Way back in the mists of time, probably about 5 000 years ago or so, some smart alec in the pot
making department of ancient Egypt, or possibly Sumer in Mesopotamia, or Greece, or maybe even
China, no one really knows, but somewhere some smart alec realized that if they made a big heavy
disc they could spin the whole thing, which made it much easier and faster to shape the pot. Sounds
very simple to our modern minds but at the time it was nothing short of revolutionary! See...
revolutionary... because it's... a it's a wheel. Anyhoo, the principle of a heavy spinning disc was
used many times over the following centuries and by the time the Industrial Revolution came along
it was embraced enthusiastically into all sorts of machinery with its fancy new name 'The Flywheel'.
They were perhaps most useful as a means to smooth out the up and down fluctuations of crankshafts in
reciprocating engines, but they were also pretty handy for providing a bit of extra oomph to things
like power hammers and riveting machines. And in the guise of a gyroscope they proved
to be an invaluable stabilizer for sensitive instrumentation like ship navigation systems. Then
in the middle of the 20th century some engineering types started to think about flywheels as a
possible way to store and release a bit of energy that could be converted into electricity to do
some useful work. An early example is this rather quaint thing called a Gyrobus, which carried
a large flywheel that could be charged up for a couple of minutes at each bus stop, causing it to
rotate at 3000 RPM, delivering enough electrical energy to drive the bus at 60 kilometres or 37
miles an hour for about 10 minutes or so - more than enough to get to the next stop. And now,
as we scramble to find efficient economically viable and environmentally friendly ways to store
intermittent energy generation from renewables like wind and solar for large utility grids,
this age-old technology appears to be enjoying something of a resurgence.
Hello and welcome to Just Have a Think. Once the world had got its mind around the idea that
electricity was definitely something useful, around about the start of the last century,
the next challenge was to reach some kind of nationally and internationally agreed method of
generating it in the first place. It was generally agreed that the cheapest and easiest way was to
burn something to heat up water until it became steam and then send that steam across a turbine
that could drive an electrical generator. It was a great system because it worked whether you were
burning coal or gas or even generating heat via a nuclear fission reaction. And of course
if you were lucky enough to have local geography that allowed for the building of dams you could
just let the water from a reservoir flow straight across a turbine and do away with the burning part
altogether. Whichever way it was done though, there was always a very heavy spinny thing in
the system. Those heavy spinny things had the extremely useful characteristic of inertia.
In other words, even after the flow of steam or water stopped, the big heavy turbines would carry
on spinning for quite a long time afterwards. And that was a feature that grid operators could
make good use of to smooth out the spikes in grid demand in a process known as Frequency Regulation.
Frequency is a function of the speed that the turbines are turning, but it's also a function
of energy demand on the grid, which has to be precisely matched by supply in real time. If
the demand spikes higher than supply then the line frequency will drop. If it deviates too
far below 60 hertz in countries like the US, or 50 hertz in some other parts of the world,
then there's a risk of brownouts, or in worst case scenarios even a complete system collapse.
When renewables like wind and solar came along they posed an additional challenge
for grid operators with their extremely variable power outputs and intermittency.
The most widely employed solution to that problem is to use energy storage like grid
scale lithium-ion batteries which can respond instantly to variations in grid frequency for
just long enough to keep everything nicely balanced, allowing grid operators to jiggle
things around a bit to properly accommodate the spike. But some clever engineers in the energy
industry applied a bit of lateral thinking and realized that they could, in theory,
build standalone flywheels that could emulate the useful inertia characteristics of the old fossil
fuel driven turbines that were being replaced. Advanced energy storage flywheels basically
consist of a giant rotor suspended by magnetic bearings inside a vacuum chamber providing an
almost friction-free environment that allows a fully charged up flywheel to rotate continually
with very little added energy input needed. If the grid needs a quick injection of energy to get
it over a frequency drop, operators can engage a generator to tap into the flywheel rotor and push
out electricity. And if demand drops unexpectedly then the unwanted electrons being generated by the
power plant can be sent back to the flywheel to get it spinning up again, taking the frequency
spike out of the grid system. Clever stuff eh? In 2020 an American company called Beacon Power
built what was at the time the world's largest flywheel energy storage system in Stephentown,
New York. It's got a generating capacity of 20 megawatts which is produced via no fewer than 200
carbon fibre flywheels levitating in a vacuum chamber similar to the one I just described.
