SUMMARY

Increasing the penetration of renewable electricity while ensuring grid stability requires low-cost, high roundtrip efficiency energy storage solutions. GLIDES (Ground-Level Integrated Diverse Energy Storage) is a novel mechanical energy storage concept developed at Oak Ridge National Laboratory that hybridizes the existing compressed-air (CAES) and pumped-storage (PSH) approaches to energy storage. Energy is stored by pumping a liquid into high pressure vessels which are pre-pressurized with a gas, until the gas pressure reaches the maximum system operating pressure. Energy is then extracted by allowing the high pressure gas to expand, pushing the high-head water through a Pelton turbine coupled to an electrical generator dispatching electricity. In addition to electrical energy input via the hydraulic pump, the system can also be hybridized to receive heat as an input. Low/medium temperature heat can be utilized to further boost the gas pressure, increasing roundtrip efficiency (RTE) and energy density (ED). GLIDES is scaleable, relatively low cost and de-couples the energy capacity from the power capacity, a challenge faced with existing storage solutions. Initial analyses predict that GLIDES could achieve roundtrip efficiencies in the 65-85% range. Analytical, transient, physics-based system models of various configurations of GLIDES have been developed and theoretical performance analyses completed. A 1.5 kWh prototype has been designed and built, and initial experimental characterizations and model calibration/validation completed. Additional work will include continued parametric testing of prototype, design improvement/optimization of the gas thermodynamic cycle to improve system RTE and ED, performance characterization and design improvement of a unique very high-head, very low-flow Pelton turbine, and thermo-economic analysis of system scale-up to kW/MW scales.