
How much energy can you store in a stack of cement blocks? - tzury
https://www.wired.com/story/battery-built-from-concrete/
======
donjoe
Previous discussion:
[https://news.ycombinator.com/item?id=17789456](https://news.ycombinator.com/item?id=17789456)

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olooney
The wired.com article says:

> assuming energy transfers are 100 percent efficient—which they aren't.

A startup doing a large scale version of this idea using commercial tower
cranes claims 85% efficiency, but take that with a grain of salt:

> The round-trip efficiency of the system, which is the amount of energy
> recovered for every unit of energy used to lift the blocks, is about
> 85%—comparable to lithium-ion batteries which offer up to 90%.

[https://qz.com/1355672/stacking-concrete-blocks-is-a-
surpris...](https://qz.com/1355672/stacking-concrete-blocks-is-a-surprisingly-
efficient-way-to-store-energy/)

Of course, the gold standard way of doing this is with pumped hydro, hovers
around 80% efficient.

> The round-trip energy efficiency of PSH varies between 70%–80%, with some
> sources claiming up to 87%.

[https://en.wikipedia.org/wiki/Pumped-
storage_hydroelectricit...](https://en.wikipedia.org/wiki/Pumped-
storage_hydroelectricity)

~~~
mikeash
85% at least seems fairly reasonable. Your main losses will be in the
motor/generator, and that sort of roundtrip efficiency is doable there. Hydro
will be a bit worse as you'll also suffer from turbine losses, but the
coupling between a motor and a concrete block will be nearly 100% efficient.

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hyperbovine
I must be getting old and cranky. "This is sort of awesome" seems like the
most asinine opening to a magazine article ever written.

~~~
rb808
Welcome to the new world of journalism where no one pays subscriptions and
writers mostly interns surviving on click bait.

~~~
ryanwaggoner
The author is a physics professor, not an intern.

~~~
Elrac
The parent poster didn't suggest otherwise.

Thanks for making me aware that the author is a prof! But I'm afraid that
makes things even worse. As I see it, the writing quality is barely acceptable
for an intern: it's so colloquial it almost buries the core message, and it's
full of very irrelevant details. Two examples: (1) We're talking about
straight vertical lifting from the start, so why bother giving the formula
that considers the angle of the force vector? (2) why analyze the energy flow
of stacking barrels when the most straightforward implementation (as discussed
later) deals with simply lifting barrels some height above ground level?

This article could have been more clear and more approachable after editing it
down to half the text.

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pjc50
Cost is listed as "less than $2m" for a capacity of 20MWh, charge/discharge
rate not specified but probably a low "C" factor of that. $100/kWH? That's
actually very favourable when compared to batteries; I see Tesla Powerwall
prices in the >$400 range.

As others have noted, it's not very space-efficient. Compare with
[https://en.wikipedia.org/wiki/Cruachan_Power_Station](https://en.wikipedia.org/wiki/Cruachan_Power_Station)
: you'd need 355 of these to equal its capacity. I suppose you could start
dotting them in groups around wind farms?

~~~
stephengillie
Driving an down some hills can regenerate 400-500 Wh, at least in my hybrid,
so it would take 40 million electric cars to convert 20 MWh in this way.

On the topic of energy density, other solutions - like the house-sized lead-
acid battery - have been proposed on the grounds that energy density isn't as
important for stationary power stations as other factors, like the vampire
effect. Losing 1% of your charge per day is a big issue when storing 20 MWh.

~~~
pjc50
Not sure about that charge loss question; it depends on how often you're
cycling the battery, if it's charged and discharged every day then self-
discharge losses may be much smaller than inefficiency losses or the wearout
cost on the battery. 1% of 20MWh is 200kWh or about £30 of electricity.

The other unclear factor is "C" rate. Is it actually possible to do a full
20MWh cycle in a day?

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dsfyu404ed
If the math works out so well then why don't elevators and other apparatus
that lift things with electric motors use batteries and regenerative braking
on the way back down in order to mostly offset the energy cost of operating
them?

I'm betting the economics of recovering gravitational potential energy don't
really work out in most use cases.

~~~
srigi
Elevators are not cranes. There is always a counterweight, so "dropping" empty
cabin is not generating energy. During that time you're lifting counterweight.

~~~
RobertRoberts
Wouldn't the counterweight only balance (a guess) an empty elevator? Therefore
any added weight would be useful for energy recapture?

I realize there may be some over compensation in play, but unless the counter
weight's weight is actual adjusted for each load, there should be something to
work with.

~~~
bunderbunder
Regenerative elevators do exist. I've no idea what they cost, but, shooting
from the hip, I'm guessing they aren't worth the added price on any but the
biggest buildings.

Any weight difference due to meatsacks in the elevator will be relatively
small compared to what a drum full of concrete weights. Going off the math in
TFA, and assuming your average meatsack weighs 75kg, lifting one of them 15
meters up (so, roughly, to the top floor of a 6 story building) stores about
half a smartphone battery worth of potential energy. So you probably want to
be lifting them _much_ more than 15 meters - and be packing your elevator cars
full of them - if you want to pay off the cost of the fancy regenerative kit
in any reasonable amount of time.

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DoofusOfDeath
I'm a little embarrassed that in all of the discussions I've heard about ways
to store solar energy for dark periods, I never noticed that this kind of
solution was omitted.

I wonder how it stacks up against the more commonly discussed approaches.

