Back in January last year I made a video looking at the concept of gravity energy storage. You
may remember me showing you a group of design students who set up a nice little demo on a very
high building that generated enough electrical energy to run a record turntable. Clever stuff!
Back then I focused on two companies who were developing their own different interpretations of
gravity energy storage at utility grid scale. One of them was the Swiss-based company Energy Vault,
whose massive open-air tower and multiple crane design got quite badly panned at the time by some
well-known YouTube debunking channels. The other company was an Edinburgh based outfit called
Gravitricity. They were pursuing a very different road to achieving a gravity energy storage system,
opting for a much safer more stable and predictable system that involves lowering massive
weights into decommissioned mine shafts. Now, one of the requests I get quite often from you good
folks out there is for me to occasionally revisit technologies that I've featured in past videos to
check out what progress they've been making. So, one year down the line from that original video,
I thought now was as good a time as any to take another look.
Hello and welcome to just have a think. This whole 'using gravity to store energy' thing is a pretty
good idea in principle. In fact we've effectively already been doing it for more than 100 years
with pumped hydro facilities that make use of reservoirs of water at different heights,
pumping water uphill when power is available and letting it flow back downhill through a turbine
when power is required. The trouble is those facilities are quite expensive to build and of
course you need the right geographical conditions to make them work so they're not something you can
simply replicate all over the world. Energy Volt's original concept was this massive
freestanding tower on top of which they planned to bolt about five cranes that could winch great
30 ton weights up and down depending on whether there was a surplus or deficit of energy on
the electricity grid. Now I'm not going to get into the weeds of why some commentators were so
critical of this system. I'll let you go and find those debunkers yourself on YouTube and
other social media platforms. Suffice to say there were some very significant questions of physics
that appeared not to have been addressed, like the fact that all the blocks at the bottom of the pile
possessed precisely zero potential energy because they were already sitting on the floor.
Plus the perfectly reasonable observation that it'd be quite tricky to stop a 30 ton
weight wandering off the vertical on a windy day, which would not only mess up the synchronization
of the system but also put untold stresses and strains on the tower structure itself.
Energy Vault now appears to have moved away from that original design concept
and pivoted towards this new idea which they tell us is the Energy Vault Resiliency Center, or EVRC.
It's a warehouse style building about the size of a very large football stadium
housing hundreds of multi-storey racking systems carrying 30 tonne blocks in each location all
of which will apparently get lifted dropped and shunted from side to side by a complex network of
computer controlled pulleys and casters. Now that is a heck of a construction project! But Energy
Volt aren't stopping there. They reckon this facility is a modular design that can be built
out into even larger configurations, presumably eventually reaching the size of a small town!
Now of course this video was not filmed at a real world construction site. It is in fact a
computer-generated rendering of what such a football stadium-sized facility would look
like - you can tell by the little white blobby trees in the background. Eh? No flies on me! So
as far as I know such a building has not yet been created anywhere in the world and Energy Vault
are still at concept stage. I must admit it does look like an awful lot of expensive infrastructure
to support the loads involved, all of which would most likely require some serious regular
maintenance over the long haul. So I think I'll let you make your own mind up about this one,
and maybe I'll have another little rummage around at some point in 2023 to see if the company has
actually broken ground anywhere in the world. In the meantime, a very different company with
a very different approach to harnessing the advantages of a gravity energy storage system
is Gravitricity in Edinburgh, who I mentioned at the start of the video. I caught up with their MD,
Charlie Blair, via Zoom recently to help with my understanding of how Gravaticity differs
from Energy Vault and to get the latest news on how their concept is progressing.
Arguably the most fundamental difference between the two concepts is that Gravitricity believe
that, outside of pumped hydro, the only serious way to achieve safe, reliable, dispatchable
grid-scale gravity energy storage is to use the geology of the earth. One of the most compelling
arguments for this approach is that instead of building a massive warehouse with miles and miles
of steel support structures inside you can simply use the planet to hold up your weight. After all,
that's precisely what a pumped hydro system does isn't it? Now, just to really confuse the issue,
the first demo structure that Gravitricity built back in 2021 was a steel frame tower above ground.
