Abstract

Current efforts to increase the share of renewable energies entail a greater need for energy storage to ensure stability of the energy system. One possibility to balance fluctuating energy production is the use of pumped hydropower storage (PHS), a method of storing energy by using water in a two-reservoir system. In abundance of energy, excess energy is used to pump water into a higher reservoir. This allows to convert the potential energy of the water into electricity when energy production from renewable energy sources is low.

However, building PHS systems impacts the environment, especially by changing water temperatures, oxygen concentrations and inducing rapid changes in water level. This study looks at how water layers of different temperatures (called thermal stratification) are impacted in the upper reservoir, when connected to a PHS system.

A 3D hydrodynamic model of a generic PHS facility was developed and used to test the influence of the temperature and the vertical location of the inflowing water. While pumping height was shown to be of minor importance, inflow temperature could be identified as a main driver for reservoir temperature fluctuations, either impacting particularly the top layer (cold inflow) or the bottom layer (warm inflow). While pumping cold water might be advantageous by inducing mixing further into the reservoir, and thereby increasing oxygen content, the strong temperature fluctuations might disturb the ecosystem.