From Fossil Fuels to Renewables: Clustering European Primary Energy Production from 1990 to 2022

Abstract

This study examines the structural shifts in primary energy production across European countries from 1990 to 2022, focusing on changes in energy sources and their implications for energy security and sustainability. Set against a backdrop of evolving geopolitical landscapes, economic pressures, and climate policies, including significant recent impacts such as the conflict in Ukraine, this research highlights the critical importance of a stable and diversified energy supply. The analysis utilizes the k-means clustering method, examining countries for which data are available in the Eurostat database and considering primary energy sources as defined by the Standard International Energy Product Classification (SIEC), including solid fossil fuels, natural gas, crude oil, nuclear energy, renewable energy sources, peat, and non-renewable waste. By categorizing European nations into clusters based on their energy production profiles, the study reveals substantial transitions from fossil fuel-based systems to those increasingly dominated by renewable energy sources. While some countries have made significant progress in integrating renewables, others remain heavily dependent on traditional energy sources such as coal and natural gas. The findings underscore the growing role of natural gas as a bridge fuel and the relatively stable contribution of nuclear energy in certain regions. A key outcome is the observed disparity between energy production and consumption across Europe, with many large economies facing a persistent deficit in domestic energy production, resulting in a high reliance on energy imports, particularly of natural gas and oil. This dependency poses significant challenges to energy security, especially given recent geopolitical disruptions and market fluctuations. The paper also discusses the environmental implications of these energy trends, emphasizing the vital role of renewable energy in achieving the European Union’s decarbonization goals.

1. Introduction

Energy security has historically been a crucial concern for European nations, evolving alongside shifts in geopolitical landscapes, economic pressures, and technological advancements. Ensuring a stable and diverse supply of energy sources is fundamental to socio-economic stability, particularly in light of recent global challenges such as energy market volatility, geopolitical tensions, and climate change. The European Union has witnessed significant changes in its energy production and consumption patterns over the last few decades, influenced by policy initiatives aimed at decarbonization and reducing dependence on fossil fuel imports. These shifts are also a result of broader social, economic, and geopolitical changes which have reshaped the energy sector in the EU. This context underlines the need for continuous monitoring and analysis of energy structures to ensure sustainable and secure energy transitions.

Over the period from 1990 to 2022, European countries faced substantial transitions in their primary energy production. The increasing prominence of renewable energy sources has changed the energy sector. However, these shifts are not uniform across the continent, with many countries maintaining a significant reliance on fossil fuels such as coal and natural gas. Cluster analysis provides a valuable approach for understanding the structure and changes in primary energy production across countries. By categorizing nations into clusters based on their energy production profiles, we can gain insights into the evolution of energy systems and identify patterns that inform policy decisions and strategic planning.

The main goal of this paper is to investigate the structure and trends in primary energy production in the European Union and other selected European countries. This article serves as a continuation of a series of studies aimed at systematically analyzing different aspects of primary energy in Europe. The author’s intention is to provide a comprehensive exploration of the energy landscape by examining interconnected areas over multiple publications. In the previous work [1], the study concentrated on primary energy consumption structures across European nations. Building upon that foundation, the present study shifts the focus to the production of primary energy, offering further insights into the European energy market. The analysis is enriched by a k-means clustering of countries into clusters with similar primary energy production structures. The study focuses on countries for which data are available in the Eurostat database, ensuring comprehensive coverage based on reliable sources. The analysis utilized data from the Eurostat database for the period from 1990 to 2022 (specifically the table nrg_bal_s) [2]. Primary energy sources considered in the analysis align with the Standard International Energy Product Classification (SIEC), which includes solid fossil fuels, natural gas, crude oil, nuclear energy, renewable energy sources, peat, and non-renewable waste.

The clustering analysis aimed to identify groups of similar countries, thereby offering valuable insights into their present energy situation and energy security, as well as changes that occurred between 1990 and 2022. The cluster analysis was conducted for both the beginning and the end of this period to capture the dynamics over time. As this paper is a continuation, the theoretical introduction to energy security and cluster analysis has been significantly abbreviated, given that these topics were comprehensively addressed in the earlier article [1]. This analysis was performed utilizing the R programming language, version 4.4.0 [3] along with RStudio IDE [4], incorporating the tidyverse packages [5].

The structure of the article is as follows: the introduction provides a concise overview of energy security and its connection to primary energy production. Subsequently, primary energy production in selected European nations from 1990 to 2022 is described, assessing how domestic production meets consumption needs. This is succeeded by a detailed presentation of the clustering analysis and its findings. The article concludes with a summary and conclusions.

