The efficient utilization of solar energy technology is significantly enhanced by the application of energy storage, which plays an essential role. Nowadays, a wide variety of applications deal with energy storage. Due to the intermittent nature of solar radiation, phase change materials are excellent options for use in several types of solar energy systems. This overview of the relevant literature thoroughly discusses the applications of phase change materials, including solar collectors, solar stills, solar ponds, solar air heaters, and solar chimneys. Despite the complexity of their availability and high costs, phase change materials are utilized in the majority of solar energy techniques because of the considerable technical improvements they provide. While numerous studies have investigated the progress of phase change materials used in solar energy applications such as photovoltaic systems, it is vital to understand the conceptual knowledge of employing phase change materials in various types of solar thermal energy systems. Investigations into the use of phase change materials in solar applications for the purpose of storing thermal energy are still being carried out to upgrade the overall performance. This paper briefly reviews recently published studies between 2016 and 2023 that utilized phase change materials as thermal energy storage in different solar energy systems by collecting more than 74 examples from the open literature. This study focuses on demonstrating the maturity of phase change materials and their integration into solar energy applications. Based on the findings, proposals for new research projects are made.

A new method for the optimization of seasonal energy storage is presented and applied in a case study. The optimization method uses an interval halving approach to solve computationally demanding mixed integer linear programming (MILP) problems with both integer and non-integer operation variables (variables that vary from time step to time step in during energy storage system operation). The seasonal energy storage in the case study uses a reversible solid oxide cell (RSOC) to convert electricity generated by solar photovoltaic (PV) panels into hydrogen gas and to convert hydrogen gas back to electricity while also generating some heat. Both the case study results and the optimization method accuracy are examined and discussed in the paper. In the case study, the operation of the RSOC and hydrogen storage system is compared with the operation of a reference system without energy storage. The results of the study show that installing an RSOC and hydrogen storage system could increase the utilization of onsite renewable energy generation significantly. Overall, the optimization method presents a relatively accurate solution to the case study optimization problem and a sensibility analysis shows a clear and logical pattern.

A Positive Energy District (PED) is a portion of urban area with defined boundaries that can produce energy in excess of its own consumption. The aim of this study is to analyse design variations among the six projects (12 case studies) of PED belonging to the European Smart Cities and Communities programme. Thus, it will be possible to identify the reasons behind the energy choices related to generation, storage and distribution that appear in the different geographical areas. To achieve this, different data were collected by consulting official documents and creating questionnaires that were communicated with the project representatives. Thus, the result of this study is a catalogue of the energy system solutions adopted in the studied PEDs with a critical analysis of the different motivations behind them in order to outline general trends in the geographical areas with similar characteristics. In conclusion, this study defined which technological choices are the most common in territories with similar profiles and how divergent those with different profiles are. Furthermore, applied to a large catalogue of PED, the methodology identified would make it possible to create different operating models for different territorial types and urban settlements.

Buildings and the mobility sectors are the two sectors that currently utilize large amount of fossil-based energy. The aim of the paper is to, critically analyse the integration of electric vehicles (EV) energy load with the building’s energy load. The qualitative and quantitative methods are used to analyse the nearly/net zero energy buildings and the mobility plans of the Europe along with the challenges of the plans. It is proposed to either include or exclude the EV load within the building’s energy load and follow the emissions calculation path, rather than energy calculation path for buildings to identify the benefits. Two real case studies in a central European climate are used to analysis the energy performance of the building with and without EV load integration and the emissions produced due to their interaction. It is shown that by replacing fossil-fuel cars with EVs within the building boundary, overall emissions can be reduced by 11–35% depending on the case study. However, the energy demand increased by 27–95% when the EV load was added with the building load. Hence, the goal to reach the nearly/net zero energy building target becomes more challenging. Therefore, the emission path can present the benefits of EV and building load integration.