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Africa is characterised by a very high solar potential, with a yearly sum of solar irradiation exceeding 2000 kWh/m2. Many African countries are heavily dependent on hydropower, however, increasingly frequent droughts have been severely affecting hydropower generation in the last few decades. The installation of floating photovoltaics (FPV) in existing hydropower reservoirs, would provide solar electricity to help compensate hydropower production during dry periods and reduce evaporation losses while helping to sustainably satisfy the current and future energy needs of the fast-growing African population. This study provides a comprehensive analysis of the potential of FPV installation in Africa, by using highly accurate water surface data of the largest 146 hydropower reservoirs in the continent. In addition to the electricity production, evaporation savings and the potential extra hydroelectricity generated by these water savings are also estimated at reservoir level for four different cases and two types of floating structures. The results indicate that with a total coverage of less than 1%, the installed power capacity of existing hydropower plants can double and electricity output grow by 58%, producing an additional 46.04 TWh annually. In this case, the water savings could reach 743 million m3/year, increasing the annual hydroelectricity generation by 170.64 GWh. • FPV on hydro reservoirs exploits Africa's solar resources and brings multiple benefits. • The total FPV potential in African hydropower reservoirs is estimated at 2922GWp. • A 1% FPV coverage doubles installed capacity and increases electricity output by 58%. • A 1% FPV coverage saves up to 743mcm/year of water and produces additional 171 GWh. [ABSTRACT FROM AUTHOR]

Pumped hydroelectric storage (PHS) is the main utility-scale storage technology. Although PHS systems generally constitute a fraction of generation, they receive increasing attention due to their potential balancing role towards higher penetration of variable renewable energy sources (RES). In the European context it is widely believed that PHS are key elements of the ongoing energy transition. The present analysis examines if this assumption is valid and PHS utilization grows parallel to RES. We collected, harmonised and analysed datasets for 1991–2016 revealing an uneven utilization among European states. While certain countries increased the utilization rates of PHS by a factor of three to four, in several others PHS units are heavily under-utilized. In three extreme cases the utilization rate, compared to the past, is at 10–25% level. We analysed this controversy by identifying tendencies in the electricity markets, ownership and management status in the various countries, as well as competition with other technologies with balancing potential. Finally, we developed a new approach to display PHS tendencies in a compact picture. Building on the growth-share matrix Economics framework, we identified the strategic direction of PHS for each of the analysed countries. [ABSTRACT FROM AUTHOR]

Recognizing the issues of land shortage and growing concerns for protecting natural lands, installers and project developers, with the help of scientists and engineers, continuously try to locate alternative spots for photovoltaic (PV) system installations. In the present paper a novel approach is suggested and analysed: installing solar PV systems on the downstream face of existing dams. This approach provides advantages that could favour even large-scale systems with a capacity of several MWp. First, produced energy could cover water reservoirs' needs supporting energy-intensive processes as water pumping and treatment in a sustainable manner. Moreover, energy provision to inhabited areas near the dams and the subsequent creation of independent mini grids could mitigate energy poverty. In the case of hydroelectric dams, the so-created hybrid system (PV-hydro) could become notably efficient, because the intermittent solar energy would be counterbalanced by the flexibility of hydropower. Finally, we found a notable number of existing water reservoirs in Africa that are either under-utilized or non-powered. That unexploited energy potential can also be amplified by PV-system installation. The analysis included data collection from various sources. Datasets have been cross-checked and extended in the newly created GIS-based model, enabling the selection of the most suitable sites in South Africa, taken as case studies. Following their identification, the selected dams have been analysed using the PVGIS tool in order to estimate the annual energy production. The results have been very encouraging, indicating that PV systems on the face of dams are an advantageous option for renewable energy production. © 2015 The Authors. Progress in Photovoltaics: Research and Applications published by John Wiley & Sons Ltd. [ABSTRACT FROM AUTHOR]

The paper reviews recent research and development activities in the field of hydropower technology. It covers emerging and advanced technologies to mitigate flow instabilities (active and passive approach) as well as emerging magneto-rheological control techniques. Recent research findings on flow instabilities are also presented, especially concerning fluid-structure interaction and transient operating conditions. As a great number of the existing large-scale hydroelectric facilities were constructed decades ago using technologies that are now considered obsolete, technologies to achieve the digitalisation of hydropower are also analysed. Advances in the electro-mechanical components and generator design are presented; their potential role to adapt hydropower to the current operating conditions is also highlighted. The text explores current efforts to advance hydropower operation, mainly in terms of European projects. It provides a detailed overview of the recent efforts to increase the operational range of hydraulic turbines in order to reach exceptional levels of flexibility, a topic of several recent research projects. Variable speed hydropower generation and its application in pumped storage power plants are presented in detail. Moreover, revolutionary concepts for hydroelectric energy storage are also presented with the analysis focusing on underwater hydro storage and hydropower's hybridisation with fast energy storage systems. Efforts to minimise hydropower's environmental footprint are also presented via the utilisation of small-scale and fish-friendly installations. • Recent research and development activities in the field of hydropower technology are reviewed. • Novel concepts of hydropower energy storage are presented. • The perspective of the digitalisation of existing and new hydropower stations is analysed. • Fish-friendly, environmental-friendly and small-scale hydropower solutions are outlined. [ABSTRACT FROM AUTHOR]

• The European hydropower fleet composition was examined and described. • Different modernization practices (MP) were investigated, estimating a hydropower gain in Europe of 9.4%. • The MP were: dam heightening, new electro-mech. equipment, floating PV, digitalization and waterway retrofitting. • Reservoir interconnection and long-distance coordinated operation can increase storage by 168.9 TWh. About 50% of all hydropower plants (HPPs) worldwide were originally commissioned more than 40 years ago, so that the advanced age of the fleet is a major concern across all continents, and especially in Europe. The modernization of HPPs can generate several benefits in terms of generation, flexibility, safety, operation, and may have neutral or even positive implications for the environment. In this work, we appraise several options for the modernization of existing plants, with the exclusion of measures expected to increase the hydro-morphological pressure on water bodies (e.g. increase of withdrawals or new parallel waterways): dam heightening, head loss reduction in waterways, increase of weighted efficiency of electro-mechanical equipment, digitalization and inflow forecast, and floating photovoltaic (evaporation reduction). We provide an indicative estimation of the additional power and annual generation that could be obtained compared to the current condition. We estimate that the overall energy generation could be increased by 8.4% for European Union and 9.4% for the whole Europe by implementing the above-mentioned strategies. The additional energy gain achievable by increasing the inflow was discussed but not included in the above mentioned overall indicator, because it is very site-specific. The additional energy storage achievable by reservoir interconnection and coordinated operation has been estimated in literature as 169 TWh. This suggests that the modernization of HPPs can generate significant benefits in terms of energy, and should be considered as an important element of energy policy, also considering the additional benefits in terms of reliability and flexibility of the energy system that it may deliver. The modernization options considered here, insofar as not entailing a worsening of the hydro-morphological alterations, are also expected to cause limited or no conflict with the environmental objectives of water policies in Europe. [ABSTRACT FROM AUTHOR]