1.1. Historical Development of Energy Security

Energy security has historically been a significant concern, gaining importance especially during the latter part of the 20th century. It encompasses various aspects, including the necessity of continuous, secure access to reliable and affordable energy sources as a fundamental requirement for the advancement of civilization [6], the pivotal role of energy in socio-economic life [7], and its undeniable influence on economic functioning and development [8], social welfare, and consumption processes [9]. Adequate energy resource availability highlights the economic and political power of nations and international organizations [10], positioning energy as a central component of both national and global security [11], significantly shaping contemporary global dynamics [12]. The concept of energy security has developed over the years, distinguishable by various phases including non-politicized, politicized, and securitized stages [10]. Key incidents, such as the oil crises of the 1970s, signified the shift toward energy politicization [13]. Initially focused on energy self-sufficiency [14], efficient project management [15], and advanced technologies [16], the definition expanded approaching the new millennium to include international cooperation, equitable energy access, and environmental considerations [17]. Recent events, such as gas price fluctuations in 2021 and the Russian invasion of Ukraine in 2022, have dramatically threatened Europe’s energy security, leading to a renewed emphasis on energy sovereignty and solidarity [18]. Moreover, climate change poses a serious threat to energy security, impacting both the accessibility and the cost of energy, prompting the need for investments in sustainable energy technologies [19,20]. Further detailed information on these aspects can be found in the referenced literature.

1.2. Modern Definitions and Components

There is no single, officially approved, and globally accepted definition of energy security, although it is frequently described as securing adequate energy supplies at reasonable costs [21]. For example, Klare considers it as ensuring the availability of energy resources to satisfy a state’s essential needs, even during crises or international disputes [22]. Similarly, the Asia Pacific Energy Research Centre (APERC) highlights the importance of prompt and sustainable energy delivery at prices that support economic stability [23]. Contemporary definitions typically include four main components, referred to as the ‘4 As’ approach: Availability (ensuring physical access to energy), Accessibility (addressing geographical, political, demographic, and technological challenges to obtaining energy resources), Affordability (providing energy at reasonable costs), and Acceptability (focusing on energy sources that are environmentally and socially sustainable) [17]. Among these elements, accessibility and affordability are considered most crucial because of their broad impact on other aspects of energy security [24].

1.3. Threats and Challenges

The literature outlines three main threats to energy security: technical issues such as infrastructure failures, social factors like fluctuating energy demand or politically driven supply disruptions, and natural risks including the depletion of fossil fuel reserves or climate change [25]. Although energy security is frequently associated with supply stability, institutions like the International Energy Agency (IEA) define it as the “uninterrupted availability of energy sources at an affordable price” [26], and the European Commission stresses the significance of diversifying energy sources to reduce dependency risks [27]. Ensuring stable energy supplies is a high priority for numerous governments worldwide [28,29]. The complex nature of energy security, along with its shifting definitions and various threats, highlights its importance in modern geopolitics and economics. As the world faces the challenges of sustainable energy, comprehending and safeguarding energy security becomes crucial.

1.4. Primary Energy Production and Energy Security

Primary energy sources are natural resources that remain unconverted into other energy forms, such as coal, crude oil, natural gas, nuclear power, and renewable sources like wind, solar, and geothermal energy [30]. The structure of primary energy production influences energy security in the following ways: The diversification of energy sources—countries producing energy from various primary sources are less susceptible to supply disruptions, encompassing both traditional and renewable sources [31]. Energy self-sufficiency—a high level of domestic primary energy production reduces the need for imports, making countries less vulnerable to external disruptions and price fluctuations [32]. Import dependency—countries reliant on imports face significant risks such as price fluctuation sensitivity due to geopolitical factors [33], supply disruption risks from political conflicts or trade decisions [34], and geopolitical dependency that can limit political and economic sovereignty [35]. Investments in energy production technologies—the development of modern technologies like small modular nuclear reactors or advanced renewable technologies enhances efficiency and reliability, reduces CO₂ emissions, and improves overall energy security. In summary, efficient and diversified primary energy production is crucial for ensuring a country’s energy security, and energy policies should focus on increasing domestic production, diversifying sources, and investing in modern energy technologies.

2. Primary Energy Production in the European Union and Other European Countries

The production of primary energy in European Union countries has changed significantly over the past thirty years. Throughout this period, there has been a downward trend in total production, decreasing by nearly 7.5 EJ between 1990 and 2021 (Figure 1). In contrast, consumption exhibited a horizontal trend over the same period (Figure 2). Consequently, the primary energy deficit has deepened, requiring an increasing amount to be imported. There is also a notable difference between the structure of primary energy production and consumption in EU countries, as well as in the dynamics over the analyzed period.

In the early 1990s, solid fossil fuels held the largest share in primary energy production in the EU. However, by the late 1990s, they fell to second place, and by the late 2000s, to third place. At that time, nuclear energy was generally second, and even rose to first place from 1998 to 2015, before returning back to second. In 1990, natural gas held the third position in the primary energy production structure but dropped to fourth in 2005. Conversely, renewable energy sources experienced a remarkable surge, moving from fourth place to first over the 30-year analysis period. The production of primary energy from other sources (including crude oil) remained insignificant (Figure 1).

