modified and expanded to form a state-funded causeway across the arm, if so desired, the permit application says.
And, although the hydrofoil design of the Davis turbine blades causes the blades to move faster than the water current, the large, open turbines would revolve quite slowly, so that wildlife such as fish and beluga whales could easily make its way through the tidal fences, Lee said.
Two fences And the proposed design involves two tidal fences. One of these would extend from near Fire Island 8 miles to the Kenai Peninsula near Point Possession, while the other would be 7.5 miles long and would be placed at least 5 miles away from the other fence. Both fences would connect to the electric grids on the Kenai Peninsula and in Anchorage using a transmission line that would serve the dual purpose of hooking up the tidal power system and creating a new connection between the Anchorage and Kenai grids — currently the grids are only connected by an intertie that passes north of Turnagain Arm and follows the Sterling Highway.
The two tidal fences would support a total of 220 10-megawatt turbines, resulting in a total rated output of 2,200 megawatts and an average output of 1,200 megawatts, the permit application says. According to data presented in the application, the Railbelt power grid currently has 1,046 megawatts of peak generating capacity, a figure a little lower than the 1,248 megawatts stated in a 2008 report by Black and Veatch for the Alaska Energy Authority. According to the Web site of the Golden Valley Electric Association, the Fairbanks-based electric utility, GVEA accounts for 296 megawatts of the total Railbelt capacity. The transmission intertie between Fairbanks and the Anchorage area would currently limit power transmission between Anchorage and Fairbanks to about 70 megawatts, according to information on the GVEA site.
Little Susitna Construction and Blue Energy Canada estimate that it would take up to one year to complete a preliminary engineering study, investigate project costs and obtain stakeholder commitment for the Turnagain Arm project. And the companies estimate that it would take about eight years to complete the permitting, design and construction of the tidal power system in the Arm.
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