Assessing Renewable Energy Growth in the European Union

Abstract

As the world’s ecological situation worsens, the development of environmentally friendly renewable energy (RE) is becoming increasingly important. The main directions of scientific research devoted to the topic of RE are national socio-economic development of the country; development in the context of sustainable development; development policy and planning; evaluation of the achieved level of development; the situation in individual countries, etc. The analysis of literature sources conducted in this article shows that problems related to RE have not been sufficiently examined at the country or regional level, including in European Union (EU) countries. Such analysis helps to highlight regularities that are important for the further development of RE. The main purpose of this paper is to develop a comprehensive methodology for the quantitative assessment of RE development during the period under review and to validate it using the example of EU countries. The present research was conducted based on the methodology proposed in this article. In order to adequately assess the development of RE, it is necessary to rely on its scale and changes that occurred during the considered period (CP), i.e., to examine this development as a process. It is reflected by two parameters—the intensity of development and uniformity. The first is determined based on a value that assesses not the RE activeness at the end of the CP, but the general nature of the fluctuations that occurred during it. The uniformity of development is the sum of the ratios of its ideal and actual development values at the end of the time periods (years). The generalized RE development index is obtained by combining the values of the above parameters in an appropriate way. This helped to highlight the regularities and trends in the further development of RE: First, the level of economic development achieved by the country, measured by the gross domestic product per capita (correlation coefficient r = 0.7), has a significant influence on the development of RE. Second, on average, developed EU countries produce 52% of the RE from all electricity production, while for developing EU countries, the figure is 42%. Third, the development of RE is 1.7 times faster in developed EU countries compared to developing EU countries. Fourth, the country’s economic development has a significant influence on the development of RE in developing countries. Based on the research conducted, some contradictory results regarding the interaction between RE and countries’ economic development have been clarified. The practical benefit of the methodology is manifested in the following aspects: allows for the identification of factors that promote or hinder RE development; allows for the prediction of measures for further RE development. Thus, the methodology can serve as a methodological basis for the assessment and analysis of RE development in countries.

1. Introduction

The ever-increasing use of non-renewable resources accompanies the country’s socio-economic development (SED). This causes unwanted climate changes, increasing waste accumulation, and air, water, and land pollution. Soil becomes degraded and people’s health, quality of life, etc., deteriorate. Due to the greenhouse effect, various disasters, such as droughts, floods, and hurricanes, are becoming more frequent [1]. The European Green Deal is the answer to these negative trends [1]. Its main goal is the harmonious and sustainable development of the member countries. This course envisages the transformation of the EU into a fair, prosperous society characterized by a modern, efficient use of available resources and a competitive economy, picturing a society wherein, by 2050, there will be no greenhouse gasses emitted into the atmosphere, and economic growth will be decoupled from the use of non-renewable resources [1]. The Green Growth Strategy provides a system of monitoring indicators that include all aspects of the SED of the EU and other countries, including environmental resources, CO₂, and energy productivity [1]. Thus, this system is designed to monitor changes in Green Growth. This is important to be able to form a targeted SED policy for further countries, as well as to inform their societies about the ongoing changes [2]. We can see that the EU’s environmental and climate improvement policy has made it possible to improve the situation. On the other hand, the scale of negative climate changes is still very large [3]. Therefore, analyzing the implementation problems regarding the EU’s Green Growth Strategy continues to be relevant in both scientific and practical terms.

Energy plays a vital role in the Green Growth Strategy, as it underscores transformations in this sector that create opportunities to reduce dependence on fossil fuels and switch to clean and technologically modern energy. Today, this is important due to the current structural setup of the EU countries’ energy systems—85% of primary energy needs are met using traditional fossil fuels, and 56.6% of fossil fuel-derived energy is emitted into the atmosphere via the greenhouse effect [4].

In the context of both this action and the ways of restructuring the energy sector, as well as the existing structures of the member countries’ energy sectors, renewable energy (RE) plays an important role. RE is the energy obtained from accessible and environmentally friendly sources, encompassing solar power, wind power, geothermal power, water power, and biomass. Thanks to developments in RE, significantly better combinations for the generation of various forms of energy can be achieved. For this purpose, it is necessary to eliminate the possibility of choosing between RE sources and conventional fuels. The EU Commission annually publishes a report on changes in energy consumption. These communications provide an action plan to, on the one hand, control and reduce energy consumption needs and, on the other, control and reduce consumption. The ambitious goal is to reduce energy consumption in the EU by 32.5% by 2030 [1]. In this context, RE plays an important role in assessing the current structure of energy production. The sustainable mobility strategy prepared by the EU is intended for this. It is expected to reduce emissions significantly, expand the range of alternative fuels, and introduce other advanced technologies for electricity production [1]. Therefore, the energy development strategies of world and regional politics are increasingly directed towards developing green energy—both its production and use [1,2]. This strategy is unequivocally aimed at promoting the development of green energy, primarily by reducing CO₂ gas emissions into the atmosphere. A new direction of research is dedicated to the formation of such policies. The transition from traditional energy to RE production is considered a future trend in electricity production strategy [5], emphasizing the importance of RE for countries’ economic growth [6,7,8]. This problem is increasingly being studied and covers many aspects. On the other hand, it can be seen that there are few studies devoted to examining the trends and regularities of RE development. There is a lack of models for quantitatively assessing the development of RE during certain periods, and such models would need to take into account changes in separate time periods over a long stretch of time. In other words, there is a lack of comprehensive assessments of RE development. Only through comprehensive assessments is it possible to highlight the interaction between the countries’ energy development and RE development, including the countries’ economic development.

