A. Odukomaiya, A. Abu-Heiba, K.R. Gluesenkamp, O. Abdelaziz, S. Graham, A.M. Momen
Oak Ridge National Laboratory/Georgia Institute of Technology,
Keywords: energy storage, compressed air, micro pumped-hydro storage, near-isothermal expansion/compression
Summary:Due to the increasing generation capacity from intermittent renewable electricity sources being brought on-line, and an electrical grid ill-equipped to handle the mismatch between electricity generation and use, there is a critical, growing need for advanced bulk energy storage technologies. Currently, pumped-storage hydroelectricity and compressed air energy storage are used for grid-scale energy storage, and batteries are used at smaller scales. However, prospects for expansion of these technologies are undermined by a number of challenges including but not limited to, geographic limitations (pumped-storage hydroelectricity and compressed air energy storage), low roundtrip efficiency (compressed air energy storage), and high cost (batteries). In addition to the above, pumped-storage hydroelectricity and compressed air energy storage are challenging to scale-down, while batteries are challenging to scale-up. Similarly to compressed air energy storage, the novel storage technology presented here is based on air compression/expansion. However, several novel features lead to near-isothermal processes, higher efficiency, greater system scalability, and the ability to site a system anywhere. GLIDES (Ground-Level Integrated Diverse Energy Storage) stores energy by compressing/expanding a gas (air) using a liquid (water) piston. The novel concept was recently introduced and extensively studied analytically. With the use of the liquid piston, GLIDES replaces the inefficient gas turbomachines used in conventional gas compression/expansion systems with high efficiency hydraulic machines. Promising results from physics based numerical system performance simulations led to the development of a 2 kWh proof of concept prototype system installed at Oak Ridge National Laboratory. The system consists of four major components, an atmospheric pressure water storage reservoir, a hydraulic pump/motor assembly, one or more high pressure vessels, and a hydraulic turbine/generator assembly. When electricity is cheap, or available from renewables, the high efficiency pump is used to pump a liquid inside one or more pressure vessels which have been pre-pressurized with a gas. As the liquid level rises, the gas is further pressurized and energy is stored. This charging process continues until electricity is no longer available, or the maximum allowable pressure is reached. When the stored energy is needed, the pressurized gas is allowed to expand, pushing the high pressure water out of the vessel, through a high efficiency hydraulic turbine which is coupled to an electrical generator and dispatches electricity. Furthermore, if low to medium temperature waste heat (for example, from the condensers of air-conditioning systems, solar-thermal hot water receivers, combined heat and power systems, geothermal wells, or waste heat exhaust from turbines or stacks) is available, that heat can be dispatched to further boost the gas pressure, increasing the amount of energy available for dispatch. The comprehensive simulation effort demonstrated an energy storage roundtrip efficiency (RTE) of up to 82% and energy density of up to 3.59 MJ/m3. The first report of experimental system performance is presented here.