Abstract
Two distributed energy supply systems with different generation efficiency were evaluated based on exergy analysis and optimized on the running cost for a few patterns of energy demand. One of the systems uses a gas turbine with generation efficiency of 30%. Saturated steam is generated in a waste heat boiler, and is used for hot water and heating, and moreover for cooling. On the other hand, another system uses a SOFC and a micro gas turbine combined system as high efficient power generator with the generation efficiency of 50%. A shortage of electric power is made up by buying from an electric power company, and a gas boiler and a refrigerator with an electrically-driven turbo compressor are also used to make up for a shortage of heating and cooling demand, respectively. As a result, the relation between the operating cost and the exergy efficiency had been clearly shown. If a gas boiler is used for heating demand, the exergy efficiency of energy supply system decreases due to low exergy efficiency of gas boiler, in spite of the higher thermal efficiency. In order to increase exergy efficiency of system, heating demand should be covered by a waste heat from generators. Moreover, operating cost reduction could be compatible with the increase of exergy efficiency of system by selling surplus power.
