A study done for Dominion Virginia Power found that one offshore substation platform with two 230-kV power lines would be appropriate to send to shore 500 MW to 700 MW of wind-generated electricity built off Virginia’s coast, Dominion (NYSE:D) said March 13.
The Virginia-based utility plans to respond to the federal Bureau of Ocean Energy Management’s (BOEM) call for information for wind generation to be developed in about 113,000 acres of leasing areas about 24 miles off the Virginia coast. The company also said it has a $500,000 grant from the U.S. Department of Energy to work with partners and find ways to reduce the costs of offshore wind generation.
The study, done by ABB Power Systems Consulting, evaluated the offshore transmission options to support future projects and built its recommendations on the company’s first study in 2010 that looked at potential onshore interconnection options and upgrades needed to support offshore wind generation projects, Dominion said.
According to the study, a proposed concept with four offshore substation platforms each outfitted with two 230-kV cables can be developed in phases, with each substation platform and associated collection and export cables representing one phase of 648 MW.
When a platform is built and installed, all of the equipment needed for the total development should be installed with the platform, according to the study. There is no easy or economical way to add substation equipment to the platform at a later time, the study added. This limits the development phase to completing one platform at a time, as needed. Submarine cables are then added to the platform as the development of the wind farms in the associated wind zone progresses, the study added.
The preliminary construction cost for a 230-kV AC interconnection system was estimated for each platform. For one 648-MW platform system, the indicative estimate is:
- $250m for an offshore platform
- $389m for 230-kV cable system, 2x72km
- $9m for 230-kV onshore variable shunt reactors, including installation
- $4m for two three-breaker bays in a breaker and a half scheme to terminate two cables and two shunt reactors.
The total indicative estimate, the study added, for one 648-MW platform and 230-kV cable installation is $652m.
Among other things, the study said that the manufacturing schedule of the cable will depend on the total length of cable to be provided and the factory loading. If several platforms are done at the same time, this could affect the schedule. The study also said it might take longer to manufacture the cable, but all of the cable can be transported and laid at one time.
Another company working on offshore wind energy transmission is the Atlantic Wind Connection, whose proposed project will be able to connect up to 7,000 MW of offshore wind when complete. The project is led by Trans-Elect Development Company and involves Google, Good Energies and Marubeni Corporation.
Dominion said in February that Atlantic Wind Connection’s right-of-way application is premature given that the project has not been approved by PJM Interconnection in its transmission planning process, nor has it gone through FERC rate proceedings. Atlantic Wind Connection CEO Robert Mitchell subsequently responded to Dominion’s suggestion that BOEM should delay the application, saying it “is not a very persuasive argument.”