The aims of this study were to prepare a methodology for the complex quantitative assessment of RE development during a certain period (2011–2021) and validate the methodology through using EU countries as examples.

2. Literature Review

With RE’s increasing importance in relation to implementing the Green Growth Strategy, the problems of its development have been examined from various perspectives. The following aspects are essential: assessments of RE’s state and impact; RE’s interaction with countries’ socio-economic development; development factors; the context of sustainable development; and further development problems, measures, and forecasts.

Most energy-related research is conducted in the context of the economic development of countries. Such development is referred to as energy-based economic development [9]. The analysis of the literature sources shows that the approach to this problem is ambiguous. In one case, it is argued that countries’ economic growth determines electricity consumption [10,11,12]; in another, economic growth is determined by the scale of electricity consumption [13,14,15]. Both discussed cases are combined in the third case, putting forward the feedback hypothesis. Studies prove a two-way relationship between electricity consumption and a country’s economic growth [16,17,18]. Representatives of another fourth line of research put forward the so-called neutrality hypothesis [19,20,21]. Electricity consumption is assumed to play a relatively minor role in economic growth, i.e., no causal relationship exists. Such conflicting results regarding the interaction between energy and economic development could have arisen for various reasons: the functional form of the chosen study, the use of different econometric methods, the inclusion of other periods of analysis, the number of analyzed countries, etc. [22].

Several studies are devoted to analyzing the state of RE [5,23,24]. It can be seen from these studies that 85% of today’s primary energy needs are met using traditional fossil fuels. As a result of fossil fuel use, 56.6% of anthropogenic greenhouse gasses are introduced into the atmosphere [4]. On the other hand, the analysis conducted in this study for 2009–2019 shows that EU countries significantly increased the share of RE in total energy production by the end of this period (see Table 1). For example, in Iceland, the share of RE increased by almost 78%, while in Sweden, an increase of 56% was observed. The most significant changes occurred in Malta (8322%) and Luxembourg (1126%). However, some EU countries did not reach the set RE targets [23]. Past studies have also analyzed the development of RE in individual countries and their regions. For example, in one study, the development of RE in China’s 29 provinces from 2008 to 2014 was analyzed. The results obtained revealed significant differences. The analysis took into account economic, institutional, and technological factors, as well as the factors of energy security and environmental protection. The potential relationship between financial instruments and energy productivity and other relevant factors, such as technological innovation, renewable energy consumption, and carbon emissions, is critical for policymakers seeking to promote sustainable development and energy efficiency. Tax exemptions are the most effective policy tool for accelerating the development, production, and sale of renewable energy projects [2,24].

RE analyses should also factor in its interaction with countries’ economic development. Past studies have examined its effect on countries’ economic growth. The results are contradictory. On the one hand, it is claimed that the development of RE can increase environmental sustainability and contribute to sustainable development. On the other hand, it is claimed that it can hinder economic growth [4,25,26]. This influence varies from country to country and depends on the nation’s stage of development.

Part of the research in the literature is devoted to examining interactions of the opposite nature, i.e., the impact of countries’ economic development on RE development [27,28]. To prove this relationship, an analysis of the impact of GDP on RE development was carried out. Again, contradictory results were obtained: RE production decreased in countries with higher GDP. This shows that wealthier societies depend less on RE sources, and such societies are usually less trusted [28].

The inseparable part of RE research is the analysis of factors influencing its development. It has been established that they are diverse, encompassing economic, technical–technological, political, and social aspects [29]. These include investments in industrial infrastructure and research; finance; the structure of fossil fuel consumption; policy uncertainty; and so on [24,25,28,30]. The appropriate distribution of RE sources is also included among the factors of RE development [28]. In turn, this allocation depends on electricity production costs, emissions of greenhouse gases (mainly CO₂, SO₂, and NOx), capital investment restrictions, resource use, and minimum electricity production requirements [27,29,30]. It has been stated that the number of wind farms, potential solar power plants, and existing coal and non-coal power plants in the region must also be considered [31].

A relevant aspect of scientific research is the importance of RE for the country’s sustainable development (SD). As indicated, the development of RE can increase environmental sustainability and thus contribute to SD. Major changes in energy sustainability are necessary to achieve sustainable development without damaging the climate system. The subject of such studies is also the development of RE in EU countries in the context of SD [4,5,24,25,26,30]. The role of national government policies in promoting RE and addressing economic development and climate change mitigation is emphasized [23,31].

A significant part of the research is devoted to RE development problems, promotion measures, etc., for examinations and forecasts. Improving RE production technologies, especially the variety of RE sources, can contribute to meeting the growing energy needs [4]. Well-researched topics include the increase in oil prices, decreased access to RE, tightened emission gas norms, and the active search for alternative fuels. Again, the countries’ governments play an essential role in forming their policies towards RE [28]. They should coordinate the development of agriculture, transport, and other sectors on the one hand and energy development on the other. A structural transformation of the global energy system based on RE is necessary [28,29,32] to stabilize the concentration of greenhouse gasses. It must include energy efficiency, the introduction of advanced technologies, the improvement of energy redistribution systems, the optimization of industrial structures, education, etc. With the development of natural gas turbines and wind and solar technology, smaller-scale installations can quickly meet large-scale energy needs [33,34]. The economic and technological potential of countries influences the development of RE. Existing risk mitigation mechanisms such as guarantees and insurance can also address project financing [35,36]. When planning RE development, it is necessary to consider national and regional characteristics, the availability of resources, etc. [37,38].