It is noteworthy that the structure of primary energy consumption in EU countries varies considerably from their production structure, with notable changes occurring within it as well. During the analyzed period, crude oil consistently remained the primary source of consumption, while significant shifts took place in the subsequent rankings. In the early 1990s, solid fossil fuels ranked as the second most common source of primary energy in EU27 countries. However, within a few years they dropped to third place, and then fell to fourth in 2018 and to fifth the following year, before rising back to fourth place in 2022. Natural gas overtook solid fossil fuels, securing second place in 1998 and holding this position until the end of the analyzed period. This shift resulted from the adoption of natural gas as a transitional fuel in the energy transition process and its substantial role in replacing nuclear energy, especially in Germany. Nuclear energy maintained the fourth position for most of the analyzed period, slipping to fifth from 2015 to 2018 as it was surpassed first by renewable energy sources and then by solid fossil fuels. It regained fourth place in 2019 but fell back to fifth in 2022. The rise in the significance of renewable energy is notable; it ranked fifth in 1990 and had climbed to third by the end of 2022 (Figure 2).

In summary, examining the primary energy production structure in European Union countries in 1990 reveals that solid fossil fuels were the largest source, making up 41.2% of total production. This was followed by nuclear energy at 25.4%, natural gas at 16.6%, renewable energy sources at 9.5%, crude oil at 5.5%, and other sources contributing smaller shares. By 2022, the structure of primary energy production had changed dramatically—the largest share was held by renewable energy sources (43.3%), followed by nuclear energy (27.7%), solid fossil fuels (16.5%), natural gas (6.2%), and crude oil (3.3%) (Figure 3).

Figure 4 and Figure 5 depict changes in the volume of energy derived from different sources. It is noteworthy that production increased only for renewable energy sources (up by 7.2 EJ, +244%) and non-renewable waste (0.4 EJ, +269%). Production from other sources decreased. The largest decline was noted for solid fossil fuels (8.9 EJ, −70%), natural gas (3.7 EJ, −72%), nuclear energy (1.4 EJ, −18%), crude oil (0.9 EJ, −54%), and the marginal sources of peat (0.1 EJ, −87%) and oil shale (0.1 EJ, −53%).

Analyzing changes in primary energy production in individual European countries (Figure 6), it is evident that the increase occurred in fewer countries, and primarily smaller producers (with the exception of Norway). The largest increase in primary energy production was noted in small countries such as Malta, Latvia, and Portugal. A significant percentage increase in primary energy production was also observed in Norway, a major global producer of petroleum and natural gas. Most large European economies experienced a decline in primary energy production, including Germany, the Netherlands, and Poland.

It is therefore not surprising that the issue of meeting primary energy demand from domestic sources in European Union countries looks very unfavorable. Excluding nuclear energy and renewable energy sources, which are typically consumed in the same country that they are produced, the percentage rates of meeting demand with domestic production are low and continue to decrease (Figure 7). The percentage of total primary energy demand met by domestic sources fell from 51% in 1990 to 42% in 2022, primarily as a result of a decline in domestic production rather than significant changes in consumption. For solid fossil fuels, this value fell from 80% to 57%. In the case of natural gas, demand was met by 49% from domestic sources in 1990, dropping to 12% in 2022. For crude oil, this indicator remained very low throughout the analyzed period, dropping from 7% to 4%. These values illustrate the extent to which European Union countries are dependent on energy imports and how significant a risk factor this is in terms of energy security. Examining the average proportion of different primary energy sources within the production structure of all analyzed countries (Figure 8) included in the Eurostat database (beyond just European Union members), it becomes clear that renewable energy sources currently hold the largest average share in the primary energy production structure (rising from 25.1% to 52%). Solid fossil fuels are in second place (declining from 26.1% to 18.3%). Nuclear energy holds the third position (declining from 18% to 13.3%). Natural gas ranks fourth, reducing its share from 13.1% to 6.8%. Crude oil is in fifth place, with its share dropping from 11.6% to 5.7%.

Figure 9 illustrates the proportion of primary energy production in relation to consumption in European countries in 2022, excluding Norway, whose unique characteristics would skew the interpretation of this chart. The highest potential for meeting energy demand through domestic production is observed in Estonia and Sweden. Conversely, countries such as Luxembourg, Malta, and Cyprus exhibit a very low proportion of primary energy production relative to their consumption. It is important to highlight that these are small countries, and two of them are islands, which explains their reliance on importing the majority of the energy they consume.

Notably, large European economies such as Germany, France, Spain, Italy, and Poland show a comparatively low ratio of primary energy production to consumption, which corroborates the dependency on energy imports mentioned earlier in the article. For instance, Germany, the largest economy in the EU, meets just over 30% of its primary energy demand from domestic sources.

Summarizing the examination of primary energy production across European countries over the past 30 years, we can observe that:

• The production of primary energy in the EU has significantly decreased over the last thirty years, with nearly unchanged consumption.
• There are significant differences between the structure of primary energy production and consumption in the EU. For some sources (such as crude oil), almost the entire consumption is met through imports.
• Renewable energy sources have become the dominant source of primary energy production in EU countries, which is a positive trend in terms of sustainable development but increases risks related to the stability of energy supplies and other aspects of broadly defined energy security.
• EU countries, especially large economies, are heavily dependent on energy imports, which poses a challenge to energy security.
• To reduce dependency on imports, further investments in renewable energy sources, energy transmission and storage systems, and improvements in energy efficiency are necessary.
• High dependence on primary energy imports constitutes a significant risk to the energy security of EU countries. Geopolitical changes, supply disruptions, and rising prices of imported energy can negatively impact the region’s energy stability. Therefore, to ensure energy security, it is essential to pursue an appropriate energy policy that combines the continued development of renewable energy sources with the assurance of stable supplies of those primary energy sources that cannot be easily and quickly replaced by renewable energy.

