###### Abstract  
Clean energy and fuel storage is often required for both stationary and automotive applications. Some of the clean energy and fuel storage technologies currently under extensive research and development are hydrogen storage, direct electric storage, mechanical energy storage, solar-thermal energy storage, electrochemical (batteries and supercapacitors), and thermochemical storage. The gravimetric and volumetric storage capacity, energy storage density, power output, operating temperature and pressure, cycle life, recyclability, and cost of clean energy or fuel storage are some of the factors that govern efficient energy and fuel storage technologies for potential deployment in energy harvesting (solar and wind farms) stations and on-board vehicular transportation. This Special Issue thus serves the need to promote exploratory research and development on clean energy and fuel storage technologies while addressing their challenges to a practical and sustainable infrastructure. thermal energy storage; electrochemical energy storage; hydrogen energy storage; salt cavern energy storage  
The major focus of this Special Issue is to explore and innovate various clean energy and fuel storage systems that can be deployed successfully for the enhancement of clean energy portfolios for both stationary and automotive applications. It also seeks to address the underlying factors affecting the sequestration and capture of carbon by developing thermochemical energy storage or alternative fuel storage approaches, such as the atomic or molecular storage of hydrogen via solid-state materials. The submitted research papers were initially screened for their originality and novelty and then reviewed by three peer-reviewers, who are experts in the field, before their acceptance for publication in this Special Issue. One review paper and 15 journal articles were published in this Special Issue of _Applied Sciences_, a journal of MDPI publications. The contents of the published papers are categorized according to their nature and application type as (i) thermal energy storage (TES), (ii) electrochemical energy storage (EES), (iii) hydrogen energy storage (HES), and (iv) salt cavern energy storage (SCES) options. The following excerpts are based on the editorial briefing about the novelty and innovation of these 16 peer-reviewed published papers in _Applied Sciences_. Thermal Energy Storage: The storage of heat energy in materials or other forms for chemical reactions is currently employed for concentrated solar power plants. During the daytime, the heat obtained from the abundant solar irradiation is focused on to dish/trough-type or central receiver-type antennas, where the heat is carried over by a fluid. The available heat is then circulated over the heat storage materials, for example phase change materials or waste slag. The heat is absorbed and hence stored in the material due to endothermic reactions, leading to the release of a gas or a change in the materials' phase structure. In the night hours, there is no constant heat available from the sun. Therefore, the material will release the heat due to external variations such as gaseous absorption or phase change due to cooling; this is referred to as an exothermic process. The reversibility of such TESis then augmented for Concentrated Solar Power (CSP) and other potential applications. In this Special Issue, at least three research articles address the design and optimization of TES systems involving various materials. [PERSON] et al. [1] demonstrated a type of new slag as an inventory material derived from an Electric Arc Furnace (EAF). Since the physical characteristics of these slag materials are similar to those of other refractory materials and ceramics, their performance with a unique design optimization for TES is evaluated for the Julich Power Tower Company in Germany.