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Stacking concrete blocks is a surprisingly efficient way to store energy (qz.com)
726 points by nabla9 on Aug 18, 2018 | hide | past | favorite | 382 comments

Huh, I'm less doubtful of this than I thought I'd be. Tower cranes are apparently surprisingly low-maintenance. I assume this is because they have to actively participate in their own disassembly [1] and major breakages are super difficult to deal with because they're at altitude, so they need to operate reliably enough that they can always take themselves down at the end of a job or if they need a major repair (cracks found in main pivot ring, etc). Concretely (pun not intended), I found a document [2] saying that 10 tradesmen and $35k/month in parts (together a bit more than $1m/year) can keep a fleet of 70 tower cranes (15 metric ton lift capacity each) at ~80% utilization over a one-year period. So, yeah, I'd definitely believe that you could run these things at the quoted price.

1: https://www.youtube.com/watch?v=Nww6MN_Lxeo&t=24s

2: Annex 9, "Example of the Use of Key Performance Indicators for Maintenance", in this PDF: https://www.mantiscranes.ie/wp-content/uploads/2017/01/CPA-T...

That kind of cranes is very reliable, but in the real world they are used maybe 10% of their capacity [1].

In a normal building site they either do very few cycles per hour (at heavy loads) or a decent number of cycles per hour at a tiny fraction of their load capacity.

Even when you use them intensively (with concrete buckets) to lift/pour concrete, that happens for a relatively short time (a few hours) each day.

A typical cycle is 5-10 minutes and you don't actually have 12 or 6 of them per hour, each hour in a normal 8 hour shift and - with some exceptions you normally have 1 shift per day, 5/7 (it is rare that a site working with cranes operates 24/7).

Besides, in a building site you don't work when it rains, and you cannot work with cranes if there is a not-so-strong wind blowing (for safety reasons).

[1] no reference, you will need to trust my word for it, coming from some 30+ years experience in building sites

No need for a reference; now that you mention it it's obvious that the duty cycle will be totally different. In fact, I'd bet that cycle time is the limiting factor - the graphic [1] shows about 100 cylindrers per layer, 18 layers already stacked, and the system looks to be around 60% loaded, so total count could be around 3k cylinders to move for a full load. Six arms, then each is doing 1000 cycles a day. Assume 4 hours down a day, 20 hours up, 50 cycles an hour, a bit less than a cycle a minute. Yikes.

I did notice that the cylinders were around twice the quoted capacities for tower cranes I was finding. It also sounds like they're building a much more expensive crane; that many cylinders, at 35 metric tons per and $90 for a yard of concrete, is upwards of $5m, and the article says that the concrete "could" be the most expensive part. Aaaaand random googling is giving me price tags for tower cranes that can't possibly be right - <$300k?! So the quoted system might be using a crane that's ten times the cost of a "normal" tower crane? I can... sort of seeing that buy a six-armed crane with twice the lift capacity but permanent construction, no need for a counterweight assembly, and better continuous performance. But now I feel like these numbers are lining up too well and I have to have done something wrong.

1. https://cms.qz.com/wp-content/uploads/2018/08/energy-vault-l...

2. http://www.wolframalpha.com/input/?i=3000+*+($90+%2F+cubic+y...)

>I did notice that the cylinders were around twice the quoted capacities for tower cranes I was finding.

A "normal" (very large) tower crane rarely exceeds 12 tons, BUT, more than that, usually these use not "single" cable, i.e. a largish crane is usually 6 tons max, but can lift up to 12 tons doubling the cable/rope (which implies halving the lifting speed).

Moreover, cranes are rated/designed (loosely) on their reach, they are intended - within limits - to cover a whole building site, so arms of 20-30-40-50-60 meters.

An electric tower crane (a "normal" one) is well below US$ 300 K, I seem to remember we paid for a very large one, 80/100 meters tall, 50/60 meters arm, 6/12 tons at arm point around 250,000 Euro a few years ago (but costs have not increased much as it is a stale market AFAIK).

The "key factor" is the "overturning" moment at the base (that implies a much sturdier tower and heavier coounterweights), and the single tower design is aimed to have a "light", "transportable" and "easily assemblable/disassemblable unit" the actual lattice is subject to very heavy tensile cycles as it is extremely flexible.

It would make much more sense (to me at least) to have a specially designed crane with an as short as possible arm, traveling on a track (which is also a setup commonly used in building sites) or a portal crane, like the ones used in quarries or pre-fabrication sites 35 tons are a lot of weight.

Besides (reinforced) concrete is at the most 2.3 tons per cubic meter, so it is not very efficient as a weight/counterweight, though possibly it is among the lower cost per kg material.

On the other hand rebar concrete is an excellent material for the actual tower, so in a fixed place it makes much more sense to build a (say) 100 m tall pier/pylon than using a "light" lattice /truss structure for the tower.

Eerecting and dismantling are key functions of typical construction cranes.

If you build a permanent crane for 30 year operation for most weather conditions it can be heavier and made of larger and heavier body segments. More like cranes in harbors.

I think the counterweights can be removed if you have symmetric working arms lifting exactly the same weight at the same time.

Thanks for sharing. This is helpful info.

If a tower crane did not need to be transported, how much would the design change? I’m guessing not much, but curious.

I was imagining there would be no counterweight but just opposing loads, then I realized that might be a safety hazard. But, I really don’t know about these things.

I just love the elegance of this solution and immediately obsessed. I think it just ruined my productivity for the day.

