The energy stored in biomass can be released to produce renewable electricity or heat. Biopower can be generated through combustion or gasification of dry biomass or biogas (methane) captured through controlled anaerobic digestion. Cofiring of biomass and fossil fuels (usually coal) is a low-cost means of reducing greenhouse gas emissions, improving cost-effectiveness, and reducing air pollutants in existing power plants. Thermal energy (heating and cooling) is often produced at the scale of the individual building, through direct combustion of wood pellets, wood chips, and other sources of dry biomass.