Photovoltaic energy (PV) is considered one of the pillars of the energy transition. However, this energy source is limited by a power density per unit surface lower than 200 W/m², depending on the latitude of the installation site. Compared to fossil fuels, such low power density opens a sustainability issue for this type of renewable energy in terms of its competition with other land uses, and forces us to consider areas suitable for the installation of photovoltaic arrays other than farmlands. In this frame, floating PV plants, installed in internal water basins or even offshore, are receiving increasing interest. On the other hand, this kind of installation might significantly affect the water ecosystem environment in various ways, such as by the effects of solar shading or of anchorage installation. As a result, monitoring of floating PV (FPV) plants, both during the ex ante site evaluation phase and during the operation of the PV plant itself, is therefore necessary to keep such effects under control. This review aims to examine the technical and academic literature on FPV plant monitoring, focusing on the measurement and discussion of key physico-chemical parameters. This paper also aims to identify the additional monitoring features required for energy assessment of a floating PV system compared to a ground-based PV system. Moreover, due to the intrinsic difficulty in the maintenance operations of PV structures not installed on land, novel approaches have introduced autonomous solutions for monitoring the environmental impacts of FPV systems. Technologies for autonomous mapping and monitoring of water bodies are reviewed and discussed. The extensive technical literature analyzed in this review highlights the current lack of a cohesive framework for monitoring these impacts. This paper concludes that there is a need to establish general guidelines and criteria for standardized water quality monitoring (WQM) and management in relation to FPV systems.

Wayside gauge face lubrication is widely used to minimize rail wear. Scientific understanding of this process is limited; however, there have been significant recent improvements in application equipment. In this paper the process is analyzed in terms of a number of interacting sub-processes, and the factors thought to be important for lubricant and application equipment are reviewed. Wheel/rail contact conditions (pressure and temperature) are also identified as significant variables. Grease stability and retentivity are significant factors that affect lubricant performance; however, significant knowledge gaps exist about the factors that influence grease pick up and carry down especially at the extremes of operating temperatures. Laboratory (two-roller rig measurement of retentivity) and field evaluation (rail friction measurements of carry down) gave the same relative ranking for the tested grease samples. Areas for future research in the area are identified.