A normal tower crane must:

1) be easily transportable, which among other things means that the lighter it is the better it is AND that in most countries the girdles cannot exceed 2.40 meters in width

2) most would be self-erecting (there are two kinds of self erecting cranes, the one in [1] is a kind limeted to smaller/shorter/less load models and it is properly "self-erecting") but any tower crane is normally assembled on the ground (using a crane truck) up to a given size/height, usually up to 30-40 m height at the most, for taller cranes, the arm and the base is assembled on the ground, but later the crane is assembled using a self-erecting "cage" or "climber" see [2], this again calls for "the lighter, the better", and implies besides the truss design the use of high tensile strength steel (which as said before is very elastic, meaning that the operation of the cranes is not as easy as you may think, particularly when high loads are involved, it is not uncommon that the point of the arm has several cms oscillation when the load is lifted/released)

3)transport/assembly/erection/disassembly is done relatively often it is rare that a tower crane remains in the same place more than a few months, at the most a couple of years, so the points above are very relevant.

A "static" crane would resemble more than anything else a port crane, more or less like this one:


[1] video of a self erecting crane:


[2] video/animation of a climber crane assembly:


> that might be a safety hazard.

You can get around that, and they probably have to anyway, by just having a perimeter around the system that must be cleared by humans before the system can go active.

The selling point of this is low relatively low capital cost and well tested technology. Power density is not that good, but if you have land that's not a problem.

The use of space to store energy is maybe double of what typical damn reservoir uses to store the same amount of energy.

Each 35MWh system requires about 1.62 acres of land. That seems perfectly reasonable to me, especially since there are still optimizations to explore.

Here's some totally useless back-of-the-envelope calculations on land requirements for this sytem.

The United States, in total, used 1,819,393,805 MWh of energy in 2016. If one plant provides 35MWh of storage, that means 51,982,680 plants are required.

That comes to 84,211,942 acres of land. There are 2.3 billion acres of land in the United States, so it would require 3.66% of the US. That's obviously a huge overestimate.

The beauty of this is the simplicity. This is something we could have built 40 years ago. And unlike LIBs, there's much less worry about degradation and we can put these out in the desert near a solar power source without worry.

Imagine it combined with solar thermal, which has dropped immensely in price per KWh.

Also, concrete reabsorbs around 43% of the co2 used to create it over a period of time.


You don't need to store everything that's consumed, that's where the absurd number of plants and needed people comes from

10% of that makes more sense, even if it goes, let's say, 50% solar

Yeah, storing (<1%) 3 days total annual supply of electricity would be a huge over estimate... and storing 10% (35 days)would still be crazy large... I'd think the grand parent posts's numbers are high by 2-3 orders of magnitude.

As others have said,they likely would be placed near the solar plant where land is cheap and dry, rather than in neighborhoods.


10% would be overkill. I don’t think we should be aiming to sacrifice our livelihoods to be concrete block stacking addicted energy horarders, but I’m not entirely against that either. It’s hard to look at a solution so tangible and transparent as concrete block stacking before ducking my head into this mangled half-commented test suite.

In this hypothetical, you also need something like ten percent of Americans to be crane maintenance workers, wouldn't you? Based on the crane numbers above it might even be more.

If anything, that's a plus.

But they'd probably be mechanized before long.

>> ten percent of Americans to be crane maintenance workers

> If anything, that's a plus.

That's the world you want to live in, where there are more construction crane maintenance workers than teachers, police officer, food service workers, lawyers and doctors combined and then tripled? Is there no possible better use for human potential that fixing machines that lift bricks?

Honest question: what's wrong with being a crane maintenance worker or a crane operator? Cranes are cool, cranes help build stuff, cranes are complex. And if anything, out of the list of "desirable" jobs you mentioned at least two (police officers and lawyers) are the result of "bugs" in our societal system, they aren't productive.

Nothing is wrong with being a crane maintenance worker, and there is nothing wrong with being an accountant. But if a fifth of the workforce was accountants I would enter a panic.

That's why I asked if that was the pinnacle of human achievement. If nothing was better. Because it crowds our other things at that level.

Gov't (fed, state, muni) employ about 23 million workers. Total workforce is about 130 million. So gov't work is roughly 1/5 of the workforce... hehehe.

Better than 10% of the US being truck drivers. Maintenance on heavy equipment like that can be remarkably complex, and the necessary skills are transferable to all sorts of industrial and fabrication jobs - not too hard to switch from fixing the hydraulics and armatures on a tower crane to fixing the same on any other sort of crane, vehicle, or chunk of factory equipment.

I wouldn't expect teachers or doctors to be transitioning into careers as power storage operators.

"Truck Driver", however, is a common job title[0] which may go away thanks to automation. Finding a replacement role would be nice.

I'm not sure you mean to insult people whose job it is to fix machines that lift bricks, by the way?

[0] https://www.npr.org/sections/money/2015/02/05/382664837/map-...

If all they did was make a battery, that's messed up. That many people? That's so much less useful to society than teachers, food service workers, doctors, lawyers and etc. combined. The insult to those people would be to have them spend their lives doing something so meaningless. Operating a crane in a construction crew has maybe a thousand times more dignity because they are making something people want. I have truck driver friends and that job isn't the best but they're doing something people want, they don't get out of bed unless something is out of place in the world, and they fix it.

> The insult to those people would be to have them spend their lives doing something so meaningless

Why is working on power storage and generation meaningless? Cheap energy is literally the basis of our civilization, tech, and standard of living. Would you consider power plant work or oil drilling work meaningless?