The existing sources of RE production influence its development. Various combinations for RE generation are necessary to ensure safe and affordable energy, eliminating the possibility of freely choosing RE and conventional fuel sources [4,31]. After analyzing the changes in the distribution of RE sources from 1995 to 2014, the authors of one study performed an analysis of their diversification trends [39]. The share of RE resources in the total primary energy supply increased twice during this period, from 8% in 1995 to 16% in 2014. An analysis of the literature sources revealed that, in 1995, the development of RE was mainly centered around hydropower, geothermal power, and bio-energy, while in 2014, the main points of emphasis were hydropower, wind power, and bio-energy. In terms of the overall energy mix, GDP per capita was the most significant factor in increasing RE volumes, power supply concentration, consumption costs of energy derived from fossil fuels, etc. [24,25,26,27,29,30]. It was also found that wind and solar energy developed the most during the analyzed period. Northern European countries invested the most in wind energy, while Southern European countries invested more in solar energy. Generally, the selection of RE sources depends on each country’s economic potential, natural and climatic factors, geographical location, etc. [29].

Scientific studies also provide forecasts for the development of nuclear power plants globally. The International Renewable Energy Agency emphasizes that by 2050, RE should account for two-thirds of the total energy supply [27].

From the analysis of the literature sources, it can be seen that the development of RE, as a process, is practically not studied. Moreover, there are no proposals on how to assess it quantitatively. The relevance of solving this problem is evidenced by Figure 1, which presents the results of the development of RE in two EU countries that differ significantly in their level of economic development in 2011–2021.

Figure 1 shows that regardless of the level of economic development of the country, RE development is characterized by the same features. Only the intensity and uniformity of the scale differ. This is due to the fact that development is affected by various factors of both objective and subjective nature. The first include natural phenomena, the impact of the surrounding environment, the general political, economic, legal situation, etc.; the others include the quality of management, organization, strategic capabilities, etc. In the case under consideration, the country’s government’s approach to RE development would be essential. The result of all this is the development changes in separate time periods (e.g., years) of the period under consideration (Figure 1).

Various methods are used to address RE issues. The most common are principal component analysis (PCA and DPCA) models [27,29], correlation–regression analysis of causality [26,31], linear programming [31], and multi-criteria evaluation (TOPSIS and ELECTRE) models [30,32]. With their help, tasks such as analyzing and forecasting RE development, optimally distributing RE sources, influencing factors on RE development, ranking countries according to the level of RE development, and justifying energy-related sustainable development decisions have been performed.

3. Research Methodology

First of all, it is necessary to justify the appropriateness of the presence of an index reflecting the development of RE. If you want to evaluate the development of a phenomenon, then you are talking about assessing the process. In addition, such an assessment makes more sense if a certain period is examined, i.e., when its beginning and end are known. In its own sense, development is a positive change in something, so the first characteristic of RE development is the scale of these changes that occurred during the considered period, or, in other words, their intensity (Figure 1) [39].

Figure 1 also shows that RE development during the period considered occurred with greater or lesser fluctuations in separate time periods. Therefore, the value reflecting them may be another parameter of RE development, which can be called the evenness of development [39].

In this case, the RE development index is a value that combines its intensity and evenness (Figure 1).

Determining the RE development—RE development can be determined in various ways: take the difference or ratio of RE development values at the beginning and end of the CP, i.e., based on absolute values or relative values [40]:

$${\tilde{K}}_{Ij}=Q_{bj}-Q_{fj},$$

(1)

$${\tilde{K}}_{Ij}={\displaystyle \frac{Q_{fj}-Q_{bj}}{Q_{fj}}},$$

(2)

$${\tilde{K}}_{Ij}={\displaystyle \frac{Q_{fj}}{Q_{bj}}}.$$

(3)

Here, ${\tilde{K}}_{Ij}$—the intensity indicator of RE development of the j-th country; $Q_{bj}$—the importance of RE development of the j-th country at the beginning of the CP; and $Q_{fj}$—importance of RE development of the j-th country at the end of CP.

From Figure 1, it can be seen that size $Q_f$ underestimates the developmental changes that occurred during the CP. This only reflects the situation of the entire CP in the last period. To ensure adequacy, it is necessary to assess the situation of all time periods. To facilitate this, we can use the well-known least squares method. This is the model obtained as the sum of the squares of the smallest distances from the points located in the correlation field. In the case under consideration, the dependent quantity, or function, is the value of RE expansion during the CP at the end of each time period, and the independent quantity, or argument, is the period numbers. In this case, the model looks like this:

$${\tilde{Q}}_f=a{t}_i+{\epsilon }_T$$

(4)

Here, ${\tilde{Q}}_f$—the transformed size $Q_f$ value, reflecting the changes in RE development during the CP; a—parameter of the equation; ${\epsilon }_T$—random error; $t_i$—i-th time period number in the entire CP ($i=\overline{1,T}$, T—number of periods).

