Toronto Star: Canada’s biggest generator of dirty power has launched a $1.5 billion hostile bid for the country’s leading developer of clean power, including the two largest wind farms in Ontario. Analysts say TransAlta Corp.’s proposed acquisition of Calgary-based Canadian Hydro Developers Inc. could be the first of many moves in an energy sector that sees big polluters trying to green up their assets, partly to limit their exposure to carbon-emission penalties once a national cap-and-trade system …