3. Cluster Analysis

3.1. Theoretical Introduction

Cluster analysis is a widely used and effective statistical method categorized as an unsupervised machine learning approach; it organizes objects so that items within the same cluster are more alike compared to those in different clusters, without requiring prior knowledge of class labels, and is used when the data structure is unknown. Its advantages include identifying natural groups in data, discovering hidden structures and patterns, and enabling dimensionality reduction by simplifying large datasets into smaller, interpretable groups. Cluster analysis methods are widely used across various fields, with extensive literature on different clustering algorithms, their applications, strengths, and weaknesses. MacQueen developed the k-means algorithm, which remains highly popular and is used in this article [36]. Comprehensive discussions on clustering algorithms and their applications can be found in works by Jain and Dubes [37], Kaufman and Rousseeuw [38], Xu and Wunsch [39], Mirkin [40], Everitt et al. [41], and Hennig [42], who proposed a new criterion for evaluating clustering quality based on the concept of true clusters.

3.1.1. k-Means Algorithm

The k-means clustering algorithm was employed in this study. It is a prominent unsupervised machine learning method for dividing data points into distinct clusters by iteratively minimizing within-cluster variance through optimal centroid placement [43,44,45]. The key steps of the k-means algorithm include:

• Initialization: Select the number of clusters k and randomly initialize k centroids.
• Assignment: Allocate each data point to the closest centroid based on a distance metric, commonly Euclidean distance, creating k clusters.
• Update: Recompute the centroids by calculating the mean of all data points in each cluster.
• Iteration: Continue repeating the assignment and update steps until convergence is reached, indicated by stable centroids or the completion of a set maximum number of iterations.
• Result: Finalize the clustering with each data point assigned to its nearest centroid, partitioning the dataset into k clusters.

• Advantages:

• Simplicity: Easy to understand and implement due to its straightforward approach.
• Scalability: Processes large datasets efficiently with linear time complexity, making it suitable for big data applications.
• Speed: Generally converges quickly because of its simple iterative process.
• Interpretability: Clusters are often interpretable, especially in datasets with low dimensions.
• Versatility: Can be applied to different data types, such as numerical, categorical, and binary data.

• Limitations:

• Sensitivity to Initial Centroids: Different initial centroid placements can lead to varying results.
• Outlier Influence: Susceptible to outliers, which can distort cluster centroids and sizes.
• Assumption of Cluster Shape: Assumes that clusters are convex and of similar size, which may not hold true for all datasets.
• Determining Optimal k: Selecting the appropriate number of clusters k is subjective and affects clustering quality.
• Feature Scaling Impact: Features with larger scales can dominate distance calculations, potentially biasing the algorithm.

3.1.2. Optimal Number of Clusters

Identifying the optimal number of clusters in the k-means algorithm presents a considerable challenge. Two common approaches to tackle this are minimizing the total within-cluster sum of squares (WSS) and using the silhouette method. The WSS minimization, often referred to as the elbow method, is a strategy for estimating the optimal number of clusters [46]. This approach involves plotting the WSS against different values of k and pinpointing the point at which the rate of decline sharply changes—the “elbow” point. This point suggests that adding more clusters does not substantially reduce the WSS, indicating an optimal balance between cluster count and variance reduction. To apply the elbow method:

• Execute the clustering algorithm (e.g., k-means) over a range of k values.
• For each k, compute the WSS, which represents the total of squared distances between data points and their respective cluster centroids.
• Plot k on the x-axis and the associated WSS on the y-axis.
• Locate the elbow point, where the reduction in WSS starts to level off.
• Select the k at this elbow point as the optimal number of clusters.

It is essential to note that the elbow method is heuristic, and the elbow point might not always be clearly defined, particularly in complex datasets. Therefore, it should be supplemented with other methods and domain knowledge [45,47].

The silhouette method provides an alternative approach for determining the optimal number of clusters by evaluating how well each data point fits within its assigned cluster relative to other clusters [38,48]. The silhouette coefficient $s\left(i\right)$ for a data point i is defined as

$$s\left(i\right)={\displaystyle \frac{b\left(i\right)-a\left(i\right)}{max\left(a\right(i),b(i\left)\right)}}$$

where

• $a\left(i\right)$ is the average distance between i and all other points in the same cluster;
• $b\left(i\right)$ is the minimum average distance from i to all points in any other cluster (the nearest cluster).

The silhouette coefficient varies between $-1$ and 1, where higher values signify better clustering quality. A coefficient near 1 indicates that a data point fits well within its own cluster and has little similarity to points in adjacent clusters. To use the silhouette method:

• Perform clustering for various values of k.
• Calculate the average silhouette coefficient for all data points for each k.
• Choose the k that results in the highest average silhouette coefficient as the optimal number of clusters.