After determining the size ${\tilde{Q}}_f$, it is possible to calculate the RE development intensity indicator:

$$K_{Ij}={\displaystyle \frac{{\tilde{Q}}_{fj}-Q_{bj}}{{\tilde{Q}}_{fj}}}$$

(5)

From Equation (5), it can be seen that when RE development did not occur during the period under consideration, then ${\tilde{Q}}_f-{\tilde{Q}}_b=0$ and $K_I=0$. The higher the value of $K_I$, the higher the intensity of RE development.

Determining the evenness of RE development—The importance of this parameter is emphasized in the literature. It is indicated that the development of RE depends to a large extent on the determination of the policies carried out by the country’s government, and even the nature of society [23,25,31]. To determine this indicator, the actual development changes in individual CP time periods need to be compared with “ideal” changes, i.e., a development that takes place without any fluctuations (in Figure 1, the straight lines refer to $Q_b-Q_f$).

In particular, the increase in RE development in the CP at the end of each time period is determined using the following:

$$∆q_{ij}={\displaystyle \frac{Q_{fj}-Q_{bj}}{N-1}}$$

(6)

where $∆q_{ij}$ is the increase in RE development of the j-th country during the CP at the end of each time period when the development proceeds ideally, i.e., when $∆q_{ij}=∆q_{ij}+1$; and N is the number of years of the considered period.

To determine RE expansion during the CP at the end of each time period when it is ideally developed, we use the formula below:

$${\tilde{q}}_{ij}=Q_{bj}+\left(i-1\right)∆{\tilde{q}}_{ij}$$

(7)

where ${\tilde{q}}_{ij}$ is the value of RE development of the j-th country during the CP at the end of the i-th time period, when it ideally takes place.

Now, it is possible to calculate the uniformity of RE development over the entirety of the CP. This is represented by the sum of the ratios of the actual values at the end of each time period of the development and the values corresponding to the ideal development. From Figure 1, it can be seen that three cases are possible: (1) $q_{ij}>{\tilde{q}}_{ij}$; (2) $q_{ij}<{\tilde{q}}_{ij}$; and (3) $q_{ij}={\tilde{q}}_{ij}$. In the third case, we have an ideal expansion, i.e., development without any fluctuations. Thus, regarding $q_{ij}$ and ${\tilde{q}}_{ij}$, the ratio in all periods will be equal to 1. In this case, the quantity representing the entirety of the CP will equal N − 2 (N—number of CP time periods).

The greater the deviations of RE development from the case of ideal development, the greater the value of the ratio should be $q_{ij}$, ${\tilde{q}}_{ij}$. On the other hand, i.e., when $q_{ij}<{\tilde{q}}_{ij}$ we obtain the opposite result—the greater the deviation, the lower the value of their ratio, so the calculations must be performed in the following way:

(a) when $q_{ij}>{\tilde{q}}_{ij},\mathrm{t}\mathrm{h}\mathrm{i}\mathrm{s}$

$$k_{ij}={\displaystyle \frac{q_{ij}}{{\tilde{q}}_{ij}}}$$

(8)

(b) when $q_{ij}<{\tilde{q}}_{ij},\mathrm{t}\mathrm{h}\mathrm{i}\mathrm{s}$

$$k_{ij}={\displaystyle \frac{{\tilde{q}}_{ij}}{q_{ij}}}$$

(9)

where the $k_{ij}$ coefficient reflects the CP of the j-th country deviation of RE development in the i-th time period.

Based on Equations (8) and (9), the coefficient of uniformity of RE development of the j-th country $K_{Tj}$ can be calculated as follows:

$$K_{Tj}={\displaystyle \frac{N-2}{{\sum }_{i=1}^{N-2}{K}_{ij}}},$$

(10)

where N is the number of years in the considered period.

The value $N-2$ is obtained in this way. In the ideal case of development, the ratio $K_{ij}$ for all time periods in the considered period is equal to one. Thus, the sum of the values of $K_{ij}$ for this entire period will be equal to N.

From Figure 1 and Equations (8) and (9), it can be seen that for the first and last years of CP the ratio of $q_{ij}$ and ${\tilde{q}}_{ij}$ will always be equal to one; therefore, they can be discarded.

Knowing the values of the coefficients $K_{Ij}$ and $K_{Tj}$, it is possible to determine a generalized RE development indicator, such as an index. The question is whether intensity, evenness, or uniformity are unambiguous in development. For this purpose, it is necessary to conduct an expert survey, during which the weights of the mentioned coefficients will be determined. In any case, the RE development index will be defined as follows:

$$K_{Pj}={\omega }_1{K}_{Ij}+{\omega }_2{K}_{Tj}$$

(11)

where $K_{Pj}$—the RE development index of the j-th country; ${\omega }_1$—development intensity weight; and ${\omega }_2$—the same, of evenness.

The structural diagram of the research is presented in Figure 2.

Based on the methodology outlined in the empirical part of this article (Section 4), the index of RE development of EU countries for the period of 2011–2021 was calculated. For a deeper analysis of RE development, it was appropriate to divide EU countries into two groups according to their level of economic growth: developed and developing countries. For this purpose, it was necessary to justify the indicator that reflects RE development. There are many suggestions for how to facilitate this. In the literature, specific requirements are placed on RE development. First of all, the RE development’s complexity must be considered, which should be as close as possible to the complexity of the phenomenon under consideration. Second, the j-th indicator must be universally recognized, i.e., it must be applied by all countries. Thirdly, its structure must be easily standardized. Fourthly, information about it must be easily accessible [41,42]. All these requirements are best satisfied by the gross domestic product (GDP) per capita. This process is complex, as it includes all essential aspects of the country’s economic development. We performed calculations according to a unified methodology, so it was possible to compare countries with each other on the basis of these calculations. International databases provide information about RE that can be included in the analysis. Today, RE development is generally accepted as an indicator of a country’s economic development.