In this case the flywheels can steadily discharge one megawatt of electricity for 15 minutes. But of
course advances in technologies like these never stand still do they, and in April 2022 the German
technology giant Siemens completed production of the world's largest single flywheel - a 177 tonne
behemoth that will be installed at the Moneypoint Power Plant in County Clare in Ireland. It's part
of an ambitious project being run by the Irish Energy company ESB to transform Moneypoint from
a dirty coal-fired facility into a renewable energy hub of the future, with a range of
renewable technologies deployed over the next decade including floating offshore wind and green
hydrogen production and storage that'll have the capacity to power 1.6 million Irish homes.
The flywheel, or 'synchronous compensator' as it's more technically known, will be capable
of providing 4,000 megawatt seconds of inertia, which is twice as much as the current Moneypoint
plant turbines can produce. But surely, I hear you ask, all this grid frequency regulation is
precisely what lithium-ion batteries are there to do, isn't it? And, well, yes it is. So why are we
bothering to introduce yet another solution to a problem that appears to have already been solved?
Well, the makers of these systems point out various advantages of flywheels versus lithium-ion
batteries. They have round-trip efficiencies of 90% to 95% which is comparable to an average
lithium-ion battery but they typically use simple and abundant raw materials that are fully and
easily recyclable and have fewer environmental impacts than the rare earths and metals that go
into lithium ion. They can be charged up in a couple of minutes or so and there's effectively
no limit on how many times they can be cycled in a day. There's pretty much negligible degradation
over their operational lifetime too, so they last for decades. They can operate in a very
wide temperature range from Arctic freeze to Saharan swelter, and they're completely safe
in operation with no chance of any inconvenient random combustion. Operation and maintenance costs
are pretty low too because there's really not that much to maintain. On the downside they don't quite
have the energy density of lithium battery systems and they have very high idle losses,
otherwise known as self-discharge rates. Despite great efforts to eliminate friction in the system,
even the best flywheels wind down from full speed to stand still within a day or so. And they're
relatively expensive to install as well. According to the International Renewable Energy Agency,
or IRENA, by 2030 the average cost of a flywheel installation will be around four thousand dollars
per kilowatt hour. That doesn't stack up too well against lithium-ion, which IRENA says typically
have installation costs of less than a thousand dollars per kilowatt hour. So we're not talking
about a fundamental market disrupter here, but perhaps something that can work alongside
batteries in specific scenarios. And that's exactly what Dutch energy storage specialists,
S4 Energy, and the Swiss Swedish manufacturer, ABB, set out to achieve with the October 2022
launch of a hybrid battery and flywheel energy storage system that aims to achieve the best
of both worlds. The installation is located in a place that's spelled like this and is almost
certainly not pronounced 'Heeer-who-go-vard'!
Anyway it's a power plant in the north of Holland and it's connected to a nearby wind farm.
The new kit combines a 10 megawatt battery system with a three megawatt flywheel providing a total
energy storage capacity of around 9 megawatt hours with a cycle efficiency of more than 92
percent and an operational lifetime of well over 20 years or more than a million cycles,
giving it a claimed levelized cost of storage of between two cents and 12 cents per kilowatt hour,
depending on the application. At the other end of the scale there's this approach from another
European firm called Stornetic. They're making small modular flywheels with power ratings up to
130 kilowatts. They may be individually small but they can each rotate at up to 45,000 revolutions a
minute, which means they can still effectively store a very useful amount of energy that can
be discharged in milliseconds for frequency regulation. This kind of modular design can be
hooked up together and housed inside a specified number of standard shipping containers which can
be linked to a wind farm or solar PV array. And it opens up the potential for domestic and
commercial buildings with solar PV installations to feed excess generation into a local flywheel
storage facility, and pull energy back out again when required, all of which could significantly
help to reduce their energy bills and smooth out fluctuations on the centralized grid. In days gone
by grids often had to ask big manufacturers to increase or decrease their production levels and
energy demand if there were big spikes happening on the grid. With this kind of local flywheel
system those manufacturers may no longer need to factor those random requests into their production
schedules, which of course will make their overall operation that bit more efficient. I don't think
anyone's rushing for phrases like 'Game Changer' or 'transformational breakthrough' when they
start describing these flywheel installations, but they do look like a very smart piece of
relatively simple and environmentally friendly technology that will quietly perform a critical
role alongside all the other technologies that National Grids are rapidly developing in order
to accelerate the transition away from fossil fuel combustion, which in the case of the UK
grid is targeted for completion by 2035. So let's see what you think about all this. Are you a grid
engineer or designer? Maybe you've got first-hand experience of flywheel energy storage and have
some nuggets of insight that you can share with us all. Or do you just have strong views one way or
the other about the rapid transition towards more sustainable energy generation. Whatever your view,
why not jump down to the comments section below and leave your thoughts there.
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