Former flywheel energy storage startup engineer here.
The economics of flywheels for this kind of application versus just using another battery tend to rest on the purported "unlimited cycle life" of the flywheel system compared to, say, Li-ion batteries that have a very well documented finite cycle capacity that degrades even further when doing sub-optimal cycling. To a lesser extent you can also bank on lower parasitic loads during standby as the environmental requirements for a flywheel aren't as stringent as batteries that need to be either heated or cooled almost all the time in many climates.
The problem is that, by and large, "unlimited cycles" is not true. You still have huge, very high speed bearings. Motors that require routine electrical testing and can fail. And now all this stuff is sitting below ground under a massive concrete lid for containment so it's not as easy to do maintenance on compared with a similarly-sized battery system. You also need uninterruptible power supply to maintain safety and control systems when grid power is unavailable since you've still gotten a huge spinning mass that you can't slow down without somewhere to send the energy (it's possible to use braking resistors, but it's another cost).
Batteries also benefit from massive economics of scale (both on the actual cells and the power electronics) that are getting better with time and driving costs down, while flywheels have been "1 year from commercialization" for the last 25 years.
I remain skeptical of the commercial benefits vs. increasingly commoditized and readily available battery systems.
Power utility engineer here. I keep imagining a giant flywheel located at every substation- could be very useful for load balancing, voltage regulation, even frequency control. I guess what I mean is, a large spinning mass could potentially have other benefits than just storage, right? Any research into substation application at that startup?
For an energy storage system, you probably don't want a synchronous machine. You want to be able to deliver (or absorb) rated power over a wide range of rotor speeds, since the difference between your lowest and highest speed is what effectively determines your energy storage capacity. To do this with a synchronous generator you'd need a big, expensive high-speed gearbox similar to what you see in synchronous generator wind turbines. So we used an induction motor/generator + back-to-back converter to tie to the grid, which is a common design very similar to what's used in most modern wind turbines. Therefore, from the perspective of the grid, no rotational inertia is coupled to the power system and the machine doesn't exhibit the inertial response of a synchronous generator that I'm sure you're familiar with.
However, if you have a fast enough control and communications system, you can provide the desired response for both frequency and voltage control and that's a big part of what we were trying to do. You can ramp from minimum to maximum active or reactive power very, very fast (like 5 AC cycles), which is much faster than any traditional generator. Due to the fast ramping capability, we also researched the possibility of using flywheels for large unit trip contingencies in small power systems (e.g. Hawaii) where operating reserve is very expensive.
At the end of the day, the biggest problem is that anything flywheels can do, batteries can do too - and batteries are getting cheaper every year.
“In the first four months of operations of the Hornsdale Power Reserve (the official name of the Tesla big battery, owned and operated by Neoen), the frequency ancillary services prices went down by 90 per cent, so that’s 9-0 per cent. And the 100MW battery has achieved over 55 per cent of the FCAS revenues in South Australia. So it’s 2 per cent of the capacity in South Australia achieving 55 per cent of the revenues in South Australia.”
I was recently reading about power factor correction and found out that "synchronous condensers", basically just large synchronous motors with no load, are sometimes used at utility scale for PFC and frequency stabilisation. Eg, here: http://www.think-grid.org/synchronous-condensers-better-grid...
Since it seems like the main source of stability in that system is the inertia in the rotor, would it be fair to describe it as a kind of flywheel? I didn't see anything about connecting an actual wheel to such a system, but it seems like it would be the same thing with more inertia, right?
Where "flywheels" in common parlance differ from synchronous condensers is that condensers run at zero torque - so they provide no active power to the system. They provide reactive power, which is needed to regulate and maintain the stability of the power system, but not active power which is used to match generation and demand or shift load. There's no actual source of energy being fed into a synchronous condenser. In a flywheel, you're drawing energy from the grid to spin up a really big mass and then storing it in rotational inertia so you can output it later very quickly. Flywheels can provide reactive power too, through their DC/AC power converters, but since you don't actually need any rotating mass to do that (recall, reactive power requires no torque), you can use a STATCOM - which is functionally like a synchronous condenser just without any moving parts.
I mostly hear about flywheels used in datacenters, to bridge the time from a utility outage to diesel generator startup. That doesn't happen very often at the typical datacenter -- monthly testing and maybe a real outage or two per year.
One of the reasons this was needed for a long time is that DC traction power systems used rectifiers that only worked one-way, so you couldn't just spit the regenerated braking energy back out on the main AC grid. So without somewhere to store it, regenerative braking would cause temporary overvoltages on your traction power system.
With modern power electronic converters, it's probably cheaper and easier to just use the main AC grid as the sink for the regen braking power.
I'd read about European high speed trains using regenerative braking and the grid, thanks for explaining why that wasn't what was being talked about! I had no idea about this earlier system.
They are on a common electrical system. The train uses regenerative braking to put power into the 'grid'. The flywheel senses this and draws power to spin up. When the train tries to draw a huge current to speed up, the flywheel senses this and dumps power to meet the demand.
There was something a bit like that for trucks a few years ago, that captured pressurised exhaust while the truck was engine braking and then used it (not sure exactly how) to help the truck accelerate again. Apparently it saved significant amounts of fuel in stop-start situations (rubbish trucks etc.), not sure what happened to it though.
Well there's rack railways[1] which are pretty close. I've been on one in India[2] and it was amazing, although a bit scary when (halfway up) one of our fellow passengers told us that one of the trains on that route had derailed and fallen into a ravine a few months prior, killing everyone on board...
I've heard of such systems using pressurized hydraulic fluid in delivery vehicles. Feeding the energy back into the car's kinetic energy worked like an automatic transmission's torque converter, I believe.
Yeah, thinking about it I'd guess that the exhaust-gas system didn't take off because of noise. Exhaust brakes are noisy and all the applications that made sense were suburban or inner city. Hydraulic would be much quieter.
