Abstract
Energy storage through hydropower leads to free surface water waves in the connected reservoirs. The reason for this is the movement of water between reservoirs at different elevations, which is necessary for electrical energy storage. Currently, the expansion of renewable energies requires the development of fast and flexible energy storage systems, of which classical pumped storage plants are the only technically proven and cost-effective technology and are the most used. Instead of classical pumped storage plants, where reservoirs are located on the surface, underground pumped storage plants with subsurface reservoirs could be an alternative. They are independent of topography and have a low surface area requirement. This can be a great advantage for energy storage expansion in case of environmental issues, residents’ concerns and an unusable terrain surface. However, the reservoirs of underground pumped storage plants differ in design from classical ones for stability and space reasons. The hydraulic design is essential to ensure their satisfactory hydraulic performance. The paper presents a hybrid model study, which is defined here as a combination of physical and numerical modelling to use the advantages and to compensate for the disadvantages of the respective methods. It shows the analysis of waves in ventilated underground reservoir systems with a great length to height ratio, considering new operational aspects from energy supply systems with a great percentage of renewable energies. The multifaceted and narrow design of the reservoirs leads to complex free surface flows; for example, undular and breaking bores arise. The results show excessive wave heights through wave reflections, caused by the impermeable reservoir boundaries. Hence, their knowledge is essential for a successful operational and constructive design of the reservoirs.
Highlights
Nowadays, pumped storage plants are the only technically proven and cost-effective energy storage technology and are the most used [1,2]
This paper describes a 3D numerical simulation, using the software OpenFOAM for the analysis of the hydrodynamic processes in the underground pumped storage reservoirs
The hybrid model is suitable for the analysis of complex hydrodynamic processes in underground pumped storage reservoirs, which is shown amongst others through the small deviations between the results of physical and numerical modelling (
Summary
Nowadays, pumped storage plants are the only technically proven and cost-effective energy storage technology and are the most used [1,2]. In case of a surplus of electrical energy, pumps move water from a lower reservoir to an upper reservoir, where it is saved in the form of potential energy. In case of electrical energy demand, the water flows inversely; through energy conversion, the machines generate electrical energy. For the height design of the reservoirs, a calculated freeboard avoids overtopping. It consists of the maximum wave height, which depends on the occurring wind and the reservoir design, and a safety margin [3]. Research into the effects of hydropeaking is ongoing [4]
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