This method helps in selecting the number of clusters that provide the best balance between intra-cluster cohesion and inter-cluster separation. It is versatile and can be utilized with clustering algorithms other than k-means.

3.2. Results

The cluster analysis was conducted using the Eurostat database and includes all European countries listed therein. The purpose of this analysis was to classify these countries according to similarities in their primary energy production structures. The analysis was conducted for two specific years: 1990, representing the start of the analyzed period, and 2022, the most recent year with available data in the database. The silhouette method was employed to aid in determining the optimal number of clusters, though its indications were treated as a suggestion rather than a definitive number of clusters.

3.2.1. Cluster Analysis for the Year 1990

Figure 10 shows the analysis results regarding how the number of clusters affects the silhouette coefficient. The automatically suggested number of clusters was four, but eight clusters were chosen instead, as this allowed for a better description of the groups of countries and more effectively captured the differences between them.

Consequently, eight groups of countries with comparable primary energy production structures were identified (

Table 1. Cluster analysis results for various energy sources and countries in 1990.

Cluster	Solid Fossil Fuels	Natural Gas	Nuclear Heat	Oil and Petroleum Products	Peat and Peat Products	Renewables and Biofuels	Oil Shale and Oil Sands	Non-Renewable Waste	Countries
1	86.49	1.63	1.58	3.54	0.00	6.60	0.00	0.15	Czechia, Greece, North Macedonia, Poland, Serbia
2	47.97	7.86	25.77	5.89	0.17	12.23	0.00	0.11	Bulgaria, Germany, Spain, Hungary, Slovenia, Türkiye, Ukraine
3	5.45	63.91	0.37	11.05	10.18	8.79	0.00	0.26	Ireland, Italy, Netherlands, Romania
4	9.44	20.93	1.64	54.28	0.00	13.36	0.00	0.34	Albania, Denmark, Croatia, Norway, UK
5	9.64	2.20	78.53	1.22	0.07	7.57	0.00	0.77	Belgium, France, Lithuania, Slovakia
6	0.00	0.00	50.41	0.00	7.81	41.38	0.00	0.40	Finland, Sweden
7	1.87	2.27	0.00	2.48	0.90	85.95	0.00	6.53	Austria, Cyprus, Iceland, Luxembourg, Latvia, Portugal
8	0.00	0.00	0.00	0.00	3.27	3.00	93.73	0.00	Estonia

). It is worth mentioning that the analysis was conducted based on the current state of countries and their borders, although in 1990 this division may have been different. The data were adjusted to reflect the current division of Europe into countries. The average structure of primary energy production in each group is shown in Figure 11, whereas the geographic distribution of the clusters is illustrated in Figure 12.

The identified groups of European countries, obtained from the cluster analysis of their primary energy production structure in 1990, can be characterized as follows. Each group has been assigned a name that reflects its specific energy production structure, accompanied by interpretations that provide insights into their energy strategies and implications for energy security.

• Cluster 1: “Coal Countries”

• Interpretation: This cluster, comprising countries like Czechia, Greece, and Poland, indicates a strong reliance on coal as a primary energy source. Such dependence reflects historical investments in coal infrastructure and the abundance of coal reserves. However, this reliance also implies significant challenges for transitioning to lower-emission energy sources and achieving climate goals.

• Cluster 2: “Coal Countries with Nuclear Components”

• Interpretation: Countries in this cluster, such as Germany and Spain, have more diversified energy production structures with substantial contributions from both coal and nuclear energy. This combination suggests a transitional approach, where nuclear energy has been used to complement traditional fossil fuels, potentially providing more energy security and flexibility but posing challenges in terms of nuclear waste management and public acceptance.

• Cluster 3: “Natural Gas Countries”

• Interpretation: This group, including Ireland and the Netherlands, indicates a significant dependence on natural gas, which has served as a cleaner alternative to coal. The reliance on gas positions these countries as better suited for meeting medium-term climate targets, but also exposes them to vulnerabilities associated with natural gas imports and price volatility.

• Cluster 4: “Oil Countries”

• Interpretation: This cluster, featuring countries like Norway and the United Kingdom, reflects an energy production heavily focused on oil, often coupled with natural gas. Such a profile aligns with these countries’ roles as major oil producers and exporters, with economic benefits but potential risks tied to fluctuating global oil prices and shifting energy policies aimed at decarbonization.

• Cluster 5: “Nuclear Countries”

• Interpretation: This cluster, including France and Belgium, highlights countries with energy systems centered around nuclear power. These nations have invested significantly in nuclear infrastructure to ensure stable and large-scale energy production. While this strategy enhances energy security and lowers emissions, it also presents challenges related to waste disposal and the public debate surrounding nuclear safety.

• Cluster 6: “Nuclear–Renewable Countries”

• Interpretation: Finland and Sweden exemplify a balanced approach with significant shares of both nuclear and renewable energy. This dual strategy promotes a high degree of energy security and sustainability, showcasing a forward-thinking approach that leverages long-term nuclear stability alongside investments in renewables.

