High temperature thermal energy storage (TES) systems have the capacity to achieve high thermal efficiencies due to their high operating temperatures. However, they tend to experience higher thermal losses which adversely affect their thermal cycles. This paper focuses on heat loss estimation from a TES system operating at 800 ℃, insulated in a cylindrical ceramic crucible, and the determination of the optimal insulation thickness of the crucible. Parameters affecting heat loss such as thermal conductivity of the ceramic material and convective heat transfer coefficient were simulated. It was observed that the thermal conductivity of the crucible had a greater effect on the rate of heat loss than the convective heat transfer coefficient. Furthermore, an increase in the length of the crucible increased the thermal mass of the crucible causing it to lose heat at higher rate. The deduced optimal radial thickness for the operating temperature range was 0.075 m. In conclusion, addition of more refractories beyond the optimal radius will not significantly reduce the rate of heat loss and will make the insulating crucible bulkier