The system described in the article is mainly automated. They probably wouldn't need a large team to manage the system or it would be completely unfeasible. Certainly no worse than a giant battery center used to store electricity.

Reservoirs are restricted in where they can be built, because water. And that real estate is in high demand for many other uses. I think it's a safe assumption that, in general, coastal properties (including those on lakes and rivers) are more than twice as valuable as inland property on average.

Reservoirs could probably be built underground. I could also see one of these block stackers existing in the sublevels of a big skyscraper. Cost and and difficulty of access for maintenance might make either thing impractical, though.

Reservoirs have a tendency to emit biogenic methane though so they're not great at scale for climate change mitigation.

Isn't making concrete a large emitter of co2 as well?

they could make steel cages, fill them with crushed and vibrated limestone (or another aggregate). Good steel for the cage would last a lifetime but not sure if it's cheaper in $$ or CO2 emissions. Basically they need to lift /drop a heavy thing that last generations and stacks well.

Concrete has the advantage of lasting "forever" in those conditions (rebar when wet ruins it, otherwise it last long, long time). Concrete also stacks perfectly as you can mold it however you want. Might bite the bullet and stick with concrete, just work on making it more efficient.

yep, hence the use of waste material wherever possible.

Probably you could throw in a small amount of nanocellulose and it could improve the strength a lot. Especially tensile strength, which is not good for concrete.

I'm assuming this is because of growth and decay between fill and release cycles. But in the long run wouldn't that be carbon neutral?

Not a true expert on the topic but from my reading it sounds like land is generally a carbon sink and water produces carbon so when you turn land into water, the net effect is additional carbon. Estimates have man-made reservoirs accounting for 0.5% of the total anthropogenic carbon emissions worldwide; fairly significant when we're considering the scale needed for energy storage with wind (blows 35% of the time, US avg.) and solar (shines 25% of the time, US avg.).


It's carbon neutral when plants decay to carbon dioxide. But they need oxygen for this to happen - and when they don't (like when they're underwater), they decay to methane.

And methane is a greenhouse gas 20-80x more potent than carbon dioxide.

< The selling point of this is low relatively low capital cost and well tested technology.

I'm sceptical of that. As the sibling comment noted, the technology is well-tested, yes but for a completely different usage pattern. You don't know how reliably construction cranes are in lifting heavy loads in back-to-back cycles, 24/7.

Additionally, I'd guess you will have to modify the cranes to realize the "recover energy" parts. I'm no expert, but I could imagine, traditional parts spend energy for both raising and lowering a weight because the design goal is reliable control of the load, not making energy. So you'd probably have to modify the motor assembly.

I've recently started working with wave and tidal energy projects.

From what I've been told, the magic isn't in the generators (almost every project I'm working on is just using a standard industrial motor as a generator) but in the smart regenerative drives which both supply and harvest power from them. Harvesting power from industrial processes to keep costs down seems like it's a very common thing to do, so these drives are available off the shelf, and are designed to plug into a variety of existing motors.

> Concretely (pun not intended), I found a document [2] saying

That's definitely a really awkward choice of word in that context for it not to be intended, so I'm thinking pun was, in fact, intended. You can try to convince me otherwise but in order to do so I'll need to see some concrete evidence (pun not intended)

"Pun not intended" should definitely be among the top 10 most common lies, along with the likes of "I'm starting tomorrow", or "I'll pay you back" ;)

Not sure why you're being downvoted, it's a fair question. Maybe your post reads a bit abrasively? ¯\_(ツ)_/¯

Anyway, I really didn't intend the pun! My reaction to the article was to try to get a rough estimate of how reliable tower cranes are, at which point I realized that they must be very reliable to work at all. But I only had that broad hypothesis of "very reliable", so I went looking for evidence to confirm it, and if so, what that broad hypothesis ended up looking like in practice. For whatever reason I found "concretely" when I went looking for a word for the segue. Probably concrete on the brain and a bit of luck.

Not sure why the downvotes, I thought the exact same thing

Question: can't we significantly reduce the number of moving parts by using a lever system to raise a single, giant weight, preferably from the bottom?

There was a project to carve a huge cylinder, kilometers wide, out of bedrock and raise and lower it with hydraulics. You could keep whatever's on top mostly intact. I don't know what's the latest status.

You can not use standard cranes, and there are obvious limits: motor power, cable strength, stability of the system with a high center of gravity, ...

Could we not do this with a medium powered motor on the ground, pushing up the load through a system of gears and levers?

If they don't call themselves Sisyphus Energy they're missing out on a great poetic opportunity.

> In Greek mythology Sisyphus was the king of Ephyra (now known as Corinth). He was punished for his self-aggrandizing craftiness and deceitfulness by being forced to roll an immense boulder up a hill only for it to roll down when it nears the top, repeating this action for eternity.

Its quite an ingenious idea. Could even hollow out a mountain to do this, avoiding the co2 cost of concrete.

I can imagine living next to one of these facilities and thinking "What the hell are they trying to build?"

or after 18000 years, after they reboot the civilization and only a few structures remain. Give a +- few years :)

"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 upto 90%."

That's quite efficient. Maybe they can get creative and build something different every day. One day you get a big pyramid, the next day you get a big elephant. That would be quite entertaining.

I think you've actually hit on the real selling point here - ADVERTISING!

Think of it as a VERY slow, VERY large TV screen. With red, green, and blue blocks, they could advertise almost anything!

The value generation from the ad would almost certainly outpace the value generation from energy storage!

