One offshore substation platform with two 230,000-V power lines is appropriate to transmit to shore every 500-700 MWs of wind-generated electricity constructed off the coast of Virginia, a study done at Dominion Virginia Power's request recommends.
The report, completed 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 on-shore interconnection options and upgrades needed to support offshore wind generation projects. The studies complement one another as transmission lines from the four recommended offshore service platforms would likely be routed to two separate onshore interconnection points.
The report acknowledges the potential cost savings that may be achieved through construction of offshore transmission infrastructure completed in stages with a potential for standardization. The approach also limits the potential for stranded transmission investment as offshore wind farms are constructed.
The report estimated the cost for each offshore service platform, its equipment and submarine transmission cables at approximately $652 million.
"As public policy is developed to support wind farms off Virginia's coast and leases are issued, Dominion will continue evaluating transmission options to ensure the identification of the lowest cost alternative for bringing offshore wind electricity to customers," said Scot Hathaway, vice president-Electric Transmission. "It is important that we continue to understand these costs and work to reduce them as we consider the possibility of offshore wind generation."
Dominion is planning to respond to the federal Bureau of Ocean Energy Management's call for information for wind generation in about 113,000 acres of leasing areas approximately 24 miles off the Virginia coast. The leasing area is divided into 19 whole blocks, each 3-by-3 miles, and 13 partial ones.
Dominion 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 DOE estimates that offshore wind generation alone would cost about 24 cents per kilowatt-hour; Dominion's residential rates today for generation, transmission and distribution services are about 11 cents per kilowatt-hour.