CNet: Clean energy has moved from the margin to the mainstream, with wind, solar, and biofuels topping a combined $70 billion in revenue last year. Market research firm Clean Edge on Tuesday released its annual report on clean technology and projected continued rapid growth in spending, even though the U.S. economy is slowing down. Revenue from biofuels, wind power, solar power, and fuel cells grew 40 percent to $77.3 billion, compared with 2006. Clean Edge projects that number …