Also, you could encase your bitcoin wallet in a block, creating the ultimate block-chain block-chain!

By god and the scientists, you're a genius maxxxxx!

> Think of it as a VERY slow, VERY large TV screen. With red, green, and blue blocks, they could advertise almost anything!

I don’t think that works if the blocks are reflecting light rather than emitting it.

Don't worry we've already pivoted. We're no longer using concrete blocks, now it's giant LEDs.

Unfortunately we lost the entire first floor when we dropped a block and filled it in.

And efficiency's down to 12% because of all the backlights for the ads and all the graphics chips got hacked and are mining bitcoin.

> I don’t think that works if the blocks are reflecting light

From a long distance the colors would merge in the eye. And this would be visible from a long distance. Imagine it on a high spot next to a city.

Use 4 colours then: cyan, magenta, yellow and black (CMYK, as used in print).

Well they could be transparent (Red/Green/Blue filter) glass blocks stacked in front of a reflective screen...

One question is... visible from the sides, from above, or both?

Or just CMYK like printers...

Why wouldn't it? Your eye does not know the provenance of the light that hits it. Red light is red light.

We used to call those 'drive ins'.

Upvoting black and white blocks.

Ok, someone does not like black and white images I guess. But downvoting because of colorphilia is cruel!

Pyramids are probably the most effective to prevent it falling down because of wind gusts

You still have to build a base, which stores no energy, and then plan for different storage amounts in different layers.

Would wind gusts impart enough force to affect barrels / blocks of concrete?

It'd basically be a skyscraper, and those certainly move in wind.

Skyscrapers are hollow...

They’re also a lot stronger because of steel construction, often incorporating a solid core. I don’t think we can attain skyscraper heights with blocks of concrete but I may be wrong on that.

I'd put money on their 90% figure being theoretical. 95% efficiency for a motor and a generator with no other losses is at the edge of possibility.

There's the horizontal version, so to speak, at https://www.aresnorthamerica.com/grid-scale-energy-storage -- it's running heavy weights up a hill on a closed rail loop to store and use them coming down to generate energy. 78% efficiency is claimed (in the press kit, the web page says "approaching 80%"). It claims to be able to store tens of gigawatt hours of energy.

The crane idea appeals to me more because the infrastructure appears simpler. Rather than having to build a lot of rail and a whole switching infrastructure, you just install the one crane and a shitload of heavy concrete blocks for it to lift. Seems like it would be cheaper.

Someone would need to run the costs per GWh stored and generated. To me it looks like once you built your rail loop you could run a lot of cars on it. Still, building instead quite a lot of cranes might be cheaper.

Rolling stock isn't cheap either, though. Not even remotely close to how cheap a concrete block is. Rolling stock typically costs in the millions per car. The rail might not even be the most expensive part.

The nice thing about the crane idea is you don't even need a lot of cranes, you just need a lot of stackable mass. The rail idea needs a lot of movable mass on wheels, and a lot of siding to store it on. It seems like the rail idea would need more land as well, plus it only works on hillsides.

You need enough cranes to smooth the dips in power generation as each crane finishes dropping one weight and has to go fetch another. The number needed would be proportional to the desired power output of the system (holding the size of the weights constant).

It looks like their prototype uses 6 cranes on a single central pillar, probably for this reason. It seems like with some basic algorithms you could get away with as few as 3 and still supply steady power as long as the cranes are tall enough.

So a few cranes?

Keep in mind these will be grid-tied too, so you only need the power to be smoothed across the entire grid; it doesn't have to be at a single location. So grid storage batteries elsewhere could play a role too.

You still want each individual power plant to provide as smooth a power output as possible because each dip puts some strain on the other plants in the network as they have to increase their output to accommodate.

You could combine these ideas, though, and have only a few cars that pull weights up/down the hill, with a crane to load it off. I'm not sure but it could probably allow for a far greater total storage and kWh/$.

Now you've got more moving parts though. You have both trains and cranes involved. I think it's probably simpler and cheaper just to have the one big crane than to do a mixed mode system.

I guess the only advantage the train approach has is if you can get a lot more height out of it -- imagine an elevation difference of 1 km from top to bottom, way more than you could get with a crane. This still uses a lot more land though and needs a lot more rail; just having several crane installations might still be simpler and use less land.

One could take it a step further and figure out to use this for excavations.

This is absolutely fascinating.

Interestingly, the cement industry produces ~5% of global c02 emissions [0]. (Cement is an important binding element in concrete [1].)

As this technology is presumably most useful for storing surplus energy from unpredictable renewable sources (e.g. wind, solar) I wonder if there is a conflict of interest? I'd love to know more about the carbon economics involved, perhaps they could use reclaimed (i.e. recycled) cement.

[0] https://blogs.ei.columbia.edu/2012/05/09/emissions-from-the-...

[1] https://www.thespruce.com/difference-between-cement-concrete...

So it uses concrete which is VERY BAD and also needs a lot of it, but at maybe 1/6th the impact of regular concrete.[1]

It's unclear how this works out in the end. Exactly how much cement do they need to scale this up? What's the CO2 impact per MW of storage, for example? I would say anything that involves significant CO2 emissions is not an ideal candidate for renewable energy storage.

[1] From the article: "Energy Vault would need a lot of concrete to build hundreds of 35-metric-ton blocks... [but they've] developed a machine that can mix substances that cities often pay to get rid off, such as gravel or building waste, along with cement to create low-cost concrete blocks. The cost saving comes from having to use only a sixth of the amount of cement that would otherwise have been needed if the concrete were used for building construction."

