New Advances in Energy Efficiency: Perspectives and Policies Towards Sustainable Development

1. Introduction

In the quest towards finding new sources of energy to ensure stable, sufficient, and affordable energy, we must consider “the most universally available source of energy” [1], i.e., energy efficiency must be considered. The measures taken to improve energy efficiency in modern times, which are characterized by a rising global energy demand, are meant to lower emissions, contributing to addressing climate change [2], with major impacts on human health, the environment, and global wellbeing [3], thereby enhancing overall sustainability [4]. A sustainable energy system based on efficiency measures implemented rationally and in a timely manner will lead to a more competitive economy and a safer and more prosperous life. New advances in technology and policies aimed at improving energy efficiency are essential for the transition to a sustainable future.

The European Union (EU) has set several targets for energy efficiency in the last few years. In 2021, EU legislation set very optimistic targets for energy, considering reductions of 36% and 39% in final and primary energy consumption, respectively, translating into a 9% increase in energy efficiency by 2030 [5]. Moreover, in 2022, the binding target was modified to a 13% increase in energy efficiency by 2030 [6] and then reset to an at least 11.7% increase for 2030 through the involvement of European legislators [7]. However, given the complexity of the energy system and the way in which the energy chain is interwoven with industry and the global economy, the pace of change and the implementation of measures must be tackled carefully as they can interfere with industrial competitiveness. In 2024, the European Economic and Social Committee released an opinion on the very ambitions climate targets and high investments needed for energy efficiency, potentially leading to higher costs for industries and threatening the competitiveness of EU industries [8].

Scientists are continuously looking for new methods of improving energy efficiency [9] to ensure the implementation of the sustainable development goals (SDGs) of Agenda 2030 [3], and a search on the Dimensions database [10] performed on 5 December 2024 revealed major interest in this area. The keywords included “energy efficiency” AND “sustainable development”, mentioned over the last 10 years, and full data (comprising titles, keywords, abstracts, and text) were retrieved. There were 183,435 publications between 2014 and 2023, with the number of publications increasing from 9578 worldwide in 2014 to 39,751 in 2023, an increase of over 400%. Many of these papers, namely, 3809, were published in Energies (an MDPI journal), with 14 articles in 2014 and 892 articles in 2023. The academic impact of the papers published in Energies, expressed as citations, also revealed a major increase, rising from 3 citations in 2014 to 19,003 citations in 2023, with a projected 22,356 citations in 2024 (as some studies are still in progress), totaling 71,252 citations, indicating a major interest in energy efficiency and its importance for sustainable development.

The purpose of this manuscript is to provide an outline of the latest results and challenges in shaping the progress in energy efficiency, all stemming from studies submitted to this Special Issue, “Analysis of Energy Efficiency: Perspectives and Policies towards Sustainable Development”.

2. Review of New Advances

Energy efficiency is vital for global energy systems. In this vein, the cheapest and most abundant form of energy is critical, with impacts on reducing the consumption of resources and lessening the strain of dependency on imported fossil fuels, offering solutions for better coping with increased energy prices and mitigating climate change.

Momete [11] focused on the performance of EU-27 member states on the road towards an energy-efficient future, providing a comprehensive yet straightforward consumption effectiveness opportunity framework. The main findings revealed that only 19% of the EU-27 member states are active performers in regard to energy efficiency, most of which are located in Northen Europe, while the rest need to make large improvements and take measures specifically tailored to national contexts. The research indicated the fundamental importance of energy efficiency for reducing consumption, dependency on fossil fuels, and emissions, thus contributing to climate change mitigation. The main findings are valuable for researchers, legislators, and stakeholders in enhancing practices based on energy efficiency.

Abolhassani et al. [12] focused on energy intensity and studied the key performance indicators for energy and labor intensity by applying two novel statistical methods. They found a strong statistical correlation (0.67) between energy intensity and labor intensity in North American automotive plants. They also identified 11 factors and suggested that strategies aimed at enhancing energy efficiency can also improve labor productivity, and vice versa.

