Jordan Taylor Profile picture
May 4, 2024 27 tweets 11 min read Read on X
In 2022, short on electrical grid inertia and long on renewable power, Ireland installed the world's largest flywheel, 130 spinning tons.

Why did we do something so preposterous?

And are there other, better storage technologies? Let's find out.

It's the grid storage thread! Image
In this thread we'll cover all the major storage techniques and what they're good for. Be warned: There is NO perfect method.

Before we get started, the difference between power & energy:

Power (MW): How much oomph/ what can you power with this.
Energy (MWh): Power x time. Image
The classical use case is load shifting: Storing electricity in low demand periods and supplying it back in high demand periods: Hours, days or weeks later. These require high energy capacity, crucial for renewable-dominated grids.

Shown: Turlough Hill pumped hydro, Ireland. Image
Another use case is grid stabilisation: Maintaining grid stability in the face of faults, sudden load or draw changes and supplying inertia. These emphasise power delivery over energy.

An example is the synchronous condensor flywheel mentioned earlier. Image
For the impatient, here's how all the different storage solutions stack up against each other, in several acronym-heavy graphs.

But you want more detail than this don't you? On with the show...
Image
Image
Pumped Hydro .

The most popular solution globally with 150GW power & 9000 GWh energy capacity, this pumps water to an elevated reservoir when electricity is cheap and sends it back through turbines later. After frictional losses, it has a 76%-85% round trip efficiency. Image
It has a lot to commend it: It's affordable, can do long term storage, is fairly efficient and has a 50 year+ lifespan.

But it's volumetric energy density is very low, so to get meaningful amounts of storage you need massive installations, which is geography dependent. Image
Compressed Air Energy Storage (CAES)

A quirky and old fashioned storage method used for power smoothing for decades and to power mining vehicles before that, it has the advantages of pumped hydro but with a higher energy density.

But a big problem keeps it off-grid: Heating.
Image
Image
When you compress a gas you heat it, and the loss of energy keeps CAES systems at just 40% efficiency.

Advanced Adiabatic CAES: Compressed air is cooled by heat exchangers, storing thermal energy (e.g in crushed rock) for re-injection during expansion, for 70% efficiency. Image
Another solution, supercritical CAES: Air is compressed & cooled to a liquid state for cryogenic storage, and heat stored elsewhere.

Both systems allow higher efficiency & energy density, trading off complexity & lessened long term energy retention. Pilot plants are underway.
Image
Image
CAES and pumped hydro represent our two "bulk energy storage" solutions, adapted for large scale, long period storage: There is a 3rd but we'll get to it later.

Now let's look to another extreme: High power density, short term storage: Flywheels! Image
Flywheel Energy Storage (FES)

A symmetric steel rotor on magnetic bearings rotates in a partial vacuum. With similar specific power but lower specific energy than batteries, it excels in low cost of power, long life, efficiency & reliability. Good for grid stabilisation.
Image
Image
Capacitors & supercapacitors.

Pitiful specific energy but high specific power, capacitors have long lifespans, high efficiency, but cannot store long term.

Used sometimes in substations, these work well for power control applications but are useless for load shifting.
Image
Image
Superconducting Magnetic Energy Storage (SMES)

Spookily storing energy in magnetic fields, you might see these in particle accelerators or fusion reactors but never as grid storage. A thread on them is linked below.
So what about the jack of all trades, the Lithium-Ion battery?

A great technological leap, the rechargeable Li-ion battery can be modified for high or low specific power or energy depending on chemistry. Suitable for grid stabilisation and short-mid term load shifting. Image
It's efficient, at 85%-95%, flexible, can be built anywhere and turn it's hand to most things. It's the fastest growing grid storage globally, though not challenging King Hydro yet.

But charge degradation means it's unsuitable for seasonal storage, and it remains very expensive Image
Sodium-sulphur batteries (Na-S)

With electrodes of molten sodium & molten sulphur, these high temperature batteries are cheap-ish, pretty efficient (75%-90%) and can do long term storage, but are let down by a poor operating lifespan: Just a few thousand cycles. Image
Thermal Energy Storage (TES)

Divided into sensible heat storage (no phase change) and latent heat storage (uses a phase change), TES can be done with a variety of materials: Advanced concentrated solar plants use molten salt TES to supply electricity at night and when cloudy. Image
Hydrogen fuel cells (proton exchange membranes).

The great white hope of green economics, hydrogen energy storage is scalable, high energy density, high power, easily transportable and suitable for long term storage.

It has a big problem though... Image
... Utterly terrible round-trip efficiency, of 25%-40%. Losses not just in electrical generation, but also hydrogen production, by conventional electrolysis or using solar or nuclear process heat (thermochemical water splitting).