So, how does the CO2 emissions of concrete production compare to that of Lithium ion battery production?

Wouldn't it be mitigated by only being created once and then have a very long lifetime of utilization (vs the battery form of storage)?

Depends on how much the inferiority of the concrete vs. that used for construction affects its durability and longevity. It needs to be able to withstand weight from blocks above, impact whenever it or an adjacent block is moved, and corrosion from any metallic material within.

I could almost imagine these blocks needing to be tougher over time than something made from cement used in construction, to avoid crumbling under those conditions.

I missed that bit in the article, thanks for pointing it out. So they are already developing ways to reduce c02 output of concrete production, nice. This would change c02 balancing estimates greatly.

You may have meant this, but just to clarify - they're developing methods of lowering the CO2 output (and financial cost) of their concrete weights, not concrete in general; they do this by not having to meet the structural strength requirements of regular concrete.

Let's investigate this!

For reference, a common electricity mix currently generates about 0.5 tons of CO2 per MWh [0][1].

Now, for the device in question: Creating 1 ton of cement releases about 1 ton of CO2 [2]. A common ratio of cement per mass of concrete is maybe 1/5 [4]. The article says they found a way to reduce that to a sixth, so we are at about 1/30 of the concrete mass in cement. From the article, each block weighs 35 tons. So we'll just assume 1 ton of cement (and CO2) per block.

The graphic in the article shows ~40 layers of no more than 20x6 concrete blocks can be stacked around the tower, each weighing 35 tons. Therefore, each such installation would cost about 5000 tons of cement or CO2.

So its building cost in cement alone is the equivalent of 10000 MWh. Fully "charged", it stores 20 MWh. It would therefore have to complete 500 full cycles of taking energy available for free (and otherwise lost) and feed it back. Roughly assuming it can do that every week (no idea, really depends), that would be ten years to become CO2 neutral, just in terms of cement. So there's your reference value.

However, I haven't seen this kind of calculation for other energy sources. That would be interesting.

Edit: Here is a review of CO2 from lithium-ion batteries: https://www.ivl.se/download/18.5922281715bdaebede9559/149604...

They say 150-200 tons of CO2-equivalent (!) per MWh stored, which is very close to the device in the article (in the above estimate it would be 250 tons of CO2 per MWh, although I did not check whether that is pure or CO2 equivalent).

[0] https://www.eia.gov/electricity/state/ (randomly sampled some states)

[1] https://www.umweltbundesamt.de/sites/default/files/medien/37... (German statistics)

[2] https://blogs.ei.columbia.edu/2012/05/09/emissions-from-the-...

[3] https://sans10400.co.za/concrete-mixes-by-weight/

Worth pointing out that if you're patient with setting times, you can use portland cement substitutes (fly ash, ground blast furnace slag) as a substitute for portland cement. Slower strength times (several days longer) but same long term strength and way lower embodied carbon.

The thing i ponder about this is the foundations needed for a setup. Concrete stacks very well (think dams) but you need very strong foundations for tall, solid concrete structures.

Nice work.

From [2]:

Cement manufacturing is highly energy- and emissions-intensive because of the extreme heat required to produce it. Producing a ton of cement requires 4.7 million BTU of energy, equivalent to about 400 pounds of coal, and generates nearly a ton of CO2. Given its high emissions and critical importance to society, cement is an obvious place to look to reduce greenhouse gas emissions.

Ignoring the geographical problems, could using the power source from which energy is stored for these devices also be used to manufacture the concrete, or would you be constrained by the power plants ability to output enough energy intensity to produce concrete?

If feasible to do, then for the geography issue, would the CO2 output from lengthening the trucking route and/or high voltage transmission lines to the storage site possibly overcome the cement issue overall? If the power is ~free, loss in transmission is less important, but then you have to consider the output of manufacturing and installing transmission lines also. Although, perhaps there's spare capacity on some lines.

Actually, once the blocks are manufactured, you can ship them anywhere.


> Actually, once the blocks are manufactured, you can ship them anywhere.

But you won't want to, because they're insanely heavy. At 35 tons a semi-trailer can only carry one.

You really need to build these on-site. The amount of diesel you'd burn to move them long distance is astronomical.

If you build it on site won't you still have to haul in all of the materials to produce it which will weigh more than the final product?

The point is that they would be made locally, not "shipped anywhere". Every city has a bunch of local concrete plants for a reason. If I buy aggregate, it's coming from nearby; it's not being shipped across the country.

Not necessarily. concrete = cement + aggregate; the aggregate might be quarried on site.

You have to haul the materials to make cement in from somewhere though anyways, right?

I know nothing about the cement business, so it's hard to have even a clue how to estimate this, even if you consider the power to be ~free..

>that would be ten years to become CO2 neutral, just in terms of cement

Goodness, this doesn't seem viable at all.

Could the system work with pallets of steel drums filled with water? It looks like 4 layers is usually the height limit.

Why not? I would estimate the lifetime being at least 30 years.

I think the better approach would be to stack limestone (density of 170 lb/ft3 vs. concrete's 150 lb/ft3) and have very little environmental impact.

Does it depend on height to be effective, or could it stack limestone just 30' up or so?

I’ve also read that concrete absorbs CO2, in significant enough quantities that an isolated ecosystem experiment had to be aborted because plants weren’t getting enough of it.

I'm not doubting it, but on the other hand I don't think that the cement will re-absorb a significant amount of its own mass in CO2 (which it would have to in order to offset this 1-to-1 CO2 footprint).