Ahn et al. [13] investigated the influence of initial pressure levels (starting from 1 bar to 3 bar) on compressed-air energy storage (CAES), an important commercial bulk-scale energy storage option. The main findings revealed that the greater the initial pressure, the lower the isothermal efficiency, leading to a decrease in air volume and mass, which, in turn, leads to a less-than-expected energy output. Their research indicated the importance of air dissolution, emphasizing that the changes in gas solubility depending on pressure are critical for understanding energy output during the expansion phase.

Murphy et al. [14] investigated the factors influencing the cost of saved electrical energy in customer-funded energy efficiency programs across most US states using an econometric model based on data reported by efficiency program administrators. Their research highlighted significant variations in cost and scale in various US states, indicating the importance of economies of scale, suggesting that the efficiency programs can be expanded without significantly increasing the costs in states where the efficiency savings were lower compared to retail sales. Their research presents valuable insights into the potential of energy efficiency as a valuable resource, offering improvements for policymakers, regulators, and system operators that forecast efficiency.

Benabdelkader et al. [15] proposed a control scheme for enhancing power quality in grid-connected single-phase photovoltaic (PV) systems. They designed an orthogonal signal generator for grid synchronization, and the results of the simulations and experiments showed better power quality and robustness against fluctuations. The proposed system used an adaptive neuro-fuzzy interference system to manage the voltage during faults at the point of common coupling. The effectiveness of this control strategy was assessed through simulations in MATLAB and experiments conducted on a small laboratory-scale photovoltaic system, which showed that the use of the PV system is beneficial for power quality.

Bigioi et al. [16] studied the financial performance of 43 energy companies based in Romania and analyzed the correlation between two variables: their governance and financial performance. The financial data were collected from the companies’ financial statements, and the governance indicators were assessed using a scoring method. The main findings indicated a moderate intensity of the two variables, suggesting that the companies’ effective governance systems aided them in achieving better performance.

Cuadros et al. [17] assessed the determinants of electrical energy generation efficiency in 24 Latin American and Caribbean countries for the 2000–2020 period by using Cragg’s regression model. The main findings showed different results for efficient and inefficient countries. While tariff protectionism positively affected both efficient and inefficient countries, opening of the electricity sector positively impacted the efficient countries and market liberalization, and private power plant ownership improved efficiency in inefficient countries. These inefficient countries have a chance to improve their electricity generation efficiency by learning from the best practices of the efficient nations. The results of this study may be of interest to policymakers and regulators seeking valuable elements to improve efficiency in electricity generation, including private investment and policies regarding the liberalization of the electricity market.

Selim et al. [18] focused on the use of a sustainable energy source based on kinetic energy by exploring the use of piezoelectric sensors present in floor tiles to harvest energy from human footsteps. Piezoelectric sensors were installed beneath floor tiles, and a simple rectifying circuit with a filter was employed to harvest the electrical energy generated by the sensors to power two light-emitting diodes. The maximum power from the floor tile reached 249.6 milliwatts, at an estimated cost of implementation of about 10 USD/tile. The results suggest that a floor based on 30 strategically located floor tiles may generate 60 watt-hours of energy over 8 h.

3. Conclusions

The contributions to this Special Issue, “Analysis of Energy Efficiency: Perspectives and Policies towards Sustainable Development”, demonstrate the progress in energy efficiency on several fronts: technological, political, economic, and social. The authors presented critical theoretical and practical aspects of energy efficiency and provided many valuable insights into the importance of energy efficiency for a sustainable future society.

The readers of this Special Issue may find interesting perspectives and technical solutions that help to unravel some of the challenges in energy efficiency. This Special Issue will be useful for policymakers, researchers, and students interested in engineering as well as economics. This collection of articles will allow readers to enrich their knowledge of energy efficiency, helping them better understand the complexity of this field as well as find inspiration to pursue further research.