EU countries were divided into two groups based on the following formula:

$$h={\displaystyle \frac{Q_{\mathrm{m}\mathrm{a}\mathrm{x}}-Q_{\mathrm{m}\mathrm{i}\mathrm{n}}}{2}},$$

(12)

where h is the size of the division interval; $Q_{\mathrm{m}\mathrm{a}\mathrm{x}}$ is the highest value of GDP among all countries under consideration; and $Q_{\mathrm{m}\mathrm{i}\mathrm{n}}$ is the same, the smallest.

The analysis demonstrates that grouping the countries into two separate groups is reasonable because it creates two homogenous groups. To one, developing countries are assigned, while to the other, developed countries are assigned. Two countries, Luxembourg and Ireland, were excluded from the calculations, as they stand out in terms of GDP. They were automatically classified as developed countries. Based on the above methodology, the development of RE in the EU countries was evaluated for the period of 2011–2021.

4. An Empirical Study

Our RE expansion studies were based on the statistical information provided in the Green Growth Strategy about the percentage of renewable electricity in EU countries based on the total electricity production for a number of years (hereinafter referred to as RE expansion) (Table 1).

As can be seen from the table, the pandemic had practically no impact on the development of RE in 2019–2021; therefore, these years were not excluded from the study.

Table 1. The percentage of renewable energy based on the total electricity production in the European Union countries from 2011 to 2021 [43].

Row No.	Country	Year
		2011	2012	2013	2014	2015	2016	2017	2018	2019	2010	2021
1	Belgium	9.33	12.86	14.28	17.12	21.08	16.88	18.49	23.22	21.00	26.50	23.06
2	Bulgaria	7.78	11.35	15.99	15.74	17.98	15.80	13.64	20.15	17.13	18.57	21.76
3	Czech	8.35	9.30	10.82	10.78	11.40	11.43	11.20	10.84	11.71	12.89	12.60
4	Denmark	40.25	48.33	45.96	55.88	65.43	60.22	70.26	68.36	78.17	81.62	78.96
5	Germany	20.43	22.99	24.07	26.13	29.39	29.41	33.40	35.01	39.99	44.19	39.58
6	Estonia	9.14	12.34	9.19	11.16	15.37	13.05	14.12	16.09	28.13	47.82	39.20
7	Ireland	19.97	19.36	22.00	24.77	27.97	24.86	28.96	33.02	38.41	42.14	36.34
8	Greece	13.76	16.69	25.12	24.19	28.66	27.37	25.01	30.33	33.14	36.45	41.11
9	Spain	30.02	29.58	39.58	40.11	34.96	38.57	32.21	38.20	37.26	43.78	46.32
10	France	11.63	15.01	17.23	16.59	15.99	17.70	16.64	19.71	19.99	23.65	21.94
11	Croatia	47.04	49.67	66.50	73.96	66.83	66.30	60.39	72.20	65.96	64.59	69.81
12	Italy	27.59	31.02	38.91	43.39	38.68	37.52	35.34	39.73	39.67	41.97	40.28
13	Cyprus	3.62	5.45	7.63	7.30	8.81	8.69	8.70	9.43	10.01	12.30	15.29
14	Latvia	50.49	66.63	56.92	54.53	50.18	54.18	72.52	52.02	49.58	63.75	63.59
15	Lithuania	26.19	26.12	36.21	40.75	39.41	56.99	70.34	73.92	73.28	54.35	60.02
16	Luxembourg	9.28	11.18	20.01	20.88	32.28	58.25	66.80	71.49	74.74	79.25	80.79
17	Hungary	7.52	7.64	9.20	10.72	10.63	10.21	10.57	11.74	13.68	15.83	19.26
18	Malta	0.46	1.13	1.55	3.34	7.82	15.90	10.42	10.14	9.80	11.33	11.88
19	Netherlands	10.81	12.09	11.91	11.27	12.40	12.83	14.88	16.55	18.79	26.71	33.05
20	Austria	65.69	74.70	78.17	81.45	76.91	78.26	75.70	76.96	77.10	80.08	78.79
21	Poland	8.05	10.44	10.41	12.52	13.80	13.73	14.19	12.74	15.59	17.95	17.05
22	Portugal	46.48	42.50	58.32	60.74	47.53	54.63	39.12	50.34	52.98	58.41	63.76
23	Romania	26.31	25.40	34.42	41.61	39.75	41.75	37.98	40.65	41.62	44.24	44.47
24	Slovenia	24.38	27.85	32.32	38.52	29.39	31.18	27.71	32.42	31.70	33.03	34.97
25	Slovakia	17.67	19.32	22.28	22.94	22.68	24.72	23.81	21.76	23.54	24.01	21.84
26	Finland	32.89	40.56	35.97	38.58	44.50	44.23	46.61	45.74	46.44	51.65	52.92
27	Sweden	55.95	59.07	54.03	55.84	63.27	57.17	57.88	55.80	58.74	68.47	66.37

Table 1. The percentage of renewable energy based on the total electricity production in the European Union countries from 2011 to 2021 [43].

