Grid-scale pumped hydro energy storage for the low countries

Penetration of intermittent renewable energy sources into the power grid requires large-scale energy storage to ensure grid stability. Pumped Hydro Energy Storage (PHES) is among the most mature, environmentally friendly, and economical energy storage technologies, but has traditionally only been feasible at sites with large natural topographic gradients. ALPHEUS addresses this by developing reversible pump-turbines efficient at low heads, that operate between an enclosed inner basin (that functions as the upper or lower reservoir) and a shallow sea or lake

The contribution of low-head pumped hydro storage to a successful energy transition

The pan-European power grid is experiencing an increasing penetration of Variable Renewable Energy (VRE). The fluctuating and non-dispatchable nature of VRE hinders them in providing the Ancillary Service (AS) needed for the reliability and stability of the grid. Today’s grid is reliant on synchronous generators. In case of sudden frequency deviations, the inertia of their rotating masses contributes significantly to the stabilisation of the system. However, as the modern power grid is gravitating towards an inverter-dominated system, these must also be able to replicate this characteristic. Therefore, Energy Storage Systems (ESS) are needed along the VRE. Among the different ESS, Pumped Hydro Storage (PHS) can be identified as particularly convenient, given its cost-effective implementation and considerable lifespan, in comparison to other technologies. PHS is reliant on difference in altitudes, which makes this technology only available if suitable topographic conditions exist. The ALPHEUS project will introduce a low-head PHS for a relatively flat topography. In this paper, a grid-forming controlled inverter coupled with low-head PHS that can contribute to the grid stability is introduced, emphasising its ability to provide different AS, especially frequency control, through the provision of synthetic system inertia, as well as fast Frequency Containment Reserves (fFCR)

Low-head pumped hydro storage: A review of applicable technologies for design, grid integration, control and modelling

To counteract a potential reduction in grid stability caused by a rapidly growing share of intermittent renewable energy sources within our electrical grids, large scale deployment of energy storage will become indispensable. Pumped hydro storage is widely regarded as the most cost-effective option for this. However, its application is traditionally limited to certain topographic features. Expanding its operating range to lowhead scenarios could unlock the potential of widespread deployment in regions where so far it has not yet been feasible. This review aims at giving a multi-disciplinary insight on technologies that are applicable for low-head (2-30 m) pumped hydro storage, in terms of design, grid integration, control, and modelling. A general overview and the historical development of pumped hydro storage are presented and trends for further innovation and a shift towards application in low-head scenarios are identified. Key drivers for future deployment and the technological and economic challenges to do so are discussed. Based on these challenges, technologies in the field of pumped hydro storage are reviewed and specifically analysed regarding their fitness for low-head application. This is done for pump and turbine design and configuration, electric machines and control, as well as modelling. Further aspects regarding grid integration are discussed. Among conventional machines, it is found that, for high-flow low-head application, axial flow pump-turbines with variable speed drives are the most suitable. Machines such as Archimedes screws, counter-rotating and rotary positive displacement reversible pump-turbines have potential to emerge as innovative solutions. Coupled axial flux permanent magnet synchronous motor-generators are the most promising electric machines. To ensure grid stability, grid-forming control alongside bulk energy storage with capabilities of providing synthetic inertia next to other ancillary services are required

The Contribution of Low-Head Pumped Hydro Storage to a successful Energy Transition

