BROOKLYN - Mayor Michael Bloomberg has announced a plan to generate energy and cut greenhouse gases across the city, but the mayor?s proposal is facing some harsh opposition from local activists. Bloomberg says he will ask private companies to install solar energy systems at buildings as part of a goal to cut greenhouse emissions 30 percent by 2017. He says the city has tripled its production of solar power and has harnessed enough energy to power 143 households. He also announced a summer campaign to spur the development of digital tools that will encourage sustainable energy practices.Environmentalists, community activists and local politicians protested the project earlier today in Manhattan.