Parametric assessment of hydrochemical changes associated to underground pumped hydropower storage

Abstract

Underground pumped hydropower storage (UPHS) using abandoned mines is an alternative to store and produce electricity in flat regions. Excess of electricity is stored in form of potential energy by pumping mine water to a surface reservoir. When the demand of electricity increases, water is discharged into the mine (i.e., underground reservoir) through turbines producing electricity. During the complete operational process of UPHS plants, hydrochemical characteristics of water evolve continuously to be in equilibrium successively with the atmosphere (in the surface reservoir) and the surrounding porous medium (in the underground reservoir). It may lead to precipitation and/or dissolution of minerals and their associated consequences, such as pH variations. Induced hydrochemical changes may have an impact on the environment and/or the efficiency (e.g., corrosions and incrustations affect facilities) of UPHS plants. The nature of the hydrochemical changes is controlled by the specific chemical characteristics of the surrounding porous medium. However, the magnitude of the changes also depends on other variables, such as hydraulic parameters. The role of these parameters is established to define screening criteria and improve the selection procedure of abandoned mines for constructing UPHS plants. This work evaluates the role of the main hydrogeological factors for three different chemical composition of the porous medium. Results are obtained by means of numerical reactive transport modeling. Potential impacts on the environment (mainly on groundwater and surface water bodies) and on the efficiency of the UPHS plants vary considerably from a hydraulic parameter to another showing the need for a detailed characterization before choosing locations of future UPHS plants.

The Impact of Hydrogeological Features on the Performance of Underground Pumped-Storage Hydropower (UPSH)

“…Previous studies have investigated the role of the hydrogeological parameters on the potential impacts induced by UPSH in the underground medium [16,30]. The present investigation goes further and shows how the K controls the potential environmental impacts on surface water bodies and on the global η of the plant.…”

“…However, since mines are generally not waterproofed, it is expected that water exchanges will occur between the underground reservoir of UPSH plants and the surrounding groundwater systems [28]. This fact may entail negative consequences in terms of the environmental impacts [29][30][31] and for the efficiency (η) of UPSH [32]. We refer to η as the ratio between the energy used for pumping water from the underground reservoir and the energy generated when water is discharged from the upper reservoir under ideal conditions.…”

Hydrodynamical and Hydrochemical Assessment of Pumped-Storage Hydropower (PSH) Using an Open Pit: The Case of Obourg Chalk Quarry in Belgium

“…In practice, however, given the flows involved, turbulence in the upper reservoir could reduce these deposits. Overall, the volume of precipitated minerals can be relatively important and periodical cleaning tasks could be needed, which would affect the global efficiency of the PSH plant [9,32] pH values in the upper reservoir increased drastically during the first pumpingdischarge cycle as a result of CO 2 degassing and calcite precipitation. After the first cycle, pH remained relatively constant throughout the following cycles, oscillating between 8.16 and 8.18.…”

Underground Hydro-Pumped Energy Storage Using Coal Mine Goafs: System Performance Analysis and a Case Study for China

“…As already known, most coal contains various amounts of (0.5-3%) sulfide that exists mainly (60-70%) as pyrite minerals. The elevated pH level can cause the precipitation or co-precipitation of metal ions such as aluminum (Al), cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), lead (Pb), and zinc (Zn) contained in the mine water and result in sediments in the seepage channels and reduce the permeability of rock mass, thus blocking the fluid exchange within the goaf (Pujades et al, 2019).…”