GreenBiz: In these dismal economic times, it’s remarkable that 15,000 to 20,000 people traveled to Abu Dhabi, of all places, for a clean-energy conference. The renewable energy business, after all, is reeling from the global recession, the credit crunch and the precipitous drop in the price of oil. Signs of distress are not hard to find. There hasn’t been a successful clean tech IPO since First Solar went public in 2006. Wind power and solar energy companies are laying off workers, according to …