
Gravitricity – Fast, long-life energy storage - lelf
https://gravitricity.com/
======
syllable_studio
I love Gravitricity. I'm the founder of a similar startup called Terrament. We
are also building gravity storage underground, but our patents are extending
this idea to use autonomous, modular weights. This enables us to maximize both
height and weight, which is the simple recipe for cheap gravitational energy
storage.

We are also working on a seed-round of investment. It's an exciting field with
plenty of room for competition. And it's so important for fighting climate
change! We need to build this asap.
[https://www.terramenthq.com/](https://www.terramenthq.com/)

~~~
mike_d
Can you explain why this is better/different than flywheels?

I know Pennsylvania and New York both have 20 MW storage systems that takes up
a few acres and are relatively cheap per unit of storage.

~~~
lightgreen
From Wikipedia: Flywheel energy storage systems using mechanical bearings can
lose 20% to 50% of their energy in two hours.

Basically flywheel cannot store energy for a long time. It needs to be
constantly used to be effective.

~~~
choeger
Could you not levitate the flywheel on magnets?

~~~
Aachen
Apparently not that easily or the half-life would be longer than two hours...
You want to try if storing energy in a flywheel while using a lot of energy
for the magnetic field can outperform gravity storage?

------
LordHeini
Why do so many of these gravity thingies show up lately?

An easy calculation shows how low the storage potential is.

Lets take a weight of 500 tones of steel, which would be 63.29 cubic meters.

Now sink those 500 tonnes into a hole a 100 meters deep that would make a
rather lowly 0.1362 MWh of storage.

[https://www.wolframalpha.com/input/?i=500+*+1000+kilograms+*...](https://www.wolframalpha.com/input/?i=500+*+1000+kilograms+*+StandardAcceleration+*+100+)

Not sure what the cost of digging a 100 meter hole where you can sink 63 cubic
meters of steel in would be, specially since water management is needed too.

I am not convinced that it is worth it.

~~~
syllable_studio
You're thinking too small though ;). You can dig a mile deep. And you can lift
enormous weights. As comments show below. Gravity is weak, but cheap. It can
scale up to provide 1 GW of storage - enough to balance the load of an entire
large city.

Lots of these ideas are popping up right now because it's a very compelling
idea which is demonstrated to work. And because climate change is driving
massive growth in renewable energy (woot) we will desperately need massive
amounts of energy storage in the very new future. The energy storage market is
expected to grow massively year over year.

~~~
LordHeini
Sure you can always get the big option but that does not mean it is feasible.

What does it cost to dig and maintain a 1.5km deep shaft?

I found is something around 8000-10000$ per meter. I can buy a whole lot of
batteries for that.

This technology just does not scale since m _g_ h always holds true.

Unlike flywheels where you get w^2.

Just making the wheel out of carbon fiber and making them go fast, squares the
amount of energy you can store.

~~~
rjmunro
$8000 to dig a 1m hole sounds very high - that's months of someone's salary.
Surely the best drilling machines can beat the cost of paying someone with a
shovel for a month?

But mostly they won't be digging the holes, they will be using shafts left
over from earlier mining operations.

~~~
LordHeini
That is what i found:

[https://minewiki.engineering.queensu.ca/mediawiki/index.php/...](https://minewiki.engineering.queensu.ca/mediawiki/index.php/Shaft_construction)

Honestly i would have thought it to be more expensive.

At higher depths the ground pressure is enormous and you need a lot of
bracing.

Then there is water management, air, transportation of the dug out material...

When there is rock you usually need blasting or gargantuan drills which i am
not sure even exists in the required diameter.

------
andbberger
I don't get how any of these gravitational energy storage startups get past
the napkin phase. There is no competition with pumped hydro. Who cares if
weights on winches are marginally more efficient when you have many orders of
magnitude more mass to move.

This site claims a max weight of 4.5e6 kg. Lake Powell, for example, has a max
capacity of 3e13 kg!

So, SEVEN orders of magnitude less mass to move. Sounds competitive.

~~~
kolinko
I may be wrong, but there is a limited capability for doing pumped hydro - you
may run out of elevated lakes in a region, and if you want to create new ones
then you will affect the environment.

A hole in the ground can be dug up everywhere, e.g. next to each single PV
plant.

~~~
kleiba
With seven orders of magnitude of difference, you'd have to dig a whole lotta
holes before hydro has to start worrying about competition on the capacity
level.

~~~
andbberger
Right, the thing to worry about is power, not energy. Ideally the pumps would
be sized to fill/drain lake Powell in 12 hours. Which is ludicrous. The
turbines in the Glenn Canyon Dam have a max (output) capacity of 890m^3/s [0].
It would take just over a year to drain the reservoir through them.

[0]
[https://web.archive.org/web/2016*/http://www.gcrg.org/bqr/6-...](https://web.archive.org/web/2016*/http://www.gcrg.org/bqr/6-1/glencanyon.htm)

~~~
_ph_
Which is fine, as many regions have a strong seasonal availability of
renewables. Storing energy for some months will be required to go fully
renewable. There are also short term storage requirements, over the course of
a day or a week.

------
mNovak
I always thought it'd be interesting to do the gravity storage inside the
column of a wind turbine. After all you've already built a tall steel tower.
Individually it's tiny storage, but in aggregate it's not meaningless,
especially as we keep building more towers.