~~~
DavidHm
Eh. (imho) Hydro pumping is way more simple, and is just limited by the fact
that you can't have it wherever you want.

Also concrete is not exactly environmentally friendly to make.

~~~
tomatotomato37
This actually seems like the more ecological design, as the concrete used for
weight here would be less than the amount used for a dam, and you wouldn't
also have to pervert the flow of a river in order to build it. Besides, one
time costs are trivial compared to running costs of industrial processes in
terms of the environment, especially in terms of power production.

~~~
konschubert
> as the concrete used for weight here would be less than the amount used for
> a dam

Think that through.

A dam probably holds 100 or 1000 tons of water for every ton of dam material.

A concrete weight holds exactly on ton of concrete for one ton of concrete
weight material.

And "amount of weight helt", be it water or concrete, is Exactly what matters
here.

------
sbradford26
So instead of using a crane, I think you could make something similar to the
chain that pulls a roller coaster up.

So you would have a tall vertical tower and at the bottom it transitions to a
horizontal conveyor belt. Each of the drums are attached to the chain that is
connected to the motor. When you run the motor is pulls the barrels from the
horizontal conveyor and up into the tower. Then when you need power you let
the barrels fall and spin the motor, and collect on the horizontal conveyor.

Still not saying it is a practical battery, just seems more reasonable than
using a crane.

~~~
t0mbstone
I'm pretty sure they just used a crane to prove the concept. It would be
pretty dumb for them to use a bunch of expensive cranes for a permanent
installation.

I have to say, though, I think you might be onto something with your
horizontal/angled conveyor idea. I would be worried about the energy lost to
friction, though? The nice thing about a straight up/down solution is that it
doesn't have that problem.

~~~
sbradford26
Definitely would have a good amount of friction losses, the issue I have ran
into is that I am not sure how you would raise blocks and add them to a stack
with low friction.

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nshr
I was wondering if it would be possible, perhaps, instead of using cranes to
stack blocks of stones, to elevate an entire building by some small amount
every day when there is enough excess energy. Lowering the building in the
night to recover some of the stored energy. This would definitely be a very
challenging engineering problem but the thought of transforming each house in
a city into a battery using only its own potential energy without being
dependent on chemical means of storage is intriguing to me.

~~~
kubiiii
I was about to post the exact same idea. I don't know if it would be efficient
(plus mechanicaly lifting up a building is an engineering nightmare to do) but
it would be a very elegant way of storing solar energy, or energy recovered
from lost calories.

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sandworm101
What are the maintenance costs of such a crane, remembering that it runs 24/7
at its max capacity?

I ask because simple lead acid batteries can be hooked into control systems,
with maintenance done via changes to electricity and fluid. With such
batteries there are no cables or bearings to need changing, no moving parts.
So I would assume that maintenance costs for oldschool batteries would be far
less than for this crane.

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jasonjayr
I've seen this tower energy storage discussed a few times, but ... what
happens in a wind storm? Does the system dump all the blocks to the ground to
protect against toppling? How about if a block at the base structurally fails?
Are these storage facilities only suitable for wide open areas with nothing
around the falling radius of the tower?

~~~
pjc50
A conical pile of extremely heavy blocks is probably a lot less likely to
collapse than any of the buildings around it.

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gwbas1c
The point is at the end:

> But that gives 2 million joules of stored energy with just 50 cement drums
> (assuming energy transfers are 100 percent efficient—which they aren't).
> That's not too bad. Of course the Tesla Powerwall can store about 50 million
> joules, so 50 drums might not be enough.

Basically, lifting and lowering cement is a poor battery.

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handruin
The article leaves me with more than a few doubts with this strategy of
storing power. One issue that concerns me is the amount of energy that will
need to be spent in manufacturing all the concrete and steel drums as well as
the amount of pollution this will generate. There will also be the pollution
in transporting the drums onto the battery locations. I get that this isn't a
unique problem and other forms of "green" power generation also suffer from
this such as wind turbines or even photovoltaic panels. Once the drums are
onsite there is likely minimal maintenance needed so once the cost of
producing is done, there should be a way to figure out how many years or
months it would take to offset that.

~~~
0xffff2
> I get that this isn't a unique problem and other forms of "green" power
> generation also suffer from this such as wind turbines or even photovoltaic
> panels.

Is there any form of energy storage/generation for which this isn't true? No
one every talks about the environmental costs of Lithium batteries, but
they're certainly not nil. Pumped storage requires substantial infrastructure
as well.

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nashashmi
There needs to better use of a stack of blocks than just moving them up and
down.

How about lifting and dropping heavy lithium batteries instead?

Or lifting and dropping cars in a parking garage?

Or lifting and dropping self contained data centers?

~~~
nashashmi
Here is another idea: concrete blocks on rails plated with solar panels,
sometimes stored vertically, sometimes stored horizontally, with rails shaped
as an "L", utilizing the most unusable land.

Laws of fluid mechanics will apply then. And the size of the motors will be
ginormous.

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larrydag
Some problems I see with this design are space, labor and logistics akin to a
warehouse, impacts from natural disasters.

Personally I like the idea of moving water up a river or behind a dam to store
energy.

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davio
Sounds like how a grandfather clock works.

