The United States, Canada, and Mexico will pledge on Wednesday to generate 50 percent of their electricity from non-fossil fuel sources by 2025, according to U.S. officials. The three nations are expected to set the ambitious goal at a North American Leaders Summit in Ottawa. The commitment includes not just renewable sources of power such as energy and wind, but also hydropower, nuclear power, carbon capture and storage at coal-fired power plants, and gains in energy efficiency. Under that definition, the three nations now produce 37 percent of their electricity from renewable sources. Canada is leading the way in non-fossil fuel power generation, with 59 percent of its electricity coming from hydropower and 16 percent from nuclear plants. Continent-wide cooperation on clean energy issues has improved since the election last year of Justin Trudeau as Canada’s Prime Minister.