But I assume there's structural issues with suspending a few extra tons on
your structure.

~~~
dragontamer
I feel like "gravity storage" should take advantage of natural landscapes
better.

ARES (rail energy storage) builds a rail-line uphill, for example. Rail cannot
handle a very steep slope, but a gentle hill climb will build up potential
energy fine.

In the case of vertical-based gravity storage, I'd imagine that lifting blocks
to the top of a cliff (or down a valley) would be most efficient.

I mean, Pumped Hydro is gravity storage, and does just that. Pumping water up
a mountain and generating energy by dropping it back down. But presumably, we
don't want to use water in the Western states (where water is scarce). So
Gravity-energy storage WITHOUT water is the goal.

~~~
syllable_studio
The issue with using natural landscapes is that it limits your height. And
adding more height is ~exponentially~ (edit: quadratically) better than just
adding more installations with an equivalent total height. (You can dig about
a mile deep). You can see more details in my comments below - search for the
text "It is worth it to dig a hole!"

~~~
andbberger
Wrong, wrong, wrong, so wrong!

Gravitational potential energy is (approximately) linear in height. I say
approximately because this assumes constant g (which is a good assumption when
h is small compared to the radius of the earth, which it is).

And in fact, a consequence of gravity's 1/r^2 nature is that one is only
subject to gravitational acceleration from what is beneath them (shells above
cancel out), so mine shafts are less efficient than towers (the effect size is
small to the depths we can mine).

So adding more height doesn't help, and if that height is underground it could
actually hurt net efficiency.

Efficiency in this context refers potential energy stored per unit height. The
field is conservative no matter what you build.

~~~
reitzensteinm
I'm assuming that the quadratic parent refers to comes from the increased
potential energy per kg of material multiplied by the ability to store more
material due to the additional volume.

If you picture a dense weight like a cannon ball on the end of a string you're
right, but if you're digging down n meters, encasing n/2 meters worth of dirt
and moving it up and down the free n/2 meters of shaft, the energy storage
would indeed be proportional to n^2.

I don't know anything about the field and had the same reaction you did, but
considering parent is running a startup in it they're either a lunatic that
doesn't know the equivalent of FizzBuzz or there's something we missed on
first inspection, and we should charitably assume the latter...

~~~
syllable_studio
Haha, thanks. It's a little of both of course. You have to be a bit of a
lunatic to think you can do these things. But someone's got to get it done.

~~~
reitzensteinm
I read the whole pitch deck and it seems like you've thought it through well.
I'm curious about the potential for failure; if one of the last links freezes
up somehow (i.e. the disengagement you mention elsewhere fails), is there a
process for clearing it?

The single shaft vs multiple parallel approach does seem a bit risky in the
early days. If there's a 10% failure rate, and you built one shaft, that's a
10% chance of an existential threat to the company. 10 shorter shafts mean one
will likely be inoperable.

Of course over the long term worrying about this doesn't make sense. Once
you've scaled, 1k large vs 10k small shafts would not matter from this
perspective.

Best of luck mate!

------
MrLeap
Is it really worth it to dig a hole? I seem to recall some other initiative
that was stacking large blocks with some kind of tested COTS construction
cranes. The stack-of-blocks way seems to intuitively scale better. You can
increase capacity without digging another super deep hole, or ever upgrading
your cabling.

~~~
reincarnate0x14
There are a bunch of these seemingly questionable ideas out there trying to
score funding. A few years ago there was one to run a train up a mountain or
create a giant compressed gas reservoir underground.

It may seem strange to use energy density in this context but in many ways
those are even worse than batteries due to the massive amount of work they
require and poor scalability because of all the physical infrastructure and
space.

In fact, this exact scheme looks to have been posted to HN in 2014. From my
understanding they are looking to re-purpose holes that have already been dug,
for the most part, which is a good idea, but if the planned prototypes are
only doing 250 kW nameplate with maybe 100 KWH of stored power, there is
almost no way it's going to beat a battery plant you can have more or less
just built to order already commercially. And said battery plants aren't even
remotely good enough at purpose for meaningful energy storage, they're mostly
used for what are considered "ancillary services" in the US power markets,
like eating or producing reactive power, voltage support, etc, because the
modern grid scale inverters can react to grid conditions faster than grid
frequencies (50-60 Hz). More rarely they might be scaled big enough to shave
the peak off a demand curve for 5-10 minutes to save transmission capacity or
congestion.

Keep in mind all this in happening when LNG is basically free except for the
cost of moving it, so you can also put in 1-60 MW combined cycle gas plants in
short amounts of time with very well understood technology and proven
manufacturers.

~~~
ajuc
I'm wondering why we don't use hydrolysis -> store hydrogen -> burn hydrogen
-> run a steam turbine for energy storage.

Efficiency would be low, at about 70% * 60% ~= 40% but capacity would be huge.
1 kg of hydrogen has specific energy of over 140 MW.

We could even capture CO2 as well with that energy and make methan and use
normal gas powerplants for retrieving the power :)

Just build double the number of solar panels to account for efficiency loses.
Should be cheaper than grid-scale energy storage with 90%+ efficiency.

~~~
_ph_
Hydrogen is difficult and consequently expensive to store. Also, the low
efficiency is a problem. Pumped storage hydroelectricity is way more
efficient.

