**Theophilos Papadimitriou**

Theophilos Papadimitriou received a Diploma degree in Mathematics from the Aristotle University of Thessaloniki, Greece, a Master's degree from the University of Nice-Sophia Antipolis, France, both in 1996, and a PhD degree from the Polytechnic School of the Aristotle University of Thessaloniki in 2000. In 2001, he joined the Department of Economics, Democritus University of Thrace, Komotini, Greece, where he currently holds the position of Professor. Dr Papadimitriou has co-authored more than 120 journal papers, conference papers, and book chapters combined. He served as a reviewer for various publications and as a member to scientific committees for conferences and workshops. Theophilos Papadimitriou worked as a member and project coordinator in various research projects. He gave invited talks at the University of Michigan, Temple University, the University of Strasbourg, and the European Central Bank. Theophilos Papadimitriou's current research interests include complex networks, machine learning, and data analysis.

#### **Preface to "Emerging Trends in Energy Economics"**

In the intersection between Economics and Engineering, Energy Economics has been an active research topic for more than 150 years. From the 19nth century, the problem of creating, processing, storing and transporting Energy based on exhaustible resources (coal initially, oil, natural gas and electricity later) was well defined. It was during the major international oil crisis of 1973, however, that the national and international sociopolitical factors integrated with energy were identified, revealed, studied extensively and were finally incorporated in the scientific debate on Energy Economics. The increased interest in this multidisciplinary topic manifested in the publication of specialized scientific journals that focus and deal with this significant and complex issue. Energy Economics is a significant and broad segmen<sup>t</sup> of this line of research. Energy economics deals with the production, supply and demand of all forms of energy, the efficiency and optimization in the use of the relevant technology and know-how that pertains on the production, distribution and storage (when possible). It affects all aspects of real economic activity, both the supply side and the consumption. Moreover, Energy Economics include the study, analysis and forecasting of all forms of energy as a financial commodity. Investment, hedging and speculation are significant areas of research interest as with all commodities. Energy as a financial commodity that is traded in organized exchanges and over-the-counter in private contracts is an interesting, rigorous and very dynamic strain of research. The reason for this attention, is of course the significant changes that are materializing especially in industrialized countries i.e the European Union, the US, etc. These countries have started distancing themselves and limiting their use of fossil fuels – especially coal and oil. There is a transition to less dependence from those types of energy and towards renewable forms of energy that are environmentally neutral. As a result, the research interest on energy is keen and the research work on this area is also facilitated for the scholars by the availability of large sets of energy data in very high frequencies. Thus, it provides a fertile ground for the application of both traditional and emerging methodologies.

When we proposed the topic of this Special Issue for Energies, we were targeting for the innovation and the novelty in the area of Energy Economics with a special focus on production, distribution, storing, forecasting, financing, risk, taxation, trading, exchanges, networks, etc., in both spot and derivatives markets. We are very proud of the attention that our call for papers attracted from researchers in the field and of the resulting quality of the special issue that we composed from their innovative approaches.

In [4], Flouros e.a. compile a panel of 171 economies and use it to study the effect of geopolitical risk on the transition to a "green" economy. Ioannidis e.a. in [7] examine the recently introduced Target Model, its application in the wholesale electricity market of Greece and its impact on electricity prices. Chen and Rehman in [2] identify the critical periods in the trading of energy-related commodities employing an unsupervised Machine Learning framework. Balashova and Serletis in [1] uncover hidden linkages between the oil price uncertainty, the total factor productivity (TFP) growth, and the critical indicators of knowledge production and associated spillovers. Christopoulos e.a. in [3] investigated the effect that the Covid-19 pandemic and the stock market volatility have on oil price volatility. Three papers apply various forecasting techniques in forecasting energy: Gupta and Pierdzioch in [5] are forecasting the volatility of crude oil using the LASSO estimator, Hu e.a. in [6] forecast the Short-Term Load using the Ensemble Empirical Mode Decomposition coupled with the Salp Swarm Algorithm, and Mouchtaris e.a. in [9] forecast the Natural Gas Spot Prices using an arsenal of Machine Learning Methodologies. The Special Issue is concluded by two review papers: Menegaki in [8] summarizes and compares results of different studies in the energy-sustainable growth nexus for various groups of countries and Oliveira and Moutinho in [10] perform a bibliographic analysis on the topics of renewable energy, economic growth and the economic development nexus.

We express our gratitude to all the researchers that trusted their valuable research papers for our Special Issue. We must also thank all the editorial people from MDPI and the Energies journal that supported us along this effort and made the editorship a peasant and productive experience for us.

1. Balashova, S.; Serletis, A. Oil Price Uncertainty, Globalization, and Total Factor Productivity: Evidence from the European Union. Energies 2021, 14, 3429. https://doi.org/10.3390/en14123429

2. Chen, J.M.; Rehman, M.U. A Pattern New in Every Moment: The Temporal Clustering of Markets for Crude Oil, Refined Fuels, and Other Commodities. Energies 2021, 14, 6099. https://doi.org/10.3390/en14196099

3. Christopoulos, A.G.; Kalantonis, P.; Katsampoxakis, I.; Vergos, K. COVID-19 and the Energy Price Volatility. Energies 2021, 14, 6496. https://doi.org/10.3390/en14206496

4. Flouros, F.; Pistikou, V.; Plakandaras, V. Geopolitical Risk as a Determinant of Renewable Energy Investments. Energies 2022, 15, 1498. https://doi.org/10.3390/en15041498

5. Gupta, R.; Pierdzioch, C. Forecasting the Volatility of Crude Oil: The Role of Uncertainty and Spillovers. Energies 2021, 14, 4173. https://doi.org/10.3390/en14144173

6. Hu, T.; Zhou, M.; Bian, K.; Lai, W.; Zhu, Z. Short-Term Load Probabilistic Forecasting Based on Improved Complete Ensemble Empirical Mode Decomposition with Adaptive Noise Reconstruction and Salp Swarm Algorithm. Energies 2022, 15, 147. https://doi.org/10.3390/en15010147

7. Ioannidis, F.; Kosmidou, K.; Andriosopoulos, K.; Everkiadi, A. Assessment of the Target Model Implementation in the Wholesale Electricity Market of Greece. Energies 2021, 14, 6397. https://doi.org/10.3390/en14196397

8. Menegaki, A.N. Towards a Global Energy-Sustainable Economy Nexus; Summing up Evidence from Recent Empirical Work. Energies 2021, 14, 5074. https://doi.org/10.3390/en14165074

9. Mouchtaris, D.; Sofianos, E.; Gogas, P.; Papadimitriou, T. Forecasting Natural Gas Spot Prices with Machine Learning. Energies 2021, 14, 5782. https://doi.org/10.3390/en14185782

10. Oliveira, H.; Moutinho, V. Renewable Energy, Economic Growth and Economic Development Nexus: A Bibliometric Analysis. Energies 2021, 14, 4578. https://doi.org/10.3390/en14154578

## **Periklis Gogas and Theophilos Papadimitriou** *Editors*
