Boiler steam in cogeneration generates both electricity and heat, so gas consumption is included in variable costs .  Boiler steam in cogeneration generates both electricity and heat, so gas consumption is included in variable costs .  Boiler steam in cogeneration generates both electricity and heat, so gas consumption is included in variable costs .  Boiler steam in cogeneration generates both electricity and heat, so gas consumption is included in variable costs .  Boiler steam in cogeneration generates both electricity and heat, so gas consumption is included in variable costs .  Boiler steam in cogeneration generates both electricity and heat, so gas consumption is included in variable costs .