How This Mechanical Battery is Making a Comeback

This is the Dinglun Flywheel Energy  Storage Power Station. At 30 MW, this is likely the biggest Flywheel Energy  Storage System on the planet. Don’t let that spin you around though.

While its sheer  size is unrivaled, It’s not alone. More and more people are turning to mechanical  energy storage systems, like flywheels, as the solution to large-scale energy woes. Why  the sudden uptick of interest in this otherwise niche mechanical energy storage device?

And  can a spinning wheel really compete with lithium batteries and all the other energy  storage systems that are available to us? I’m Matt Ferrell … welcome to Undecided. This video is brought to you by Incogni.

We took a spin at this topic almost four years  ago now, and there’s been a lot of movement with flywheels since then. California-based Amber  Kinetics has been rolling out installations, and as I just mentioned, China has brought  one of the largest systems online recently. But in case you aren’t familiar, what  is a flywheel?

Or, more accurately, what is a Flywheel Energy Storage System (or  FESS)? It’s essentially a mechanical battery made by combining a dual-action electric  motor and a big, heavy … well … wheel. You can charge a FESS by using excess electricity  to spin up the flywheel.

Once it’s spinning, it wants to keep spinning, meaning only a little  electricity is needed to maintain its speed. Then, when electrical energy is needed, the flywheel’s  inertia is used to turn a generator. The wheel will spin the generator’s rotor, and voila  electricity, sorta like regenerative braking in an electric vehicle.

This makes for  a very efficient mechanical battery. Flywheels have a unique edge in energy  storage—and that advantage becomes even clearer as we dive into their perks. But  before we get into the latest breakthroughs, here’s the big question: why choose  a flywheel over a chemical battery?

Understanding this is key to seeing why  flywheels are really picking up speed. Flywheels are especially valuable for pairing  with renewables like wind and solar, which have variable output due to shifting conditions.  For example, wind turbines produce more power in high winds and none when still, leading  to inconsistent power output (amplitude).

A major advantage of flywheels is their rotational  inertia. As heavy, fast-spinning devices, they can store and release energy quickly,  stabilizing the grid during short-term power fluctuations. This inertia is crucial for grid  stability, especially with renewables that don’t provide constant output.

While most power  generation, including renewables with inverters, needs to carefully control frequency to deliver  the standard 60 Hz AC in the U. S. (or 50 Hz elsewhere), flywheels help with this by operating  at steady speeds, minimizing conversion losses.

Though flywheels can spin at extremely  high speeds (up to 50,000 rpm), their mechanical inertia primarily addresses  amplitude fluctuations, making them a steady partner for renewables. Their rotational speed can  be adjusted during spin-up and generation modes, resulting in less energy loss to heat. Plus, their  ability to charge and discharge at supercapacitor speeds makes them incredibly responsive. 

This quick responsiveness is invaluable for patching over grid dips and absorbing extra power  during spikes. It’s also handy in emergencies. Another FESS perk is its high round-trip  efficiency (RTE)—the percentage of stored electricity that can be retrieved.

No system  has perfect RTE; energy is always lost as it transfers between mediums, and flywheels  do lose more energy over time than chemical batteries. But as long as you’re not storing  that energy for extended periods, a flywheel can achieve an RTE of 90-95%. That’s better  than pumped hydro or industrial-scale batteries, which reach about 80%.

This efficiency makes  FESSs an excellent fit with renewables. Flywheels offer other advantages, too.  Their simplicity means they often last 30 years or more, and, unlike batteries,  they don’t rely on chemical storage, so they can handle tens of thousands of full  cycles without degradation.

They also don’t require rare earth metals; the most advanced  flywheels are made from carbon fiber, which, while not cheap at around $7 per pound, has  dropped significantly from $15 a few years ago and is expected to continue falling  as production becomes more widespread. At this point, you might be wondering,  ‘Why aren’t flywheels everywhere? ’ I’ve hinted at some reasons why FESSs remain  niche, but there’s something else that’s not limited to a niche.

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So back to why flywheels aren’t everywhere. If you’ve been wondering how a spinning wheel  can store energy without eventually slowing down to a stop, wonder no more—because it can’t.  There’s still friction between the wheel and the generator, air resistance on the wheel, and  many other points where energy converts to heat.

