**6. Conclusions**

The household sector is an important contributor to overall energy consumption in the economy and should therefore be actively involved in measures to improve environmental quality. For a common future, it is necessary to include renewable energy in the long-term planning process of the energy sector. The use of renewable energy has numerous benefits, but investment in new RES technologies often proves costly, so many countries rely on the cheapest solutions using, for example, primary solid biofuels. Nevertheless, every year there is an increase in the use of RES in EU households, with diversification of the sources of this energy.

As in other aspects of life, there is a certain polarization among EU countries regarding the use of RES in the household sector. In central and eastern European countries there is a greater use of energy sources such as primary solid biofuels, while households in western European countries are more likely to install ambient heat, solar thermal systems or use biogases.

Many factors influence the disproportion between EU countries in the use of RES. Each EU Member State should look for optimal and efficient solutions to develop RES in the household sector in order to improve its position in terms of their use. The literature review shows that an important factor is an active State policy and extensive education of citizens on RES. Raising citizens' awareness of the opportunities and benefits of installing RES-based solutions with parallel taking care of the energy efficiency in residential building should bring tangible benefits in the long term.

The conducted analyzes gave answers to the research questions posed in the introduction to the study. Based on the analyses carried out, the following conclusions can be drawn:



Some limitations in this research should be considered. Identifying the situation of RES use by the household sector at the country level gives only a general issues characterizing the discussed subject understanding of the topic under study is a considerable limitation for this study. The household sector is diversified in terms of demographic and socio-economic characteristics. Thus, a number of studies could be usefully developed basing on these results. Subsequent research should take into account the RES use by specific types of households, for example, by demographic, social, economic and culture characteristics.

The research could be extended with the analysis of specific categories of renewable energy sources and could also include other countries, outside Europe. This can be helpful in an assessment of the influence of various factors (e.g., social, economic, legislative, environmental, political, etc.) on the cluster structure. Similar future studies will also give a guidance to determine if there are any changes in the structures of separate clusters.

For energy policy makers and managers offering modern RES technologies, the information that the country remains low in RES consumption by household sector is a signal to deepen the work to raise public awareness about the advantages of introduction this modern and environmentally friendly technology into households.

**Funding:** This research was funded by Warsaw University of Technology" and "The APC was funded by Warsaw University of Technology.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Data available on request due to restrictions. The data presented in this study are available on request from the corresponding author.

**Conflicts of Interest:** The authors declare no conflict of interest.