So what was all that about then? Well Charlie explained that it was a simple matter of making
things as easy as possible for the test rig so that all the mechanical elements could be
simply monitored and viewed by the engineers. The tower only needed to be quite small compared
to a full-size configuration too. The rig was essentially built to assess the dynamic behaviour
of the weight during the stop start phases of the system, and specifically the speed of
response that the system could achieve as gravity competed with inertia to get that weight moving.
That sort of test data is absolutely crucial for any device providing grid frequency regulation.
Engineering simulations showed that the system would operate within acceptable parameters,
so the test rig was there to validate those results. And happily for Gravitricity,
validate them it did! The concept demo uses a naturally high density iron ore aggregate derived
from magnetite. At full scale each weight will be around 500 tons so having it in lots of small
pieces rather than one big solid lump obviously makes it infinitely more manageable for transport,
as well as on-site handling and maintenance and even for decommissioning at the end of the
facility's operational lifetime. The winches and motor generator systems that allow the weights to
be gently lowered and raised work on very similar principles to the regen braking system in an
electric vehicle, which harnesses the energy that would otherwise be wasted as the vehicle slows
down or goes down a hill. Except of course in this case the energy is going directly into the grid
rather than into a battery. The core elements of the system like the shafts and the weights and the
structural elements holding the winches and motor generators
all have projected operational lifetimes of more than 50 years. The cables are good for
75,000 cycles which is about 10 times the number of cycles that a typical battery can manage.
At full scale the shaft depth will be between 300 and 500 metres and the containers of iron ore
will be between three and five metres in diameter and perhaps four or five metres deep. The system
is designed to be extremely versatile in terms of duration of discharge. It can be used for anything
from instant response frequency regulation with a single weight system in an existing mine shaft,
which is extremely useful in conjunction with intermittent sources like wind power,
right up to long duration discharge times of between two and eight hours in purpose-built
multiple weight configurations to complement solar power and to provide extra electricity for
peak hours of the day. Now, the question many of you quite rightly ask me about any of the
energy storage systems I look at on the channel is 'what's the levelized cost of storage or LCOS?'
And the answer to that question is it depends on which variables and parameters you put
into the calculation. Gravitricity commissioned Imperial College London to assess their system,
and the parameters they input look like this for a storage system with a discharge time
of two to six hours. For a 24.4 megawatt hour system cycling 730 times a year for 25 years
the Gravitricity system stacks up very favourably indeed, not just against
lithium-ion batteries but also against a range of other energy storage options currently available.
The next step for Gravitricity will be to assess different locations all over the world
to establish which ones are suitable for this kind of system. And there'll be no shortage of options.
The European Union is keen to accelerate coal mine closures as part of its REpowerEU initiative,
and it obviously makes sense to look for ways to do something useful with those decommissioned
facilities. In fact, Gravitricity is already in contact with mine owners in countries like
the Czech Republic and Poland, and similar opportunities exist in North and South America
and in Africa. Having derived very positive data from their proof of concept tower up in Scotland,
Gravitricity are now in the early stages of an 18-month engineering design phase for their
first full-size fully operational facility. Once that work has been done and the location
has been finalized then there'll be a further 18 months of build time, which takes us up to
somewhere like 2025 or 26. After that though the turnaround time for subsequent projects
is likely to be relatively quick. So there you have it folks. A progress report as promised.
I guess what it shows is it's bloody hard work to get from design concept to a real world commercial
operation. Gravitricity are a pretty pragmatic and realistic team of predominantly engineering types
who understand that there are no shortcuts and no amount of slick marketing will make the
process move any faster. But their system does look like it could serve a very useful purpose
in a very large number of otherwise useless and redundant locations all over the world,
and if it can achieve that then it really will be offering a meaningful contribution
to the sustainable energy transition. Now, you're probably chomping at the bit to voice
your opinion on this one, so by all means jump down to the comment section below and leave your
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