~~~
rklaehn
At small scale, this is correct. At very large scale, hydrogen is incredibly
easy to store. You can just fill up and old depleted gas well and store
terawatt-hours of energy easily.

Germany has enough gas well storage to survive several months. This
infrastructure is currently used for natural gas, but it can be repurposed for
hydrogen.

I still think that commoditized battery storage will win in the end, but
storage cost is not an argument against hydrogen.

~~~
_ph_
Besides it is not trivial to repurpose natural gas storage for hydrogen - you
need an entirely different level of tightness, you would be disappointed about
the amount of energy you can store this way, as hydrogen is way less dense
than natural gas, so the capacity of the storage would be poor.

~~~
rklaehn
For very large scale storage we are not talking about steel pressure vessels
that are subject to hydrogen embrittlement, but depleted natural gas
reservoirs which are just gas-tight geological formations and have no issues
whatsoever with hydrogen embrittlement.

For small and medium scale storage you are right. Which is why hydrogen for
cars and even trucks is a bad idea.

~~~
_ph_
And you would get much less hydrogen stored at the same pressure than methane.
To store reasonable amounts of hydrogen, you need very high pressures. Gas
powered cars use like 60 bars of pressure, hydrogen 700.

~~~
rklaehn
Yes, that is correct. But the end to end efficiency of Electricity -> H2 ->
Electricity is much better than Electricity -> H2 -> CH4 -> Electricity.

Hydrogen at 0°C and 100 Bar (~10MPa) has a density of 8.3447 kg/m^3. It has an
energy density of 120 MJ/kg. So about 33 kWh/kg. So you end up with 278
kWh/m^3.

Now of course you have to multiply this by the H2->Electricity efficiency.
Let's be very pessimistic and take 0.6 or 60%, which is what a gas turbine
plant can achieve today.

You end up with 166 kWh/m^3 of usable electricity per cubic meter.

One of many german gas storage facilities [https://www.nafta-
speicher.de/en/company](https://www.nafta-speicher.de/en/company) has a volume
of 1.8e9 m^3. That translates into 300 Terawatt-Hours of storage capacity for
just this one facility.

~~~
_ph_
And at what pressure do those storage facilities operate?

~~~
rklaehn
Can be quite high, in the 100 bar range and above.

------
syllable_studio
Quite a few comments question the cost of digging -- which is understandable.
But the context to remember is that these are huge infrastructure investments
that will return revenue from that investment over 20-100 years with little
maintenance costs. The excavated shaft is like a factory not a product. The
product is each cycle of energy generation giving you a profit day after day.
The shaft is a one time investment that will yield that product forever.

There's lots of research showing how the costs work out (see my other comments
here)

~~~
dx034
Also, hasn't digging become much cheaper in recent years with new technologies
from the oil industry? I'm sure some of that efficiency gain can be used for
those shafts (they're obviously bigger than a bore hole for oil).

------
mullingitover
Why not merge all the energy storage ideas?

Pump air into a giant pressure chamber...that's also a super-deep hole with a
pulley system...and the weight for the pulley is a flywheel sealed in a vacuum
chamber, magnetically levitating to avoid any friction losses. Oh, and the
mass for the flywheel? A bunch of batteries.

~~~
syllable_studio
This is probably a joke, but it's not so crazy. Many designs are combining one
or more of these.

~~~
mullingitover
Not entirely joking. I just saw the big hole and immediately thought it'd be a
great place to store pressurized air, and then I continued thinking of other
energy storage mechanisms you could cram in there.

------
throwaway189262
Isn't pumped water storage the same thing but much easier to manage? Like
think of a 10 ton weight suspended from cables 100m high vs a $300 above
ground pool on a 300 foot hill. Isn't pumped water storage going to be
hundreds of times cheaper for amount of energy stored?

I didn't do the math but this reeks scam to me

~~~
shajznnckfke
$300 for an above ground pool? Where do I sign up?

~~~
throwaway189262
All you need is walmart, a hose, and a parking lot!

------
rklaehn
This will work, obviously. But I don't see how it can be competitive with
batteries.

High energy density lithium batteries are currently being commoditized. They
are also increasingly able to handle many thousands of cycles. E.g LiFePo4
cells.

The raw materials for batteries are not actually that expensive or rare, so
that leaves the manufacturing.

You might think that making something as complex as a battery can never be as
cheap as hanging a weight from a rope. But there are examples of very complex
products (solar cells, LCD displays) that became incredibly cheap due to mass
manufacturing.

A square meter of solar cells, requiring extremely pure silicon and nanometer
scale engineering, is now not much more expensive than a square meter of good
roofing shingles.

------
peter_d_sherman
>"Our patented technology is based on a simple principle: raising and lowering
a heavy weight to store and release energy. The Gravitricity system suspends
weights of 500 - 5000 tonnes in a deep shaft by a number of cables, each of
which is engaged with a winch capable of lifting its share of the weight.
Electrical power is then absorbed or generated by raising or lowering the
weight."

Idea: Could elevators be retrofitted with something like this?

Then they could use/store energy only while going up, and regenerate some of
it going down... and take passengers to various floors while doing that!

"The Regenerative Elevator"!

Stores energy going up, regenerates some of it while going down!

Invented here on Hacker News, by yours truly, 9/8/2020!

(Yes, I know, it's a stupid related idea! <g>. But my other related idea was
more stupid, and that one was to fill up a U-Haul truck with trash, put a
steel cable on it, find a hill, and use the steel cable (in conjunction with
the overweighted U-Haul truck and hill!) to drive a motor/generator/winch
assembly that uses electricity going up the hill, and regenerates some of it
back, going down the hill... <g>)

On a serious note however (for non-passenger elevator energy storage), I think
Gravitricity has a good idea, and I wish them much success with it!