Some flywheels are built in a vacuum chamber to  reduce air resistance, and others use magnetic bearings to ‘float’ the wheel instead of letting  it drag on ball bearings. Even so, Newton’s first law is unforgiving: even a perfectly lubricated,  magnetically levitated flywheel, with literal tons of inertia in a low-friction vacuum, will  eventually slow down. Magnetic losses from eddy currents also slow the wheel, and these losses  grow with rotational speed.

Without maintenance, flywheels tend to last about 15 minutes,  limiting them to short-term applications. This also means flywheels have fast self-discharge  rates compared to chemical batteries, losing about 5 to 20% of their energy per  hour. At that rate, stored power could be gone in under a day, so using flywheels  for long-term energy storage is a no-go.

Then there’s cost. Flywheels are still quite  expensive, despite their overall cost-efficiency. Sure, you can have a functional FESS without  extras like magnetic bearings, a vacuum chamber, or a high-tensile rotor.

Just look at their use  in the Swiss Gyro-Bus—often cited in flywheel discussions, including my own. But for grid-scale  systems, optimization is crucial, requiring specialized materials, precision machining,  and price tags that reflect these demands. And surprisingly, the lowest-tech part of a  flywheel system is often the most expensive: the well.

Flywheels are typically buried for a  good reason—they’re massive, heavy components spinning up to 50,000 rpm, practically trying to  tear themselves apart. If anything goes wrong, you don’t want chunks of flywheel—or  the entire machine—flying around. With that kind of weight and speed, it’s  a recipe for disaster.

Though rare, it’s still a risk that requires careful  design. And while flywheels usually take up less real estate than chemical  storage, the excavation alone is pricey. So, flywheels are highly effective in short  bursts and overall a tidy energy storage device, but they come with their fair share  of limitations.

That makes it a cool-but-niche tech, so throw it back  into the steampunk curiosities pile? Not so fast. Despite these challenges,  flywheels really are gaining popularity.

Let’s start with the record-breaking  flywheel facility currently online: the 30 MW Dinglun Flywheel Energy Storage Power  Station (or Dinglun, for short) in Changzhi, China. For context, that’s much smaller than  the average coal power plant’s capacity, but a full 10 MW above the previous  record holder in Stephentown, New York. The Dinglun project broke ground in July 2023  and was connected to the grid by September 2024—a remarkably quick turnaround.

It’s equipped with  120 high-speed magnetic levitation flywheels, grouped into sets of 10, with a total of 12  energy storage and frequency regulation units forming an array that connects to the power grid  at a voltage of 110 kV. That’s a lot of power. This system is pioneering a sort of  half-buried style.

Most of the tech is housed underground in a setup  reminiscent of wells with windows, allowing Dinglun’s operators to monitor  the wells. This setup provides a safer, clearer view, so workers can easily assess  operations and spot maintenance needs. The point of the project is two-fold.

First, China  is rapidly growing its green energy portfolio and, again, FESSs pair really well with wind  and solar energy. It just patches over the energy shortfalls and intermittent zones  of those technologies with ease. It acts like a buffer.

That leads into Dinglun’s second  point: it’s a pilot project. It’s still early, but if all goes well then we could see  a lot for Dinglun-scale FESSs popping up around China to help all those  other renewable energy facilities. Let’s look at another record breaking flywheel. 

German company, Siemens, provided the largest single flywheel for Moneypoint station in  Ireland. Moneypoint is Ireland’s only coal plant, and with an output of 915 MW at its peak,  it was the single largest power producer in Ireland and capable of providing 25% of  the entire country’s energy. Of course, these features also make it the single largest  greenhouse gas emitter in Ireland.

That’s why the country is enacting a multi-phase plan to  transition the station into a green energy hub, dubbed Green Atlantic @ Moneypoint. Yes,  the “@” is part of the official title. Phase one of this plan is this  massive flywheel.

The rotor alone weighs over 130 tons! It’s a big  boy. When combined with a smaller, 66 ton synchronous rotor condenser (a  close cousin of a FESS) they produce around 160 megawatt-hours in the rotating  mass, which can be tapped into on demand.

With the flywheel up and rolling just days  before 2023, Ireland’s ESB has turned to phase 2: the construction of a 1,400 MW offshore wind  farm which will be connected to the FESS. The following phases will revolve around turning  the area into a wind turbine manufacturing hub as well as the production and storage of green  hydrogen. This might give you pause considering hydrogen’s perennial status as a “any day now  it's going to solve all of our problems” kind of technology.

