Multi-input, Multi-output Hybrid Energy Systems

Abstract

This paper describes novel hybrid energy systems that synergistically incorporate diverse energy sources, including renewable, nuclear, and fossil with carbon capture, that offer potential to provide environmentally sustainable, cost-effective and reliable power, heat, mobility, and other energy services, more effectively. In contrast to competitive assessment of single energy sources, hybrid energy systems offer distinct comparative advantages via utilization of multiple feedstocks to create multiple products and services through increased coordination and direct hybridization, allowing dynamic optimization of supply and demand. The intelligent design of these increasingly complex, multidimensional energy systems is a significant challenge. Innovations required include approaches to formulate and optimize the complex, dynamic, multiscale interactions among energy sources, electricity generation and distribution, energy services, energy-intense processes and products, and markets. Jurisdictions and industries are setting ambitious goals to decarbonize energy systems. Low-cost wind, solar, and natural gas and the resultant dynamic electric grid require energy technologies to adapt in order to meet key attributes for modern energy systems: resilience, reliability, security, affordability, flexibility, and sustainability. When considering energy sources independently and competitively, value-added synergies among energy technologies may be overlooked for meeting demanding, multidimensional requirements. This paper presents novel concepts for tightly coupled hybrid energy systems that leverage capabilities of diverse energy generators, including renewable, nuclear, and fossil with carbon capture, to provide power, heat, mobility, and other energy services. The paper also presents a framework for engineering-based modeling and analysis for complex optimization of energy generation, transmission, services, processes and products, and market interactions. New modeling capabilities are needed to adequately represent multi-input, multi-output tightly coupled hybrid energy systems that utilize multiple feedstocks to create multiple products and services in novel and synergistic ways through increased coordination of energy systems and tightly coupled hybrid system configurations. Jurisdictions and industries are setting ambitious goals to decarbonize energy systems. Low-cost wind, solar, and natural gas and the resultant dynamic electric grid require energy technologies to adapt in order to meet key attributes for modern energy systems: resilience, reliability, security, affordability, flexibility, and sustainability. When considering energy sources independently and competitively, value-added synergies among energy technologies may be overlooked for meeting demanding, multidimensional requirements. This paper presents novel concepts for tightly coupled hybrid energy systems that leverage capabilities of diverse energy generators, including renewable, nuclear, and fossil with carbon capture, to provide power, heat, mobility, and other energy services. The paper also presents a framework for engineering-based modeling and analysis for complex optimization of energy generation, transmission, services, processes and products, and market interactions. New modeling capabilities are needed to adequately represent multi-input, multi-output tightly coupled hybrid energy systems that utilize multiple feedstocks to create multiple products and services in novel and synergistic ways through increased coordination of energy systems and tightly coupled hybrid system configurations. Jurisdictions around the world and private industries, including utilities, corporations, and energy consumers, are setting aggressive energy goals that are aimed at reducing carbon emissions,1International Energy Agency and OECD PublishingWorld Energy Outlook. OECD), 2019Google Scholar ushering in a transition in decision criteria for technology developers, energy planners, producers, and users. Concurrently, the global energy demand has reached historic levels and has the potential to double by 2040 as emerging economies grow and global poverty levels decline—trends that are projected to continue.2United Nations Transforming our world: the 2030 agenda for sustainable development.https://sustainabledevelopment.un.org/post2015/transformingourworldDate: 2015Google Scholar Furthermore, additional attributes ranging from resilience to economics (see Table 1) are becoming more important in valuing modern energy systems.3Arent D. Balash P. Boardman R. Bragg-Sitton S. Engel-Cox J. Miller D. 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Energy Rev. 2017; 69: 596-609Crossref Scopus (620) Google Scholar These evolving goals are changing the way we think about, evaluate, plan, and operate energy systems to maintain resilience, reliability, affordability, and security while increasing flexibility and sustainability.Table 1Key Attributes for Modern Energy Infrastructure and SystemsAttributeDefinitionResilienceTo hazards or disruptive events of all types and having the ability to adapt to resource availabilityReliabilityfor uninterrupted, everyday operations and energy delivery to dependent usersSecurityfrom the increasing and evolving number and types of physical and cyber threatsEconomicsto enable an adequate return on capital investment and positive cash flow, often captured as a NPVAffordabilityof energy to achieve and sustain a high standard of living and economic equityFlexibilityto respond to the variability and uncertainty of conditions at one or more