**4. Results**

*4.1. Changes in the Use of RES in European Households*

 *Y.*

The aim of this section is to analyze the changes in the use of renewable energy sources in EU-28 households between 2004 and 2019.

In absolute terms, the leaders in household sector RES consumption are the French, Germans and Italians. In 2019, RES energy in these households represented between 6508.6 thousands of tons of oil equivalent (ktoe) in Italy, 8293.3 ktoe in Germany and 9094.3 ktoe in France. The least RES energy consumed households in Malta (14.0 ktoe) and in Luxembourg (19.3 ktoe) (Figure 3). Between 2004 and 2019, the highest increase in energy in absolute units was observed precisely in the mentioned leader countries. In Italy the amount of energy used in the household sector increased by 4247.9 ktoe, in Germany by 3348.3 ktoe and in France by 2123.4 ktoe. Relatively large increases in RES consumption over the 16-year period were also observed in the UK (by 1897.8 ktoe) and the Czech Republic (by 1027.4 ktoe). Even though in the majority of EU countries an increase in household RES consumption was observed, there were also decreases, such as in Latvia (by 255.6 ktoe), Portugal (by 110.4 ktoe), Croatia (by 96.0 ktoe), Lithuania (by 57.1 ktoe) and Slovenia (by 2.1 ktoe).

**Figure 3.** Energy from RES in EU households in 2004 and 2019, in thousands of tons of oil equivalent. Source: own elaboration based on data from [7].

> In absolute terms, the consumption of RES by the household sector depends, among others, on the country size and the number of households in it. In the further section of this paper, the RES consumption in relative terms and the type structure of the energy used will be analyzed. Thus, in 2019—in relative terms—the first place in the ranking of renewables use by EU-28 households had Croatia, where RES accounted for more than

46% of household energy exploited. A high share of RES in the energy carriers used in households was also recorded in Slovenia and Latvia—more than 43% of final energy consumption each. In turn, Estonian, Romanian and Portuguese households had more than 36% share of RES in energy carriers used. At the other end of the scale were households of Ireland, Iceland, Luxembourg, the UK, the Netherlands and Belgium, where the share of RES in household final energy consumption did not exceed 9% (Figure 4).

The greatest progress—in relative terms—in the use of RES in EU-28 households was observed in Cyprus. Over a period of 16 years, the increase in the percentage of RES used by these households was 27.3 p.p. However, it is worth mentioning that the first data for this country appeared in 2005, where 11.1 p.p. of RES in household final energy consumption was recorded and all of this energy came from solar thermal system. The next highest increase in RES use by households was in the Slovak Republic (increase by 22.1 p.p.). A relatively high progression was observed in the case of RES usage between 2004 and 2019 by households of Hungary, the Czech Republic, Malta, Italy, i.e., by about 14 p.p. Here it should also be noted that in the case of Malta—as well as the aforementioned Cyprus—no RES usage was recorded in households in 2004 at all. In 2010 Maltese households started using RES (6.2%), which came mainly from solar thermal technology (close to 83%), as well as from primary solid biofuels.

The largest decrease in RES consumption in the household sector was recorded Between 2004 and 2019 in Latvian and Lithuanian households, with a 9.0 p.p. and by 3.1 p.p., respectively, decrease in the share of energy used from RES by these households.

**Figure 4.** The share of energy from RES in the final energy consumption in European Union households in 2004 and 2019. Source: own elaboration based on data from [7].

The main renewable energy sources used in the EU-28 households are primary solid biofuels. In 2019, the share of primary solid biofuels in the total consumption of renewable energy sources in households was 83%, while in 2004—96.6%. This was followed by ambient heat at 11.6% (0.9% in 2004) and solar thermal technology at 4.0% (1.3%). Charcoal and biogases each accounted for 0.6% and geothermal heat for 0.1% (Figure 5).

**Figure 5.** Structure of RES used by the household sector in 2004 and 2019, percentage. Comment: ST—Solar thermal system, G—Geothermal system, PSB—Primary solid biofuels, C—Charcoal, B—Biogases, RMW—Renewable municipal waste, BBG—Blended biogasoline, PB—Pure biodiesels, BBD—Blended biodiesels, OLB—Other liquid biofuels, AH—Ambient heat. Source: own elaboration based on data from [7].