Portland cement is at least 80% CaO, so in theory it's 63% of the cement's dry mass (CaO + CO2 -> CaCO3)[1]. In practice it's ~43% that value, or 27% of the cement's dry mass.[2]

[1] https://en.wikipedia.org/wiki/Cement_kiln#Carbon_dioxide

[2] https://www.nature.com/articles/ngeo2840

So apparently it depends on the type of cement - non-hydraulic cement hardens as you described, while hydraulic cement does not absorb CO2 but instead hardens in the presence of water. I guess they wouldn't have a reason to use hydraulic cement for this though, so it seems you're right.

It's true that hydraulic cements (eg Portland cement) harden by a different mechanism, but they too will fully carbonatate over time.




They could make the concrete (the cement) in plants with CO2 capture. Sure, costs a lot more, but then it'd CO2 negative (as curing concrete binds CO2 from the air).

It’s not like they have to make concrete all the time, you would amatorize the concrete capital and environmental costs over the lifetime of the tower.

Would it matter if it was containers filled with water, soil, trash instead?

Aside from mass density, the problem here would be structural integrity. How high can you stack buckets of water before the tower collapses? Probably not 120 meters. It comes as no surprise to me that this would use the same kind of material as a 120 m tall "normal" building.

Considering that water isn't compressible, I'd think you could stack them even higher. Just use cylindrical containers with high strength in the radial direction.

Also, how about compressing plain old air in an array of individual columns? It might be reasonable to improve the efficiency with some sort of heat exchanger.

That would be a lot of steel. 100 meters of water is submarine territory. You need some thick walls to stem the radial pressure alone, probably at least 5 inches or 13 cm of steel (consider [0] and [1], this value also agrees with my intuition from engineering education). Assuming a barrel of 2 m radius and 3 m height (volume ~36 m³), that's 5 cubic meters (or 8 tons) of steel you'd need for the cylindrical hull alone, costing around 8000 USD in material [2] (varies wildly of course, but you're probably not using submarine grade steel). Per ~40 ton barrel. Would make about 40 million in steel costs alone for the number of barrels shown.

I have no idea what your air compression idea entails, but it doesn't sound more realistic. Concrete is pretty good at being stacked (source: look around you).

[0] http://www.madehow.com/Volume-5/Nuclear-Submarine.html

[1] https://en.wikipedia.org/wiki/Submarine_hull#Dive_depth

[2] https://www.wolframalpha.com/input/?i=steel+cost

Compressed air energy storage is also being investigated in a variety of forms:


Way less dense than concrete. So less energy stored.

Sand and water?


They're not containers, they're structural. They need to be stackable dozens tall. You're basically limited to the kinds of materials you can build tall buildings out of -- concrete or steel. And concrete is much cheaper.

Couldn't they just use recycled concrete (from broken up roads and buildings) or just rocks instead?

No, the whole point is that they need to stack these blocks up very high. You need uniformly shaped blocks for this, so no rock, and recycling concrete doesn't let you reuse the cement as binding agent -- it's already inactivated. You just get to use reuse the aggregate, which isn't the environmentally expensive component to manufacture.

People have turned rocks into uniformly shaped objects for thousands of years...

Presumably they would need to build a vessel to hold the concrete rubble in, as opposed to casting their concrete directly in the shape they desire.

Similar concept using trains: https://www.aresnorthamerica.com/grid-scale-energy-storage

I wonder though, the density of concrete is only about 2.5 higher than that of water. So, a concrete tower, comparable to a pumped-storage hydroelectricity plant would be gigantic. Seems infeasible to me.

A local company [1] is taking a similar approach to the extreme and is developing a concept which involves cutting a 100-250m (328-820ft) diameter piston out of solid rock and then pumping water underneath to store up to 8GWh of energy.

Sounds quite crazy at first but actually looks quite reasonable after looking at it a little closer [2].

[1] https://heindl-energy.com/ [2] https://heindl-energy.com/technical-concept/engineering-chal...

That's amazing!

Any idea how they will separate the bottom of the piston?

I wonder how they will balance it too, so that it doesn't seize in the cylinder. It seems like (re)moving material would be straightforward enough, but figuring out what the current balance is, maybe not so much.

How do they make the seal at the bottom of the piston?

“The Gravity Storage is cut out of surrounding rocks. Because rocks nearly always have crevasses and fine cracks through which water can flow, it is necessary to completely seal the piston and the surrounding piston cylinder against the surrounding area.

For this purpose, all freely exposed surfaces are sealed with a geomembrane and concrete.”

There still needs to be the equivalent of a series of O-rings between the piston and the cylinder bore to prevent the piston from sinking. I'd guess that it is the second-hardest technical problem, after the considerable challenge of isolating the piston.

The 'rolling membrane' that they are proposing is described here: https://heindl-energy.com/technical-concept/engineering-chal...

Build one inside Fort Knox :-)

I also think it might be easier to do away with the crane and just put the weight on a huge moving platform. Where available, you could sink that into a disused mine shaft.

Might come down to things like, how efficient are cranes & conveyors & so forth, vs water pumps & hydro generators. The nature of each material leads to different techniques which could have very different efficiencies.

Upfront costs can sink a project, but so can ongoing maintenance. Materials that don't foul as easily have a long term advantage. And when there's a drought people won't be too happy about all that fresh water you're taking to make electricity ('course, how much water does it take to make a cubic foot of concrete, cradle to grave?).

> how much water does it take to make a cubic foot of concrete

The article does mention that they expect to use 1/6th the cement of construction concrete.

