Climate change represents one of the major challenges of our century with great potential to alter water quality, and hence, find suitable solutions becomes a must. Stanca–Costesti reservoir is one of the most important in Romania and one of the most affected by the hydrologic variability. The studies regarding the trophic state of this reservoir are few, even if there are some environmental issues in its hydrological basin that could be further investigated. According to the National Administration “Apele Romane” (ANAR) yearly reports, the Stanca–Costesti reservoir is, from the trophic state point of view, an oligotrophic lake. The current research is based on chemical and some biological data collected over 10 years (ANAR) for the trophic state of the Stanca–Costesti reservoir, using the Carlson index. The research investigates the hydrological data and spans over 10 years that were classified into three categories, namely: wet year, normal year, and dry year and the influences generated by the contrasting weather (flow and temperature changes) on the trophic state of the lake. The research findings show that the trophic state of the lake is directly influenced by the hydrological variability, namely evolving to a hypertrophic status due to concentrations of nutrients. Moreover, over the years, according to ANAR data, the water quality in the reservoir alternated. Hence, at times, the quality of the water was poor, with possible negative influences on water usage. As a consequence, we proposed that the water quality be verified monthly, and this should be done by means of a more reliable method, such as a multiparameter index or multicriteria analysis.
The paper presents a variable speed solution for optimal operation of a group of Small Water Turbines integrated in a medium voltage AC grid. As the efficiency of hydro machines is dependent on the water flow, which usually exhibits a large variation, operation at variable speed is considered. Due to the fact that all hydro generators are AC machines, the connection to the 50 Hz power grid can be done using an AC/DC-DC/AC interface. This power electronics-based interface, additional to transferring the energy from the generator to the grid, will also operate as a reactive power and a harmonic voltage compensator. A small AC micro grid was designed, comprising an 45 kW Frances turbo group, an 7kW Diesel synchronous generator, an 1.2 kW Ballard Fuel Cell, an 1.5 PV solar panel, an 3kW energy storage acid lead battery and various loads.I.
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