The UPS system, at normal times, serves as an electric motor to control the flywheel to spin at its rated speed in a low-friction vacuum housing. Magnetic control reduces the weight borne by the lower part of the bearing, allowing efficient rotation by the heavy rotor to store kinetic energy with minimal power consumption. 　
During outages or under similar conditions, the system switches roles, serving as a generator to supply backup power for emergency load by converting the kinetic energy of the rotor (which continues spinning due to inertia) into electrical energy.

These flywheel UPS systems protect emergency load against all nine IEEE power disturbances: power failures, sags, surges (spikes), undervoltage, overvoltage, line noise, frequency variations, switching transients, and harmonic distortion. When used in combination with a generator, the systems operate for the time required to switch to generator power in the event of an emergency, ensuring stable, uninterrupted operation. In recent years, these systems have also been used to stabilize industrial microgrids and renewable energy sources. 

Examples: Data centers, healthcare and pharmaceutical industries, telecommunications/broadcasting, manufacturing, semiconductor industry, logistics, aviation, finance, leisure/casino facilities, microgrids

With the many options available for UPS energy storage, versatility is a key differentiator. Each application has its own requirements for how long a system must cover for outages; the solutions must be tailored to these needs. While energy-dense options are appealing for longer periods, power density is the key factor when rapid bursts of energy are needed for a minute or less.
Unlike conventional energy-dense alternatives, flywheel UPS systems stand out for unmatched sustainability, longevity, safety, compact size, and TCO.
Flywheels have earned a reputation for their outstanding reliability. They’re simpler than battery systems, with fewer parts prone to failure. This reliability allows flywheels to continue supplying power to critical equipment during outages.
Maintenance is minimal, reducing long-term operating costs. With flywheels, it is easy to visualize operating conditions, which adds to stable performance. These systems last longer than battery systems, allowing use over many years. They are also environmentally-friendly products—free of hazardous chemicals and concerns about ultimate disposal. They’re highly efficient and can reduce energy consumption.
　
These advantages set apart flywheel technology as a reliable, sustainable option for UPS systems that can effectively meet mission-critical power needs across many fields.

The parallel online architecture of flywheel UPS systems places the inverter and charger circuitry or transformer in parallel with the AC power supply. With this design, the power consumed is supplied directly from the grid while the UPS system's capacitors and electronic controls compensate for over- or under-voltages in the incoming power to eliminate transients, voltage fluctuations, and other disturbances. 
In other constant inverter power supply (double conversion) UPS systems, all power is rectified from AC to DC and inverted from DC to AC, ensuring a perfect sine wave and frequency protection on the output. However, this approach requires significant energy for inversion. In cases involving low load factors, the efficiency losses tend to be especially noticeable. Recent years have seen developments such as eco mode, which promises higher efficiency by relying on electrical grid power most of the time, but because power conditioning is completely abandoned, it may lead to long-term damage of protected loads. 
The flywheel UPS system also controls frequency fluctuation (kept as low as ±0.2 %) to provide compensation equivalent to that of a constant inverter power supply, but in a simpler, more energy-efficient design.

The parallel online architecture of flywheel UPS systems configures the inverter and charger circuitry or transformer in parallel with the AC power supply. With this design, the power consumed is supplied directly from the grid while the UPS system's capacitors and electronic control compensate for over- or under-voltages in the incoming power and eliminate transients, voltage fluctuations, and other disturbances. 
In other constant inverter power supply (double conversion) UPS systems, all power is rectified from AC to DC and inverted from DC to AC, ensuring a perfect sine wave and frequency protection on the output. However, this approach uses a significant amount of energy for inversion. In cases involving low load factors, the efficiency losses tend to be especially noticeable. Recent years have seen developments such as eco mode, which promise higher efficiency by relying on electrical grid power most of the time, but because power conditioning is completely abandoned, it may lead to long-term damage of protected loads. 
The flywheel UPS system also controls frequency fluctuation (kept as low as ±0.2 %) to provide compensation equivalent to that of a constant inverter power supply, but in a simpler, more energy-efficient design.

The high energy efficiency and less stringent cooling requirements of flywheel UPS systems can reduce their carbon footprint when in use. They also require up to 90 % less carbon to manufacture the necessary parts than lead-acid batteries.
And in contrast to the nearly 100 % steel content of the flywheel itself (the most recyclable material), lead-acid and lithium-ion batteries must be carefully disposed of and pose various environmental impact and pollution risks.