Limited reserves of fossil fuels, rising environmental concerns, and a remarkable increase in electricity demand have led to the necessity of harnessing solar energy on a large scale. For this purpose, there has been a noticeable stimulation into photovoltaic power plants (PVPPs) over the last three decades, but the land requirement for PVPPs is still a handicap in many countries since valuable lands are considered for other purposes such as agriculture and livestock. For effective conservation of valuable lands and water resources, PVPPs are preferred to be installed on various water bodies such as oceans, seas, lagoons, lakes, rivers, dams, canals, wastewater treatment plants, irrigation ponds, fish farms, wineries, reservoirs, etc. PV systems on water bodies are called floating PVPPs, and they have outstanding advantages compared with land-based PVPPs including better energy generation owing to passive cooling effects, higher system efficiency and reliability, and lower dirt and dust accumulation on PV modules thus lower operating costs. There are also some significant environmental features provided by floating PVs. Shading effects due to PV coverage reduce water losses arising from evaporation. Moreover, algae growth is limited because of mitigated solar radiation, which yields better water quality. This review presents more insight on floating PVPPs in terms of several aspects such as electricity generation, system efficiency, reliability and sustainability, experimental applications and facilities in operation, water and carbon saving as well as challenges.

Urban and rural areas are the cradles of human development and civilization as all practical progress and feasible products have emerged from these places. Having a clear understanding of the sustainability of these areas, especially the progress of research in this field, is highly important. This study undertakes a comprehensive scientometric analysis to visualize and quantitatively measure the outcome of the scientific enterprise to construct sustainable urban and rural areas. The scientific productivity of recorded publications, their impacts, and their importance were systematically measured in diverse aspects by virtue of ten distinctive techniques. A critical assessment of the respected criteria for sustainable urban and rural areas is presented in order to further clarify its boundaries with other related topics, as well as providing a clear benchmark for future studies. After screening the search results between 1900 and 2018 on the Web of Science database, 7397 publications explicitly related to sustainable urban and rural areas were extracted and analyzed by the CiteSpace software via the relevant bibliometric indicators. The results of this study shed light on the trends and patterns, consisting of kernel research areas, countries, journals, institutions, and how these entities have been concatenated, inside the bibliographic records around sustainable urban and rural areas. The findings facilitate in identifying the barriers and weakness in the current sustainable urban and rural areas research, and consequently help in identifying auspicious directions for prospective investigations.