*Editorial* **Special Issue on "Integrated Energy Systems towards Carbon Neutrality"**

**Pei Liu 1,\*, Ming Liu <sup>2</sup> and Xiao Wu <sup>3</sup>**


Energy systems have played an essential role in the history of human civilization. As our civilization evolves, energy systems are expected to adapt to the environment and fulfill people's desire for more sustainable development whilst meeting the ever-increasing energy demands of society. To address global warming and its threats to sustainable development on multiple fronts, major economies around the world have announced low-carbon, carbonneutral, or negative-carbon development targets. To meet these goals, energy systems as we know them today need to undergo substantial structural changes in terms of the way primary energy is extracted from nature, converted to secondary energy, transmitted from conversion sites to end use, and shifted between time slots to coordinate supply and demand. The share of renewable and fossil energy in the overall energy portfolio could experience unprecedented structural change of a kind not witnessed since industrialization. To cope with this harsh transition, energy systems should be planned, designed, retrofitted, and operated in a revolutionary manner.

This Special Issue, "Integrated Energy Systems toward Carbon Neutrality" (https:// www.mdpi.com/journal/processes/special\_issues/Integrated\_Energy\_System, accessed on 1 November 2022), aims to present the most recent advances in energy systems analysis towards low-, zero-, or negative-carbon emission targets via integration amongst different primary energy supplies, between multiple energy supplies and demands, across geographically separated regions, and over different time scales from seconds to seasons. We cover topics including:


Typical topics and specific applications of energy systems engineering in various circumstances are summarized as follows.

The energy systems in the future may exhibit rather different structural styles. Shen et al. [1] present methods for improving the thermoeconomic energy efficiency of integrated energy systems. Feng, Wang, and colleagues [2] present an optimization approach to pipeline networks in an integrated energy system with multiple heat sources. Wang et al. [3] analyzed the dynamic behavior of yet another promising type of energy system—the supercritical carbon dioxide power cycle. Dai and colleagues [4] further analyzed the control strategy of a supercritical carbon dioxide power cycle. Fuel cells are expected to play an important role due to their theoretical high energy conversion ratio and potential applications closer to

**Citation:** Liu, P.; Liu, M.; Wu, X. Special Issue on "Integrated Energy Systems towards Carbon Neutrality". *Processes* **2023**, *11*, 439. https:// doi.org/10.3390/pr11020439

Received: 15 November 2022 Accepted: 20 December 2022 Published: 1 February 2023

**Copyright:** © 2023 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/).

end consumers. Ramadhani et al. [5] reviewed development of solid oxide fuel cell-based polygeneration systems in residential applications from the asepects of technology, planning, and design. Lee and Chen [6] investigated energy saving potential of heat recovery networks in industrial processes.

In a low-carbon world, renewable energy is expected to be used extensively, and gas turbines, due to their fast load-changing properties, can compensate the intermittency renewable energy might bring to a power grid. Ren, Li, and colleagues [7] studied heat transfer issues in gas turbine vanes via data-driven analysis. Qian et al. [8] present regional short-term load forecasting methods for the purpose of better matching power supply to consumption.

Carbon mitigation in the industrial and consumer sectors are of special importance for a deeply decarbonized economy. Liu, Li, and colleagues [9] delivered a low-carbon transition pathway for the transport sector of China using multi-scale temporal and special modelling and optimization methods. Zhao and colleagues [10] present a two-step intelligent control strategy for the energy supply of an electric vehicle station. Peng, Ou, and colleagues [11] present a life-cycle analysis of greenhouse gas emissions in the primary and recycled aluminum sector in China. Wang and colleagues [12] discuss potential of cascaded cooling in the polysilicon industry.

These studies present the most recent theoretical and technical approach in low-carbon energy systems research, with potential applications in various circumstances. We hope the works collected in this Special Issue can contribute to the transition from our current energy systems to low-carbon ones in the future in a more energy-efficient, cost-effective, and realistic way.

**Funding:** This research received no external funding.

**Acknowledgments:** We would like to thank all the authors who contributed to this Special Issue, the Editor-in-Chief for their enthusiastic support of the Special Issue, as well as the editorial staff of *Processes* for their efforts, Pei Liu, Ming Liu, Xiao Wu, *Guest Editors*.

**Conflicts of Interest:** The authors declare no conflict of interest.

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