The Don Pedro hydropower project, just west of Yosemite National Park, has been churning out carbon-free electricity for nearly a century. As the Tuolumne River flows from the Sierra Nevada to the Central Valley, it passes through Don Pedro Dam, spinning four turbine generators. None of the electricity is counted toward California’s push for more renewable energy on its power grid. A new bill advanced by state lawmakers last week would change that — and it’s being opposed by environmental groups, who say it would undermine the state’s landmark clean energy law by limiting the need to build solar farms and wind turbines.