Row No.	Country	Year
		2011	2012	2013	2014	2015	2016	2017	2018	2019	2010	2021
1	Belgium	9.33	12.86	14.28	17.12	21.08	16.88	18.49	23.22	21.00	26.50	23.06
2	Bulgaria	7.78	11.35	15.99	15.74	17.98	15.80	13.64	20.15	17.13	18.57	21.76
3	Czech	8.35	9.30	10.82	10.78	11.40	11.43	11.20	10.84	11.71	12.89	12.60
4	Denmark	40.25	48.33	45.96	55.88	65.43	60.22	70.26	68.36	78.17	81.62	78.96
5	Germany	20.43	22.99	24.07	26.13	29.39	29.41	33.40	35.01	39.99	44.19	39.58
6	Estonia	9.14	12.34	9.19	11.16	15.37	13.05	14.12	16.09	28.13	47.82	39.20
7	Ireland	19.97	19.36	22.00	24.77	27.97	24.86	28.96	33.02	38.41	42.14	36.34
8	Greece	13.76	16.69	25.12	24.19	28.66	27.37	25.01	30.33	33.14	36.45	41.11
9	Spain	30.02	29.58	39.58	40.11	34.96	38.57	32.21	38.20	37.26	43.78	46.32
10	France	11.63	15.01	17.23	16.59	15.99	17.70	16.64	19.71	19.99	23.65	21.94
11	Croatia	47.04	49.67	66.50	73.96	66.83	66.30	60.39	72.20	65.96	64.59	69.81
12	Italy	27.59	31.02	38.91	43.39	38.68	37.52	35.34	39.73	39.67	41.97	40.28
13	Cyprus	3.62	5.45	7.63	7.30	8.81	8.69	8.70	9.43	10.01	12.30	15.29
14	Latvia	50.49	66.63	56.92	54.53	50.18	54.18	72.52	52.02	49.58	63.75	63.59
15	Lithuania	26.19	26.12	36.21	40.75	39.41	56.99	70.34	73.92	73.28	54.35	60.02
16	Luxembourg	9.28	11.18	20.01	20.88	32.28	58.25	66.80	71.49	74.74	79.25	80.79
17	Hungary	7.52	7.64	9.20	10.72	10.63	10.21	10.57	11.74	13.68	15.83	19.26
18	Malta	0.46	1.13	1.55	3.34	7.82	15.90	10.42	10.14	9.80	11.33	11.88
19	Netherlands	10.81	12.09	11.91	11.27	12.40	12.83	14.88	16.55	18.79	26.71	33.05
20	Austria	65.69	74.70	78.17	81.45	76.91	78.26	75.70	76.96	77.10	80.08	78.79
21	Poland	8.05	10.44	10.41	12.52	13.80	13.73	14.19	12.74	15.59	17.95	17.05
22	Portugal	46.48	42.50	58.32	60.74	47.53	54.63	39.12	50.34	52.98	58.41	63.76
23	Romania	26.31	25.40	34.42	41.61	39.75	41.75	37.98	40.65	41.62	44.24	44.47
24	Slovenia	24.38	27.85	32.32	38.52	29.39	31.18	27.71	32.42	31.70	33.03	34.97
25	Slovakia	17.67	19.32	22.28	22.94	22.68	24.72	23.81	21.76	23.54	24.01	21.84
26	Finland	32.89	40.56	35.97	38.58	44.50	44.23	46.61	45.74	46.44	51.65	52.92
27	Sweden	55.95	59.07	54.03	55.84	63.27	57.17	57.88	55.80	58.74	68.47	66.37

Based on the proposed methodology, first of all, the intensity of RE development in EU countries through the CP was calculated. For this purpose, according to Equation (4), the quantity, ${\tilde{Q}}_{fj}$, which evaluates the fluctuations in RE development during the CP, was calculated (

Table 2. Development of renewable energy in EU countries from 2011 to 2021, as measured through quantities reflecting RE development in the considered period (source: compiled by the authors).

Row No.	Country	Renewable Energy Development Indicator
		${\tilde{\mathit{Q}}}_{\mathit{f}\mathit{i}}$	${\mathit{K}}_{\mathit{I}\mathit{j}}$	${\mathit{K}}_{\mathit{T}\mathit{j}}$	${\mathit{K}}_{\mathit{P}\mathit{j}}$
1	Belgium	25.5	0.63	0.35	0.59
2	Bulgaria	20.8	0.63	0.35	0.58
3	Czech	12.8	0.34	0.37	0.44
4	Denmark	83.6	0.52	0.48	0.56
5	Germany	42.7	0.52	0.54	0.58
6	Estonia	35.9	0.75	0.29	0.63
7	Ireland	39.8	0.50	0.41	0.53
8	Greece	38.7	0.64	0.53	0.64
9	Spain	43.0	0.30	0.33	0.38
10	France	22.4	0.48	0.43	0.52
11	Croatia	71.3	0.34	0.25	0.39
12	Italy	42.1	0.34	0.24	0.39
13	Cyprus	13.3	0.73		0.67
14	Latvia	59.9	0.16	0.02	0.26
15	Lithuania	73.0	0.64	0.26	0.57
16	Luxembourg	90.0	0.90	0.48	0.78
17	Hungary	16.4	0.54	0.37	0.52
18	Malta	13.9	0.97	0.36	0.79
19	Netherlands	25.7	0.58	0.27	0.51
20	Austria	80.1	0.18	0.21	0.31
21	Poland	17.5	0.51	0.44	0.54
22	Portugal	57.0	0.18	0.21	0.27
23	Romania	46.4	0.43	0.35	0.47
24	Slovenia	33.9	0.28	0.28	0.36
25	Slovakia	24.2	0.27	0.13	0.32
26	Finland	52.4	0.37	0.54	0.48
27	Sweden	63.8	0.12	0.22	0.28

). Based on Equation (5), $K_{Ij}$, the size value was determined (Table 2). In the second stage, based on Equations (6)–(10), the evenness index of $K_{Tj}$, pertaining to the RE development of the EU countries, was calculated (Table 2).