### *4.2. Identification of Household Types in Terms of RES Consumption*

The aim of this section is to identify the types of European households showing similarities in the structure of use of the different renewable energy sources. In the first step of the analysis, the EU countries were divided into similar groups, according to the total amount of energy used from RES in households and the structure of particular sources of this energy in 2019. The EU countries were divided into six clusters (k-means method), based on the assumed optimal number of groups (Ward's method). The adopted division was made on the basis of the first significant jump in the bonding distance related to the bonding stages (Figures 1 and 2, Table 1).


Source: own elaboration based on data from [7].


In accordance to the analyses performed, measures of intra- and inter-cluster variation and degrees of freedom (df) were determined. The obtained values of the F-statistic, which is the ratio of the variation between clusters to the variation within clusters, made possible to identify the most important clustering variables in terms of their discriminatory power. This means that the higher value of the F-statistic for a given variable, the more important the assignment of given countries to particular clusters.

The analysis of variance showed that blended biodiesel use played the greatest role in the assignment of EU countries to particular clusters. The value of the F statistic for this variable was the highest at 2995.72, followed by geothermal energy (47.05). Biogases, for which the value of the F statistic was 3.07, were the least significant factor in the assignment of EU countries according to the criterion adopted. However, it is worth remembering that each diagnostic variable, i.e., each renewable energy source, ultimately influenced the grouping of EU countries into homogeneous clusters both in terms of structure and volume of energy exploited from these sources.

As blended biodiesels and geothermal heat were important factors in assigning EU countries to particular clusters, countries using these sources formed single-element clusters. The compositions of the formed clusters and the distance from their centers (cluster centers) are presented in Table 2. The greater the distance of a given EU country from the center of the cluster in which this country was located, the greater its variability in relation to the countries whose distance from the cluster center was smaller.


**Table 2.** Analysis of variance for renewable energy consumption in households' sector.

Source: own elaboration based on data from [7].

The results indicate the homogeneity of two clusters (the1st and the 3rd clusters). Sweden (the 1st cluster—Specific A), as the only country using blended biogasoline and blended biodiesels, is located in the 1st cluster. No other country has reported the use of this renewable source in households. The Swedes were also ones of the few to use biogases (3.2%), while primary solid biofuels consumption accounted for nearly 94% (Figure 6, Table 3).

Cyprus (the 3rd cluster—Specific B), on the other hand, was one of the few countries with a relatively high geothermal energy consumption in households (1.6%). Cypriot households are also leaders in the use of solar thermal energy (62.5%) and also a relatively low use of primary solid biofuels compared to other countries (18.5% of total household RES consumption) is reported there. In addition, ambient heat (11.4%) and charcoal (6.0%) and geothermal heat (1.6%) appeared among the RES sources in households of this country. The overall use of RES by Cypriot households in final consumption energy was 27.3%.

The 2nd cluster (Follower) comprised seven countries with total RES use ranging from over 14% in Germany to 30% in Austria. These countries were characterized by relatively high use of primary solid biofuels, i.e., from nearly 62% in Greece to over 98% in Hungary. In almost all countries the RES categories observed in the renewable energy mix were solar thermal energy (from 1.0% in Hungary to 26.7% in Greece), charcoal (from 0.1% in Slovakia

to 4.4% in Greece, in Hungary this category was generally absent) and ambient heat (from 0.7% in Hungary to 13.9% in Germany).

**Figure 6.** Mean values of energy consumption from renewable energy sources for individual clusters (results of the nonhierarchical grouping of similarities between the EU countries in final energy consumption from renewable energy sources in households' sector in 2019 using the k-mean's method). Source: own elaboration based on data from [7].

The obtained results revealed that the six countries in the 4th cluster (Sleeper) acquired the lowest average value of energy obtained from RES, ranging from 2.5% in Ireland to over 15% in Poland. Primary solid biofuels in this cluster were the relevant source of RES for households ranging from nearly 35% in Ireland to over 93% in the UK. The second place was for heat pumps, i.e., its total household RES use was from 5% in the UK to 47% in Ireland. Luxembourg and Ireland had also relatively high use of solar thermal energy, i.e., 13% and 19% of household RES consumption, respectively.

