Hybrid renewable energy systems

In the pursuit of ecologically sustainable and resilient energy systems, increasingly more attention is being devoted to a diversity of energy generation and storage methods. As the landscape of generation technology gains nuance and complexity, a wide-ranging set of technical questions has emerged, touching on topics that range from control and optimization of hybrid systems to finance and economic viability to multi-fidelity modeling and scientific machine learning. In the context of this special issue, hybrid renewable energy systems are any systems that consider the combined dynamics of more than one form of generation, storage, or grid subsystem. Research endeavors have delved into improving the flexibility of energy systems by utilizing existing resources, introducing novel operational strategies, deploying enhanced renewable forecasts, and exploring emerging technologies. The interconnection among various sectors has garnered heightened attention, not only due to the provision of additional tradable energy products but also for furnishing flexible headroom to system operators.

Hybrid energy systems encompass a spectrum of tightly or loosely integrated energy systems, drawing from diverse energy sources to fulfill power, heating, transportation, and various other energy requirements. This approach offers a versatile solution to address challenges inherent in contemporary energy systems, leveraging a diverse array of resources and seamlessly integrating systems to attain resilience, reliability, and sustainability.¹ 

This collection of articles explores these topics within hybrid renewable energy systems (HRES) to inform scientists and engineers working in this space and to advance HRES technology to ensure a renewable future for global energy systems, unraveling their potential for intelligent energy control and optimization, adept navigation of diverse energy generation and storage dynamics, and the overarching economic viability that positions them as practical solutions for future energy needs.

We were delighted to receive a diverse array of submissions encompassing a broad spectrum of hybrid energy systems topics. The excellence of the contributions and the wholehearted engagement from the community were truly commendable. After a thorough and stringent peer-review process, we ultimately identified and selected six submissions for publication. The chosen submissions for this special issue delve into research spanning a wide range of topics, neatly categorized into three main groups: (i) control and optimization strategies for smarter energy, (ii) diverse energy generation and storage dynamics, and (iii) economic viability for practical solutions.

The collection begins with a focus on devising strategies for control and optimization of energy systems. Rahman and Zhang's work introduces a multi-timescale approach to electricity markets within Nuclear-Renewable Hybrid Energy Systems (N-R HES).² Beyond energy generation, their research highlights the strategic contribution of ancillary services, establishing these systems as not just energy producers but also reliable contributors to a resilient energy infrastructure. Additionally, Sinner et al.'s investigation into coordinated wind power plant and battery control underscores the importance of joint active power control in enhancing overall grid reliability.³ The proposed joint active power control method enables a simulated wind-battery plant to more closely follow a power reference signal compared to an uncoordinated power maximization strategy. This coordination enables the wind-battery plant to provide a more stable power output, avoiding penalties that the plant would receive for either under- or over-generation.

A second theme of the collection hones in on the exploration of how HRES must combine dynamics from a diverse set of energy generation and storage technologies. Jacob and Zhang's work focuses on integrated energy systems involving nuclear and renewables, showcasing adaptability to shifting energy demands.⁴ A central challenge in this area lies in ensuring these systems seamlessly handle fluctuations associated with various energy sources, providing both flexibility and stability to grid systems. Further contributions by Poudel et al. highlight the intricacies of designing nuclear-powered integrated energy systems, addressing the challenge of effective heat utilization in addition to electricity.⁵ 

The third theme accentuates the economic viability of advanced energy systems. Poudel et al.'s examination of co-designing microgrids with combined heat and power systems not only optimizes costs but also ensures effective resilience to disruptions.⁵ The authors discovered that integrating thermal energy storage into the district heating system effectively balances thermal generation and demand, ensuring a consistent rated temperature for the district heating supply water. Thermal energy storage is crucial for regulating district heating supply temperature and maintaining a stable heat supply, particularly under varying demand profiles. Wu et al.'s co-design optimization framework for CHP-based microgrids provides a robust methodology for stakeholders, optimizing both design and operation parameters for cost-effective, resilient systems.⁶ Cox et al.'s exploration of financing mechanisms for Fully Integrated Hybrid Energy Systems adds a crucial layer, demonstrating how principles can be adapted to capture the value and mitigate financial risks.⁷ These practical approaches underscore not only cutting-edge technology but also smart, cost-effective solutions for sustaining our world.

This collection of articles offers profound insights into shaping our energy systems to be not only greener but also smarter and economically viable. From the nuanced strategies in HRES to managing the dynamic nature of diverse energy sources and maintaining a keen eye on practical economics, this journey is about crafting solutions that are not only efficient but also accessible and beneficial for all. As we continue to navigate the complexities of the energy transition, these contributions serve as guideposts, illuminating pathways toward a more sustainable and resilient future.

The guest editors for the Hybrid Renewable Energy Systems Special Issue extend their heartfelt thanks to all the authors who contributed their original work to this collection. Their dedication to advancing knowledge in the field of renewable energy and hybrid systems has been instrumental in shaping this special issue. We also extend our gratitude to the reviewers whose thoughtful feedback and insights helped ensure the quality and rigor of the published articles. Additionally, we thank the editorial and production teams for their support and assistance throughout the publication process. Finally, we acknowledge the funding agencies and institutions that have supported this research, without which this work would not have been possible.

This work was authored in part by the National Renewable Energy Laboratory, operated by Alliance for Sustainable Energy, LLC, for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. Funding was provided by the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Wind Energy Technologies Office. The views expressed herein do not necessarily represent the views of the DOE or the U.S. Government. The U.S. Government retains and the publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for U.S. Government purposes.