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RESEARCH PAPERS

# Fuel Cell Hybrids, Their Thermodynamics and Sustainable Development

[+] Author and Article Information
Wolfgang Winkler

Hamburg University of Applied Sciences, Berliner Tor 21, D 20099 Hamburg, Germanywinkler@rzbt.haw-hamburg.de

J. Fuel Cell Sci. Technol 3(2), 195-201 (Aug 29, 2005) (7 pages) doi:10.1115/1.2174069 History: Received August 05, 2005; Revised August 29, 2005

## Abstract

The increasing demand on primary energy and the increasing concern on climatic change demand immediately a sustainable development, but still there remain open questions regarding its technical realization. The second law of thermodynamics is a very simple but efficient way to define the principle design rules of sustainable technologies in minimizing the irreversible entropy production. The ideal, but real process chain is defined by a still reversible structure or logic of the process chain—the reversible reference process chain—but consisting of real components with an irreversible entropy production on a certain level. It can easily be shown for energy conversion and for transportation that hybridization in general can indeed be a measure to meet the reversible process chain and to minimize the entropy flow to the environment. Fuel cells are principal reversible converters of chemical energy and thus a key element within hybridization. Depending on application, combined heat and power process (CHP) may be a hybridization step or only a slight improvement. There is a fundamental difference in heating a house or in supplying an endothermic chemical reaction with reaction entropy. The use of heat recovery and isolation is a necessary measure to minimize the entropy flow to the environment and can be described by a reversible reference process as well. The application of reversible reference process chains shows that hybrid systems with fuel cells are a technical feasibility to approach very closely the thermodynamic potential. This development differs from the past where the technical possibilities of materials and manufacturing limited the technology to meet reversibility and thus sustainability.

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## Figures

Figure 1

Sustainable development and hybrid systems

Figure 2

The development of the potential utilization of the fuel exergy

Figure 3

Principles of combustion engines and their reversibility

Figure 4

The reversible fuel cell-heat engine process

Figure 5

The motion of a pendulum as a pattern of the system layout

Figure 6

Reversible system structure efficiency

Figure 7

Hybrid car concept with a SOFC-GT

Figure 8

Sustainable development and hybridization

Figure 9

The conventional heating and the demand on heating energy

Figure 10

The reversible room conditioning process (ideal residential heating)

Figure 11

The entropy flows to the environment and its quality

Figure 12

Simplified fuel cell-heat engine hybrid system as a reference cycle

Figure 13

The system efficiency of the ideal and the real fuel cell-hybrid system with an exergetic efficiency ζHE=0,7 and hydrogen as a fuel

Figure 14

Process model for integrated reforming in SOFC hybrids

Figure 15

The influence of the excess air λ and the efficiency ηAH of the air heater on the system efficiency ηsyst of the SOFC hybrid λ

Figure 16

Design principles of future hybrid systems

Figure 17

Reversible systems and hybrid technology mapping

Figure 18

Overview of the minimal entropy production strategy (MEPS)

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