Wind-power producers are rushing to take advantage of a green energy tax credit extended by Congress—and, in a new twist, many are using it to renovate existing wind farms, not just build new ones. . . In rough numbers, a 100-megawatt project with modern turbines and strong winds might produce $10 million a year in tax credits, according to an analysis by Fitch, the credit rating firm. The current government credit is 2.3 cents per kilowatt-hour of electricity produced, but it is adjusted for inflation and has jumped 53% since it began in 1992.