The pan-European power grid is experiencing an increasing penetration of Variable Renewable Energy (VRE). The fluctuating and non-dispatchable nature of VRE hinders them in providing the Ancillary Service (AS) needed for the reliability and stability of the grid. Today’s grid is reliant on synchronous generators. In case of sudden frequency deviations, the inertia of their rotating masses contributes significantly to the stabilisation of the system. However, as the modern power grid is gravitating towards an inverter-dominated system, these must also be able to replicate this characteristic. Therefore, Energy Storage Systems (ESS) are needed along the VRE. Among the different ESS, Pumped Hydro Storage (PHS) can be identified as particularly convenient, given its cost-effective implementation and considerable lifespan, in comparison to other technologies. PHS is reliant on difference in altitudes, which makes this technology only available if suitable topographic conditions exist. The ALPHEUS project will introduce a low-head PHS for a relatively flat topography. In this paper, a grid-forming controlled inverter coupled with low-head PHS that can contribute to the grid stability is introduced, emphasising its ability to provide different AS, especially frequency control, through the provision of synthetic system inertia, as well as fast Frequency Containment Reserves (fFCR)

Drivetrain architectures for a mechanically decoupled contra-rotating reversible pump-turbine

With the rise of renewable energy production in the pan-European grid, the need for flexible energy storage is experiencing a rapid increase. Pumped hydropower storage has proven viability due to its long lifespan and cost-effectiveness. The ALPHEUS project will implement pumped hydropower storage for flat topographies to augment grid stability in adjacent regions. To ensure optimal efficiency and fast switching times in these low head applications, a contra-rotating axial Reversible Pump-Turbine (RPT) is designed. The runners will be driven by two separate Axial-Flux Permanent Magnet Synchronous Motors (AF-PMSM) to ensure optimal efficiency and flexibility at variable speed and flow rate. In this new setup, great attention is needed for the drivetrain architecture. The AF-PMSMs can be placed either outside or inside the water tube, using respectively tube elbows or bulbs. Furthermore, coaxial shafts allow the machines to be placed together, on one side of the RPT. This paper proposes four drivetrain architecture concepts, which are evaluated qualitatively based on their influence on RPT and AFPMSM performance as well as bearing arrangement

Axial flux PMSM power take-off for a rim-driven contra-rotating pump-turbine

Pumped hydropower storage (PHS) is a costeffective and mature energy storage technology. However, it has inherently been limited to locations with suitable topographies. Therefore, the ALPHEUS project aims to implement PHS for shallow seas and coastal environments with the goal to support grid stability. To ensure optimal efficiency and fast switching times in these low-head applications, a 10 MW Contra-Rotating (CR) axial Reversible Pump-Turbine (RPT) is designed, which has a rim diameter of 6.4 m and a high efficiency - maximum 84% and 90% for pump and turbine, over a large operating range. Furthermore, the RPT is rim-driven, which averts the hydraulic impact caused by shaft-driven systems. To ensure optimal efficiency at variable speed operation, the runners are driven by two separate Axial-Flux Permanent Magnet Synchronous Machines (AF-PMSMs). This paper proposes a Power Take-Off (PTO) design, where the electric machines and bearings are integrated in the rim of the CR RPT. The AF-PMSM dimensional design results in an outside diameter of 6.87 m. Next, active hydrostatic bearings are proposed due to their higher lifetime compared to roller bearings and better start-stop behaviour compared to hydrodynamic bearings. Finally, the advantages of the rim-driven PTO design with AF-PMSMs are elucidated by means of a comparison with the PTO of a shaft-driven CR RPT with similar power ratings. Next to the differences in hydraulic impact and bearing and sealing complexity, the active mass of both PTOs is examined. It is shown that the rotary mass and the total mass the rim-driven PTO is respectively three times and six times lower than that of the shaft-driven PTO, while the permanent magnet usage for both PTOs remains similar, with the total permanent magnet mass being 1.1% lower for the rim-driven PTO

Grid-scale pumped hydro energy storage for the low countries

Penetration of intermittent renewable energy sources into the power grid requires large-scale energy storage to ensure grid stability. Pumped Hydro Energy Storage (PHES) is among the most mature, environmentally friendly, and economical energy storage technologies, but has traditionally only been feasible at sites with large natural topographic gradients. ALPHEUS addresses this by developing reversible pump-turbines efficient at low heads, that operate between an enclosed inner basin (that functions as the upper or lower reservoir) and a shallow sea or lake