Developing easy-to-use mathematical models for describing temperatures of solar storage tanks is important for the practice, since solar storages are unavoidable elements in solar heating systems, where some heat should be stored in the form of hot fluid. In this paper, a new, general and easy-to-apply black box model, called LR model (where LR is the abbreviation of linear regression), is proposed for solar storages on the basis of multiple linear regression. This linear model may be the simplest black-box type model, which can follow the transient processes of solar storages precisely. Accordingly, the LR model proves to be more precise than a slightly modified version of a physically-based storage model used successfully for different applications in the literature. The modified physically-based model accounts for the short circuit effect occurring in storages. Comparing measured and simulated data on a real solar storage, both models are validated and their efficiency is discussed in details. The general and simple usability of the LR model is mentioned and future research proposals are given. (C) 2018 Elsevier Ltd. All rights reserved.