Layout of a flywheel UPS system

Intro to the Flywheel UPS: Powered by Motion

In the world of emergency power, your equipment is only as good as its ability to stay on when the lights go out. Most backup power comes in the form of generators or batteries and within these categories, the choices can be overwhelming in terms of size, load capacity, generator or UPS life, repair costs, etc. To make things easier, it helps to better understand what the main types of emergency power systems look like, how they operate, and what functions and applications they best serve before deciding what you need. Today we will look more closely at one of these emergency systems types, the Flywheel UPS. Let’s start with the basics.

Flywheel UPS- What is it?

First of all, what is a flywheel? A flywheel is defined as a mechanical device specifically designed to store rotational energy. Flywheels resist changes in their rotational speed by their momentum of inertia. This inertia is what makes the flywheel work. The amount of energy a flywheel can store is the square of its rotational speed. The way to increase or decrease the flywheel’s rotational speed is by applying a torque to its axis of symmetry. In the case of a flywheel UPS, its most common function is to convert the kinetic energy it stores to produce DC power. It also provides power conditioning and run-time in short bursts in the event of a power outage.

Flywheel technology is some of the oldest in existence. In the Neolithic Period, one of the first primitive flywheels was developed in the form of a spindle and an early potter’s wheel, to create vessels to store food and tools. In the Renaissance in Europe, Leonardo DaVinci developed fairly advanced flywheel models to demonstrate movement. During the Industrial Revolution, James Watt contributed to flywheel development in steam engine technology.

Modern Topology

Today’s flywheel technology is much more sophisticated, though it is still based on a simple premise of storing kinetic energy. Modern flywheel generators use a rotor made of steel or carbon-fiber. Newer systems use carbon-fiber composite rotors that have a higher tensile strength than steel and are typically much less heavy. The rotor acts as a motor, generator, and an energy storage system.

It is important to note that, due to its reliance on mechanized rotation to provide kinetic energy, this type of UPS cannot in any way sustain an extended run time. In fact, even when paralleled with other flywheels, it can typically only support critical loads from 10 to 30 seconds at a time.

what is a UPS


The Flywheel UPS is good for some very specific use cases. They are particularly well designed for harsh environments like a factory floor in manufacturing or in the oil and gas industry. They incorporate total protection from transient over-voltages, dips and sags to total power outages with no time constraints. They are also great for applications where you have “trash” power coming in and you are able to “clean” this power and provide a clean, stable sine wave on the output.

One of its best uses is for load leveling on larger battery systems.  This is accomplished by paralleling a flywheel with a traditional VRLA battery and using the inertia of the flywheel to help during a short duration and prevent constant discharge and recharge of batteries. Since a batteries life is measured in cycles, it can extend the life of a typical VRLA batter.  It will also likely save the organization space over a traditional UPS.

Many test labs use a flywheel in several motor generator sets for interrupting different currents. They can also be used in grid energy storage as a short-term spinning reserve for momentary grid frequency regulation, balancing sudden changes between supply and consumption. Wind turbines also use flywheels to store energy generated during off-peak hours or high wind speeds. One downside of using the flywheel UPS is it does take some time for it to get back up to inertia once its kinetic energy is used. Currently, flywheel UPS systems only represent less than 3% of the 3-phase UPS installed base (page 2, see diagram).

Flywheels have many benefits if used in the right situation. It’s best to talk with one of our experts at

Quality Power Solutions about your environment and what makes the most sense for your company or organization. Please contact us and let us help you find your right fit!

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  1. […] Flywheel UPS System: The life cycle for this type of system is typically around 20 years. Maintenance for this type of system is typically annual, IF the system contains no batteries. If the system DOES contain batteries, you must factor in the life cycle of battery replacement as a component of this system. The bearings on a flywheel UPS system may also need to be replaced every 5 to 8 years. This type of replacement requires specialized equipment and a prolonged downtime for the replacement, which can be very expensive. […]

  2. […] now we have examined flywheel UPS machines from several different angles: their history, how they work, and how to properly maintain them. We also need to examine the most obvious […]

  3. […] we discussed the history and basic workings of the Flywheel UPS system, but did you know that there are also several different types and configurations of these systems? […]

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