A Review of Flywheel Energy Storage System Technologies

Overview

The review asks how flywheels contribute to power quality and stability in grids made more complex by renewable energy. It examines flywheel rotors, motor types (induction, permanent-magnet), mechanical, magnetic and superconducting bearings, power-electronic converters and application areas, and also covers the use of machine learning, digital twins and data-driven methods for simulation, fault prediction and life assessment.

The comparison table gives flywheel efficiency of 85-95% versus 70-80% for chemical batteries; specific power of 180-1800 W/kg versus 100-700 W/kg; discharge time of 15 s-15 min; service life above 20 years versus 3-15 years; and a maintenance cycle above 10 years versus under 6 months. Operating temperature range is -40 to +50 °C, with low environmental requirements and no contamination. Since about 97% of AC voltage flicker events last under 3 s and standby generators start in under 10 s, the authors argue a short-duration high-power flywheel can completely replace a battery in the UPS bridging role.

Commercial examples include Active Power's 250-2000 kW CleanSource UPS flywheel series and SatCon's 315-2200 kVA rotary UPS; Piller installed a 7 kWh/5 MW flywheel at a Dresden semiconductor plant to guarantee 5 s of ride-through. Cited UPS flywheels run at 7700 rpm (Active Power), 36,000 rpm (VYCON, magnetic bearings) and 53,000 rpm (Powerthru).

Limits: moving parts introduce more uncertainty in failure modes than batteries, especially for high-speed composite rotors, and carbon-fibre cost slows adoption, with high-strength steel rotors favoured for large stationary use. As a review it has no new measurements, and comparison values are compiled from different sources.

Key points

1. Comparison table: flywheel efficiency 85-95% vs 70-80% for chemical batteries; specific power 180-1800 W/kg vs 100-700 W/kg; discharge time 15 s-15 min; service life >20 years vs 3-15 years; maintenance cycle >10 years vs <6 months.
2. Flywheel operating temperature range is -40 to +50 °C, with low environmental requirements and no contamination.
3. Commercial examples: Active Power's 250-2000 kW CleanSource UPS flywheel series and SatCon's 315-2200 kVA rotary UPS.
4. About 97% of AC voltage flicker events last under 3 s and standby generators start in under 10 s, so the authors argue a short-duration high-power flywheel can completely replace a battery in the UPS bridging role.
5. Piller installed a 7 kWh/5 MW flywheel at a Dresden semiconductor plant to guarantee 5 s of ride-through; UPS flywheels run at 7700 rpm (Active Power), 36,000 rpm (VYCON, magnetic bearings) and 53,000 rpm (Powerthru).
6. Moving parts introduce more uncertainty in failure modes than batteries, especially for high-speed composite rotors; carbon-fibre cost slows adoption and high-strength steel rotors are favoured for large stationary use.

Using it in design

• In UPS designs that only need bridging until the generator starts, evaluate a flywheel as a battery alternative, checking that a 15 s-15 min discharge range and a generator start under 10 s are adequate for the duty.
• In total-cost-of-ownership comparisons of flywheel versus VRLA or Li-ion, show efficiency, service life and maintenance cycle (over 20 years and over 10 years versus 3-15 years and under 6 months) as separate columns.
• Add moving-part failure modes and containment requirements for high-speed rotors to the risk analysis and layout decision.

Who should read it

Electrical designers and storage specialists choosing between flywheel and battery as UPS bridging technology.

Document contents

1. 1. Introduction
2. 2. Installed Capacity
3. 3. The Operation Principles and Components of Flywheel Energy Storage Systems (2.1 Structure, 2.3 Flywheel Rotors, 2.4 Flywheel Motors: induction and permanent-magnet, control; 2.5 Flywheel Bearings: mechanical, magnetic, research on bearings; 2.6 Power Electronics)
4. 4. Flywheel Energy Storage System Applications (3.1 Power Quality, 3.2 High-Quality Uninterruptible Power Supply, 3.3 Pulse Power Supply, 3.4 Energy Recovery, Storage, and Utilization, 3.5 Commercial FESS Systems and Advantages)
5. 5. Achievements, Challenges, Future Trends, and Case Study (4.1 Achievements and Challenges, 4.2 Future Trends: material and component optimization, control systems, loss, failure modes and containment, safety and longevity, hybrid systems, artificial intelligence; 4.3 Case Study)
6. 6. Conclusions

Related standards

• IEC 62040-3
• IEC 88528-11

Read the document

Publication details

Authors

Kai Xu; Youguang Guo; Gang Lei; Jianguo Zhu

Publisher

Energies (MDPI AG)

Year

2023

Volume

16

Issue

18

Pages

6462

Document language

English

Source type

Scientific

Access

Open licence — downloadable

DOI

10.3390/en16186462

Licence

CC BY 4.0 — share with attribution

Licence evidence

www.mdpi.com

Citation