This paper https://www.nature.com/articles/s41893-017-0009-5 gives an idea: 2 Gt of water per 21.3 Gt of not-water.

Assuming perfectly dry concrete (and none of the water converting to not-water mass, both of which I believe are counter-factual), that means a 2130 kg block of concrete would have needed 200 kg of water. Pumped hydro, assuming identical efficiency, would need all 2130 kg of water.

2Gt of water was mixed into the concrete, but when you're calculating water footprint you need to look at how much water went into creating all of the ingredients. That can be pretty substantial.

That article does go on to cover the water footprint, but what troubles me is that they switch units, and report it as 16.6km^3 of water. Which seems like they're trying to obfuscate the results (they have obfuscated them, whether that was intentional or not is another question).

That's all the water for all the concrete. Which for a hydroelectric perspective, is about 5% of the volume of water behind Grand Coulee Dam, for all the concrete we currently make every year. So maybe concrete blocks make sense for power.

> 2Gt of water was mixed into the concrete, but when you're calculating water footprint you need to look at how much water went into creating all of the ingredients.

True, though the paper makes a point, early on, that much of it is used in producing the aggregate, and the article makes a point of (potentially) using recycled/discarded aggregate, which would incur no additional water consumption.

> report it as 16.6km^3 of water. Which seems like they're trying to obfuscate the results

That's a remarkably harsh characterization, especially since that was parenthetical. The main reported amount was 16.6 × 10^9 m^3.

With water having the convenient density of 1000kg/m^3 (1 ton/m^3) and 10^9 being equivalent to the SI G prefix (both facts which one reasonably expect a reader of a physical sciences journal to know casually), it seems hardly obfuscatory. I'd attribute, instead, a change of units to a desire to compare it to household use, later in that paragraph, which is more typically measured by volume.

Although for commercial concrete block of 2130kg, that would, indeed, change the amount of water to be 1660kg from my original 200kg. However, I'm fairly confident that the ability to use 1/6th the cement combined with not needing any particular aggregate (even recycled) will bring the number for the article's application much closer to the smaller one than the larger one.

Here's an idea: It's possible to make unreinforced concrete using seawater. Wonder if that would work here.

The efficiency is comparable, pumped hydro gets ~80% at large scale practice, while this is promised to be 85% and might turn out to be the same after all the implementation issues and wear&tear comes in.

Which it should be - IMHO, despite the material, both systems get very similar techniques, at the core in both cases you have the loss of a motor+generator pair plus the friction of your mechanical system.

I wonder if you could compromise and use powdered concrete in a closed system? High powered fans could blow the fine powder upward in a silo so it would act like a liquid. Then large paddlewheels catching the powder could power a generator coming back down. I have no idea if powder going up a tube has less friction than blocks on a cable/pulley, however.

That's not a good idea. You would have turbulent airflow with dust, most energy would get lost, resulting in low efficiency. Weights on cables pulled by electric motors is as efficient as it gets. Not to mention dust bucking up the gears and sockets.

> So, a concrete tower, comparable to a pumped-storage hydroelectricity plant would be gigantic.

There's nothing to suggest that each tower would need to be comparable.

My reading of the article suggests the converse, that each installation is feasible at a fraction of the size of pumped hydro [1].

Although the article does mention land availability being an issue, to say the same for pumped hydro would be a gross understatement, since the latter requires not just land but a specific (vertical) shape of land in a continguous piece.

[1] Article mentions "each 35 MWh system". I found it remarkably difficult to find the usable storage capacity of a PSH station.

There's no citation for that, so it could be what WP calls "original research". It is, however, pretty likely the right OOM.

That would put the storage capacity at around 1000x, and, if the estimates of the cranes' generating capacity elsewhere in the thread are correct, approximately proportional to that, as well.

It seems to me, that for smoothing generation from solar, the important metric is more like "max power over ~8 hours", rather than "total energy storage".

Concrete doesn't evaporate though, so there are some positives in its favor.

Pumped hydro has the downside that water evaporates too.

and water is a rather precious resource in many localities.

The majority of the world’s economy is at or near the seaside. I find this approach more practical, similarly low tech (which is a good thing, simple and reliable) but uses hydrostatic pressure instead of gravity. http://theliquidgrid.com/2016/12/27/marine-energy-storage/

Sea floor is underutilized, but you can do a lot of things on a piece of land.

Below certain small depth the sea is always calm, atmosphere is not, I anticipate catastrophic consequences with these tall cranes when hurricanes, tornados or lightnings.

That seems harder to me. Anything done deep underwater costs at least an order of magnitude more, plus they still have all the same concrete requirements because they need ballast to keep the air balloons from rising to the surface.

Seems easier to just use that same mass on land with a crane.

> Anything done deep underwater costs at least an order of magnitude more

They don’t need to do much underwater, only install. But I agree capital costs might be higher because of this.

> all the same concrete requirements because they need ballast

Depends on the geology of the sea bed. Where I live, the sea bottom is mostly solid rock, it’s possible to attach stuff to the bottom without putting much ballast.

> use that same mass on land with a crane.

The idea’s nice I just worry about disasters. I read in local news about falling construction cranes every couple of years, because stormy weather for a few months each year. It’s possible to make cranes strong enough even for bad weather (like bridges), but such weather proof cranes will become more expensive than regular ones.

The installation process dominates overall effort, so if that's a lot harder then it ends up being a lot more expensive and thus a lot less cost competitive. It is absolutely insane how expensive an underwater oil well costs to tap compared to one on land, for example.

