Washington Post: BOSTON — The nation’s inaugural offshore wind farm, planned for waters off Cape Cod, has reached its first deal with a utility to purchase its power. Under the agreement announced by both companies Friday, National Grid would pay 20.7 cents per kilowatt hour starting in 2013 for half the power produced by the 130-turbine Cape Wind project planned for Nantucket Sound. The price would go up by 3.5 percent annually to keep pace with inflation. The deal is considered …