~~~
hoytech
I'm not sure if you are joking or not, but regenerative elevators exist, and
have existed for over 100 years:

> DC-driven winding-drum elevators—the leading design until the 1930s—use a DC
> motor in the basement that winds and unwinds the elevator’s steel cable on a
> steel drum, thus lifting and lowering the car from pulleys atop the elevator
> shaft. DC drive was the only way to go at the time for a speedy elevator,
> because only DC could deliver variable-speed operation for smooth starts and
> stops. The DC motors were also energy efficient, capable of something that
> has only recently become possible with modern elevator designs: regenerating
> power when the elevator descends.

[https://spectrum.ieee.org/tech-history/dawn-of-
electronics/s...](https://spectrum.ieee.org/tech-history/dawn-of-
electronics/san-franciscos-secret-dc-grid)

------
gglon
Eduard Heindl's gravity storage: [https://heindl-energy.com/](https://heindl-
energy.com/)

Potentially reaches a storage capacity between 1 and 10 GWh. Lifting a (huge)
rock by pumping water underneath.

Interview: [https://omegataupodcast.net/299-gravity-
storage/](https://omegataupodcast.net/299-gravity-storage/)

~~~
syllable_studio
Yeah, this is another promising one. The other disadvantage with that design
is that the weight of the water is actually working against them. So if their
rock/concrete is about 2.5x heavier than water, the weight of water is
subtracted and you only get 1.5x the weight of water. Also their height is
limited by the height of their piston. So I'm not yet convinced that their
solution is better than just using underground pumped hydro.

~~~
gglon
It may be so. But an underground pump hydro is just boring.

------
abdullahkhalids
The video has some numbers in it about performance. They say dig a shaft of
150-1500m and hang a weight of 500-5000 tonnes. This translates to energy
storage of between 204-20400 KWh storage.

Obviously, this seems very technically challenging. 500 tonnes is 64 m^3 of
iron. We will see if their engineering is good enough to pull off their
claimed 171 US$/MWh.

~~~
jayd16
26 m^3 of tungsten is what, less than a 3x3x3m cube? If they stack 10 cubes at
the bottom they get mostly the full storage (-3m at least) for each weight.
Seems feasible.

~~~
9nGQluzmnq3M
Tungsten costs around $30k/ton, so you'd be looking at a cool $15M for that
500T cube.

Lead goes for around $2k/ton, so this might be a more feasible compromise.

~~~
brohee
Depleted uranium prices are very hard to find, but should come as cheaper than
tungsten.

Civilian sales look at least possible, I heard of at least one sailboat with a
DU keel.

------
yongjik
Sorry for repeating myself, but gravity is weak. If you hang a 500t weight in
a 150m vertical tunnel, it only holds 500 * 1000 * 9.8 * 150 = 735000000 J, or
735 MJ, that is, 204 kWh.

A Tesla model 3, basic model (MSRP ~$38k) has battery capacity of 50 kWh, so
we're talking about four Tesla 3's.

I don't think digging a 150m hole is cheaper than four Teslas - and Teslas
come with the rest of the car you can use for driving.

~~~
syllable_studio
Gravity is weak, but it's cheap. It is indeed surprising, but plenty of
research shows that the levelized cost of gravity storage is cheaper than Li-
ion batteries - even if you assume that Li-ion will get 4x cheaper in the next
20 years. There are other problems with Li-ion as well that will prevent it
from scaling up to the amount of storage that our grid will need. I discuss
all this with lots of citations in a white paper here
[https://github.com/syllable-hq/uphs-feasibility-
study](https://github.com/syllable-hq/uphs-feasibility-study)

~~~
gspr
> Gravity is weak, but it's cheap.

I'm sorry, I'm not trying to be pedantic, but what does "gravity is cheap"
even mean?

~~~
syllable_studio
No worries. Here is a good resource that talks about the levelized costs of
gravity storage. It's estimated to be much cheaper than Li-ion battery storage
on large scales.

[https://www.storage-lab.com/gravity-based-storage](https://www.storage-
lab.com/gravity-based-storage)

------
zaroth
If you wanted to build one at the scale of a PowerWall (5kW/13.5kWh) what kind
of height/weight combinations would be required?

By my calculations you would need to raise 40 tons up 3 meters to store
13.5kWh. Definitely not a home storage revolution!

Now, if the entire house was built on a lift....

~~~
mkj
Isn't that 0.326 kWh? 40e3 * 9.8 * 3 / 3600

~~~
zaroth
Damn, you're absolutely right. Off by a factor of ~40...

You would need to raise the 40 tons up 120 meters, or conversely, you would
need to raise 1,600 tons up 3 meters.

------
simonebrunozzi
Energy storage by lifting or releasing a weight, in their case, in a well
underground. Nothing new; I am wondering what's special about them, compared
to tens of other companies trying to offer the same type of energy storage.

