Hailed as one of the largest in the state, the 5.76 megawatt solar plant being installed at the old coal plant along Route 5 in Holyoke is considered a big win for environmental and community activists. But their battle with coal isn’t over. Toxic waste created during decades of coal-fired energy production led to the creation of 21 ash ponds and two dumps on the 128-acre, Connecticut River-adjacent property. There’s also the issue of energy supply. Though reliance on the Mt. Tom coal plant had significantly diminished over the years — when it shut down, the plant was only running during peak demand times in the winter — the plant was built with a 146 megawatt-production capacity.