Measurements and Modelling of the Discharge Cycle of a Grid-Connected Hydro-Pneumatic Energy Storage System

Luke Aquilina, Tonio Sant (), Robert N. Farrugia, John Licari, Cyril Spiteri Staines and Daniel Buhagiar
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Luke Aquilina: Department of Mechanical Engineering, University of Malta, MSD 2080 Msida, Malta
Tonio Sant: Department of Mechanical Engineering, University of Malta, MSD 2080 Msida, Malta
Robert N. Farrugia: Institute for Sustainable Energy, University of Malta, MXK 1531 Marsaxlokk, Malta
John Licari: Department of Electrical Engineering, University of Malta, MSD 2080 Msida, Malta
Cyril Spiteri Staines: Department of Electrical Engineering, University of Malta, MSD 2080 Msida, Malta
Daniel Buhagiar: FLASC B.V., Paardenmarkt 1, 2611 PA Delft, The Netherlands

Energies, 2024, vol. 17, issue 7, 1-33

Abstract: Hydro-pneumatic energy storage is a form of compressed-air energy storage that can provide the long-duration storage required for integrating intermittent renewable energies into electrical power grids. This paper presents results based on numerical modelling and laboratory tests for a kilowatt-scale HPES system tested at the University of Malta. This paper presents measurements of the discharge cycle, in which energy stored in compressed air within a pressure vessel is hydro-pneumatically converted back into electricity via a Pelton turbine and fed into the national electricity grid. The tests were conducted using a hydraulic turbine operated under different fixed-turbine rotational speed settings, with the pressure being allowed to decrease gradually during the HPES system’s discharge cycle. The system’s overall efficiency accounted for flow losses, turbine inefficiencies, and electrical losses. The tests showed that this efficiency was practically independent of the compressed-air pressure of specific water turbine runner speeds, despite the water turbine operating at fixed speeds. A numerical model developed in MATLAB Simulink (R2022a) was also presented for use simulating the hydraulic performance of the system during the discharge cycle. The model used secondary loss coefficients for the hydraulic circuit and derived velocity coefficients from computational fluid dynamics (CFD) for the Pelton turbine nozzle. We achieved very good agreement between the predictions based on numerical modelling and the measurements taken during laboratory testing.

Keywords: hydro-pneumatic energy storage; Pelton turbine; numerical modelling; computational fluid dynamics; experimental testing (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2024
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