processes Review Modeling and Simulation of Energy Systems: A Review Avinash Shankar Rammohan Subramanian 1, Truls Gundersen 1 and Thomas Alan Adams II 2,* 1 Department of Energy and Process Engineering, Norwegian University of Science and Technology (NTNU), Kolbjørn Hejes vei 1B, NO-7491 Trondheim, Norway; [email protected] (A.S.R.S.); [email protected] (T.G.) 2 Department of Chemical Engineering, McMaster University, 1280 Main St. W, Hamilton, ON L8S 4L7, Canada * Correspondence: [email protected]; Tel.: +1-905-525-9140 (ext. 24782) Received: 12 October 2018; Accepted: 18 November 2018; Published: 23 November 2018 Abstract: Energy is a key driver of the modern economy, therefore modeling and simulation of energy systems has received significant research attention. We review the major developments in this area and propose two ways to categorize the diverse contributions. The first categorization is according to the modeling approach, namely into computational, mathematical, and physical models. With this categorization, we highlight certain novel hybrid approaches that combine aspects of the different groups proposed. The second categorization is according to field namely Process Systems Engineering (PSE) and Energy Economics (EE). We use the following criteria to illustrate the differences: the nature of variables, theoretical underpinnings, level of technological aggregation, spatial and temporal scales, and model purposes. Traditionally, the Process Systems Engineering approach models the technological characteristics of the energy system endogenously. However, the energy system is situated in a broader economic context that includes several stakeholders both within the energy sector and in other economic sectors. Complex relationships and feedback effects exist between these stakeholders, which may have a significant impact on strategic, tactical, and operational decision-making. Leveraging the expertise built in the Energy Economics field on modeling these complexities may be valuable to process systems engineers. With this categorization, we present the interactions between the two fields, and make the case for combining the two approaches. We point out three application areas: (1) optimal design and operation of flexible processes using demand and price forecasts, (2) sustainability analysis and process design using hybrid methods, and (3) accounting for the feedback effects of breakthrough technologies. These three examples highlight the value of combining Process Systems Engineering and Energy Economics models to get a holistic picture of the energy system in a wider economic and policy context. Keywords: energy systems; modeling and simulation; multi-scale systems engineering; sustainable process design; energy economics; top-down models; hybrid Life Cycle Assessment 1. Introduction Energy is one primary driver of the modern economy that involves several stakeholders such as energy production and distribution firms, energy investors, end users, as well as government regulators. Population growth and improving standards of living, especially in developing countries, are expected to significantly increase energy consumption. The IEA predicts an increase in total primary energy demand (TPED) from 13.8 billion tonnes of oil equivalent (toe) in 2016 to 19.3 billion toe under its “current policies” scenario in 2040 [1]. Alternatively, in the “sustainable development” scenario where policies are enacted in order to achieve the objectives of the COP 21 Paris agreement Processes 2018, 6, 238; doi:10.3390/pr6120238 www.mdpi.com/journal/processes Processes 2018, 6, 238 2 of 45 (2015)Processes together 2018, 6, withx FOR PEER universal REVIEW access to energy services and a large reduction in energy-related2 of 45 pollution, TPED grows to 14.1 billion toe in 2040. In this period, CO2 emissions would increase from(2015) 32.1 billiontogether tonnes with universal to 42.7 billion access tonnesto energy under services the current and a large policies reduction scenario in orenergy would-related have to pollution, TPED grows to 14.1 billion toe in 2040. In this period, CO2 emissions would increase from decrease to 18.3 billion tonnes in the sustainable development scenario. Transitioning to a sustainable 32.1 billion tonnes to 42.7 billion tonnes under the current policies scenario or would have to decrease energy future through the accelerated adoption of clean energy technologies and energy efficiency to 18.3 billion tonnes in the sustainable development scenario. Transitioning to a sustainable energy practicesfuturerequires through the accelerated engagement ado ofption various of clean decision energy makers technologies from the and scientific, energy efficiency financial, practices industrial, andrequires public-policy the engagement communities of various with decision an interdisciplinary makers from the approach scientific, that financial, combines industrial engineering,, and economics,public-policy and environmentalcommunities perspectiveswith an interdisciplinary [2]. approach that combines engineering, ecAnonomics energy, and system environmental is defined perspectives by the Intergovernmental [2]. 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