When flywheels make sense and when they don’t
April 9, 2025
Flywheels have long been a key part of machines and vehicles, from smoothing out engine power to stabilizing generators. But today, these spinning discs are stepping up as energy storage powerhouses. In this blog, let’s dive into how these mechanical devices are evolving into a key solution for modern energy challenges.
What is a flywheel?
A flywheel is a mechanical energy storage system that captures and stores kinetic energy. At its core, it’s a rotating mass, typically a rotor, that spins at very high speeds. When energy input exceeds demand, the surplus energy accelerates the flywheel. When demand spikes, the flywheel decelerates slightly, releasing the stored energy almost instantly.
This makes flywheels ideal for bridging short but intense power demands. Instead of oversizing generators or drawing unnecessarily from the grid, a flywheel smooths out peaks and troughs in energy consumption. It offers precise, immediate power—without relying on chemical storage.
When to use flywheels (and when not to)
Flywheels are engineered for scenarios that require fast, high-power energy delivery in short bursts. They respond almost instantly, handle millions of cycles without degradation, and perform reliably across a wide temperature range. These qualities make them ideal for applications with frequent power spikes or variable loads—such as operating cranes, industrial shredders, or stabilizing small generator systems on dynamic sites. Some of the key advantages include:
Instantaneous power delivery with response times as fast as 0.03 seconds enabling real-time load balancing
Exceptional cycle life over 15 million cycles with no loss in performance, ideal for high-frequency applications
Low maintenance due to minimal wear from reduced friction and no chemical aging
Temperature resilience with reliable performance from -20°C to 45°C without degradation
However, flywheels are not designed for long-duration energy storage. This limitation arises from several technical factors such as, limited energy density, high self-discharge rates and mechanical stress. Alternative solutions are therefore more appropriate for energy storage that spans hours or days
Batteries for the long haul
Flywheels are ideal for quick power bursts, but what about when energy needs to be stored for longer durations? This brings us to batteries, a complementary technology built for sustained, reliable energy delivery.
Batteries offer a distinct advantage when it comes to longer-duration, steady energy discharge. Technologies such as lithium-ion, sodium-ion, and flow batteries offer high energy density and are increasingly cost-competitive. They are ideal for storing kilowatt-hours to megawatt-hours of energy for several hours or even days, that can be released gradually. This makes batteries a go-to solution for consistent power delivery. Their ability to deliver energy independent of immediate input makes them essential for processes such as:
Grid backup during outages or periods of instability
Overnight storage of renewable energy, such as solar or wind
Load shifting, where energy generated during off-peak hours is stored for use during peak demand
Off-grid systems, where prolonged autonomy is critical
Nevertheless, batteries also face limitations such as finite cycle life, degradation over time (especially in high-cycling applications), and sensitivity to temperature extremes.
A hybrid solution
In practice, a hybrid system brings out the strengths of both technologies. By integrating flywheels and batteries, businesses can tap into the rapid power bursts provided by flywheels while benefiting from the consistent, long-term energy storage of batteries. This combination optimizes energy efficiency, meeting both short-term power needs and long-duration demands.
On a construction site, for example, a flywheel can absorb daytime power spikes from cranes and compressors, while batteries supply steady power to site offices and lighting at night. This synergy enables smarter generator downsizing, improved fuel efficiency, and reduced CO₂ emissions. Certainly making it a powerful solution for mobile and temporary energy setups.
Use case examples of flywheels
Tower cranes on construction sites
Traditional crane operations often require oversizing a diesel generator to handle peak loads. By pairing a 150 kVA generator with a flywheel instead of using a 250 kVA unit, diesel use is reduced significantly, without sacrificing performance. The result: reduced costs and quieter operation.
High-rise demolition
Demolition sites often require bursts of power for equipment like hoists, dust control, and machinery. Rather than relying on a larger 300 kVA generator to handle these power spikes, a smaller generator paired with a flywheel handles the surges more efficiently, reducing the need for extra fuel and emissions.
Urban redevelopment projects
Construction in cities must meet noise and emissions regulations. By integrating flywheels, contractors are able to downsize their generators across multi-year projects. The result: quieter sites, cleaner air, and full regulatory compliance.
Let’s talk smart energy
In conclusion, flywheels represent a new chapter in energy storage: one that prioritizes speed, precision, and sustainability. Their ability to reduce generator size, stabilize energy delivery, and cut emissions makes them a powerful tool for forward-thinking businesses.
Curious how flywheels could fit into your operations? Explore flywheel suppliers on our marketplace.
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