Or battery systems, like cars. "mild hybrids" only need a relatively small battery. It's a common technology on buses, for example, which do a lot of stop-and-go.
> You also need uninterruptible power supply to maintain safety and control systems when grid power is unavailable since you've still gotten a huge spinning mass that you can't slow down without somewhere to send the energy
Why? If it's safe in it's vault when powered, why is it unsafe when in it's vault unpowered? Hell, you could use one flywheel to power the rest, and as they lose too much velocity the next one becomes the generator, until either they're all spun down, or power comes back, then you have at least some of the flywheels ready to go. Now, let's say you just don't do anything, they're spinning away slowly slowing, then power comes back and they don't have to spin back up from a dead stop. Why is that not true?
The rotor spins in a vacuum to reduce standby friction losses, and it requires power to maintain that vacuum. The bearings also need active cooling. Without these support systems you won't have a catastrophic failure, but you'll be damaging your equipment and reducing its lifespan.
As for using the flywheel(s) themselves as the source of backup power, that was our original design and definitely feasible at a conceptual level, but there's a lot of engineering in getting that to work properly while maintaining grid code compliance. You need your grid-tie inverter (which also provides the 60 Hz AC used by the support systems) to disconnect from the grid and transition to island mode /without interruption/ very, very fast (since utilities have standards on how fast generators need to disconnect during a system fault) and basically it required us to write our own firmware for the VFDs we were using which in turn invalidated their safety certifications. So definitely a solvable problem but we just didn't get there.
I would think that a momentary loss of power wouldn't be a big deal, even with active cooling and a vacuum pump. As long as your disconnect is fast, if it takes 500-1000ms for the pump and cooling to come back online from flywheel power, that seems like a much easier solution than worrying about five nines. The wear in that second can't be significant.
Gut feel suggests flywheels would last longer, be less expensive to recondition.
I can only make a (barely) educated guess at the difference between Li-ion battery cycle life (single digit thousands of cycles to 80% capacity seems to be what I see everywhere?) compared to bearing replacement schedules and motor/controller maintenance (and I don't have even best guess anecdotal data for this? A little Googling suggests some Rolls Royce airliner jet engines have 15,000 hours between overhauls, but that at least one has made 42,000 hors without an overhaul).
I'd _guess_ you probably don't dump energy back into the flywheel as fast as you pull it out? (I base this on calculating a Tesla 100KWhr battery requires 600(+)KW to recharge in 10 mins, and if you could pull that off the grid easily, you'd just do that. They seem to get enough grid power to charge a Tesla in ~1hr, so they've got ~100KW available I guess?) For back of the envelope calculations I'm gonna use 1 hour as "one cycle" (discharge in 10 mins, recharge in 50 mins seems a reasonable/conservative estimate) - that'd implie a flywheel with similar bearing longevity to a 747 engine bearings would last about 10 times as long (15k - 40k hours) as a Li-ion battery takes to drop to 80% capacity (say 1.5k to 4k cycles?).
The big difference would be a flywheel with new bearings is "as good as new", whereas there's nothing besides replacing the Li-ion battery that gets it back to new.
Pretty sure "charge directly off the grid" is the optimal option for "supercharger like charging stations" (perhaps not for the grid operator), but if you want 600+KW per charging station, and the grid cannot deliver that (economically) where you need it, I'd be surprised to find flywheels would come out something like an order of magnitude cheaper to operate long term than Li-ion battery storage.
(But I'm certainly not a "Former flywheel energy storage startup engineer" - I'd love to know where I screwed up my calculations to indicate and order-of-magnitude benefit that _probably_ doesn't exist???)
Your numbers are reasonable. 5-10x as many cycles on a flywheel versus best-available Li-ion tech was what we figured, too. The initial construction cost per kWh is much higher for a flywheel, though, basically enough to wipe out that advantage. Also, even if a flywheel is cheaper in the long run, it's a tradeoff of upfront capital cost vs long-term maintenance costs - and when you refurbish your battery in 10 years, cells are probably going to cost 20-30% less than they do today.
The other problem we had was that we were making 10s of flywheels per year and competing against Samsung and LG's battery manufacturing efficiencies. And buying an ultra-low-volume product from a startup that might not be around to maintain it in 20 years is also a tough sell in the risk-averse power industry.
As usual - the actual problem isn't reflected in "assume a perfectly spherical cow of uniform density" physics, or in the "Hey, I know a tiny bit about a related problem to this, I'll just extrapolate from there, WCPGW?" analysis.
I reach towards both those oversimplifications way to often.
Glad to see the guestimates/calculations I did bares at least an order-of-magnitude level of correctness. I _mostly_ do these quick calculations so I can rule out thinking harder about things that are 3 or 4 orders of magnitude away from possible.
"Yeah boss, we can do that, it'll take <scrible scrible, estimate, google, calculate, double check> something like $800k of Amazon resource per month, maybe only half a mil if we commit to 12 months up front. How much did you say we could sell this for? To how many customers?"
Happy that I was learning a lot by getting to do hands-on product design but constantly checking in with my professional contacts to see if there would be somewhere for me to land if it all went belly-up. ;)
>You also need uninterruptible power supply to maintain safety and control systems when grid power is unavailable since you've still gotten a huge spinning mass that you can't slow down without somewhere to send the energy (it's possible to use braking resistors, but it's another cost).
The braking resistors are however a much lower cost, which for this (infrequently used) application is mostly what matters.
It seems like spending >10x more on a contingency system just to save a few hundred kWh (costing a few tens of dollars) every few years seems suboptimal. Especially since those batteries could be in a daily cycling installation, so the opportunity cost (compared to using those batteries elsewhere) is very high.
Why buy X kWh of batteries to sit idle 24/7/364, plus X kWh of flywheel storage? Why not A) eliminate the flywheel, use the battery, and be done with it? Or B) use the braking resistor? It seems like either A or B should always be preferable to a "hybrid" given reasonable assumptions.
Favoring energy recapture over resistor heat dump seems like very suboptimal high-level design coming from a flywheel storage engineer, so what am I missing here?
