Table 1.

Typical characteristics of flywheels.

Characteristics	Low-speed flywheel (LSF)	High-speed flywheel (HSF)	Micro high-speed flywheel (micro-HSF)
Operating speed	<10,000 rpm	>10,000 rpm	>10,000 rpm
Rotor composition	Steel	Carbon fiber composite	Carbon fiber composite
Bearing type	Conventional	Low friction	Conventional
Typical specific energy	∼5 Wh/kg	Up to 100 Wh/kg	∼10 Wh/kg
Typical weight	n/a (stationary equipment)	n/a (stationary equipment)	15–60 kg
Expected (full depth) discharge cycles	105–107	105–107	105–107
Expected lifetime	∼20 years	∼20 years	∼20 years

Sources: based on Bolund et al., 2007, Hadjipaschalis et al., 2009, Doucette and McCulloch, 2011, Dhand and Pullen, 2013, Akinyele and Rayudu, 2014, and Mahlia et al. (2014).