In order to obtain a generalized picture of RE development throughout the CP, the indices $K_{Ij}$ and $K_{Tj}$ were combined into one summarizing value. For this purpose, an expert assessment of the importance of the intensity and uniformity of RE development for the overall process of its development was carried out. The expert team consisted of nine people. The literature sources indicate that their minimum number is 7–8 [44,45]. There were representatives of our large electricity supply and transmission enterprises, universities and companies whose activities are based on RE. The consistency of opinions, taking into account that only two indicators were assessed, was checked based on the Kendall concordance coefficient W [46]. Experts assessed the parameters of RE development and their importance for RE development in various ways. A weight of 0.7 was given to the intensity of development, and a weight of 0.3 was given to uniformity. The value of the index $K_{Pj}$ was determined based on Equation (11). The calculation results are given in Table 2.

Based on Equation (12), all EU countries were divided into two groups according to their level of economic development (

Table 3. Classification of EU countries into groups according to level of economic development (source: classified by the authors based on Eurostar data).

Economically Developed EU Countries	Economically Developing EU Countries
Austria	Bulgaria	Malta
Belgium	Croatia	Poland
Denmark	Cyprus	Portugal
Finland	Czech	Romania
France	Estonia	Slovenia
Germany	Greece	Slovakia
Ireland	Italy	Spain
Luxemburg	Hungary
Netherlands	Latvia
Sweden	Lithuania

).

The division of EU countries into two groups based on Equation (12) allowed them to be compared both in terms of RE development intensity, uniformity, and the generalized development index (

Table 4. RE development indices for developed and developing EU countries.

RE Development Rate	Average Value of Indicator		Value Ratio
	Developed Countries	Developing Countries
$\mathrm{Intensity} K_I$	0.48	0.47	1.02
$\mathrm{Evenness} K_T$	0.89	0.82	1.09
$\mathrm{Development} { K}_P$	0.60	0.57	1.05

).

Table 4 shows that the intensity of RE development was practically the same for both developed and developing EU countries, while greater uniformity of development was characteristic of developed countries. This may be due to their significantly higher financial potential, greater experience in RE development, etc. Thanks to the evenness index, the summary indicator of RE development in the developed countries in the EU was higher compared to developing countries.

The obtained research results can clarify some contradictory statements regarding the development of RE. Researchers have paid a lot of attention to the interaction between RE and countries’ socio-economic development [4]. In one case, it is argued that the determinants of RE development are the economy and politics of countries [27,28,30]. On the other hand, there are opposing claims; for example, it is claimed that the development of RE can hinder countries’ economic growth [25,26]. It all depends on the policy of the country’s government, i.e., which is given priority: purely (exclusively) economic growth or sustainable development that conserves natural resources and increases ecological sustainability. The correlation–regression analysis of the interaction between GDP and RE development provides the answer. This analysis was carried out based on two aspects: what the situation is today and what effect the changes in the economic development of the countries had on the development of RE during the considered period, i.e., during 2011–2021.

The calculations are based on the following models:

$$Q_{fj}=f\left({GDP}_{fj}\right)$$

(13)

$$K_{Pj}=f\left({GDP}_{Ij}\right)$$

(14)

where ${GDP}_{fj}$ is the GDP value of the j-th country at the end of the CP, i.e., in 2021; and ${GDP}_{Ij}$ is the intensity of changes in the GDP of the j-th country during the considered period (2011–2021).

The size ${GDP}_{Ij}$ is determined as follows:

$${GDP}_{Ij}={\displaystyle \frac{Q_{fj}}{Q_{fj}+∆Q_j}}$$

(15)

$$∆Q_j=Q_{fj}-Q_{bj}$$

(16)

where $∆Q_j$ is the GDP changes in the j-th country during the considered period.

The analysis according to models (13)–(14) showed that the impact of countries’ economic development on the development of RE is very high (r = 87). Economic development positively affected the development of REs during the entire period (2011–2021) (r = 0.7).

The question arises as to whether it is correct to claim that the development of RE can hinder economic growth, bearing in mind that the latter promotes the development of RE. The answer to this question was provided by the correlation–regression analysis of the impact of the increase in the scale of the country’s total electricity production on the development of RE. This analysis showed that as these scales grow, RE development slows down (r = −0.24). Such a situation is more typical for developed EU countries (r = −0.37) than for developing countries (r = −0.27). Wealthier societies are less dependent on RE sources than developing ones. Moreover, economic development, rather than sustainable development, is still prioritized to this day. Thus, we see a contradiction between the International Energy Agency’s aspirations to increase the scale of RE production to two-thirds of the total energy supply by 2050 and reality [35]. In summary, the further development of RE, as indicated, depends on the joint energy development policy implemented by the governments of the EU countries.

