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 electricity storage concept which hybridizes the existing compressed-air (CAES) and pumped-storage (PSH) approaches to energy storage. Energy is stored by pumping a liquid into 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 liquid through a hydraulic 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. Analyses predict GLIDES roundtrip efficiencies in the 65-85% range. End-to-end analytical, transient, physics-based system models of various configurations of GLIDES have been developed and theoretical performance analyses completed. A first-generation 1.5 kWh prototype has been designed and built, and experimental characterizations and model calibration/validation completed. A second-generation, 1 kWh prototype which is mobile/portable and integrates spray cooling/warming to manage the heat of compression and cold of expansion as well as waste-heat integration has also been designed, built, and characterized. In addition to the above, the use of volatile fluids as an alternative working fluid to air is explored as a means of improving system RTE and ED. Some consideration is given to the choice and design of the energy recovery hydraulic machine. Finally, cost-analysis of the scale-up prospects of GLIDES is conducted.