AFAIK, the most common is done around hydro dams, by pumping water upstream as
a form of energy storage. The infra is already there, but it's not as
efficient as systems like Gravitricity. But it costs a negligible amount of
money to "activate" energy storage in a pre-existing dam.

~~~
mNovak
I believe the argument for new storage concepts is that renewables will drive
a need for large amounts of new energy storage capacity, batteries are
expensive, and that not everyone is situated near a suitable geography for
pumped hydro.

------
kaliszad
My father has an idea to use sodium (Na) as fuel for fuel cells. This could
easily replace batteries by having more or less instant reactions to demand,
being much more energy dense and being simple to handle. Also, there is no
CO_2 that would need to be captured compared to "bio" fuels. The resulting
sodium hydroxide (NaOH) and hydrogen (H_2) can easily be used further e.g. in
the chemical industry or recycled, electrolysis of NaOH is well known and also
produces hydrogen as a byproduct. The resulting sodium metal can again be used
as fuel. It creates a circular economy. Handling sodium securely at scale is
also probably even easier than handling gasoline or diesel. Most of these
reactions at industrial scale are more than 50 years old but nobody bothered
to actually implement it (even though a hint about sodium cells for
electricity generation is present in "Twenty Thousand Leagues Under the Seas:
A World Tour Underwater" by Jules Verne already) instead of the more complex
approaches like e.g. synthetic gasoline.

You can look at the orgpage about these ideas
[https://orgpad.com/s/energiewende](https://orgpad.com/s/energiewende) my
father also gave a talk last week about it, there is a recording, which will
be posted during the next days.

Disclaimer: I work for the small startup OrgPad, which tries to create a tool
for easier decomposition of linear ideas/ content into a network of ideas/
content. An ex-Googler, Pavel Klavík PhD. describes the technology (hint
Clojure and ClojureScript) and approaches behind OrgPad in a recent talk
[https://www.youtube.com/watch?v=4UoIfeb31UU](https://www.youtube.com/watch?v=4UoIfeb31UU)

~~~
willis936
Many years ago I briefly had a thought experiment about converting a
gasoline/oxygen combustion engine into a sodium/water combustion engine. Solid
fuel mixing concerns aren’t the primary issue. The primary issue is the energy
density is just so danged low compared to gasoline. However, compared to
electric batteries, sodium is far more energy dense.

~~~
kaliszad
Well, there are patents for running diesel engines with sodium, at least I was
told so much by my father who researched the problem thoroughly. The density
isn't that low considering using a fuel cell, you can convert the energy a lot
more efficiently. Also you don't just burn up the fuel into the air as
currently, there is no industrial process to collect the CO_2 and other gases
produced from the exhaust.

------
klunger
This reminds of Energy Vault [1], which is based on the same principle, just
above ground. Doing this above ground seems to make a lot more sense when you
consider all of the additional costs associated with digging and maintain
massive shafts. I am not clear why the underground approach is at all
appealing. Can anyone explain?

[1] [https://energyvault.com/](https://energyvault.com/)

~~~
syllable_studio
Yeah, very similar. The main reason is that you can get about 10x more height
underground. You can dig about a mile deep. An Energy Vault tower is about 500
feet tall. And as mentioned below in other comments, adding more height gives
you more storage per weight, so it's super important. Adding more height and
weight scales quadratically while just adding more weight (in side by side
towers) only scales linearly.

[https://docs.google.com/presentation/d/17FI-
jrI9RWS3q7Ng44Yh...](https://docs.google.com/presentation/d/17FI-
jrI9RWS3q7Ng44YhiHs7il8JvnxK-cV6_g_-cGo/edit#slide=id.g844fb8814b_1_136)

~~~
klunger
Wow, I see you have already thought about this exact question a great deal.
This was a clear and compelling answer.

Your pitch deck is impressive. Good luck!

~~~
syllable_studio
thx!

------
scythe
If you dig a well with cross-sectional area _A_ and depth _D_ , the amount of
energy you can store with compressed air at 10 MPa is 10 _AD_ MJ if _A_ and
_D_ are expressed in m^2 and m respectively. [1]

If you drop a steel weight down the same well of cross-section _A_ and height
_H_ in the same units the energy stored is 0.08 _HA_ ( _D_ - _H_ ) MJ[2].
Again, _H_ is in meters, and _AD_ > _A_ ( _D_ - _H_ ), and in order to beat
compressed air 0.08 _H_ > 10, so your steel weight needs to be 10/0.08 = 125
meters long! That's taller than most of the buildings in downtown San
Francisco -- and in order to get any use out of this thing, your hole should
be at least twice that deep.

Of course, compressed air has its inefficiencies and complexity, but the
feasibility of a metal rod even close to that long seems pretty low to me.
Compressed-air caverns use as much as 7.5 MPa, but a purpose-built well could
potentially go much higher. Plus you don't have to deal with the damn thing
vibrating from Coriolis forces and seismicity.

Now, I know what you're saying -- you're saying, if you're so smart, why don't
you do it? -- but there are simply too many huge caverns out there to even
think about constructing CAES chambers. There are several GW in service today.
And even with that huge resource people wonder if batteries won't simply
corner the market. Storage is getting here painfully slow, it seems like, but
the competition is very fierce.

1: True isothermal decompression cycles are impossible, so of course I'm
approximating by using the ideal gas law.