• Cluster 7: “Renewable Countries”

• Interpretation: This cluster, comprising countries like Austria and Portugal, represents a strong commitment to renewable energy as the predominant source of primary energy production. Such a focus underscores a proactive approach to climate change and energy sustainability, though it may require robust energy storage and grid infrastructure to mitigate variability and ensure consistent supply.

• Cluster 8: “Oil Shale Country”

• Interpretation: Estonia stands as a unique case with its significant reliance on oil shale. While this provides a measure of energy independence, it comes at the cost of higher carbon emissions and environmental concerns, positioning the country at a crossroads between maintaining energy self-sufficiency and transitioning to cleaner energy sources.

The map of clustered countries in 1990 (Figure 12) illustrates the geographical distribution of eight distinct clusters identified based on primary energy production structures. The clusters reflect the diversity in energy dependency among European nations. For example, Central and Eastern European countries like Poland and the Czech Republic were found to be heavily reliant on solid fossil fuels, forming the “Coal Countries” cluster. In contrast, countries like France and Belgium, with a significant share of nuclear energy, were categorized under the “Nuclear Countries” cluster. This visual representation highlights the concentration of different energy strategies and resource utilizations across Europe, showcasing the regional energy production tendencies prevalent during that period.

3.2.2. Cluster Analysis for the Year 2022

The silhouette method for the 2022 data suggested 10 groups of similar countries, and this number was selected for the analysis (Figure 13). The results of the cluster analysis are shown in

Table 2. Cluster analysis results for various energy sources and countries.

Cluster	Solid Fossil Fuels	Natural Gas	Nuclear Heat	Oil and Petroleum Products	Peat and Peat Products	Renewables and Biofuels	Oil Shale and Oil Sands	Non-Renewable Waste	Countries
1	69.58	1.64	0.00	2.14	0.00	26.28	0.00	0.35	Bosnia and Herzegovina, North Macedonia, Poland, Serbia, Kosovo
2	40.90	1.06	2.30	2.27	0.00	51.96	0.00	1.52	Germany, Greece, Montenegro, Türkiye
3	45.05	0.42	31.65	0.16	0.00	21.69	0.03	0.99	Bulgaria, Czechia
4	0.04	50.46	0.00	42.56	0.00	6.82	0.00	0.12	Norway
5	4.16	41.52	5.57	5.59	1.36	38.71	0.00	3.07	Ireland, Netherlands, Romania
6	3.06	10.61	0.00	30.06	0.00	54.61	0.00	1.65	Albania, Denmark, Croatia
7	6.42	2.40	56.50	2.19	0.00	30.10	0.00	2.38	Belgium, France, Hungary, Slovenia, Slovakia
8	0.00	0.33	36.24	0.00	0.58	61.41	0.00	1.75	Spain, Finland, Sweden
9	0.52	1.41	0.00	2.60	0.02	91.73	0.00	3.70	Austria, Cyprus, Georgia, Italy, Lithuania, Luxembourg, Latvia, Moldova, Portugal
10	0.00	0.00	0.00	0.00	0.00	40.85	58.06	0.74	Estonia

.

The identified groups of European countries, derived from the cluster analysis based on the structure of their primary energy production in 2022, are characterized as follows. Each group is interpreted in the context of their energy strategies and potential implications for energy security and sustainability.

• Cluster 1: “Coal Countries”

• Interpretation: This cluster, consisting of countries like Poland and Serbia, shows a significant reliance on coal, supplemented by renewable energy. This mix indicates that while these countries are beginning to integrate renewable sources, coal still dominates their energy production, posing challenges for emission reduction and climate commitments.

• Cluster 2: “Renewable–Coal Countries”

• Interpretation: Countries in this group, such as Germany and Turkey, have a primary energy mix that reflects a balance between renewables and coal. This dual reliance suggests efforts to transition toward cleaner energy while managing the realities of existing coal infrastructure. The integration of renewables highlights progress, but the continued use of coal points to ongoing challenges in fully transitioning.

• Cluster 3: “Coal–Nuclear Countries”

• Interpretation: Bulgaria and Czechia represent this cluster, where coal and nuclear energy play significant roles. This combination implies a strategic emphasis on energy security through the use of established nuclear facilities, balanced by the presence of coal, which may hinder rapid decarbonization.

• Cluster 4: “Oil–Gas Countries”

• Interpretation: Norway, as the sole member of this cluster, leverages its rich natural resources to focus on oil and natural gas production. This profile aligns with its status as a major energy exporter, ensuring economic benefits but presenting challenges related to global shifts toward low-carbon policies.

• Cluster 5: “Gas–Renewable Countries”

• Interpretation: This cluster, including Ireland and the Netherlands, shows a balance between natural gas and renewables. This reflects a transitional strategy where natural gas serves as a bridge fuel while investments in renewables grow, providing a pathway towards lower emissions while still susceptible to external gas market pressures.

• Cluster 6: “Renewable–Oil Countries”

• Interpretation: Countries such as Denmark and Croatia demonstrate significant shares of both renewable energy and oil. This structure indicates active investment in renewables while still maintaining oil as a strategic energy source, potentially for economic or energy security reasons.

