Storing energy in hydrogen deposits balances the operation of energy systems and is an effective tool in the process of energy transformation towards achieving Sustainable Development Goals. To assess the validity of its use as an alternative renewable energy carrier in dispersed energy systems of hybrid configuration, a comprehensive review of scientific literature was conducted in this study, based on bibliometric analysis. The bibliographic database used in the study was the international Web of Science database. This review contributes to a better understanding of the characteristics of the selected research area. The evolution of research trends implemented in the design of energy systems associated with hydrogen technologies is revealed, clearly indicating that it is a developing field. In recent years, there has been an increase in the number of publications, although the territorial range of research (mainly simulation) conducted in the domain does not include areas with the most favourable infrastructural conditions. The analysis reveals weak cooperation between South American, African, East Asian, and Oceanic countries. In the light of earlier, thematically similar literature reviews, several research gaps are also identified and proposals for future research are presented. They concern, in particular, the parallel implementation and optimization of the operation of hydrogen (HRES—Hybrid Renewable Energy System and HESS—Hybrid Energy Storage System) solutions in terms of economics, ecology, lifespan, and work efficiency, as well as their feasibility analysis. With the support of other researchers and those involved in the subject matter, this review may contribute to the further development of hybrid hydrogen systems in terms of increasing competitiveness and promoting the implementation of these technologies.

The use of greywater reduces the consumption of many resources and is an effective tool for achieving Sustainable Development Goals. In order to assess the rationality of its use as an alternative source of energy and water in buildings, a holistic literature review was carried out based on a bibliometric analysis of publications in these fields. The main bibliographic source was the Web of Science database. This review contributed to a better understanding of the analyzed research field. It also revealed trends in greywater energy recovery and recycling research, indicating that these are developing fields. In recent years, there has been a marked increase in the number of publications on the most popular ways of using greywater in buildings, with the territorial scope of research carried out in the greywater recycling domain being considerably larger than research on greywater energy recovery. The analysis revealed poor cooperation between different universities, especially in the field of greywater energy recovery. In light of previous literature reviews, some important research gaps and further proposals for future research were also identified. They concern, in particular, the simultaneous use of greywater as an alternative source of energy and water. Together with the findings of other researchers and people related to the subject matter, this review can contribute to the further development of greywater energy recovery systems and greywater recycling systems.

The potential for recovering heat from wastewater exists at various stages, including generation, transport, and treatment. As a result, various technologies for thermal energy recovery from wastewater are now successfully employed in many countries. In order to synthetically present the current state of knowledge on heat recovery from wastewater, a bibliometric analysis of previously published studies indexed in the Web of Science database was performed. The review was further extended with strategic SWOT and SOAR analyses to identify internal and external factors determining the competitive advantage and weaknesses related to the use of wastewater heat exchangers and heat pumps. These analyses indicated the need for further research on the possibilities of heat recovery from wastewater as the use of this technology, both at the building level and on a larger scale, contributes to the implementation of sustainable development goals, especially in terms of improving energy efficiency and reducing CO₂ emissions. Particular emphasis should be placed on research into the use of warm wastewater together with other, better known and accepted, renewable energy sources. It is also important to continuously educate the public and promote heat recovery technologies at various levels, as well as to increase the involvement of legislators and other stakeholders.