This inefficiency makes it niche storage only. Image
So how does everything stack up? In terms of long or short term, here's the breakdown. The bulk storage solutions, long period and with the heft to manage entire wind farms going down, are pumped hydro & CAES, though sodium-sulphur batteries could do it if the price is right. Image
At the low end the usual suspects: Capacitors, flywheels and many battery types, though flywheels can chip into the lower reaches of load shifting applications and lithium ion remains jack of all trades, constrained mainly by price. Image
Speaking of price...

The full levelised cost of storage holds some surprises on the bulk long term end: Pumped hydro, a mature technology, won't get cheaper but keep an eye on advanced compressed air & sodium-sulphur battery systems!

Hydrogen remains hamstrung by inefficiency. Image
At the short-term, current quality end, li-ion will continue it's march downwards in price and across in capability, driven by a now-colossal consumer industrial base. Flywheels, already stealthily popping up everywhere, have more room to run, but will fight with Li-ion.
Image
Image
The surprising reality is that not only is storage getting cheaper, and fast, but that's it's mostly mechanical, not battery driven.

There are many storage niches, see graph shown, and great profit potential, but no single technology ticks all the boxes. Image
Like it or not, the vast expansion of renewable power will drive a many-fold explosion in grid storage capacity worldwide, and it will be a smorgasbord of different technologies, including some genuine surprises!

It is, at least, getting cheaper. Image
I only included the most mature technologies here, so I'm sorry if I missed your favourite one! You can read about 47 (!) different methods in the paper shown.

But it's a long paper: Charge your batteries...

I hope you enjoyed this! Image

• • •

Missing some Tweet in this thread? You can try to force a refresh
 

Keep Current with Jordan Taylor

Jordan Taylor Profile picture

Stay in touch and get notified when new unrolls are available from this author!

Read all threads

This Thread may be Removed Anytime!

PDF

Twitter may remove this content at anytime! Save it as PDF for later use!

Try unrolling a thread yourself!

how to unroll video
  1. Follow @ThreadReaderApp to mention us!

  2. From a Twitter thread mention us with a keyword "unroll"
@threadreaderapp unroll

Practice here first or read more on our help page!

More from @Jordan_W_Taylor

Aug 30
It's the greatest story never told: It's the story of how a frugal county in the North of England invented the modern world.

Put on a flat cap and call up the whippet, because this is a thread about my home county, and the inventions that came out of Yorkshire! Image
Image
Steel!

Benjamin Huntsman invented high homogeneity crucible steel in Sheffield in the 1740s, firing with coke to fully melt the steel and homogenise the carbon content.

This became used… everywhere, and supercharged the ongoing industrial revolution. Image
Steam trains.

Steam locomotion had been in development for some decades by 1812, but arguably the world's first commercially successful steam locomotive was Matthew Murray's Salamanca. To him, we owe speed. Image
Read 14 tweets
Aug 26
A liquid rocket boost stage needs to pump fuel and cryogenic oxidiser to the combustion chamber at a rate that beggars belief: The 33 engines on the boost stage of SpaceX's monstrous ‘Superheavy’ booster each chew through about 700 kg of propellant every second. Put all those engines together and the flow rate of liquid fuel & oxygen would be sufficient to empty an Olympic swimming pool in under 2 minutes, if you could find an Olympic swimming pool for cryogenic propellant.

Can you think of any conventional lightweight pump that can do this? Me neither. You need something special…

The turbopump comprises a typically-axial turbine powered by hot, pressurised gas flow that powers centrifugal compressor pumps that pump the colossal quantities of propellant required and pressurize it to, potentially, hundreds of standard atmospheres.

It's a handy, lightweight way to provide pumping power, but it does require that you have a source of hot, high-pressure gas to work with.

Now, where would you find that in a rocket engine?

Indeed. In order to burn fuel, we must pump it. In order to pump it, we may have to burn some of it.

Um…Image
Image
The Gas Generator Cycle.

A small quantity of the pressurised fuel & oxidiser flows are tapped, brought to a small combustor, vaporised, ignited then expanded through a turbine that powers the fuel and oxygen compressor cycles.

Inevitably the gas generator can't run with a completely nominal fuel:oxy mix, as it would get so hot that it would melt the turbine blades, so typically a gas generator will trade off some efficiency and run fuel rich to power the turbopumps.

-Why not oxy rich? Because fuel has a higher specific heat at constant pressure (Cp) and so you need less mass flow through the gas generator if it's fuel rich than oxy rich, meaning more useful propellant goes to the main combustor & nozzle that moves the rocket.