Considering that the quantitative assessment of RE development, as a methodology, combines several methodologies (intensity, uniformity, general assessment of the development process), it is appropriate to present its essence, for example, in the form of a table, which would present its stages, their content, and the results obtained in detail (

Table 5. Methodology and results of the quantitative assessment of renewable energy development in the European Union countries (source: compiled by the authors).

Research Stage	Research Stage Name	Research Stage Content	Research Stage Result
I	Overview of the status of quantitative assessment of RE development.	Analysis of literature sources on issues of quantitative assessment of RE development.	It was determined that today there is practically no methodology for quantitative assessment of RE development.
II	Development of a methodology for quantitative assessment of RE development.	Identification of the characteristic features of RE development through CP. Search for an indicator that adequately reflects the intensity of RE development through CP. Search for an indicator that reflects the uniformity of RE development. Determination of a generalizing index of RE development through CP.	It was determined that the development of RE through CP is reflected by two essential characteristics—intensity and uniformity. An intensity index of RE development through CP has been established, which assesses the fluctuations in development that occurred during it. An evenness index of RE development through CP has been established, the essence of which is the sum of the ratios of the actual and ideal values of its development in separate time periods (years). A multi-criteria model for calculating the general index of RE development through CP, which assesses the importance of intensity and evenness for the overall development process.
III	Empirical study.	Calculation of the RE development uniformity index of EU countries. Calculation of the RE development summary index of EU countries through CP. Determination of the interaction between economic and RE development of EU countries	The RE development uniformity index was determined for EU countries. Based on the values of the RE development intensity and uniformity indices and expert assessments, their importance was determined, and the general RE development index for all EU countries during the CP was calculated. The nature of the impact of EU countries’ economic development on RE development was determined.

).

The methodology for the quantitative assessment of RE development through CP presented in Table 5 is universal, since practically all socio-economic processes are characterized by the same characteristics—intensity and uniformity of development.

5. Conclusions

The European green course strategy has been formed and implemented in response to the world’s worsening ecological situation, which is due to the increasing use of “dirty” technologies for the production of non-renewable natural resources, among other factors. It aims to ensure member countries’ economic development while reducing electricity consumption. Despite the positive changes achieved thanks to such policies, the problematic ecological situation has practically remained the same. This is evidenced by the fact that today, 85% of primary electricity needs are met using traditional fossil fuels.

Electricity is the driving force behind countries’ economic development, and much research has been devoted to examining this interaction. Prior analyses reveal a contradictory picture of the results obtained. In one case, it is claimed that developing each country’s energy sector is essential to economic development. In another case, it is claimed that this development depends primarily on energy development. In the third case, an attempt is made to integrate these two extreme views by arguing that it is a two-way relationship, i.e., growth in the electricity production sector leads to the country’s economic development and this, in turn, leads to further energy development. The different limitations of these previous studies could explain these conflicting results.

Localization of the environmental impact of electricity as a significant source of pollution largely depends on the development of nuclear power plants. Therefore, a lot of research is devoted to it. Here, again, conflicting results have been obtained. In one case, it is asserted that the development of RE can hinder the economic development of the country; in another, it is stated that economic development is an essential factor in the development of RE. To extend these studies and obtain a more adequate picture, the analysis should be based on the country’s GDP and the RE development trends. For this, examining the changes that took place over a sufficiently long period is necessary. Two characteristic aspects can be singled out, comprehensively reflecting any process’s development: evenness or uniformity and intensity. To obtain a general development assessment, the indices that reflect them should be combined to assess their importance for the overall development process. Experts gave a significance estimate of 0.7 to the intensity of development and an estimate of 0.3 to uniformity.

For a deeper analysis of RE development, we divided EU countries into two groups according to their level of economic growth (GDP per inhabitant of the country). It was found that the intensity of RE development in both groups of countries during the considered period was practically the same, while developing countries had superior uniformity. This is the result of their economic and financial potential and stability.

Based on the research conducted, some contradictory results regarding the interaction between RE and countries’ economic development have been clarified. In the first case, it was based on the last years of the analyzed period, and in the second, it was based on the entire period of 2011–2021. In both cases, the countries’ economic development positively influenced the development of RE (correlation coefficient r = 0.33/0.36). This partially contradicts the results of some studies, stating that the development of nuclear power plants can hinder a country’s economic development. The researchers answered this question. GDP growth does not cause a decrease in the production of renewable electricity, but an increase in the total volume of its output. After exceeding a certain ratio, the negative impact of the scale of electricity production exceeds the positive impact on GDP, and the development of RE slows down. The methodology for the quantitative assessment of RE development is relevant both in scientific and practical terms. The scientific relevance of the methodology is manifested in the following aspects:

−

allows for a quantitative assessment of RE development in individual countries;

−

provides an opportunity to compare countries or their groups according to RE development;

−

allows for the analysis of the interaction between RE and the country’s economic development;

−

allows for the analysis of the interaction between RE development intensity and uniformity.

−

The practical benefit of the methodology is manifested in the following aspects:

−

allows for the identification of factors that promote or hinder RE development;

−

allows for the prediction of measures for further RE development.

Thus, the methodology can serve as a methodological basis for the assessment and analysis of RE development in countries.

It is essential to determine the significance of this ratio for further RE development research, as the purposeful formation of strategies for the further development of RE largely depends on it. One of the issues to be resolved concerns determining an adequate length for the period analyzed. Today, this problem can be seen as a research limitation.