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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 .