Holistic simulation of a subsurface inflatable geotechnical energy storage system using fluid cavity elements. (November 2020) - Norlyk, Peter
Abstract: With the rapidly increasing capacity of renewable energy production, the volatile nature of, e.g., wind and solar power necessitates solutions for storing excess energy. A finite-element model for simulating a geomembrane energy storage system is developed, in order to aid the development of the system and provide first insights into the performance of the system. Conceptually, energy is stored by pumping water from a nearby surface reservoir into a subsurface reservoir confined by a geomembrane, which lifts the overlying mass of soil, thereby increasing the potential energy due to gravity. An axisymmetric finite-element model is developed employing fluid cavity elements and fluid exchange links to simulate inflow and outflow of the reservoir, which resembles energy storage and energy re-harvest, respectively. A sophisticated constitutive model for a granular soil is employed using a hypoplastic model with intergranular strain extension, which includes essential characteristics as stress and density dependency, critical-state behavior as well as stress reversals. Analysis of repeated storage cycles provides realistic but undesirable deformation patterns, encountered by increasing irreversible displacements with advancing cycles. The reliable results of the model directly provides estimates of energy efficiency and can serve as a tool for further development and optimization of the energy storage system.