So the upside of a gas generator cycle is relative simplicity and robustness, which is why it's used on the most reliable rocket motors around, the SpaceX Merlin. The downside is that you trade away efficiency by throwing away some of your propellant, meaning that the tyranny of the Tsiolkowsky rocket equation will kick you where the sun don't shine.Image
Image
Staged combustion attempts to address this, by taking either a fuel rich or oxy rich preburner, operating at a much higher flow volume than a standard gas generator, and routing the hot gases that leave the turbine straight to the combustion chamber so that they're not lost. This not only increases the average propellant exhaust velocity (since none of it is lost) and therefore efficiency, but also allows a lower average temperature in the preburner and turbine, since there's a higher volume throughput instead.

On the flipside you must deal with hugely increased engineering complexity, an increased potential for feedback control problems between the different parts of the engine, and also a much higher pressure preburner, since it will still need to deliver high working pressures to the combustion chamber after the losses of the turbine and injectors.

The Soviets got there first, and some of their genius manifested in the Russian RD180 oxy-rich staged combustion engine, which was bought by the Americans and used in Atlas rockets for many years. Its unique oxy-rich staged combustion cycle was efficient but not without drawbacks, as high temperature gaseous oxygen is brutal to exposed metal surfaces, demanding an enamel coating on many parts of the engine.

And it gets even more complex than that…Image
Read 5 tweets
Jul 18
Last month Rolls-Royce won the UK's small modular reactor competition to develop and build SMRs in the UK. It could be a new dawn for nuclear power.

But who else was in the competition, what was special about each design, and which is your favourite?

An SMR thread… Image
What's an SMR?

A small modular reactor is a way of beating the brutally high capital costs of building nuclear power: By simplifying assembly (modularity) and minimising subsystem size so almost all of it is factory built you harvest industrial learner effects and low costs. Image
Boiling water vs pressurised water reactors.

All designs in this list are either PWRs or BWRs, the most common reactor styles today. I've a thread on the basics if you need it, but otherwise on with the show!
Read 21 tweets
Jul 4
In April on a mountain in Chile the Vera Rubin observatory gathered first light, and this telescope will be world-changing! -Not because it can see the furthest… but because it can see the fastest!

The Vera Rubin telescope thread! The value of speed, and unique technology… Image
Who was Vera Rubin?

She first hypothesized the existence of dark matter, by observing that the rotation speed of the edge of the galaxy did not drop off with radius from the centre as much as it should. The search for dark matter, and other things, will drive this telescope… Image
Does it see a long way?

Yes, but it’s not optimized for that: The battle of the big mirrors is won by the Extremely Large Telescope which, yes, is meant to see a long way. Vera Rubin is not that big, but that doesn’t matter because it has a different and maybe better mission. Image
Read 22 tweets
Jun 20
Rotating detonation engines: Riding the shockwave!

A technology that could revolutionise aviation, powering engines with endlessly rotating supersonic shockwaves. It could bring us hypersonic flight, super high efficiency and more.

The detonation engine thread… Image
Almost all jet engines use deflagration based combustion, not detonation, but while fuel efficiency has been improving for decades, we're well into the phase of decreasing returns and need some game-changing technologies.

One is the rotating detonation engine (RDE). Image
To understand the appeal of RDEs, you need to know that there are two forms of combustion cycle: Constant pressure, where volume expands with temperature, and constant volume, where pressure goes up instead.

Most jet engines use constant pressure. RDEs use constant volume. Image
Read 21 tweets
Jun 6
As a new graduate I once had to sit down and draft an engine test program for a subsystem of a new model of Rolls-Royce aero engine. It was illuminating.

So here's a thread on some of the weirder things that this can involve: The jet engine testing thread! Image
Fan Blade Off!

Easily the most impressive test: A jet engine needs to be able to contain a loose fan blade. In the FBO test, either a full engine or a fan & casing rig in low vacuum is run to full speed, then a blade is pyrotechnically released.
Frozen.

The Manitoba GLACIER site in Northern Canada is home to Rolls-Royce's extreme temperature engine test beds. Not only must these machines be able to start in temperatures where oil turns to syrup, but in-flight ice management is crucial to safe flying. Image
Read 15 tweets

Did Thread Reader help you today?

Support us! We are indie developers!


This site is made by just two indie developers on a laptop doing marketing, support and development! Read more about the story.

Become a Premium Member ($3/month or $30/year) and get exclusive features!

Become Premium

Don't want to be a Premium member but still want to support us?

Make a small donation by buying us coffee ($5) or help with server cost ($10)

Donate via Paypal

Or Donate anonymously using crypto!

Ethereum

0xfe58350B80634f60Fa6Dc149a72b4DFbc17D341E copy

Bitcoin

3ATGMxNzCUFzxpMCHL5sWSt4DVtS8UqXpi copy

Thank you for your support!

Follow Us!

:(