Abstract

Long-duration, grid-scale energy storage technologies provide a potential pathway to enable full penetration of renewables on the electricity grid and still maintain grid reliability and security. One approach is to use a pumped thermal energy storage (PTES) system, which is charged by using a heat pump (consumes electrical energy) to raise the temperature of a warm medium while lowering the temperature of a cool medium, creating hot and cold media stores, respectively. The PTES system is discharged by using a heat engine (produces electrical energy), which is the reverse of the charge cycle. PTES is a promising technology that offers high potential system performance, implementation versatility, no geological or geographical constraints, and leverages many existing component technologies. However, no such air-based system has been built and demonstrated at any scale, which is necessary for validation and eventual commercialization.

This paper describes the development of turbomachinery for a first-of-a-kind demonstration of a PTES system. At the kilowatt scale, no off-the-shelf machinery exists to meet all performance and operability requirements, so custom turbomachines were required — one for the charge (heat pump) cycle and one for the discharge (heat engine) cycle. Each machine comprises a compressor, turbine, and a motor/generator that has an operating speed range up to 55,000 rpm. The scope of this paper focuses on the design of the turbomachines, including description of the machine performance requirements, bearing and damper designs, rotordynamics, mechanical design, manufacturing, assembly, and commissioning activities.

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