Hydropower remains a key renewable energy source in the pursuit of the decarbonization of the economy, although the relatively high potential impact of the hydro-morphological alterations it may cause poses significant concerns for aquatic ecosystems. In the last years, new technologies and practices have been increasingly adopted to minimize the impacts of hydropower plants, while improving efficiency and flexibility of energy generation. The overall effect of these innovations may be a more sustainable design and operation of hydropower, striking a better balance between the objectives of decarbonization and ecosystem protection. This contribution presents and discusses a few representative examples of hydropower installations from companies in Italy, France, Switzerland, Belgium and the USA, where solutions have been adopted in this direction. The case studies cover (1) ecologically improved and low head hydropower converters (Vortex turbine, Hydrostatic Pressure Machine, VLH and Girard-optimized turbines, hydrokinetic turbines), hydropeaking reduction (2) new control systems, governors and digitalization, (3) hydropower as a strategy for local sustainable development and (4) energy recovery in existing hydraulic infrastructures and aqueducts. It was found that better-governing systems can extend the life span of runners, for example avoiding the runner uplift during a trip. Digitalization can improve efficiency by 1.2%. New sustainable practices and turbines with better ecological behavior can minimize environmental impacts, like the reduction of fish mortality, improvement of fish habitat availability, reduction of oil for lubrication purposes and generation of economic incomes for local development. The use of existing structures reduces the total installation cost: examples are the total saving of 277 €/kW by reusing irrigation pipes and reservoirs, or the reduction of the investment period from 9 years to 6 years by turbining the environmental flow. Innovative low head hydropower converters can exhibit good ecological behavior, with reduced costs (<5000 €/kW) especially when installed in existing weirs. Results are discussed, contextualized and generalized to provide engineering data and tools to support future realizations of similar case studies; normalized costs, efficiency improvement, best practices and new technologies are discussed.

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Herein we describe the syntheses of a series of molybdate and polyoxomolybdate ionic liquids (ILs), their full spectroscopic characterisation (FT-IR, 1H-, 13C-, 31P- and 95Mo-NMR) and a comparison of their...

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A series of dihydroxybenzene‐derived ILs was synthesised via a halide‐free, eco‐friendly methodology and fully characterized. Their activity as single component catalyst towards synthesis of cyclic organic carbonates (COCs) via CO2 insertion into terminal epoxides was evaluated, observing that methyltrioctylammonium hydroquinolate, [N1888][HYD], was the most active catalyst in the proposed optimized conditions ([N1888][HYD] 10 % mol, T=120 °C, t=6 h, p0(CO2)=2.0 MPa, 12 examples, conversion >99 %, yield up to 98 %). Interestingly, [N1888][HYD] was also an active catalyst for CO2 insertion reactions with cyclohexene oxide (CHO), observing formation of both the COC and polycarbonate product. It is proposed that for p0(CO2)≥1.0 MPa, the catalytically active species is the hemicarbonate derivative of the hydroquinolate anion, active towards epoxide ring opening via an unusual hemicarbonate‐alkoxide pathway.