With an extended lumped capacitance method applied to account for the internal heat conduction resistance in a solid (for Biot number larger than 0.1), a general model of thermal energy storage with various solid-fluid structural combinations is presented and verified using numerical results. The thermal energy storage system has a heat transfer fluid (HTF) flowing through a packed bed of solid materials structured in different configurations, such as in the form of solid pebbles, parallel plates, solid rod-bundles, or solids with fluid tubes imbedded through them. The model of energy conservation in the liquid and solid is transient, one-dimensional in nature, due to the introduction of a modified lumped capacitance method that counts for the effect of three-dimensional heat conduction in the solid structures. The computational workload using this modified model is significantly less compared to that of a comprehensive CFD analysis. Numerical results obtained from a CFD analysis of the thermal energy storage in the solid and liquid are used to verify the model. The CFD simulated results of temperatures of HTF are compared with the 1D model results, and they show excellent agreement. In conclusion, the 1D model is recommended as a convenient and accurate tool for general analysis and sizing of thermal energy storage containers that have various solid-fluid structural combinations. (C) 2014 Published by Elsevier Ltd.