• Cluster 7: “Nuclear Countries”

• Interpretation: This cluster, comprising countries like France and Slovakia, highlights heavy reliance on nuclear energy, complemented by renewables. Such a structure underscores these nations’ commitment to stable, low-emission energy production, balancing nuclear stability with growing renewable capacities.

• Cluster 8: “Renewable–Nuclear Countries”

• Interpretation: Spain, Finland, and Sweden fall into this category, showcasing a primary energy structure dominated by renewables and significant nuclear contributions. This mix supports energy security and sustainability, illustrating a strategic approach that prioritizes a blend of low-carbon energy sources.

• Cluster 9: “Renewable Countries”

• Interpretation: Countries like Austria and Italy are characterized by very high shares of renewable energy. This commitment to renewables reflects strong environmental policies and a push toward sustainability, although it also requires advancements in storage and grid management to handle variability and maintain supply reliability.

• Cluster 10: “Oil Shale Country”

• Interpretation: Estonia remains a unique case with its significant reliance on oil shale production, supplemented by renewables. This reflects national resource availability and energy policy but poses challenges related to higher emissions and environmental impacts compared to more sustainable energy sources.

Figure 14 presents the average structure of primary energy production for each group, whereas Figure 15 illustrates the geographic distribution of the clusters, which presents the updated clustering map for the year 2022, showing significant shifts in energy production structures among European countries. The clustering analysis in 2022 identifies ten distinct groups, reflecting a significant rise in the use of renewable energy sources. Countries like Germany and Turkey are now part of the “Renewable–Coal Countries” cluster, signifying their dual reliance on both renewables and fossil fuels. In contrast, nations such as Spain, Finland, and Sweden are categorized as “Renewable–Nuclear Countries”, emphasizing their focus on a combination of renewable energy and nuclear power.

3.2.3. Key Changes Between 1990 and 2022

Analyzing the changes between 1990 and 2022, the following key issues can be observed:

Growth in renewable energy sources: One of the most noticeable changes between 1990 and 2022 was the rapid growth in the significance of renewable energy sources within the primary energy production structure. In 1990, renewable energy sources constituted a relatively small share of primary energy production in most European countries, especially in those relying heavily on fossil fuels, such as Poland, Czechia, and Germany. By 2022, renewable energy sources had gained significant importance in many groups of countries.

Reduction in coal usage: In 1990, many European countries relied on coal for their primary energy production, especially in Central and Eastern Europe. Countries like Poland, Czechia, and Serbia had a very high share of solid fossil fuels. However, over the next three decades, there was a significant decrease in coal’s share in primary energy production.

Increased importance of natural gas: Natural gas, considered a transitional fuel, gained importance in countries that sought to reduce their dependence on coal and oil. The rise in the importance of gas was due to its lower carbon emissions compared to coal and relatively lower energy production costs, particularly in the context of the European Union’s carbon emission fees.

Stability of nuclear energy: Nuclear energy, which was the foundation of the energy sector in many European countries in 1990, maintained its position in 2022. In many cases, there were no significant changes in its share, although in some countries there was an increased role for renewable energy as a complement. The stability of nuclear energy stemmed from long-term investments in nuclear technologies and the relative resilience of this form of energy to changing economic and political conditions. However, in some countries, such as Germany, decisions were made to phase out nuclear energy as part of a broader strategy to transition away from this energy source.

Diversification of primary energy sources: A notable development between 1990 and 2022 is the shift from a production structure dominated by a single primary energy source to a more diversified mix. In 1990, most clusters were characterized by a predominant reliance on one primary energy source. By 2022, however, the majority of clusters had two main sources of primary energy, often with renewable energy playing a significant role. This shift toward diversification can be interpreted as a positive step for energy security, as it reduces dependence on any single source and enhances resilience against supply disruptions.

4. Conclusions

During the period from 1990 to 2022, there were significant changes in the structure of primary energy production in European countries, which affected the differences between energy production and consumption as well as issues related to energy security.

In 1990, renewable energy sources had a marginal share in energy production in most European countries, particularly in those dependent on fossil fuels, such as Poland and Germany. By 2022, renewable energy sources became the dominant energy source in some countries. This growth results from investments in green technologies, technological advancements, and EU regulations supporting the energy transition. In the 1990s, many European countries, especially in Central and Eastern Europe, relied on coal for energy production. Over the next three decades, the importance of coal decreased, reflecting changes in energy strategies and growing pressure to reduce CO₂ emissions. Although countries such as Poland and the Czech Republic still rely on coal, its share has been systematically reduced. Natural gas has become a key transitional fuel in the energy transition of many countries. Nuclear energy has maintained its significance, but some countries, like Germany, have decided to phase out nuclear energy; in most countries that traditionally relied on this form of energy, it remains a critical element of the energy mix.

The analysis shows significant transformations that have direct implications for energy security across the continent. Understanding these dynamics is essential to addressing current and future challenges related to reliable and stable energy supplies.