timescales, including a range of potential energy futures that may vary based on regionSustainabilitythrough an adequate provision of clean energy, energy efficiencies, and stewardship of scarce natural resources Open table in a new tab The advent of low-cost wind and solar energy, the recent surge in low-cost natural gas production, and the resultant highly dynamic electricity grid have motivated energy systems that extend beyond the segregated energy production approaches that historically have depended largely on independent contributions from technology-specific energy sources within either regulated or market-oriented structures. For example, there is growing interest in leveraging decarbonized power systems for a broad set of cross-sector coupling solutions, from various energy storage technologies ranging from batteries to thermal storage, to the production of hydrogen, ammonia, and other energy carriers as well as low-carbon, high-density liquid fuels. In addition, there is significant interest in further integration with industrial processes, such as steel production and chemical manufacturing, to achieve broader, economy-wide decarbonization ambitions. Energy systems that best leverage the desirable attributes of each energy resource and conversion technology in an integrated and unified manner can provide a pathway to a future energy infrastructure capable of meeting expanded demand while enhancing environmental stewardship and maintaining affordability.9Editorial A world in transition.Nat. Energy. 2016; 1: 15026Crossref Scopus (4) Google Scholar In contrast to traditional approaches that consider individual energy production differentiated by the primary energy source, this paper presents novel concepts for tightly coupled hybrid energy systems (HESs) that leverage capabilities of diverse energy resources, including renewable, nuclear, and fossil with carbon capture, to provide power, heat, and mobility, produce energy carriers, and provide storage and other energy services. We outline the key aspects of evolving energy solutions that incorporate an expansive set of technology pathways for integrating multiple energy sources and energy forms (e.g., electricity, heat, steam, and chemicals) in hybrid configurations to provide multiple benefits, including flexible output streams to maximize utilization and profit across various energy sectors to provide services such as electricity, high-value heat, and chemicals (e.g., hydrogen, hydrocarbons, carbon-based products, and ammonia). We also introduce requirements for an engineering-based multicomponent, multiscale modeling framework that enables this broader multiscale view of energy infrastructure planning and optimization and a broader exploration of options for transformational energy systems. This new approach expands traditional energy strategies for evaluating how the natural resource potential of each location can be leveraged in the most efficient and cost-effective manner to provide needed energy services while meeting social and environmental objectives within a country context.10Debnath K.B. Mourshed M. Challenges and gaps for energy planning models in the developing-world context.Nat. Energy. 2018; 3: 172-184Crossref Scopus (35) Google Scholar,11Miniard D. Kantenbacher J. Attari S.Z. Shared vision for a decarbonized future energy system in the United States.Proc Natl Acad Sci USA. 2020; 117: 7108-7114Crossref PubMed Scopus (11) Google Scholar An evaluation of energy system options for a selected region or application begins by determining the necessary energy form (i.e., electricity, heat, or steam) and the magnitude and variability of the demand. Such evaluation must also consider the available resources and the potential interrelation between multiple energy demands in the region. Rather than assess the potential contribution of independent energy resources, one might additionally consider coordinated and tightly coupled HESs that connect multiple energy-generation options and dynamically apportion energy in various forms to provide responsive generation to the electricity grid while also supporting the production of other energy products. Key definitions of energy system options are provided in Table 2 and an example is shown in Figure 1.Table 2Definition of Energy System ConfigurationsConfigurationsDefinition and Distinctive CharacteristicsCoordinated energy system•geographically distinct resources that interact through infrastructure (e.g., the electrical grid, natural gas network, and food-energy-water nexus) to meet energy demands•coordination typically occurs via market mechanismsTightly coupled hybrid energy system (HES)•direct thermal and/or electrical integration of multiple energy-generation technologies, behind the grid, to meet multiple energy demands•systems may include multi-input, multi-output (MIMO); single-input, multi-output (SIMO); or multi-input, single-output (MISO) options; the conceptual process design shown in Figure 1 represents a potential thermally and electrically integrated MIMO system Open table in a new tab To date, energy economies have primarily been developed considering individual energy sources differentiated by the primary energy source and optimized for specific sectors (e.g., electricity, heating, and fuels); as such, these can be considered single-input single-output (SISO) systems. While most energy sectors are served by SISO solutions, in some cases various relatively uncomplicated SISO, single-input, multi-output (SIMO), and multi-input, single-output (MISO) HES configurations are being deployed, both domestically and internationally, with examples that include battery-solar or battery-natural-gas hybrid configurations12Ericson S. Anderson K. Engel-Cox J. Jayaswal H. Arent D. Power couples: the synergy value of battery-generator hybrids.Electr. J. 2018; 31: 51-56Crossref Scopus (5) Google Scholar,13Borges Neto M.R. Carvalho P.C.M. Carioca J.O.B. Canafístula F.J.F. Biogas/photovoltaic hybrid power system for decentralized energy supply of rural areas.Energy Policy. 