The most numerous cluster was formed by 8 countries (the 5th cluster—Leaders). This cluster had the highest value of renewable energy used by households. It was found that in 2019 the use of renewable energy sources in final energy household consumption ranged from just over 31% in the Czech Republic to over 46% in Croatia. These households relied mainly on primary solid biofuels, ranging from over 89% in Slovenia to 100% in Estonia.

In the 6th cluster (Active), which includes five countries, there are countries with rather low total RES use, i.e., from 14% in Malta to 37% in Portugal. In these countries there was relatively less use of primary solid biofuels in the household sector (in total RES use ranging from 12% in Malta to 80% in Denmark) and more use of ambient heat (ranging from 19% in Denmark to 52% in Malta). In Malta, solar thermal was a relatively popular source of RES, with more than 36% of RES coming from this source. An overview of the average RES energy shares for each country, cluster by cluster, is presented in Table 3.

Between 2004 and 2019 a diversification of RES sources is observed. Even though primary solid biofuels still remain the dominant source of RES in households, other sources are emerging, notably ambient heat and solar thermal system. In 2004, a sector of households in nine EU-28 countries used ambient heat, while 16 years later this source appeared in 23 countries. In 2004, households in 16 countries used solar thermal energy, while in 2019—in 24 countries. Another RES source, charcoal appeared in households of six EU-28 countries in 2004, while in 2019—it extended to 12 countries.


**Table 3.** Groups of EU-28 countries due to the use of RES in the household sector in 2019, in percentages.


*Energies* **2021**, *14*, 5560

**Table 3.** *Cont.*

### *4.3. Changes in the Use of RES in Households from Poland, Slovakia and Germany*

The aim of this subsection is to analyze changes in the use of energy carriers in Polish households and selected neighboring countries, i.e., Slovakia and Germany. The case of Poland was chosen due to the fact of high use of hard coal in this country. Poland is the largest hard coal producer and the second largest brown coal producer in the EU, generating about 80% of electricity from coal. Resistance to limiting coal mining and consumption comes from various sides, namely coal corporations, trade unions, parts of civil society and the government—and their coalition partners. Their objection centers around the prospect of lost business, previous negative experiences of structural change, fears of rising energy prices and concerns about energy security, as well as potential unemployment in regions almost entirely dependent on coal [81].

Germany and Slovakia were chosen for comparison for the following reasons. Firstly, they are neighboring countries. The winter climate in these countries is quite cold, which makes it necessary to use heat energy in every sector, especially in households. Secondly, Germany is a country from the so-called 'richer' west of Europe, while Slovakia, similar to Poland, is a central and eastern European country with a similar history and socio-economic development. There are more than 20 countries in the world whose share of renewable energy sources in total energy consumption exceeds 20%, and Germany is among these countries. By 2050, Germany plans to achieve a 60% share of renewable energy in the country's total energy balance and 80% in electricity production [82].

Raising the level of economic and human development has increased the demand for fossil fuels. Currently, conventional energy sources dominate in terms of resources used by economies, including some European households. Many countries in the world, facing the problem of energy and national security, have intensified their efforts to transition from conventional energy sources (primarily fossil fuels) to alternative energy sources [83]. However, these transitions differ from country to country.

Polish households are a kind of "coal island" on the map of Europe [84]. In 1990, the use of hard coal in total energy consumption in Polish households accounted for 38.2%, and for nearly three decades this percentage has been reduced by 10.8 p.p. In the same period the use of hard coal in German households decreased from 15.3% to 0.6% and in Slovak households from 19.4% to 1.1% (Figure 7). Thus, the progress in this respect— beneficial from the environmental point of view—was definitely better in the countries neighboring Poland.

**Figure 7.** Use of solid fuels and renewable energy sources in the Polish, German and Slovak household sector in 2019. Scheme 7.

Between 1990 and 2019, the use of RES in households in relative terms increased, most notably in Slovak households—by 23.3 p.p., while German (10.9 p.p.) and Polish (15.2 p.p.) households had smaller achievements in this respect. Even though looking at this aspect in absolute terms, between 1990 and 2019 the use of RES by the household sector in Poland increased by 1662.7 ktoe, in Germany by 5308.8 ktoe and in Slovakia by 615.5 ktoe. However, it is worth noting that in 1990 in Slovakia there was no RES consumption in the household sector at all.