It's not X kWh of batteries for X kWh of flywheels, it's 0.01 kWh of batteries to provide enough power to run the flywheel's protection and control systems while it 'freewheels'. Ideally, you don't want to brake the flywheel while the grid is down, because then you're losing all the storage energy and need several minutes to spin back up when the grid is back.
Surely you can power the control electronics from the flywheel, right? That should always work except when the thing is stopped, which is a safe state.
The grid is the primary power source. Flywheel when no grid. Battery would be third. It might be enough to have a passive resistor load for the third option. But at the scale of these things, a battery to run a few hours of controller is not a big deal.
It is, and there is actually a really neat passive and stable solution to this (circular Halbach array with compensation coils running from one side to the other).
I saw a startup, Velkess with a flexible lasso type flywheel (safety), I think 15 kWh. It folded though.
Do you know any companies doing in the 15kWh ballpark type flywheel batteries? It's an idea I really like - I wanted to pair it with a small hydropower installation.
I am a member of a forum for professional car mechanics. You would not believe the number of people who abuse their car by driving with brake rotors down to ridiculous thicknesses, or only changing their oil once in 40,000 miles.
Consumers are bad at maintaining mechanical things.
We now have government-mandated maintenance standards for some types of power utility equipment (mostly protection systems) in North America because it turns out even big companies with hundreds of engineers on staff sometimes aren't very good at maintaining stuff.
You seem to be the correct person to ask what are the do's and dont's regarding lithium battery maintenance and to increase device (say mobile phone) battery capacity?
The car still has a battery, this goes in the stationary charging system. It's used to increase the current when charging electric batteries. Most electric batteries can accept much more current than commercial electricity drops can provide. This system stores the current in stationary flywheels and then discharges it quickly when a car pulls up and plugs in.
So this provides something like a Tesla super charger, without having to call up the power company to rewire your gas station. They call it a "Kinetic Battery". In the video below, the CEO makes the claim that flywheels are much better for this because you can get many more discharge/charge cycles out of flywheels than with chemical batteries.
You can imagine that rewiring electric infrastructure all over the country would be quite a bit more expensive than just plugging in their system. You could also imagine a solar powered system (off the grid even) slowly being charged and then recharging a car in 10 minutes.
-I've seen a small-ish one disintegrate under test.
(Some 480kg of mass in a ~600mm diameter configuration, at some 8-9000rpm maximum if memory serves)
It amazes me how hard it is to contain that kind of energy if it wants to get out. They're really terrifying devices.
Particularly when left in the hands of engineers who do not fully appreciate that any sufficiently rapid release of stored energy is indistinguishable from an explosion.
When I used to work on turbo generators, the kind you find at power plants I saw carnage of what happens when those blow up. The retaining rings on the ends, typically a few thousand pounds were prone to breaking on older generators because of the alloy used. When that would happen it would send the projectiles through steel and concrete walls.
The balance bunker for load testing and balancing these at the shop I worked in was a pit 40 feet underground with 50 ton caps placed over top.
I was thinking about this the other day, why not use a liquid as the mass? Say water? If the spinning disk is treated like the tanks in a liquid tractor trailer, with slots to divide the mass up evenly.
When the disk starts spinning all the liquid turns into essentially a solid, if there is a massive failure, simple venting could easily disperse the liquid 360 degrees or away from people, etc... (ie, a giant massive mist explosion)
I've worked with power washers that are dangerous when focused, but when the water is dispersed, it's practically harmless.
The "secret" to dense flywheel energy storage is in the equation: Energy = 1/2 * I * w^2
Where "w" is rotational speed in radians/sec, and I is rotational-inertia / rotational-mass. So you store the most energy by rotating it as fast as possible. 20,000 RPM stores 4x the energy of 10,000 RPM.
The issue with water, or really... anything outside of steel and other such incredibly strong materials... is that water doesn't hold itself together very well. As such, the RPM limit would be smaller than a steel-flywheel.
Indeed, steel is still not used in advanced flywheels, because some forms of plastic IIRC are superior at the kinds of stresses we're talking about. Thus, these plastic / composite material flywheels, while much lighter, can spin much faster.
Leading to more efficient energy storage.
-----------------
In effect, you need every part of the flywheel designed to hold itself together to reach maximum efficiency. Water is the exact opposite. Its a lot of mass but basically no ability to handle stresses. Solid Steel would be better and would spin faster.
I'm surprised that Aluminum wins over Steel in this use case. I figured Steel's higher strength would be more important, but I guess the increased mass makes it have issues.
It depends - the "v^2" term quickly passes the linear "m" term for some scenarios. If I've got a choice between making it ten times as heavy or capable of spinning 10 times as fast, I don't want more mass there.
Well, in the context of storing energy, you want mass in the flywheel. Having a lightened flywheel is beneficial in, say, racing applications however... But that's not really important in this discussion.
No - as the immediate prior post correctly stated, stored energy increases linearly with m (flywheel mass) and as the square of rotation rate (omega^2) So a flywheel having 0.1m rotor mass spinning at 10omega stores 10 times as much energy as a flywheel of 1.0m spinning at 1omega. 10% of the mass, 1000% of the stored energy of the heavier, slower rotor.
Of course, the rotor has to be able to handle increased circumferential and radial stresses resulting from increased omega. Carbon fiber (like T1000 grade) has extremely high tensile strength (lets you spin a carbon fiber rotor very fast) but low density. T1000 rotors store more energy at lower mass than steel (or any other metal) because of the proportionality to omega^2 and their high tensile strength.
But for commercial storage, it's really about the $/kWhr/mass in terms of the overall rotor economics. By that metric, it's hard to beat a composite rotor with E-glass as the major fiber. It's cheaper than carbon fiber by easily 100X and has about 30% to 50% of CF tensile strength. It's a bit denser than CF, but its cost metric is why most modern large energy storage flywheels use glass/CF hybrid composites and magnetic bearings (for high speed and zero wear).