2010; 38: 4497-4506Crossref Scopus (63) Google Scholar and district heating and cooling systems, which have long been considered cross-sector coupled energy system implementation.14Vandermeulen A. van der Heijde B. Helsen L. 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Boardman R. Bragg-Sitton S. Engel-Cox J. Miller D. Ruth M. Summary report of the tri-lab workshop on R&D pathways for future energy systems. National Renewable Energy Laboratory, 2018https://www.nrel.gov/docs/fy19osti/72926.pdfGoogle Scholar,22Chen Q. Lv M. Gu Y. Yang X. Tang Z. Sun Y. Jiang M. Hybrid energy system for a coal-based chemical industry.Joule. 2018; 2: 607-620Abstract Full Text Full Text PDF Scopus (23) Google Scholar,23Shih C.F. Zhang T. Li J. Bai C. Powering the future with liquid sunshine.Joule. 2018; 2: 1925-1949Abstract Full Text Full Text PDF Scopus (203) Google Scholar MIMO HESs would utilize a portfolio of energy sources to provide multiple benefits, including flexible output streams, to maximize utilization and profit across various energy sectors to provide services, such as electricity, high-value heat, and chemicals. As an example, consider a tightly coupled industrial energy park that utilizes heat and electricity pathways from advanced nuclear reactors—small-scale, highly flexible, fossil generators that incorporate carbon capture and renewables (e.g., solar, wind, geothermal, and hydropower). Depending on market pricing, electricity/heat can be sold into the grid, utilized on-site, or stored for later distribution and use. These output streams could be used to produce hydrogen (through water or steam electrolysis or thermolyzed natural gas24Dagle R. Dagle V. Bearden M. Holladay J. Krause T. Ahmed S. R&D opportunities for the development of natural gas conversion technologies for co-production of hydrogen and value-added solid carbon products. Pacific Northwest National Laboratory and Argonne National Laboratory, 2017https://www.osti.gov/servlets/purl/1411934Google Scholar, 25Robertson S.D. 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Chiang Y.-M. et al.Net-zero emissions energy systems.Science. 2018; 360: eaas9793Crossref PubMed Scopus (505) Google Scholar Despite the potential benefits, widespread deployment of MIMO HESs has been hampered in part by a lack of modeling tools to appropriately quantify these benefits and optimize HESs for the most impactful performance. The emerging energy ecosystem is increasingly dynamic and interconnected, requiring greater interoperability of modeling and analytical tools to link energy generation, distribution, and use. HESs are expected to be inherently more dynamic for synergistically integrating multiple processes and energy sources while also interacting with broader electricity and product markets.31Bragg-Sitton S.M. Miller D. Engel-Cox J. Balash P. Boardman R. Arent D. Tarka T. Ruth M. Summary report of the tri-lab workshop on modeling & analysis of current & future energy systems, April 25–26, 2019. National Energy Technology Laboratory, 2019https://www.netl.doe.gov/energy-analysis/details?id=4449Google Scholar Thus, a modeling and analytical framework to support the identification, optimization, and evaluation of future HESs must consider multiple questions at different temporal and spatial scales as well as the bidirectional interaction among systems. These include the need to evaluate the following levels of interaction:(1)Design and operation of inherently dynamic processes that produce electricity and other outputs from one or more primary energy sources (e.g., nuclear, renewable, and fossil) and potentially produce multiple products (e.g., heat, hydrogen, or other chemicals), including the conceptual design of novel MIMO HESs and the rigorous exploration of innovative design options that extend beyond current experience.(2)Dynamic interactions of the energy system with the electricity grid, as often represented in unit commitment/production cost models, to evaluate system dynamics at the subhourly to hourly level to evaluate reliability, operating costs, and potential revenue based on actual operating scenarios and their interaction with current and potential markets, including electric vehicles, smart grid-connected buildings, and numerous cross-sector coupling configurations.(3)Interactions of the energy system over longer time horizons with broader supply chains (e.g., electricity grid and pipeline networks) and markets, as often represented in capacity expansion models such as the Regional Energy Deployment System (ReEDS)32Brown M. 