2: (8000 kg/m^3)(10 m/s^2)/(mega = 1000000) = 0.08

~~~
syllable_studio
Yeah, compressed air is a very viable and promising solution. It does have
efficiency trade-offs as you mention though. And typical compressed air
designs still use fossil fuels in the compression process. There are some new
designs I've seen that get around using fossil fuels.

One of the most prominent new startups out there exploring advanced compressed
air is hydrostor. Note that they also dig underground :)
[https://www.hydrostor.ca/technology/](https://www.hydrostor.ca/technology/)

------
lebuffon
How does it compare to liquified air storage? It might have a sweetspot
somewhere but liquid air uses a lot of off-the-shelf technology.

[https://www.rechargenews.com/transition/liquid-air-
storage-o...](https://www.rechargenews.com/transition/liquid-air-storage-
offers-cheapest-route-to-24-hour-wind-and-solar/2-1-635666)

------
diimdeep
Where is innovation and efficiency ?

To me it smells like
[https://www.youtube.com/watch?v=uzV_uzSTCTM](https://www.youtube.com/watch?v=uzV_uzSTCTM)
and all about patents, marketing and money burning, but I don't know as much
as these professors do so maybe I am wrong.

~~~
Blammar
Oh, there are definitely interesting problems to solve. See my post below for
some issues.

------
_ph_
The concept is quite obvious and has been proposed several times in the past.
The key question is, what are the costs? Even if the costs for drilling the
hole are written off over a very long time span, the wires that hold the
weight and the machinery have constant operation costs. It probably can't
compete with pumped storage, but pumped storage isn't viable without at least
some hills. This concept could be deployed in many regions, also wouldn't take
much surface space, you could deploy it even in densely populated regions. The
question is: how does it compete with e.g. batteries?

------
neilwilson
Interesting idea.

Why would this be better than a set of railway lines down a hill side into a
forest pulling up standard goods carriages full of rocks?

You get a forest (which buffers runaway carriages and does all the other
lovely forest things) and energy storage on the hill. All using largely
commodity items and you can build it anywhere there's a spare slope.

~~~
dx034
That's what ARES promised 4 years ago. But their website looks abandoned. [1]

[1] [https://www.aresnorthamerica.com/](https://www.aresnorthamerica.com/)

------
nicexe
You could theoretically store energy by winding springs and making use of it
by letting them unwind (by spinning a generator or whatever). Toy-car style.

This doesn't involve digging a deep hole in the ground and hope that the earth
keeps it level.

A drawback would be the hazards that heavy tension/forces bring with them.

~~~
tgvaughan
This was precisely the basis of the energy storage systems in Paolo
Bacigalupi's novel, The Windup Girl.

------
wqsz7xn
Isn't this the exact same concept as a dam which pumps water back up when you
have excess power? Also how heavy does that weight have to be to be able to
store enough energy worth digging a hole that large? Can you even get a weight
heavy enough to store a significant amount of energy?

~~~
syllable_studio
You can in fact! Pumped hydro is already the cheapest form of energy storage -
about 95% of all energy storage is pumped hydro. We can't build more pumped
hydro because it's not feasible to build enough dams. (We've used up the best
locations)

The US Gov has studied plenty of research showing that underground pumped
hydro is cost effective and obviates the need for dams. (See my white paper
here: [https://github.com/syllable-hq/uphs-feasibility-
study](https://github.com/syllable-hq/uphs-feasibility-study))

So startups like Gravitricity (and Terrament, my startup) are innovating on
what is already well-researched territory.

------
deeviant
Why does every gravity storage startup claim they invented gravity storage?

It's not just not true, it's like, _obviously_ not true. Anybody that took
high-school level physics understands gravitation potential energy and it's
not a huge leap from there.

------
markvdb
Does anyone know if something like this has been implemented in some way
already? In old mine shafts maybe? The geology has been studied, and some
shafts at least there already...

~~~
syllable_studio
Yeah, I did a feasibility study on underground pumped hydro which you can find
here: [https://www.terramenthq.com/uphs/](https://www.terramenthq.com/uphs/)

UPHS has never been fully built to my knowledge, but it's been well studied
and quite a few projects have tried to get funding for it.

U.S. DOE research from 1984:
[https://www.osti.gov/biblio/6517343.pdf](https://www.osti.gov/biblio/6517343.pdf)

Projects trying to work on this: [https://utilitymagazine.com.au/pumped-hydro-
storage-the-futu...](https://utilitymagazine.com.au/pumped-hydro-storage-the-
future-for-old-mines/)

Other proposed projects: \-
[https://www.waterpowermagazine.com/features/featureinvestiga...](https://www.waterpowermagazine.com/features/featureinvestigating-
aquabank-)

\- [http://www.eaglecrestenergy.com/project-
description.html](http://www.eaglecrestenergy.com/project-description.html)
[https://www.osti.gov/biblio/6517343.pdf](https://www.osti.gov/biblio/6517343.pdf)

------
beefman
If that weight were a fission reactor you wouldn't have to move it up and
down. And it would be 100% efficient. And you wouldn't need an external power
plant.

~~~
syllable_studio
The nuclear debate is interesting, with valid talking points on both sides.
But even if nuclear were safer and cheaper than wind+solar+storage (which it
isn't), it would take decades to build. We might not have that much time.

Climate change is urgent and we need all hands on deck to build as fast and as
cheap as possible. May the best designs win asap in this fight!

~~~
p_l
Some of the known SMR designs are amenable for mass production, _if someone
would kickstart the line by putting money on the table_. Very safe ones at
that.

