Search

Horizontal bar racks have been used as trash racks at hydropower plants since the 1920s. With the installation of the first horizontal bar rack bypass system at a hydropower plant as a downstream fish passage facility in 2006, these racks rapidly gained importance as fish protection measures. Since then, they have been installed at more than 100 small- to medium-sized hydropower plants in Europe. Despite the large number of installed racks, systematic investigations of the head losses and velocity fields were missing. On the basis of detailed hydraulic experimentation with a large number of rack parameters and including up-to-date foil-shaped bars, the layout of horizontal bar racks and their hydraulic performance were assessed in the current study. This paper reports the results of the rack head loss investigation, whereas the accompanying paper entitled Velocity Fields at Horizontal Bar Racks as Fish Guidance Structures focuses on the up- and downstream velocity fields. By applying foil-shaped bars instead of rectangular bars, the loss coefficient was reduced by more than 40%, depending on the rack configuration. Bottom and top overlays are used to increase the guidance efficiency for fish, sediments, and floating debris. However, the altered flow field results in increased head losses. A new set of equations is proposed to predict head losses for current horizontal bar racks, including overlays for various hydropower plant layouts. The predictions are compared to literature data. [ABSTRACT FROM AUTHOR]

Horizontal bar racks used as fish protection measures at hydropower plants have rapidly gained importance in recent years. Despite the large number of installed racks in Europe, systematic investigations of the hydraulic losses and velocity fields were missing. To fill these research gaps, the hydraulic performance of horizontal bar racks was systematically investigated in a laboratory flume for a large number of rack parameters and different hydropower plant layouts. The results of the head loss assessment are published in a paper entitled Head Losses of Horizontal Bar Racks as Fish Guidance Structures, whereas the present paper focuses on the velocity fields. The measurements show that the bar shape, the horizontal approach flow angle, and the clear bar spacing have only a minor effect on the velocity fields. In contrast, bottom and top overlays might enhance the fish guidance efficiency for bottom and surface oriented fish, while the asymmetric downstream velocity field can reduce turbine efficiencies. The hydropower plant layout strongly affects the approach flow field to horizontal bar racks. For block-type hydropower plants, the installation of a dividing pier or partial opening of the spillways improves the flow field for better fish guidance. [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]