Geotechnical gravity energy storage (GGES): A proof of concept using holistic numerical simulations

The global energy transition requires significant energy storage capacity to mitigate the natural fluctuations of renewable energy such as photovoltaic and wind power caused by alternating weather patterns. This paper presents the innovative concept of the so-called geotechnical gravity energy storage (GGES) system. In this concept, excess renewable electrical energy is stored as potential energy of an elevated mass of soil in the underground space using a pressurized fluid pumped in a soil-covered cavity. Due to the high pressure in the fluid, induced by an overburden height of several hundreds of meters, the resulting displacements and deformations at the ground surface can be kept small. A turbine regenerates the stored electrical energy on demand. Numerical simulations using a hypoplastic and a high-cycle accumulation constitutive model for sand are presented and demonstrate the system’s ability to store several MWh of energy combined with negligible energy losses within the soil, even after 40 000 simulated energy storage cycles. As a reference variant, a GGES system with a capacity of up to ≈ 5 MWh and a soil mechanical efficiency of η ≈ 98 % is investigated. The overall efficiency - including additional energy losses due to pipe friction and energy transition - of a GGES system is comparable to that of a conventional pumped hydro energy storage (PHES) system. The GGES concept is scalable, and much larger energy storage capacities can be achieved in reality. Notably, the efficiency of the GGES system increases with increasing lifetime and soil compaction effects occur. The GGES system shows positive degradation effects, which distinguishes it from most existing energy storage systems. The results provide a simple design formula for a GGES and depict the geometric and operation limits within which the long-term stability of the system is guaranteed. For systems with a height-to-radius ratio of H / R > 2 , operated at a soil mechanical efficiency of η > 95 % , the stability of the GGES system is demonstrated and failure can be excluded. • GGES can achieve both large energy capacity and high efficiency. • GGES is long-term stable for systems with geometric ratios H/R > 2, operated with a soil mechanical efficiency of η > 95%. • GGES is only slightly sensitive to soil mechanical constraints. • GGES exhibits positive aging effects without degradation of the energy capacity and the efficiency and leads to compaction effects on the overlying soil. • GGES can be designed practically using a simple formula, without complex numerical investigations.