A lot of the cost goes down when the reactor isn't a practically one-off
build, and when you can for example use prefabricated components to "assemble"
a power plant quickly.

Some designs go even further, and have power blocks that are essentially
something you slap on large railcar, including option that instead of
refueling you send back the module while the vendor sends you a freshly-fueled
one.

------
steeve
5000 tons at 1500m is ~20MWh [1], assuming 100% efficiency (frictionless free
fall).

That means that the theoretical maximum is 50x (!) less than 1 nuclear reactor
can do in 1 hour (1000 MW for 18 months or 13 140 000 MWh). Put it
differently, you'd need to dig 50 of these to output the equivalent of 1
nuclear reactor (and nuclear plants have 2 or more reactors) for one hour.

That's also assuming digging a hole this deep in a stable manner.

[1].
[https://www.wolframalpha.com/input/?i=5000+tons+*+9.8m%2Fs%2...](https://www.wolframalpha.com/input/?i=5000+tons+*+9.8m%2Fs%2Fs+*+1500m)

~~~
LordHeini
You are completely mixing up MWh and MW which are two different things.

~~~
steeve
You are right. The actual number for a nuclear reactor is 13 140 000 MWh.
(1000MW * 18 months). But I figure people would get the idea better.

------
graiz
Interesting concept but digging a big hole sounds expensive and prone to
flooding. I can see how this would have better efficiency than pumped-storage
hydro but I wonder if you couldn't raise and lower weight near cliffs rather
than drilling wells.

If it does work, I would imagine the Boring company would be all over this.

~~~
syllable_studio
I can see why you'd suspect that. But it turns out that the oil and gas
industry has 100 years of precedent demonstrating how to build such shafts
into bedrock. Flooding and earthquakes are all real concerns, but we have
well-proven solutions.

~~~
imtringued
Oil rigs only need to drill a hole with the diameter of a pipe. With gravity
storage you would want the hole to be as large as possible.

~~~
syllable_studio
Maybe not as large as possible, but we're looking at about 10m diameter and
about 1 mile deep. Here's an example of existing mining tech that meets this
capacity.
[https://www.youtube.com/watch?v=z5vAWR7rpco](https://www.youtube.com/watch?v=z5vAWR7rpco)

------
thelastname
Am I the only one to expect the goatse on the bottom of the site?

------
um_ya
Can we stop with these convoluted systems and just do nuclear already?

~~~
X6S1x6Okd1st
With nuclear you still need storage to flatten the peaks and troughs though
right?

Also this does not seem very convoluted, it's using an electric engine pretty
directly. If you are actually boring straight down it seems like the failure
modes are pretty okay.

~~~
core-questions
> With nuclear you still need storage to flatten the peaks and troughs though
> right?

Why? Just build more. Keep expanding capacity so the base load covers the
peaks and thensome. Push the price of electricity down while keeping it
carbon-neutral and crush competition. Get everyone 2c/kwh power. Wouldn't that
be more fun?

~~~
_ph_
The problem is the speed at which the reactors can be ramped up and down, this
is very limited. Also, if you have enough capacity to cover all peaks, most of
the time the reactors are not running at full power. That increases the cost
of operating the reactors, which is far higher than you claim. Currently,
projects building new nuclear reactors are challenged by their costs. Never
mention the safety concerns and of course the waste problem.

~~~
jabl
Current versions of the traditional LWR design can ramp at about 5% of full
power per minute, which is about the same ramping rate as a CCGT plant. With
steam bypass it's possible to ramp even faster.

Demand response, frequently promoted as a way to increase penetration of
intermittent renewables, can also be used to reduce the cost of a system
composed on high capital cost, low marginal cost dispatchable generators like
nuclear. Charge the EV's and run heat pumps to warm thermal storages during
the night when demand is lower, say.

~~~
_ph_
Yes, demand response will play a huge role in the grids of the future. But
when you say "current versions", which current operating nuclear plant
achieves this ramp speed?

Also, it means you have to run your reactors regularly at below 100%, so you
still can react on additional demand, which increases further the cost of a
very expensive technology.

~~~
jabl
> But when you say "current versions", which current operating nuclear plant
> achieves this ramp speed?

IIRC that 5% figure I read was wrt EPR and AP1000, presumably older generation
LWR's are slower, by how much I'm not sure. France has run older generation
PWR's in load-following mode for decades, but I'm not sure which ramp speeds
they achieve; fast enough in practice in any case it seems. CANDU reactors in
Canada have steam bypass and can apparently ramp at >10%/min.

In any case, my point is that ramp speed is in practice not a technical
limitation. Of course you want to run a generator with high capital cost but
very low marginal cost at 100% as much as possible, but if you now and then
need to ramp (say, if the wholesale price goes negative) you can do it.

> Also, it means you have to run your reactors regularly at below 100%, so you
> still can react on additional demand, which increases further the cost of a
> very expensive technology.

To be clear, I'm not advocating a 100% nuclear grid. I'm just pointing out
that the "nuclear can't ramp and is thus unsuited for the grid of the future"
isn't correct. In particular, I think solar and a moderate amount of storage
is very well suited to cover the daily variation in many parts of the world. I
also think that dispatchable low-carbon sources (which could be hydro, or
nuclear, or something else like geothermal where available, CCS where
geological formations for storing CO2 are available, etc.) have a role to play
in least-cost deep decarbonized grids. See e.g.
[https://doi.org/10.1016/j.joule.2018.08.006](https://doi.org/10.1016/j.joule.2018.08.006)

~~~
p_l
From my understanding some of the "delay" in ramping up is related to
enrichment level of the nuclear fuel and thus how fast the speed of the
reaction can change.

~~~
jabl
Kind of. When reducing power there's a buildup of a particular Xenon isotope,
which is a powerful neutron adsorber. So until that isotope decays away
sufficiently you might have problems starting the reactor back up again.
Unless you have enough excess reactivity, such as by having fresher fuel
loaded.

AFAIU France primarily uses reactors which are earlier in their fuel cycle for
load balancing, and ones which are near the end run with a flatter profile.