In the old days, they made flywheels out of solid steel, then switched to piano wire (higher tensile strength). Then fiberglass, aramids and carbon fiber happened.
That is really interesting, thanks for explaining it.
I want to ask then, based on other comments, that size can greatly improve the amount stored. So wouldn't a larger safer flywheel work in many places?
Also, my thought on the water as a solid, consider a steel wheel where instead of steel all the way through, put a liquid inside of a cavity. Since water doesn't compress, it would essentially be part of the same wheel, only safer in a collision? (arm-chair engineer)
I enjoy reading comments like yours so I can move on/let go of my from my silly pet ideas. :)
> Also, my thought on the water as a solid, consider a steel wheel where instead of steel all the way through, put a liquid inside of a cavity
Well, consider that solid steel is considered too weak for a modern flywheel. So that questions why you'd be removing steel instead of adding more of it.
Modern flywheels spin really, really, really fast. Again, fast enough that modern solid steel is too weak. Newer composite materials are superior, but still need to be designed for maximum structural integrity.
Once a flywheel spins fast enough, it literally rips itself apart due to centrifugal forces. Any "cavity" weakens the structure and will break sooner.
You are missing something (but don't worry, it is good to brainstorm like this).
At maximum speed (maximum energy storage) you want every part of the flywheel to be about to break. By introducing a non-structural material (liquid water), you have added mass but not the strength to get to higher speeds.
Imagine filling a bucket with water and spinning it around your body. All of the force to keep the bucket from flying away has to be held by the handle of the bucket. A better bucket flywheel would be all handle... Hopefully someone else can give you a better analogy.
Fluid flywheels are used for hydraulic couplings in automobile transmissions.
They're not good for long-term energy storage, since the fluid loses energy to friction and turbulence much faster than a solid-- think about how long a swirling vortex lasts in a cup versus how long spinning top can continue.
Ya, I was thinking that the water wouldn't be sloshing around, only being inside a sectioned donut wheel. The water could be hermetically sealed (with some kind of preasure relief for temp changes) in chambers, no sloshing or friction issues. Externally it would look exactly like any other fly wheel.
The thought being that since it's a safe medium to explode out, you could spin it faster than other mediums. The steel would just be a shell to hold the water, and therefore the containment vessel wouldn't have to be as robust, as the amount of steel that would fail would not be as much, and as soon as the water exploded out , the remaining steel would dramatically loose kinetic energy and possibly not even flyout.
Another comment said that 20k rpm would hold 4x the energy as 10k rpms. That implies that if you truly aren't afraid of the spinning medium hurting anyone, it would seem that water/steel hybrid would be better than solid steel, because you could spin it faster more safely.
Having seen a flywheel + clutch assembly disintegrate on a drag car in the lane next to me (10,000rpm - bits of flywheel came through the bodywork of his car), I can understand why you'd be hesitant to sit on top of something spinning at 140,000rpm.
Isn't that fairly typical turbocharger turbine speed though?
I saw a Mazda RX3 Sport Sedan (a circuit racing class here in Australia ~25-30 years back) spectacularly blow a flywheel/clutch at the end of the main straight (at Oran Park) a long time back - it pretty much perforated all the bodywork in the plane of the flywheel - bonnet and both guards - as though it was a tearoff line on a set of stamps. We could hear bits landing 10+ seconds later hundreds of meters behind us in the parking lot. Depending on what port job he had, that could have been up around 12k rpm (if my vague 30 year old car modifying memory serves...)
> Isn't that fairly typical turbocharger turbine speed though?
I believe so, but compressor/turbine wheels don't have a lot of mass to them, so fragments don't usually escape very far if they blow up. I've seen a few compressor housings split, and the main damage is done to the engine itself really.
I guess if your turbo was sitting high up and exposed, it might be a danger.
Flywheels however just seem to fail more regularly from my experience.
(Also, yeah anything rotary powered deals with scary rpm's, haha!)
He wasn't sitting on top of it, it was rather behind his ass. He either felt the vibrations or the hizzing sound, and that made him very uncomfortable.
Velkess (bill gray) solved that problem before they went bankrupt.
The answer is to make the flywheel from a flexible kinetic lasso such that when it blows up, the forces tangle the parts in a manner that it is safely destroyed.
What is amazing is the rotational speeds involved. Say the flywheel weighed as much as a tesla. Think of the energy. Say you want to store enough energy so that a tesla can accelerate itself from zero to 100mph ten times. That amount of energy in a flywheel weighing the same as the tesla would mean the flywheel spinning at +/- 1000mph. Either this flywheel weighs hundreds of tons, or it is spinning at supersonic speeds. Either way, you better have some good bearings.
The magical word here is „angular momentum“. The energy that a chunk of mass can store in a flywheel is squared with the distance of that mass to the center of its rotation axis. If you distribute the Tesla sized mass around the edges of a 4m sized Flywheel now (spare a few % for the wheel and structural support), it can store quite a few dozen times the energy of the same sized Tesla going the same speed.
I'm pretty sure it doesn't matter whether the eneergy is stored in rotating body, or one moving in a straight line. Kinetic energy of rotation is 0.5 * I * w^2, or for that extreme case of "concrete ring" - 0.5 * m * r^2 * w^2, which is exactly equal to 0.5 * m * v^2, or kinetic energy as calculated for body moving in straight line.
So let's do a little high school "perfectly spherical cow of uniform density" physics here.
Imagine we take that 1 Tesla mass and turn it into a infinitely thin ring of infinite density material. Now we can calculate how fast it's need to be spinning to get all that mass doing "1000mph".
Lets make our infinitely dense 1 Tesla mass into an infinitely thin ring 1m in radius. Each point on that ring moves around it (2pir) circumference every revolution so ~6.3m per revolution. 1000mph =~ 440m/s SO we only need to spin this flywheel ay ~70 revolutions per second, just over 4000RPM.
