Underground pumped hydroelectric energy storage in Wallonia (Belgium) using old mines - Hydraulic modelling of the reservoirs

Pumped Storage Hydroelectricity (PSH) is a well-known and efficient technology to store and release various amounts of electricity. To overcome the problem of available land surface to create new reservoirs, an alternative consists in using underground volumes to build so-called Underground Pumping Storage Hydroelectricity (UPSH) plants. A research project is currently investigating the feasibility of such UPSH plants in Wallonia (Belgium) using abandoned mines and underground quarries. The paper presents the main features of this multidisciplinary project and focuses on the numerical models developed specifically to consider the reservoirs’ hydraulics. Indeed, the detailed prediction of the water mass movements in the reservoirs is a key element of a feasibility analysis, as they may affect the turbomachines operation as well as the solicitations of the reservoirs limits. On the other hand, such prediction is challenging because of the complex geometry, the continuous discharge variations and the possible exchanges with the surrounding soil or the interaction with air in underground reservoirs. The application of the hydraulic model to an abandoned slate quarry highlights the usefulness of the approach and also its limitations.