energies Article Polish Energy Transition 2040: Energy Mix Optimization Using Grey Wolf Optimizer Damian Hasterok 1 , Rui Castro 2 , Marcin Landrat 3 , Krzysztof Piko ´ n 3 , Markus Doepfert 1 and Hugo Morais 2, *   Citation: Hasterok, D.; Castro, R.; Landrat, M.; Piko ´ n, K.; Doepfert, M.; Morais, H. Polish Energy Transition 2040: Energy Mix Optimization Using Grey Wolf Optimizer. Energies 2021, 14, 501. https://doi.org/ 10.3390/en14020501 Received: 14 December 2020 Accepted: 13 January 2021 Published: 19 January 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 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/). 1 Department of Electrical and Computer Engineering, Instituto Superior Técnico-IST, Universidade de Lisboa, 1049-001 Lisbon, Portugal; damian.hasterok@tecnico.ulisboa.pt (D.H.); markus.doepfert@tecnico.ulisboa.pt (M.D.) 2 INESC-ID, Department of Electrical and Computer Engineering, Instituto Superior Técnico-IST, Universidade de Lisboa, 1049-001 Lisbon, Portugal; rcastro@tecnico.ulisboa.pt 3 Department of Technologies and Environmental Engineering, Faculty of Energy and Environmental Engineering, Silesian University of Technology, 44-100 Gliwice, Poland; marcin.landrat@polsl.pl (M.L.); krzysztof.pikon@polsl.pl (K.P.) * Correspondence: hugo.morais@tecnico.ulisboa.pt Abstract: Poland is facing demanding challenges to achieve a sustainable energy mix in the near future. Crucial and tough decisions must be made about the direction of the national energy economy, safety, and environmental impact. Considering the electricity and heating demand forecast, this paper proposes an optimization model based on the Grey Wolf Optimizer meta-heuristic to support the definition of ideal energy mix considering the investment and operational costs. The proposed methodology uses the present energy mix in Poland (the most recent values are from 2017) to calibrate the model implemented in the EnergyPLAN tool. Afterwards, EnergyPLAN relates to an optimization process allowing the identification of the most convenient energy mix in 2040 in Poland. The values obtained are compared with those proposed by Polish public entities showing advantage regarding the global costs of the project nevertheless respecting the same levels of CO 2 and the energy import and export balance. The expected savings can achieve 1.3 billion euros a year and more than 8 million tonnes of CO 2 emission reduction. Sensitivity analysis considering the decrease of the global cost of renewables-based sources is also presented. Keywords: cost optimization energy efficiency; energy sources; energy transition; Grey Wolf Opti- mizer; Poland 1. Introduction Based on a BP (British Petroleum) report in 2020 [1], Poland produced 74.4% of electricity from coal in 2019, which represents a decrease of about 4% in comparison to 2018. However, the percentage of coal in the energy mix in Poland is four times more than the average in European countries (17.5%). The CO 2 emission reached 309 million tonnes overall and 151 million tonnes in heat and electricity sectors [2]. Poland’s environmental targets to 2030 are a 40% decrease of greenhouse gases (GHG) from the 1990 year level, an increase of renewable energy sources (RES) in total energy consumption to 32%, and an increase of energy efficiency to 32.5% [3]. In 2018, the two last objectives were adjusted to 27% [4]. Nevertheless, environmental targets are demanding challenges for Poland. In the European Parliament, they are much more ambitious. According to [5], Europe intends to achieve carbon neutrality by 2050. To achieve those targets, a model of electro-energetic and heat systems for 2040 was built. This model is explained sufficiently in the Energy Policy of Poland 2040 (EPP 2040). According to EPP 2040, the aim is to achieve 28.5% of RES production in overall energy uti- lization in 2040 (39.7% in electricity production). (The target values are different according Energies 2021, 14, 501. https://doi.org/10.3390/en14020501 https://www.mdpi.com/journal/energies