Flywheel Energy Storage for Automotive Applications

Abstract

A review of flywheel energy storage technology was made, with a special focus on the progress in automotive applications. We found that there are at least 26 university research groups and 27 companies contributing to flywheel technology development. Flywheels are seen to excel in high-power applications, placing them closer in functionality to supercapacitors than to batteries. Examples of flywheels optimized for vehicular applications were found with a specific power of 5.5 kW/kg and a specific energy of 3.5 Wh/kg. Another flywheel system had 3.15 kW/kg and 6.4 Wh/kg, which can be compared to a state-of-the-art supercapacitor vehicular system with 1.7 kW/kg and 2.3 Wh/kg, respectively. Flywheel energy storage is reaching maturity, with 500 flywheel power buffer systems being deployed for London buses (resulting in fuel savings of over 20%), 400 flywheels in operation for grid frequency regulation and many hundreds more installed for uninterruptible power supply (UPS) applications. The industry estimates the mass-production cost of a specific consumer-car flywheel system to be 2000 USD. For regular cars, this system has been shown to save 35% fuel in the U.S. Federal Test Procedure (FTP) drive cycle.

Reluctance Machine for a Hollow Cylinder Flywheel

“…A new era of high-speed flywheel energy storage (FES) started with the advent of carbon composite flywheels, a technology that has become more viable due to a trend of decreasing costs of power electronics, position sensors (for magnetic bearings) and microprocessors [1]. The commercial potential for FES systems has recently gained attention in various applications.…”

“…FESs are used to provide fast regulation power for maintaining the grid frequency, decreasing the use of inefficient coal plants with low ramp rates for the task. On a distribution grid and end customer level, FESs are used to improve power quality for industries and data centers [1].…”

“…Assuming a requirement of 10 6 cycles, the battery system weight would be increased to 20 kg, and with a discharge rate of 1C, the maximum power is then only 4 kW. To meet the power requirements combined with cycling properties, the system weight would have to be increased to 150 kg, which is 10-times heavier than a modern flywheel system [1]. Li-ion batteries can be and are currently used in F1 racing at higher power levels, but the battery life becomes very limited.…”

“…The specific energy of state-of-the-art automotive FESs (GKN Hybrid Porsche GT3R Flywheel [6]) is 2.7-times larger than state-of-the-art automotive EDLCs (Maxwell 125V Heavy Transportation Module [7]), while retaining a specific power 1.8-times larger [1]. However, FESs are considered to be systems of high complexity, when compared to batteries and supercapacitors.…”

Optimal Power Management Strategy for Energy Storage with Stochastic Loads

“…Flywheels and supercapacitors are more suited for the high power flows deriving from the hoist motor (both when motoring and generating), and they have been the subject of multiple studies [12,[14][15][16][17]. Flywheel energy storage systems (FESSs) in particular have been found particularly suited for this task, as they show similar performance to supercapacitors, while being characterised by excellent ageing characteristics, which are independent of the charge rate or depth of discharge [1,18], allowing their lifetime to match that of the portal frame. Their disadvantage is high standing losses, which are particularly evident in more resilient designs (such as the use of normal ball bearings instead of magnetic bearings), as are the ones used on cranes; however, this does not affect the use for short power loads, and it only requires the storage to be charged shortly before use.…”