This paper presents the performance assessment of stratified sensible thermal energy stores (SSTES) on the basis of the normalized exergy efficiency, (eta) over bar (x). Assessments based on (eta) over bar (x) provide comparisons with performances of both the perfectly stratified and the fully mixed stores, which offer the best and worst performances, respectively. This is in contrast with energy and exergy efficiencies, which compare SSTES with only the perfectly stratified store. A dimensionless unsteady axisymmetric model of vertical cylindrical SSTES was implemented using a finite volume numerical scheme. The effect of some significant parameters on SSTES performance were considered by performing computations for aspect ratios (AR) between 1 and 4, Peclet number (Pe(D)) varying from 5 x 10(3) to 100 x 10(3), Richardson number (Ri) varying from 10 to 10(4), and overall heat loss coefficients (U) varying from 0 to 100 W m(-2) K-1.(eta) over bar (x) increases with Pe(D), Ri and AR, with the most significant increases occurring at low values of these parameters, and appreciable increases are no longer obtained beyond Pe(D) approximate to 30 x 10(3), Ri approximate to 10(3) and AR approximate to 3. (eta) over bar (x) also falls monotonically as the U values increase. (C) 2016 Elsevier Ltd. All rights reserved.