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Energy cogeneration systems and energy management strategy

Abstract : ÐAn energy cogeneration system allows the optimisation of the use of energy sources through a maximal exploitation of energy products. The investment is higher than for conventional energy systems but the pay-back time is shorter and the bene®t is even higher beyond this time. Moreover, in addition to these economic advantages, energy cogeneration systems allow the preservation of the environment due to a rational use of energy sources. The assessment of a thermoeconomic balance, on one hand for a cogeneration system producing heat and electrical power, and on the other hand for a conventional energy system producing the same amount of heat using the same type of energy resource, leads to an expression for the minimum cost of the produced electrical power which depends on the cogeneration system's electricity production e-ciency and on the global eciencies of the cogeneration system and of the conventional system due to the introduction of the unit cost of heat production. These cogeneration systems have to present well-designed thermal energy recuperation and electrical energy production devices in order for the unit cost of the produced electrical power to be higher than that of a conventional system. A thermoeconomic analysis of three existing cogeneration systems was conducted and led to the conclusion that these cogeneration systems were not pro®table enough due to a lack of a strong energy management strategy which is constrained by the taring of local utilities. The main analysis was focused on the cogeneration system of a hospital. This later is based on a thermal engine using natural gas as a primary resource and producing 2.8 MW of electricity and 2.7 MW of heat coupled with the heat production of natural-gas-®red boilers ranging about a maximum of 31 MW. Based on the particular taring of the local utilities, the investment cost of this cogeneration system should not exceed 64% of the cost of a conventional electrical production system in order to present a shorter pay-back time. We have shown how this cogeneration system will not be competitive with a conventional system if it was operated at some taring mode and that the lifetime of the equipment has an impact on the pro®tability of the system. # 1998 Elsevier Science Ltd. All rights reserved Energy cogeneration Optimisation NOMENCLATURE C=Capacity rated investment cost (FF/W) E=Primary energy rate (W) k=Ratio of investment costs P = Pro®t versus the capacity (FF/W) Q=Thermal energy rate (W) W=Mechanical (electrical) energy rate (W) Z=Annual cost Greek letters l E =Unit cost of primary energy (FF or cts/W) l I,q =Unit cost of thermal energy produced by a conventional system (FF or cts/W) l w =Unit cost of mechanical (electrical) energy (FF or cts/W) Z I,q =Eciency of the conventional system Z cg =Eciency of the cogeneration system Z q =Thermal eciency of the cogeneration system Z w =Electrical eciency of the cogeneration system x=Irreversibilities G=Operating life (years) G h =Operating life (hours) G r =Pay-back time (years) Indices cg=Cogeneration system cv=Conventional system
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https://hal.univ-lorraine.fr/hal-02994530
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Submitted on : Wednesday, February 10, 2021 - 1:10:50 PM
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Riad Benelmir, Michel Feidt. Energy cogeneration systems and energy management strategy. Energy Conversion and Management, Elsevier, 1998, 39, pp.1791 - 1802. ⟨hal-02994530⟩

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