Abstract
This paper applies the Exergy Cost Theory (ECT) to a hybrid system based on a 500 kWe solid oxide fuel cell (SOFC) stack and on a vapor-absorption refrigeration (VAR) system. To achieve this, a model comprised of chemical, electrochemical, thermodynamic, and thermoeconomic equations is developed using the software, Engineering Equation Solver (EES). The model is validated against previous works. This approach enables the unit exergy costs (electricity, cooling, and residues) to be computed by a productive structure defined by components, resources, products, and residues. Most importantly, it allows us to know the contribution of the environment and of the residues to the unit exergy cost of the product of the components. Finally, the simulation of different scenarios makes it possible to analyze the impact of stack current density, fuel use, temperature across the stack, and anode gas recirculation on the unit exergy costs of electrical power, cooling, and residues.
Highlights
A hybrid system refers to the combination of two or more different energy technologies to produce a more efficient, flexible, reliable, and nature-friendly system
When solid oxide fuel cell (SOFC) are combined with other technologies to yield hybrid systems, there exists the possibility of increasing the efficiency of the entire system and decreasing the costs [3]
Considering flow no. 6, it is the energy flow leaving the afterburner and it can be seen that the environment accounts for 96% of its total cost, whereas the residues account for only 4%
Summary
A hybrid system refers to the combination of two or more different energy technologies to produce a more efficient, flexible, reliable, and nature-friendly system. The vast majority of the proposed hybrid systems are mostly based on renewable energy technologies such as solar, wind, or biomass, or alternative ones such as fuel cells, in combination with conventional technologies such as steam or gas turbines. When SOFCs are combined with other technologies to yield hybrid systems, there exists the possibility of increasing the efficiency of the entire system and decreasing the costs [3]. Much of the current literature on hybrid systems based on solid oxide fuel cells pays particular attention to the evaluation of their thermodynamic performance through either exergy or thermoeconomic analysis. One study by Rokni [4], for example, evaluated the thermodynamic and thermoeconomic performance of a 120 kWe small-scale integrated gasification-solid oxide fuel cell and Stirling engine. A broader analysis is proposed by Baghernejad et al [5] who made a comparison, based on an exergoeconomic method, Energies 2019, 12, 3476; doi:10.3390/en12183476 www.mdpi.com/journal/energies
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