• Key aspects of energy security

• Dependence on imported energy sources: One of the most pressing issues for many European countries is their heavy reliance on imported fossil fuels, such as natural gas and oil, from non-European countries. This dependency increases their vulnerability to geopolitical tensions and supply disruptions. Events like the Russian invasion of Ukraine in 2022 and the resulting gas supply restrictions illustrate the risks of over-reliance on single suppliers. The need for diversified energy sources has become more urgent to avoid being subject to external political pressures and market volatility.
• Renewable energy and its limitations: While renewable energy sources such as wind, solar, and hydropower have seen substantial growth, they also introduce new challenges to energy security. The variability and intermittency of renewables mean that energy production can be unpredictable, especially in regions where sun and wind resources are not consistent. Without significant advances in energy storage technologies and grid infrastructure, the over-reliance on renewables could lead to instability in energy supply during peak demand or unfavorable weather conditions.
• Role of natural gas as a bridge fuel: Natural gas has been positioned as a transitional fuel to bridge the gap between high-emission fossil fuels and low-emission renewable sources. Its lower carbon footprint compared to coal makes it a preferred option for many European countries aiming to reduce emissions while ensuring energy security. However, the geopolitical implications of natural gas imports, especially from Russia and other non-EU countries, remain a significant risk factor. Efforts to increase LNG (liquefied natural gas) imports from diverse global suppliers are steps toward mitigating this risk, but infrastructural and logistical challenges persist.
• Nuclear energy’s stability and controversy: Nuclear energy continues to serve a crucial role in maintaining energy security for many European nations due to its ability to provide a stable and continuous energy supply. Countries like France have leveraged their nuclear infrastructure to reduce reliance on fossil fuel imports significantly. However, nuclear energy remains controversial due to concerns about nuclear waste, safety risks, and the high costs associated with plant construction and decommissioning. The decision by some countries, such as Germany, to phase out nuclear energy poses additional challenges in balancing their energy needs with sustainable practices.
• Impact of geopolitical events on energy security: The geopolitical landscape greatly influences Europe’s energy security. Conflicts, such as the situation in Ukraine, have highlighted the vulnerabilities of relying on imported energy resources from politically unstable regions. In response, the European Union has been actively seeking ways to reduce its dependence on external suppliers by promoting energy sovereignty and solidarity among member states. This involves enhancing intra-EU energy cooperation, investing in cross-border energy infrastructure, and developing a unified energy policy that can withstand external shocks.

• Strategies to enhance energy security

To address these challenges and enhance energy security, several strategic initiatives are critical:

• Diversification of energy sources: European countries need to further diversify their energy supply sources, both in terms of energy types (e.g., expanding renewables) and supply origins (e.g., reducing dependency on specific countries). This includes increasing investments in alternative technologies such as hydrogen, biomass, and small modular reactors (SMRs), which can provide stable and scalable energy solutions.
• Investment in energy storage and smart grids: The advancement of energy storage technologies is crucial to counteract the intermittency of renewable energy sources. Developing large-scale battery systems, hydrogen storage, and other innovative solutions can significantly enhance grid stability. Moreover, smart grid technologies can help manage energy distribution more effectively, balancing supply and demand in real time.
• Strengthening regional energy infrastructure: Enhancing the interconnectedness of Europe’s energy grid is vital for energy security. Building robust cross-border energy infrastructure, such as gas interconnectors, electric grids, and LNG terminals, will enable more efficient energy sharing among EU countries. This infrastructure will help mitigate the impact of local disruptions by distributing resources across the region more flexibly.
• Enhancing energy efficiency: Improving energy efficiency across industries and households is a key strategy to reduce overall energy demand. Lower consumption not only lessens the pressure on energy imports but also contributes to achieving decarbonization goals. Energy efficiency measures, including modernizing industrial processes, building renovations, and promoting energy-saving technologies, are fundamental to sustainable development.
• Policy and regulatory measures: Strong and coordinated policy frameworks are essential to drive the energy transition and ensure long-term energy security. The European Union’s Green Deal and Fit for 55 initiatives are examples of policy efforts focused on lowering greenhouse gas emissions and promoting the adoption of renewable energy. Regulatory measures should also focus on encouraging investment in clean energy technologies and establishing clear goals to decrease reliance on imported fossil fuels.
• Geopolitical alliances and partnerships: Forming strategic alliances with energy-exporting nations that are politically stable and environmentally conscious is crucial for enhancing Europe’s energy security. Diversifying natural gas imports through LNG partnerships with countries like the United States, Qatar, and Australia, alongside fostering stronger ties with renewable energy leaders, will reduce Europe’s exposure to geopolitical risks.

The transformation of primary energy production in Europe from 1990 to 2022 marks a significant shift towards sustainability and cleaner energy sources. However, this transition also underscores the complexities of ensuring energy security in a changing geopolitical and technological reality. The need for a balanced approach that incorporates renewable energy while addressing its limitations, along with investments in diversified and resilient energy infrastructure, is more critical than ever. Europe’s ability to navigate these challenges will determine its success in achieving a secure, sustainable, and sovereign energy future.