In Poland, residential heating is mainly provided by hard coal. In the total consumption of energy carriers in Polish households, hard coal and other bituminous coal accounted for 54.5% in 2019. In the 16-year period, since 2004, coal consumption in the household sector has decreased slightly, i.e., by 2.6 p.p. [7]. The high share of coal in the total consumption of energy carriers is the cause of air pollution, among others in sulphur dioxide, nitrogen oxides and dusts. The household sector is responsible for total atmospheric emissions of sulphur dioxide in nearly 23%, nitrogen oxides in about 8% and dusts in nearly 36% [85].

Based on the directional coefficient of the trend, it can be concluded that the consumption of renewables in Polish households has statistically significantly increased between 2004 and 2019, on average by 31.1 thousands of tons of oil equivalent (ktoe). Similar to other European households, among renewable energy sources, primary solid biofuels are here in the lead, accounting for 88.4% of total RES consumption in these households. Ambient heat accounts for 8.5%, solar thermal system for 2.4% and geothermal energy for 0.7%. Thus, the hierarchy of RES consumption in Polish households is consistent with that observed in European ones. Regarding the different types of RES, a significant increase was recorded for solar thermal (by 4.47 ktoe on average per year), geothermal power (0.77 ktoe) and ambient heat (15.5 ktoe). In addition to the increase in renewable energy sources, Polish households enhanced the natural gas consumption, on average by 28.4 ktoe per year. Other energy sources showed a decrease (manufactured gases, gasworks gas, oil and petroleum gases, gas oil and diesel oil) or stabilization (solid fossil fuels, other bituminous coal, lignite, coke oven coke) (Table 4).


**Table 4.** Trends in the use of energy sources in Polish households in 2004–2019.

Comment: Tables 3–5 include the categories of energy sources that are used in a given country. The list of energy source categories in Tables 3–5 differs due to the differences (the absence of certain categories) in their use between countries. Source: own calculations based on data from [7].

Slovak households in 2019 were dominated by two energy carriers, natural gas and RES, which accounted for 42.4% and 23.3% of the total consumption of energy carriers, respectively. Since 2004, natural gas consumption in the household sector has decreased by 13.4 p.p., instead of renewables and biofuels, which have increased by 22.1 p.p. In particular, between 2018 and 2019 consumption of renewables and biofuels in Slovak households increased markedly, due to the increase of primary solid biofuels in total consumption. The share of hard coal in the total consumption of energy carriers in Slovak households was 1.1% in 2019, while 16 years earlier it was 3.9% [7].

The directional coefficient of the trend demonstrates that the changes in consumption of renewable energy sources in Slovak households in 2004–2019 were not statistically significant. However, the analysis of particular types of renewable energy sources shows that the significant increase was recorded only in relation to solar thermal energy (by 0.52 ktoe on average per year) as well as other bituminous coal (average annual by 0.95 ktoe) and brown coal briquettes (average annual by 0.09 ktoe) (Table 5).


**Table 5.** Trends in the use of energy sources in Slovak households in 2004–2019.

The same comment as in Table 3. Source: own calculations based on data from [7].

Regarding German households, three energy carriers dominate the overall consumption of energy carriers, i.e., oil and petroleum products, gas oil and diesel oil, renewables and biofuels, which accounted for 20.6%, 19.0% and 14.4%, respectively, in 2019. Since 2004, consumption of oil and petroleum products in the household sector has decreased by 6.7 p.p., gas oil and diesel oil by 6.6 p.p. and renewables and biofuels have increased by 6.7 p.p. The share of hard coal in the total consumption of energy carriers in German households in 2019 was—0.6% [7].

From the directional coefficient of the trend, it can be concluded that the consumption of renewable energy sources in German households increased statistically significantly between 2004 and 2019, on average by 198 ktoe. As for the individual types of renewable energy sources, significant increases were recorded for solar thermal technology (average annual increase of 34.7 ktoe), geothermal heat (1.81 ktoe), biogases (22.7 ktoe) and ambient heat (68 ktoe). In German households, apart from the increase in renewable energy sources, there was no significant increase in the consumption of other energy carriers (Table 6).


**Table 6.** Trends in the use of energy sources in German households in 2004–2019.

The same comment as in Table 3. Source: own calculations based on data from [7].
