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a b s t r a c tThe integration of wind power in power systems results in a reduction in greenhouse gas emissions. Thus, it has a positive environmental impact. However, the operation of these power systems becomes increasingly complex, owing mainly to random behaviour of the wind.In the case of island power systems, this problem is even more difficult. The traditional solution is to use diesel generators as an alternative power supply. For a wind-only power supply, an energy storage system is required. If the topography of the island makes possible the use of pumped storage hydropower plants, this is, nowadays, the most suitable energy storage system. This paper presents a novel method of Pelton turbine operation with no water flow, as a way to provide fast power injection in the case of an abrupt wind power decrease, or a wind-generator trip. This operation mode allows maximizing wind power penetration in a reliable and efficient way. This method has been validated by computer simulations, and will be tested during the commissioning of a combined wind-pumped storage power plant in an autonomous power system, on a small island.

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.