Power Storage Systems- Flywheel

Kinetic Flywheel Energy Storage System (K-FESS)

Kinetic Battery 101 Background: Kinetic batteries (in the form of flywheels) have been in operation since about 2400 BC when ancient Egyptian potters would spin-up their stone potter’s wheels. In the years between 1800 and 1950, traditional steel flywheels gained application areas in train, car and bus transportation, and smoothing power draw from electrical sources. Modern flywheel systems began in the 1970’s with systematic improvements utilizing high strength composite materials, magnetic lift bearings, efficient power electronics and modern control systems. Modern flywheels are primarily used to recoup power in vehicle regenerative braking (<1KWh), in server farm Uninterruptable Power Supplies (1-3 KWh) and in large scale utility Frequency Regulation systems (>100 KWh).

Modern and developing systems use high tensile strength composites to make a spinning rotor operate between 16,000 and 50,000 rpm where energy is transferred to and from the spinning rotor by a high speed motor/generator. Electrical power is converted by the motor/generator to kinetic energy and is stored in the spinning rotor by increasing its rotational speed. On demand, the kinetic energy can be withdrawn from the spinning rotor by slowing it down and converting kinetic energy back to electrical power. Round trip energy efficiency with current commercial systems ranges from 85% to 92% (compared with 70-85% for chemical battery systems).

General Flywheel Operation Overview:

  • A fully composite rotor design, minimizing the danger of traditional failure modes (no high speed axial shards)
  • Designed primarily for deployable, but stationary applications
  • Contain no hazardous materials and are fully recyclable
  • Contain no hazardous materials and are fully recyclable
  • Systems are temperature, humidity and weather insensitive
  • Allow for virtually unlimited, 99% depth of discharge (DOD) cycles
  • 20+ year operational life with 170,000 hrs MTBF of the rotor unit

GTL specific K-FESS specifications:

  • K-FESS Gen-1 energy densities of 250-300 watt-hr per kg are typical, allowing for lighter weight and smaller volume energy storage units. Developmental Gen-2 and Gen-3 units are designed for 500 and 1000 watt-hr/kg
  • Meeting power requirements in the 15-50 KWh range per unit, up to 250KW power throughput
  • Units are modular and capable of being installed in parallel to meet higher user power requirements
  • Utilizes permanent magnetic lift bearings and a vacuum sealed enclosure to create a virtually frictionless rotor spinning environment (<1% power loss)
  • Designed under the value engineering principles of KISS (Keep It a Simple System) focusing on minimal maintenance and a “plug-n play” alternative or replacement for traditional chemical batteries

BIGGEST ADVANTAGE over chemical batteries:

  1. 20 year lifecycle costs are up to x5 less (no required replacements of exhausted chemical batteries)
  2. Simplified maintenance, operation and monitoring
  3. Real-time power status based on flywheel rotational speed vs. voltage based estimate of chemical batteries
  4. True energy storage levels and availability. What you order is what you get for the unit’s 20+ year life.
  5. Kinetic Batteries have no issues with temperature degradation, end-of-life losses, rapid charge/discharge losses or high cycle capability losses which plague chemical battery systems.

Answers to Common Flywheel Questions:

What is the Storage and Power Capacity?
Current designed capability includes 15, 25 and 50 KWh modular units with throughput up to 250 KW than can be combined in parallel for user specified storage and power requirements
What is the Load Cycle Range?
With daily use, over 35,000 charge/discharge cycles are available over a 20 year period at a 99% depth of discharge
What are the Cost Advantages?
Initial purchase costs: Equivalent to an Li-ion chemical battery system
20 year Lifecycle cost: 2.5x to 5x less than Li-ion system, due to no chemical battery replacements
What about a Challenging Climate at the operational site?
K-FESS unit designs are sealed, plug-n-play units, which are insensitive to temperature, humidity and weather. Basic maintenance is to keep the motor/generator shielded from rain and its heat sink radiator fins free of dust and collected debris.

Additional KFESS Information


Please Contact:
Dr. James Clegern, PhD
GTL Engineering Manager & K-FESS project manager
james.clegern@gtlcompany.com