Solar thermal energy storage is important to the daily extended operation and cost reduction of a concentrated solar thermal power plant. To provide industrial engineers with an effective tool for sizing a thermocline heat storage tank, this paper used dimensionless heat transfer governing equations for fluid and solid filler material and studied all scenarios of energy charge and discharge processes. It has been found that what can be provided through the analysis is a series of well-configured general charts bearing curves of energy storage effectiveness against four dimensionless parameters grouped up from the storage tank dimensions, properties of the fluid and filler material, and operational conditions (such as mass flow rate of fluid and energy charge and discharge periods). As the curves in the charts are generalized, they are applicable to general thermocline heat storage systems. Engineers can conveniently look up the charts to design and calibrate the dimensions of thermocline solar thermal storage tanks and operational conditions, without doing complicated modeling and computations. It is of great significance that the generalized charts will serve as tools for thermal energy storage system design and calibration in energy industry. (C) 2011 Elsevier Ltd. All rights reserved.