Abstract
Hydrogen is yet to be widely accepted as a fuel for everyday operation due to stringent safety regulations involved around it. In the meanwhile, methanol could be a potential fuel of the future. In this work, an extensive thermodynamic investigation on an energy storage system with a reversible solid oxide stack at its core is presented. The current investigated system can operate either as an electrolyzer or as a fuel cell. It uses steam for electrolysis (charging mode) and methanol for fuel cell operation (discharging mode). A process model of the entire system is formulated by using Aspen Plus™. Energy and exergy efficiency have been reported for both modes of operation, along with maximum roundtrip efficiency that can be achieved for the entire system operation. Results indicate that during electrolysis mode, a maximum energy and exergy efficiency of 67.94% and 72.30% can be achieved and for fuel cell mode operation, the numbers are 74.14% and 62.61% respectively. The maximum reported value of RT efficiency is 64.32% which is quite high considering the infancy of reversible solid oxide technology and the fact that methanol is used as the fuel.
Highlights
Energy and exergy efficiency have been reported for both modes of operation, along with maximum roundtrip efficiency that can be achieved for the entire system operation
It is thermodynamically feasible and practical to realise such a system and it does makes sense from both an energy and exergy efficiency point of view to build such systems because the numbers are greater than 50% for many of the operating points
Since the performance of the system greatly depends on the operating pa rameters/conditions, the authors have provided comprehensive design maps for system energy and exergy efficiencies
Summary
Europe is making a transition to a low carbon economy by harnessing and maximising the potential of renewable energy technologies and by investing in energy storage technologies which are seen as key and supplementary to renewable energy sources. A broad framework of the policy is available in the Europe 2020 agenda [1]. The Eu ropean Commission aims for 80–95% reduction in carbon dioxide (CO2) generation by 2050 in comparison with CO2 produced during 1990. The increase in CO2 emissions has skyrocketed by 70% during the period. 32 billion tonnes of CO2 were emitted in 2014. CO2 annual emissions are expected to rise to 50 billion tonnes by 2050 [2]
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