~~~
p_l
Makes sense!

Didn't know about specific as it's not really my area, but would running a PWR
with very high enrichment level (AFAIK some designs use 93% U-235) allow quick
spin down and spin up?

~~~
jabl
> would running a PWR with very high enrichment level (AFAIK some designs use
> 93% U-235) allow quick spin down and spin up?

Well.. there are a lot of factors in a reactor design affecting the ability to
increase or decrease power quickly. Geometry, fuel/moderator ratio, fuel
density, burnable poisons (for flattening the reactivity swing over the fuel
cycle), amount of control rods etc etc. Fuel enrichment being only one thing,
which in turn affects other things as well (e.g. reactors using highly
enriched uranium tend to use different fuel designs than low enriched fuels).

But yes, military reactors for navy ships obviously have very different
demands on them than civilian power reactors, and are designed accordingly.

And yes, while US navy reactors use 93% enriched fuel, it's not necessary,
e.g. French and apparently Chinese submarines use low enriched fuel (7% for
French).

------
dave333
All this is moot. Hydrino energy will make storage largely unnecessary except
possibly for small handheld devices.
[https://brilliantlightpower.com/news/](https://brilliantlightpower.com/news/)

~~~
syllable_studio
Wow, this is surprisingly less-debunked than I expected. Though, of course my
first reaction is extreme skepticism. But I guess we'll see!

[https://www.quora.com/What-is-wrong-with-Dr-Mills-Hydrino-
Th...](https://www.quora.com/What-is-wrong-with-Dr-Mills-Hydrino-
Theory?share=1)

[https://en.m.wikipedia.org/wiki/Brilliant_Light_Power](https://en.m.wikipedia.org/wiki/Brilliant_Light_Power)

~~~
gryfft
Ahem.[1][2]

"We'll see?" This guy has been milking this since 1991. As Aaronson's article
so sardonically points out, there's _nothing there to debunk._ Every claim
that can be made about the "hydrino" can be made with equal weight about the
"doofusino," so what's the point?

He's had three DECADES to set up any kind of publicity stunt or get the
attention of any number of existing billionaires or just scrape together the
resources he needs to build the no-shit this-changes-everything prototype. Or
maybe Elon Musk and everyone who knows him is an idiot without vision who
think they can make a buck on solar when this guy's world-changing technology
is _right around the corner this time for really real I promise._

[1]
[https://en.wikipedia.org/wiki/Brilliant_Light_Power#Criticis...](https://en.wikipedia.org/wiki/Brilliant_Light_Power#Criticism)

[2]
[https://www.scottaaronson.com/writings/doofusino.html](https://www.scottaaronson.com/writings/doofusino.html)

~~~
dave333
The Wikipedia article has been policed by skeptics and is not a fair
assessment of Mills. Doofusino theory article is just satire and offers no
serious rebuttal. Mills has made considerable progress over the decades
overcoming engineering challenges in harnessing hydrino energy release. Recent
advances of electromagnetically pumped liquid metal electrodes (to solve the
problem of tungsten electrodes instantly melting), and a ceramic cell liner
(solves the problem of the hydrinos melting a hole in the side of the reaction
vessel) have got Mills close to a field prototype and he has prototypes that
produce hundreds of kW continuously (hundred hour run) with water bath
calorimetry. The skeptics will soon have scoffed their last.

~~~
gryfft
Policed by skeptics? That's the POINT of Wikipedia! Are you saying that a
communal resource based on accurately documenting actual reality should be run
by credulous people who will accept any statement without applying one
second's worth of critical thinking?

As I said, Doofusino doesn't NEED to be a rebuttal. THERE IS NOTHING HERE TO
REBUT. The proof is in the pudding and Mills has _no pudding whatsoever._ All
he has are his claims about all the magical fairytale things his wonderful
technology can do.

I don't care if he says it can braid my hair and create free cheerios on
demand because he finally found the right alloy to use in his psychogravitic
negamatrix. It's not real until there's proof and he hasn't offered any in
thirty years. See you in another thirty, I guess.

~~~
dave333
Wikipedia doesn't support debate - only authoritative sources are allowed -
which means novel theories yet to be fully accepted get locked out and
ridiculed by the skeptically correct.

There are many experimental papers that show hydrinos exist and have the
properties predicted by Mills classical model of the hydrogen atom.
[https://brilliantlightpower.com/](https://brilliantlightpower.com/) has many
videos of working prototypes producing excess energy. Dark matter exists and
interacts gravitationally like baryonic matter but is electromagnetically
inert like hydrinos are predicted to be. The expansion of the universe
accelerates (Mills predicted in the 1990s). Etc.