4000RPM doesn't seem unreasonable...
(Note:I don't think your 1000mph stacks up though. The kinetic energy of a moving mass is 1/2mv^2. So the speed of a 1 Tesla mass object which has 10 times the energy of a 1 Tesla object doing 100mph is only sqrt(10)*100 closer to 320mph than 1000. My high school physics flywheel might only need to spin at 1500RPM...)
This is a pretty common way to bridge the gap between when utility power drops and when emergency generators are started and ready to handle the load. I believe flywheel systems can be more compact and don't have the same maintenance demands, but may be more limited as to energy capacity and duration of service.
When I was in middle school? maybe high schoo? 1990s somewhere, there was a long article about flywheel batteries for cars, they were claiming some very impressive range and power numbers.
I remember it was one of a million things I read about in sciencey magazines that never went anywhere, but maybe it was the one I was most sad about never happening (at least so far)
The one product I do remember happening that I first read about back then was e-paper! That happened! Cool.
I always wondered how they dealt with gyroscopic forces in flywheel vehicles. Maybe I'm being naive and the effects can be compensates for with gimbals, but I'm stuck with the mental image of cars that don't turn corners
> Most electric batteries can accept much more current than commercial electricity drops can provide.
Just how much headroom is there? I'm under the impression that avoiding excessive heat is the key to battery longevity, so the question is whether or not this extra current increases heat levels to degrees that will have a measurable negative impact on the long-term capacity of the battery.
The single data point I have of 75k miles, once a week charging at 120kW from ~20% -> 60% shows very little degradation to the pack on our Model S.
Also, when it's warmer out I've seen warnings that in-cabin AC is lowered to divert to help cool the pack so I'm sure it's a question of thermals + number of parallel modules.
That's still a lot of DCFC(~20k miles based on 0.33kwH/mi) and even then it's limited down to 90kW from 120kW.
FWIW you only see 120kW on the first ~35% of the pack and quickly tapers down to sub 100kW after that approaching home charging speeds for the last 80-100%.
TLDR; Faster chargers are useful now and more of them would be great!
The cells charge in parallel (there are on the order of 15,000 cells in car batteries), so at least right now the charger power is the constraint and not the battery chemistry.
The most power you'd ever really need to deliver is maybe 3-400 miles of range in 5 minutes. So at a point, that we are pretty close to, you don't really need to charge any faster.
Using Tesla as an example of our current charging constraints:
The Level 1 chargers that plugin into a normal outlet are at 2 kW.
In-home charging (Level 2) maxes out at about 17 kW, (close to the most the average house circuit can handle). An average gas station or retail parking lot is probably close to this. More likely it is down at 11 kW.
At Super chargers, the Model 3 can currently accept a max of 120 kW, and the chargers can put out a max of 200 kW.
Very roughly, kW is proportional to how much range you get for the amount of charge time. So 120 kW charging is about 10 times faster than 11 kW Level 2 charging.
Also very roughly, a Tesla Model 3 could charge it's 300 mile (75kWh) battery in about 5 minutes at a 1000 kW charging rate.
It is worth noting is that this particular need, dumping 75kWh of power in 5 minutes, will exist even as battery technology improves. Fast charging is not gating on electric cars because home and work charging works quite well. But there will be demand for fast charging as a convenience to electric car owners.
According to WolframAlpha that 75 kWh over 5 minutes equals 900 kW or about the power developed by the most powerful road going car - Bugatti Veyron Super Sport.
-We're about to try out the same idea locally, on a larger scale - ferries are about to go electric, the grid is not stiff enough to handle the peak load (4.7MW for 5 minutes every 30 minutes) and hence bunkers (for lack of a better term) containing tons and tons of li-ion batteries are needed to make for a sustainable draw from the grid.
The battery storage facilities won't win any architectural awards as they are currently envisioned, but I can't wait to see whether this will actually work reliably; our first few attempts at electric ferries had some teething problems, mostly with the charge process taking too long to establish. The ferries run on a tight schedule; hence charge time dropped significantly as establishment was slow, and ferry batteries slowly depleted over the course of the day.
Anyway - 4.7MW translates into some quite massive shore power connectors, and they need to mate quickly and reliably - and when the weather gets rough, everything in the surrounding environment will be soaked in salt water. Interesting times.
It doesn’t really matter. The charger will convert whatever voltage it’s supplied with to the voltage needed by the battery at any given moment. You could theoretically run a fast charger off 120V, you’d just need massive conductors to handle the massive current.
It would most likely be current in this case. 480V is available commercially, based on a quick search. Tesla batteries seem to provide around 400V.
To fully charge an 85 kWh battery in one hour, using a 480V supply, you would need to draw over 177A, assuming perfect efficiency. That is an absolutely ridiculous amount of current, and that would only charge one vehicle.
My house can load 105A. I sometimes use 120 kWh on a really cold day, so it's not peaking anywhere near that current, at least not for long.
I'm not driving 400km every day so the grid will definitely handle it. But there is a lot of potential to reduce network costs if the charger negotiated with the grid.
Your house can load 105A, but that's most likely at 120V/220V, and as you said, it doesn't maintain that for long.
Based on 120 kWh over 24 hours, your house, on a cold day, draws around 500 W. To fully charge a single 100 kWh battery, like you'd find in a new Model S, in an hour, you would need to draw 100 kW. That would be 200 times the average load on your house, drawn continuously, and that's only to charge one vehicle.
Something like a flywheel battery does have a lot of potential to save money, or even earn money, if it communicated with the grid. A large rotating mass could potentially store a lot of energy, and would be increasingly useful with the rise of renewable energy.
Still, that would be 20 times the average load on those homes, to charge a single vehicle. To move that power 100 feet, like from a busbar (I think, I'm not an electrician) to the charger would require a 3/0 AWG copper cable (which has a diameter of around 2 1/2", or 5.8mm). That cable costs around $2.59 a foot, or $259 to get power to that charger. That would be undersized, since I calculated it out at exactly capacity, and that price wouldn't include conduit (since the cable isn't direct burial) or installation.
