Adiabatic compressed air energy storage with packed bed thermal energy storage

AbstractThe majority of articles on Adiabatic Compressed Air Energy Storage (A-CAES) so far have focussed on the use of indirect-contact heat exchangers and a thermal fluid in which to store the compression heat. While packed beds have been suggested, a detailed analysis of A-CAES with packed beds is lacking in the available literature. This paper presents such an analysis. We develop a numerical model of an A-CAES system with packed beds and validate it against analytical solutions. Our results suggest that an efficiency in excess of 70% should be achievable, which is higher than many of the previous estimates for A-CAES systems using indirect-contact heat exchangers. We carry out an exergy analysis for a single charge–storage–discharge cycle to see where the main losses are likely to transpire and we find that the main losses occur in the compressors and expanders (accounting for nearly 20% of the work input) rather than in the packed beds. The system is then simulated for continuous cycling and it is found that the build-up of leftover heat from previous cycles in the packed beds results in higher steady state temperature profiles of the packed beds. This leads to a small reduction (<0.5%) in efficiency for continuous operation

Resource assessment for offshore green hydrogen production

Hydrogen is a low carbon energy carrier with the ability to reduce emissions from a variety of sectors such as heating, transportation, heavy industry and power generation. With renewable energy expanding further offshore, there is potential to repurpose existing oil and gas infrastructure for transporting energy to land in the form of molecules, such as hydrogen, rather than building expensive new cables to connect wind farms to an already constrained grid. Hydrogen can help to balance intermittent renewable energy supply as well as store the excess power that would otherwise be curtailed. Areas around Scotland have been determined, which match offshore renewable and oil and gas areas of interest that could be used to produce green hydrogen offshore. A resource assessment was carried out on one of the identified sites to estimate approximate annual energy yield available for hydrogen production. The average annual energy yield (P50) was 5576.3 GWh/year with the capacity factor for the ‘grid-less’ wind farm of 42.4%. Four different scenarios were used in order to analyse the impact of the availability of the electrolyser on the capacity factor for ‘grid-less’ wind farms. Capacity factor can vary up to 4.1%, which translates to 27.7 tons of hydrogen lost per day. This could power up to 155 trains, 2,770 buses or provide a full tank for up to 5,540 cars contributing towards the 2045 net zero carbon target in Scotland