NRG Energy Inc., Princeton, N.J., has purchased Bluewater Wind, Newark, Del., the first U.S. developer with a purchase agreement for the sale of power generated from an offshore wind farm. The deal brings the financial strength of NRG, which had $6.8 billion in sales last year, to Bluewater, helping the startup firm realize its dream to develop a $1-billion, 79-turbine commercial wind farm off the Delaware coast.