Multiply that by three chargers, which I'd consider to be on the very low end of what a commercial installment would need, and you have quite a high demand for power. Five hundred amps at 480V is no joke. On the plus side, all this could spur adoption of renewable energy; with enough demand for power, investors will shovel money into renewable energy faster than it can even be used.
Flywheels are useful when you have a fixed installation with no weight constraints because you get certain benefits over LiPo cells, namely longevity. As a matter of energy density though, they are awful compared to LiPo and could never efficiently be used in a vehicle. Also, the gyroscopic forces would be such that it would be impossible to steer the vehicle.
> the gyroscopic forces would be such that it would be impossible to steer the vehicle.
That's a solvable problem, and has in fact been solved by F1 teams that have used it - Mclaren won two titles with their KERS equipped cars. The cars are demonstrably far from 'impossible' to steer...
All you have to is mount two of them rotating in opposite directions to cancel it out. The axles need to be able to handle the load but the rest of the car sees nothing.
I could see it being used as a "quick-charge" portion of the capacity. i.e. you have a full-sized battery, but also a small flywheel so that if you're really in a pinch you can rapidly charge enough to get somewhere without waiting for an hour. It'd be like having a small SSD paired with a large HDD.
Angular momentum increases linearly with mass but with the square of the radius. So another key solution to capacity is to increase the size of the flywheel. Obviously there are real limits to this in a car.
I think it could be useful in congested cities with lots of stop and go driving. If there were magnetic flywheels in the street that mated with magnetic flywheels in the vehicle, energy could be transferred at stop lights. Provided the field didn't move the whole car, and if gyroscopic forces were mitigated, as another poster pointed out
I think the first year F1 had kers some of the teams used flywheels, but I think since then everyone seems to have moved to standard battery pack type systems, so I assume there are downsides to them.
At least if you drive a bit above the speed limit when commuting :)
So now they have a cache invalidation problem, right? When do they move power to the flywheel (friction expires the electrons) and when do they allow for cache misses to hit their connection with the power company?
Safety concerns raised... since the maximum amount of power the flywheel can be expected to store is a known quantity, and the amount of kinetic energy that can be stopped by concrete or metal shielding is a known quantity, it's just a matter of burying the flywheel underground, with enough concrete/metal around it (particularly above it) to prevent shrapnel from penetrating to the surface. Easy peasy. It's just a cost problem.
We keep those levels of potential energy in underground gas tanks at every gas station, and no one freaks out about that.
edit: For perspective, a typical gas station has 12,000 to 24,000 gallons of gasoline storage underground. A gallon of gas is about 120 megajoules of potential energy. So there are billions of joules sitting there - much more than these flywheels. Of course, without air, gasoline isn't dangerous. But a 90% empty tank has a lot of air in it, a lot of potential boom.
NO, an empty gas tank has a lot of gasoline vapors mixed in that air - the concentration is high enough that the vapors will not burn. One of the advantages of gasoline is it will only burn in a fairly narrow window of concentration (IIRC 5-30%, but since I don't feel like looking it up you will have to if you care)
Still, if containment is violated somehow, it's a LOT of power for fire/explosion. These flywheels are much smaller, by comparison.
The tank of gas in a car probably has over 400kwh of energy. How much will these flywheels contain, considering a full charge for an electric car is on the order of 100kwh (electric cars are more efficient than internal combustion)? The energy of two or three tanks of gasoline is enough to get several charges out before needing to spin up the flywheel again.
But a nearly "empty" flywheel is a lot less dangerous than a "full" one. While a full gas tank, even if cracked open and lit on fire, would probably burn, not explode.
I imagine seeing a flywheel leap out of the ground and short through the foundations of a skyscraper...
That gets back to my original point, though - we know from the start the maximum power of the flywheel. Putting enough reinforced concrete above it to keep it from penetrating in case of catastrophic failure is a straight-up engineering problem.
It's not comparable. Gasoline is limited in how fast it can release energy, by how much air it can get. So you get a fire but not an explosion.
In contrast a flywheel can (and will) dissipate 100% of its energy at once, leaving you with white-hot pieces of metal if your containment worked, and supersonic pieces of metal flying everywhere if it did not. (Or some combination of the two.)
It's far more dangerous. The amount of potential energy is irrelevant, it's the power (how fast the energy can be released) that matters.
Surely the danger can be largely mitigated by siting the flywheel underground, surrounded by some energy absorbing walls - assuming the catastrophic failure mode ejects debris in the same plane as the flywheel is turning
Boy, flywheel batteries. At the Ford Museum (in Ann Arbor I think?) they have some of the earliest versions of these, for steam generators I believe. Maybe 30 feet in diameter, must weigh a couple tons at least? The idea of one spinning even at 20 or 30 RPM was a scary demonstration of potential energy. If it got loose it seemed like it would blast through the wall and roll halfway across the country. But they were beautiful, well made, and instructive.
That said, it's an interesting way to store energy and I hope it can be deployed safely and beneficially.
> The idea of one spinning even at 20 or 30 RPM was a scary demonstration of potential energy.
Grid FES rotate at above 10k RPM. Munich has a control & stabilisation FES whose flywheels max out at 45000 RPM. Though they're probably not 60 feet wide the 28 flywheels store up to 100kWh.
Recently had the opportunity to tour the Sima powerplant [s]. They have an installation showing a broken turbine, somehow a stone got in that was big enough to jam up the turbine, leading to the single-cast steel contraption bending and ripping. Thankfully they managed to cut off the water before catastrophic damage occurred (to the installation/people).
The explanation is all the more mesmerising for being held next to two such beasts going full tilt just under the floor.
You can't see the damage in this picture (from a Google search), but you get a feel for the size (some of the "hands" were bent and broken before the emergency shut-off). The black shape in the back is one of the two operating turbines:
...so that was where Williams F1 got their idea from!
