Citation: Lee, J.-Y.; Isafiade, A.J.; Liu, Y. Special Issue on “Multi-Period Optimization of Sustainable Energy Systems”. Processes 2022, 10, 1386. https://doi.org/10.3390/pr10071386 Received: 1 July 2022 Accepted: 13 July 2022 Published: 15 July 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). processes Editorial Special Issue on “Multi-Period Optimization of Sustainable Energy Systems” Jui-Yuan Lee 1, * , Adeniyi Jide Isafiade 2 and Yongzhong Liu 3 1 Department of Chemical Engineering and Biotechnology, National Taipei University of Technology, Taipei 10608, Taiwan 2 Department of Chemical Engineering, University of Cape Town, Rondebosch 7701, South Africa; aj.isafiade@uct.ac.za 3 Department of Chemical Engineering, Xi’an Jiaotong University, Xi’an 710049, China; yzliu@mail.xjtu.edu.cn * Correspondence: juiyuan@ntut.edu.tw; Tel.: +886-2-2771-2171 (ext. 2524) 1. Introduction Sustainable energy systems are an essential response to climate change challenges. Important measures include energy efficiency enhancement, the increased use of renewable energy, and carbon capture and storage. A holistic management system would thus be necessary to integrate these initiatives for a low-carbon-emission society for climate- resilient economic growth. Systematic methods for the optimal synthesis, design, and operation of efficient, low-carbon energy systems have been developed. Efficient and multi- functional energy systems are considered an important engineering solution to reduce carbon emissions. For example, polygeneration systems can take advantage of process integration from the simultaneous production of multiple products, thereby achieving improved fuel efficiency and reduced carbon emissions. The integration of renewables into the energy mix can achieve similar benefits. Process Systems Engineering (PSE) methods can be applied to the synthesis of such sustainable energy systems, which may need to be designed with multi-period consideration to account for variations in product demand and resource availability, as well as changes in external factors such as electricity price. This Special Issue, entitled “Multi-Period Optimization of Sustainable Energy Sys- tems”, aims to curate novel advancements in the development and application of PSE methods and alternative tools to address longstanding challenges in the synthesis and design of sustainable energy systems for multi-period operations. Three contributions addressed multi-period optimization for negative-emission polygeneration plant design [1], biorefinery supply network synthesis [2], and inter-plant hydrogen integration [3]. In addition, two contributions dealt with multi-objective optimization for the allocation of dis- tributed generation (DG) and electric vehicle charging stations (EVCSs) [4] and multi-stage membrane separation system design [5]. 2. Brief Synopsis of Papers in the Special Issue Pimentel et al. [1] employed the P-graph framework for the design of polygeneration plants with negative-emission technologies (NETs). In their case study, a polygeneration plant which integrated NETs to further reduce the carbon footprint was synthesized for multi-period operations. Potrˇ c et al. [2] developed a multi-period optimization model for the synthesis of a biorefinery supply network with the objective of maximizing sustainabil- ity profit. Their case study evaluated the capabilities of countries in the European Union to meet the renewable energy target in the transport sector by 2030. Han et al. [3] developed a simultaneous optimization approach to the design of multi-period inter-plant hydrogen networks for the minimum total annualized cost. They presented an industrial case study of a three-plant hydrogen network to demonstrate their approach. Processes 2022, 10, 1386. https://doi.org/10.3390/pr10071386 https://www.mdpi.com/journal/processes