Abstract
To achieve the carbon free electricity generation target for 2050, the penetration of renewable energy sources should further increase. To address the impacts of their unpredictable and intermittent characteristics on the future electricity grid, Pumped Hydro Energy Storage (PHES) plants should enhance their regulation capability by extending their continuous operating range far beyond the optimal normal working range. However, for the time being, the regulation capability of the new generation of PHES, equipped with reversible pump-turbines due to their cost-effectiveness, is limited at part load by instability problems. The aim of this paper is to analyse, during a pumping power reduction scenario, the onset and development of unsteady phenomena leading to unstable behaviour. A 3D transient numerical simulation was carried out on the first stage of a variable-speed two-stage pump-turbine from full load to the unstable operating zone by progressively reducing the speed from 100% to 88% rpm corresponding to a power reduction from full load to about 60% with a ramp rate of 1.5% per s. Two three-dimensional unsteady flow structures affecting the return channel and the wicket gates at the end of the first stage were identified and their evolution in the power regulation scenario was fluid-dynamically and spectrally characterized to determine the fluid-dynamical conditions causing the head drop in the hump zone.
Highlights
Even though renewable energy sources have largely increased in the last years, their penetration in the world electricity generation should become much more significant in order to contribute to the reduction of greenhouse gas emissions (GHG)
The electricity grid is still a highly centralized interconnected network consisting of energy generating systems, transmission lines and demand centres with a limited use of energy storage
In order to validate the accuracy of the numerical simulations, the experimental data obtained according to ISO standards from Dep
Summary
Even though renewable energy sources have largely increased in the last years, their penetration in the world electricity generation should become much more significant in order to contribute to the reduction of greenhouse gas emissions (GHG).The European Union policy has made great efforts towards developing these resources in response to environmental concerns, but their unpredictable and intermittent characteristics have restrained their deployment because of the negative impact on power system security, stability, reliability and efficiency [1]. Even though renewable energy sources have largely increased in the last years, their penetration in the world electricity generation should become much more significant in order to contribute to the reduction of greenhouse gas emissions (GHG). A significant energy storage capacity will be necessary to favour the deployment of an increasing share of renewable sources and to balance demand and supply continuously, by ensuring grid stability [1,2]. Pumped Hydro Energy Storage plants (PHES) certainly represent one of the most cost-effective large-scale storage technologies [3,4] with a cycle efficiency range of 75%–85% and competitive costs (800–1500€/kW 2016€) [5]. To face the more demanding performance of future electricity grids, PHES should increase their regulation capability by extending their continuous operating range far beyond
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