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Hartin C. et al.GCAM v5.1: representing the linkages Between energy, water, land, climate, and economic systems.Geosci. Model Dev. 2019; 12: 677-698Crossref Scopus (94) Google Scholar to determine their ability to enhance environmental sustainability. A variety of modeling and analytical tools have been developed to address these needs and answer specific questions. Interaction among the four operational scales has largely been unidirectional, with energy system characteristics being abstracted into a few key characteristics, such as a cost and performance curve, that are used by higher-level models that address broader aspects of the electricity grid, economy, or environment. Such simplifications are less reasonable as electricity markets become more diverse and dynamic and energy ecosystems become increasingly cross-coupled. In the case of HESs, such simplifications cannot capture the potential value of dynamically utilizing multiple inputs to produce multiple products while taking into account changing market conditions and needs (such as grid stability). For example, dynamic coupling of residential loads (and consumer preferences and behaviors), industrial processes, power generation, and heat supply could provide economic advantages while simultaneously reducing environmental impact and increasing reliability; however, such concepts are not readily considered within existing modeling and analytical frameworks. In addition, most expansion-planning models and IAMs incorporate only commercially available and well characterized (with regard to cost and performance) technologies, which hinder transparent evaluation of new technologies, particularly MIMO HESs, and novel opportunities to integrate existing and greenfield assets. Finally, existing modeling and analytical tools lack the necessary data and data analytics to project temporal, spatial, and demographic forms of energy demands and resources that are required to make investments in energy infrastructure. This limits a comprehensive approach to establishing interconnections from the process level up to the energy carrier level, end services, pipeline or grid networks, and commerce supply networks. As we consider the requirements for a new modeling and analytical framework, we recognize that such a framework should leverage the capabilities of the broad suite of energy models and analytical tools that have already been developed by government agencies, national laboratories, academia, nongovernment organizations, and industry. The framework must not only adequately capture the performance of a wide variety of energy systems and the complex interaction of energy infrastructure components but also guide the design of new HESs by including engineering-level design and dynamic optimization to address spatial and temporal variability in resource availability and energy demand. Furthermore, such a framework must integrate both traditional and novel approaches to energy system design and implementation, incorporating not only SISO and SIMO options but also MIMO technologies in the energy resource planning, asset planning, and operational tools. The framework must also enable the simultaneous, multicriteria optimization of inherently dynamic energy systems to evaluate the costs and benefits of traditional and innovative configurations of energy technologies across a number of attributes (see Table 1). This contrasts with traditional modeling approaches, which often employ competitive least-cost frameworks to meet the projected energy demand within an “energy outlook,” or traditional scenario analysis, as exemplified by decades of prior work as captured by the Intergovernmental Panel on Climate Change (IPCC) or similar multimodel efforts.35IPCCGlobal Warming of 1.5°C. IPCC, 2018https://www.ipcc.ch/sr15/Google Scholar, 36van Ruijven B.J. De Cian E. Sue Wing I. Amplification of future energy demand growth due to climate change.Nat. Commun. 2019; 10: 2762Crossref PubMed Scopus (94) Google Scholar, 37Duan H. Zhang G. Wang S. Fan Y. Robust climate change research: a review on multi-model analysis.Environ. Res. 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Thus, these approaches must enable the robust design of energy systems and consider edge cases to ensure reliability and resilience. Assessing any individual attribute requires integrating multiple perspectives, time, and spatial scales via appropriate models. For example, assessing sustainability requires understanding the impact on natural resources, including long-term accessibility; consideration of permanent land and water withdrawals; potential for land, water, and atmospheric pollution; the ability to recycle essential resources for future use; and, ultimately, societal and ecological impacts. When implemented on a large scale, new technologies may also have significant geopolitical and national security impacts that result from limitations in domestic supply or a reliance on foreign supply for fuels or raw materials (e.g., rare earth metals) that are necessary to support implementation.40Sovacool B.K. Ali S.H. Bazilian M. Radley B. Nemery B. Okatz J. Mulvaney D. Sustainable minerals and metals for a low-carbon future.Science. 2020; 367: 30-33Crossref PubMed Scopus (104) Google Scholar,41Bazilian M. Bradshaw M. Goldthau A. Westphal K. May 01 Model and manage the changing geopolitics of energy.Nature. 2019; 569: 29-31Crossref PubMed Scopus (23) Google Scholar Furthermore, assessing the economics of an energy system in order to estimate revenue and operating expenses requires understanding not only the capital costs but also how it will dynamically interact with power, energy, and product markets over its lifetime. For MIMO HESs, this also includes interactions with the markets and supply chains for non-electricity coproducts. Because the HES will operate dynamically, tighter linkages among model scales will be required than has historically been necessary for these analyses. Finally, the performance and value of any energy system will be highly dependent on location due to resource availability, local infrastructure, market structure, demand for coproducts, climate, regulations, incentives, etc. While considerable advancements have been achieved in the development a