The last 'failed flywheel' project that I know of is the Williams F1 solutions for 'KERS' - kinetic energy something system...
This system lost out to normal batteries in F1 and Williams sold on their flywheel business to GKN. GKN now sell the Williams flywheel solution for things like buses.
For a while Porsche 911 style cars (RS-whatever) had the Williams flywheel, this took up the passenger seat so you could be sat next to one of the things in your roll cage, with helmet and flameproof suit on. That project died a death.
Before anything was known of the Williams system I was 'hoping' it would be entirely mechanical, no electrons needed. However, their solution was electric so the motor driving the wheels could go in re-gen mode and another motor/generator in the flywheel pack spun the flywheel up to speed.
The Williams system never exploded and there were no safety concerns, which is of note as F1 (thanks to Jackie Stewart) is extremely safety aware.
The problem was less technical, more psychological. Nobody wanted to sit near such a 140K rpm thing, with a razor sharp crazy sound. Worse then nuclear, which you don't hear at all.
It's kinetic energy if you consider rotation around the center of the flywheel (I * omega^2/2), but only potential energy to move around and destroy stuff (m * v^2/2). If you let the flywheel loose, it becomes just a wheel and it's not potential energy anymore. :-)
That probably was a solid wheel, right? Modern flywheels are usually made of carbon or glass fiber and have much simpler failure modes. They just break if anything goes wrong, not rolling anywhere.
Yeah, a high velocity chunk of fiber can be pretty nasty too. Still, it's much easier to contain compared to a huge metal wheel, because they literally disintegrate on failure when saturated.
Technically gas is "soft" but doesn't seem that way when powder explodes.
It doesn't seem trivial to contain this energy - the vessel would still explode, given enough energy in the wheel? Certainly safer than launching a giant death Frisbee... But lots of energy is still lots of energy.
I guess it's a bit machine gun bullet vs hand grenade - about equal energy - but the grenade will just blow up a room while the bullet will go through walls and lodge in an engine block.
> They just break if anything goes wrong, not rolling anywhere.
I saw a video of a flywheel being deliberately destruction tested. "just break" is putting it mildly - it looked like an explosion, and left white-hot pieces of the flywheel behind.
Yeah if they're using flywheels, I hope they're planning on putting them in the ground, under a thick block of concrete, far enough away from where people will be charging.
I remember a fly wheel battery concept from the early 90's. Spin light weight tiny flywheels on magnetic bearings in a near vacuum and take advantage of the fact that energy storage is linear with mass, but the square of velocity. Put the flywheels in opposing directions and spin them really fast. If I remember correctly, there still was a bit of a safety problem: my understanding was if one of the tiny flywheels fell off the magnetic bearing it would rip through 9 feet of steel. Not great for a battery in a vehicle. However I don't see why you can't tune the amount of energy you decide to store, and the amount of safety barriers to handle catastrophic failure.
Makes me wonder if there is anyway to do something akin to a MEMS flywheel.
I'm assuming what they're doing here (they don't really say) is using a flywheel in the equipment in the charging station to charge a "regular" electric car -- a car that stores the electricity in batteries. And the flywheel is used because the environments they want to deploy these charging stations have lower quality electric grids, "where upgrading the grid for fast electric vehicle charging can be prohibitively expensive".
They even say they can "...charge a battery in ten minutes..." This sounds great! But I'm not sure what cars they'd be charging. Can, for example, you charge a Tesla that fast? I assume not, or Tesla would be charging them that quickly. (https://www.tesla.com/supercharger says it takes 30 minutes)
So I'm assuming that they're charging cars with smaller batteries. It sounds interesting, but not as good as my initial reading ("you can charge your car way faster") made me think.
Maybe, but there is another charging standard that's starting to be rolled out that provides up to 350kW with a water-cooled cable. https://arstechnica.com/cars/2018/04/electrify-america-will-... That would take 17 minutes to charge even a 100kWh Tesla battery (if you could maintain that rate of charge the whole time, which battery packs generally can't).
It takes about 1 Mega Joule of energy to bring 2500kg car to a stop from 60 mph. The model s with a 100kwh battery can store 360MJ and weights about 2500kg with passengers.
Is it wrong that I get uncomfortable with the idea of a spinning mass able to charge a model s that fits within the artists rendering of the charging station?
Yes, because a flywheel is a very efficient device for producing flying shrapnel. It's already storing kinetic energy, it's simply a matter of letting all that kinetic energy loose. Energy storage flywheels have injured people in the past and even led to some flywheel energy storage startups going out of business[0]. However, with proper safety standards we can prevent many disasters.
[0]http://www.sandiegouniontribune.com/business/sdut-quantum-en...
Would putting a vertical axis flywheel in a deep basement containment be a good start? Cap with rebar & concrete,
or steel like a liquid storage tank - depends on wheel material and failure modes?
By the time you're considering building a concrete bunker, it's clearly better to give up on flywheels and stick with chemical batteries. A bunker will cost a lot more to construct than a few Powerwalls.
Just one Powerwall costs more than the cost of burying an underground gas tank, and you'd need 10 of them to store enough power to charge one Tesla 100 kWh car. That's $35,000 in batteries alone without the cost of installing them. $35,000 is much more than it would cost to put down an underground concrete foundation to drop a flywheel into. House-size basement foundations can cost 1/8th that.
Also consider the relative availability of battery chemicals vs steel and concrete. We already have the infrastructure set up to efficiently produce huge quantities of those building materials.
A full gasoline tank is pretty safe. But not if you place it next to a detonator in the form of a massive, spinning fly-wheel... If nothing else you might vaporizer the gasoline up into an improvised fuel-air explosive... Maybe even superheat the gasoline first (due to high energy, little oxygen).
Not saying it can't be done, just saying setting up a flywheel right next to your volatile chemicals might not be a good idea..
It is odd; if these are targeting rural areas, surely they could just move the flywheels away from the charging station and connect them by cable. Maybe the cost of a cable capable of supporting that current is prohibitive?
