Segmented packed beds for improved thermal energy storage performance

A scheme for bulk electricity storage known as Pumped Thermal Energy Storage (PTES) is described. PTES uses a heat pump during the charging phase to create a hot and a cold storage space. During discharge, these thermal stores are depleted using a heat engine. This version of PTES uses packed beds (or pebble beds) as the energy store. A relatively new design feature which involves segmenting the packed beds is introduced. Various thermodynamic benefits can be achieved by reservoir segmentation, such as reduced pressure losses and increased energy stored per cycle. This report includes modelling of the storage phases, and it is found that segmentation can reduce the thermal equilibration losses that occur. A simple economic model of the PTES system is introduced so that multi-objective optimisation of efficiency and capital costs can be carried out. Sensitivity to the economic factors is briefly explored. The results show that cold packed beds in particular benefit from being segmented.The work described in this paper was undertaken as part of a project funded by the UK Engineering and Physical Sciences Research Council (EPSRC Grant No. EP/J006246/1). The first author was supported by an EPSRC-funded studentship and attended the Off-Shore Energy and Storage Conference (OSES) 2015 with the assistance of the Energy Storage Research Network (ESRN).This is the author accepted manuscript. The final version is available from the Institution of Engineering and Technology via http://dx.doi.org/10.1049/iet-rpg.2016.003