But hey, at least they’ve installed  five wind turbines capable of producing 17MW, and the flywheel is up and running.  Or should I say up and spinning? Let’s get back to the FESS-tivities but on a  smaller scale.

U. S. -based company Torus just signed a deal to supply the Gardner  Group, a commercial real estate firm, with nearly 26 MWh of energy storage using  Torus’s hybrid flywheel and battery energy storage systems (BESS).

FESS and BESS pair  well because they have complementary strengths: FESS is great for short-term, reactive storage,  while chemical batteries handle longer-term stuff. Torus has also developed a proprietary software  platform, enabling smart energy management, demand response, and integration  with renewable energy sources. Apparently, it plays well with EV charging,  too.

Standard “smart monitoring” stuff perhaps, but still nice to see as we move to smarter  grids, and putting flywheels in more places. Torus and Gardner Group plan to begin  installations of the FESS/BESS systems in Q4 2024, aiming for completion  by Q1 2026. Once fully operational, these systems will be able to store and dispatch  nearly 26 MWh of energy—approaching Dinglun-scale capacity.

According to Torus, that’s enough  to power nearly 1,000 homes for a full day. The exact facilities Torus’s hybrid systems  will support aren’t public yet. Historically, flywheels have been ideal for emergency power,  not just for the grid but for energy-intensive spaces like data centers or hospitals.

Gardner  Group manages various commercial properties, from malls and offices to tech centers and  even some residential communities, by the look of it. Maybe flywheels are widening their  niche a little bit. We’ll have to wait and see.

Let’s end with a familiar face:  California-based Amber Kinetics. We last checked in with them a few years ago when  they debuted their all-steel M32 FESS. Back then, the company had recently deployed some FESS  units to the West Boylston Municipal Lighting Plant as part of a solar array.

As of 2023,  the plant still mentions its flywheel assets, so I’m guessing they’re still rolling—and in this  case, no news is probably good news. At the time, Amber Kinetics was also teaming up with Chinese  company Yungao Renewables to support a 60 MW solar installation. As of 2024 that solar  plant is still in operation, though I can find no mention of the flywheel system.

That  could be a language barrier issue, though. Since then, Amber Kinetics has expanded further,  installing flywheels in Hawaii, Taiwan, the Philippines, and beyond. These aren’t massive FESS  installations like Moneypoint or large arrays like Dinglun, but it’s impressive to see just how many  places have adopted Amber Kinetics’ flywheel tech.

Amber Kinetics is also partnering  with Key Energy of Sydney, Australia, to install a system at a residence in Sawyers  Valley, Perth. With wildfires being common, the owners wanted a system that posed no fire  risk yet offered energy security, given frequent blackouts in the area. Sounds like a job for  a flywheel!

Key Energy has developed a way to install Amber Kinetics’ flywheels above ground,  avoiding the costly excavation. If they’ve truly found a cost-effective and reliable approach,  this could make FESS a lot more affordable. Amber Kinetics has also expressed interest  in further expansion in the Philippines.

Infrastructure is a challenge on this  tropical island chain—though honestly, it’s tough to maintain anywhere. In rural  parts of Mindanao, the second-largest island, high electricity costs and grid unreliability  are common. Installing flywheels to stabilize microgrids could make a real difference for  these communities.

As promising as this sounds, it’s just a stated goal for now, so we’ll  have to wait and see if it comes to fruition. Are flywheels the ultimate solution to all  our energy problems? You’ve watched this far, so you know the answer is ‘no.

’ But they’re  incredibly effective for smoothing out grid fluctuations—a role that’s becoming more essential  as we add more renewables like wind and solar to the grid. So, while flywheels may never be the  star of the renewable energy storage world, they’re a pragmatic supporting cast  member. And in the near future, I expect to see many facilities following in the  footsteps of Dinglun, Moneypoint, and others.

But what do you think? Do flywheels have a  spot in our energy storage arsenal? Jump into the comments and let me know and be sure  to listen to my follow up podcast Still TBD where we’ll keep this conversation  going.

Thanks as always to my patrons for your continued support and a big welcome  to new Supporter+ member: TheNocturnist (the best username). Keep your mind open, stay  curious, and I’ll see you in the next one.