For example, some wind tunnels are powered using flywheels (c.f. high enthalpy wind tunnel F4 from ONERA in France is using a 15 tons flywheel to get the necessary power).
This matters because with a battery, it's Very Hard(tm) to get the energy to discharge at a high enough rate to cause catastrophic effects, like for example why Mike Tyson can punch with ~1600 Joules (uncited, popularly referenced), about the same as a 5.56mmx45mm round fired from an M16/AR-pattern rifle. Because the Joules are distributed over space (bigger cross section) and time (slower impact), Mike Tyson's punch doesn't immediately shred your tissue and bones.
However, it's Very Easy(tm) to get a flywheel to have a tiny mechanical failure that causes the entire thing to release all its kinetic energy rapidly. Additionally, there's no conversion penalty with the flywheel. So the battery under catastrophe can and generally does shed its energy relatively slowly as rapidly-dissipating heat (see videos of cell phone batteries on fire), whereas a rotating wheel that just fell of its drive shaft is... markedly different.
Conclusion: Even if the flywheel only holds enough energy for a single charge, it would have to be buried far underground and still might create a crater in the gas station asphalt it sits underneath when (not if) mechanical failures happen.
Therefore, this is dumb and won't happen. Please help me understand where I'm wrong :)
This is half of something. Charging a car battery in 10 minutes dumps a crap-ton of heat and risks damaging the cells, lowering the useful life of the battery substantially.
This is a pretty neat idea, I do worry about the 'one and done' problem where the spinning flywheel charges a car and then then needs an hour to get up to speed again (more if its just using solar power). That means you either need a lot of flywheels to service cars.
It is also an amazing amount of energy to be holding in the box next to the car (if you can believe the artist's conception in the article). I would be much happier if they put the flywheel horizontal in a vault under the charging station, that way if a bearing failed the wheel wouldn't go careening off into the next county mowing things down.
This problem needs to be solved for electric trucks as well.
I remember following that amazing accident. But as I recall, the turbine jumped up out of its vault, and that's what started the whole failure.
IIRC, the speed of a water-powered generator is regulated by the load on it. Take that load away, it spins faster and faster (think that's what happened to the other generators). So that one guy had to climb up to the top of the dam to close the gate.
Wow, that is pretty amazing article. About 2 orders of magnitude more energy than I think we're talking about here, but still. These things are scary when they get away from you.
You'd need a new sort of AA battery; rechargeable nickel chemistries are a bit finicky and they are usually not charged faster than 1C, similar to the rate of lithium chemistries. It is also bad for NiMH batteries to charge them constantly at those voltages; typical recommendations are to avoid "steady-state" charging them at rates faster than 1/40 - 1/20C [1]
Lithium-hybrid supercapacitors are often rated for 10C charge/discharge without the low cycle limits or volatility of lithium batteries, but they are a young technology and it looks like commercial options are currently very expensive with capacities in the 1-10mAh range @ 2.3-2.8V.
Active Power's UPS systems do use magnetic bearings:
Immediately after the output is transferred from bypass to
the power stage, the flywheel field is excited which also
provides magnetic lift to unload the flywheel bearings.
Fly wheels are not new. I wonder why they haven't caught on (seeming like a pretty good way of stationary energy storage), but using one for an EV charger doesn't seem very innovative.
It may not be a huge innovation, but it's an interesting potential business model. And as an investor, I'd be looking at financial potential, not "innovation".
This could be a cool low cost option. Imaging if a solar panel could spin up a fly wheel which you could then pull power from at night. Cheaper than regular or expensive lithium batteries, and "unlimited" assuming motors don't wear out. I'd love to see something like this to help power my home. Or maybe have it run on the grid at night during free power times and then pull from during the day.
FES is currently as expensive or more expensive than battery, and while it could go down faster than batteries that's unlikely considering how old FES tech is.
If you want to store lots of power in a flywheel, you need big flywheels spinning very fast without spinning out of control and blowing themselves up (because then all the power they stored remains kinetic but stops being contained).
They've got plenty of advantages over battery (inert materials, less affected by temperature variations, potentially infinite lifespan for magnetic bearings in vacuum-sealed enclosures) but safe large-scale flywheels are not cheap.
Neither Beacon Power nor Amber Kinetics provide any pricing information on their pages, despite specs in the same range as battery storage: a Powerwall 2 is 13.5kWh/5kW, an Amber Kinetics M32 is 32kWh/8kW. The M32 is also ~4.5 tons.
The M32 does have the advantage of an estimated 30 years lifespan, and no health danger outside of the rather immediate effects of a containment breach,
I'm with you. Given that flywheels are a relatively old tech, I've got to think there's a reason we don't do this. Maybe they require too much space or are too dangerous? I'd like to hear from someone who knows something about the subject.
The economics of flywheels for this kind of application versus just using another battery tend to rest on the purported "unlimited cycle life" of the flywheel system compared to, say, Li-ion batteries that have a very well documented finite cycle capacity that degrades even further when doing sub-optimal cycling. To a lesser extent you can also bank on lower parasitic loads during standby as the environmental requirements for a flywheel aren't as stringent as batteries that need to be either heated or cooled almost all the time in many climates.
The problem is that, by and large, "unlimited cycles" is not true. You still have huge, very high speed bearings. Motors that require routine electrical testing and can fail. And now all this stuff is sitting below ground under a massive concrete lid for containment so it's not as easy to do maintenance on compared with a similarly-sized battery system. You also need uninterruptible power supply to maintain safety and control systems when grid power is unavailable since you've still gotten a huge spinning mass that you can't slow down without somewhere to send the energy (it's possible to use braking resistors, but it's another cost).
Batteries also benefit from massive economics of scale (both on the actual cells and the power electronics) that are getting better with time and driving costs down, while flywheels have been "1 year from commercialization" for the last 25 years.
I remain skeptical of the commercial benefits vs. increasingly commoditized and readily available battery systems.