> Depends on the geology of the sea bed. Where I live, the sea bottom is mostly solid rock, it’s possible to attach stuff to the bottom without putting much ballast.

It's likely to be more expensive to attempt to attach to the sea floor than it is to just sink large weights. In fact, I'm not aware of any large structures that are anchored to the sea floor in a way that resists an upward force rather than a downwards one. It might be a wholly unsolved problem.

> The idea’s nice I just worry about disasters.

Falling construction cranes are dangerous because they tend to happen in inhabited areas, adjacent to other buildings. The energy storage cranes, on the other hand, would likely be in the middle of nowhere where land is cheap, so even if they do fall there's nothing to damage beyond the energy storage installation.

> I'm not aware of any large structures that are anchored to the sea floor in a way that resists an upward force rather than a downwards one

Marine vessels can be very large and helical screws are widely used, here’s an example https://helixmooring.com/square-shaft-anchors-2/

> even if they do fall there's nothing to damage beyond the energy storage installation.

Very expensive installation. Maybe they don’t need the reliability of bridges but they need to be able to withstand any weather.

Disasters are conceivable with ocean storage too. If a ship's anchor damaged the facility and caused the release of air, the rising air could well sink the ship.

There’re many reasons why anchoring might be forbidden or not recommended in some areas.

Global marine community has developed special signs to mark various locations on water, http://www.sailingissues.com/navcourse9.html

Captains normally follow these rules because the ships they’re controlling are often very expensive.

The Ares Project (https://www.aresnorthamerica.com/) did something like this with robot trains shuttling concrete blocks up and down a slope. No news on that project in awhile tho. I hope this idea is more successful.

Quick question: how does the electricity get from the train (in motion) to the grid? Using the rails as conductors could work, but I'm not sure how efficient that would be.

One way would be using a funicular: The "train" is just the weight, pulled up/lowered on a cable that's connected to a motor-generator at the top.

Would also make it cheaper to build extra wagons, with a storage yard at the top and bottom.

Third-rail electric distribution is an established technology.

They may as well make the concrete blocks in the shape of cups. Open a drain hole when the cups are on the ground. When the cups are on top of the towers, let them fill with rain.

Rainfall is 50 cm/month in the absolute wettest parts of the US, and less than half that in most of it. This wouldn't really move the needle.

That would make it partially, an indirect hydro dam.

It's about concrete's density. Denser means more energy.

This is why there are so many harebrained energy ideas - because people suggest ideas like this that sound vaguely plausible but when you spend a few seconds thinking about how much energy you'd get you realise it is pointless or just an idiotic version of an existing idea (hydro in your case).

Same for all the energy from pedestrians/cars ideas, solar roadways, etc.

The amount of energy depends on how long the average cup would sit. A better critism might be complications in climates where water freezes. In any case, there is nothing so wrong with my comment that necessitates a negative attitude. I would not be surprised if it is an ‘idiotic’ form of hydro, or if it is not an idiotic form. But it’s clear that nobody has shown it to be one or the other as of yet, so your comment is negative with little justification.

Finally a useful application of block and chain based storage... Hides

What I don't get, why the complicated design to assemble the blocks into stacks? This seems to add a lot of non-essential complexity: Now you need cranes, a hooking/unhooking mechanism (that seems to even require cameras and image recognition!), the ability to move blocks horizontally and lots of computing power to coordinate the whole thing.

Even more, the up-front cost to recover energy is higher because you need to lift the blocks from the stacks before you can drop them.

Why not simply use a fixed hook/rope/motor/generator assembly per concrete block? Or, if there are too many blocks for that, use a hydraulic system? (But then again, what is the advantage of using many small blocks instead of a few large ones?)

Nothing against the company - the idea is awesome - but it seems weird that almost all the advertised innovations are solutions to problems that wouldn't exist without the "put the blocks into stacks" design:

>The innovation in Energy Vault’s plant is not the hardware. Cranes and motors have been around for decades, and companies like ABB and Siemens have optimized them for maximum efficiency. 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 upto 90%.

Pedretti’s main work as the chief technology officer has been figuring out how to design software to automate contextually relevant operations, like hooking and unhooking concrete blocks, and to counteract pendulum-like movements during the lifting and lowering of those blocks.

(Not counting the described innovation of finding a new mixture that includes waste and reduces the amount of cement needed.)

The tower in the video looks like it contains hundreds of these blocks. You would therefore need hundreds of assemblies to do it that way, and each one has to lift the same weight that the crane is lifting. All of this to save on the cost of making the crane complex enough to move about, and the cost of the software involved.

But what is the advantage of having a large number of small vs a small number of large blocks?

In the system you envision without stacking, are all of the large blocks suspended from the crane simultaneously when the system is fully "charged"? That would require the crane to support a much higher max load.

Honest question. Is there a reason to use a crane rarther than digging a hole? It seems all that needs to happen is for a weight to be lifted and then allowed to fall. If that was done below ground, that would cut out the weather issues and I feel like the structure itself would be a lot more robust.

Holes are expensive

Not all of them. Sometimes they are waste products of some other industry. Eg old mines / quarries.

Yes, you could use a pre-existing big hole, and carry concrete blocks from the bottom of the hole to the top of the hole. All you're really doing with this approach is swapping out the tower crane for a gantry crane though, for negligible savings. The hole's not really helping you out that much.

Hard to scale them though. And they are not uniform/standardized.

The general principle is converting kinetic energy -> potential energy (storage) and vice versa (consumption). My intuition is that using existing technology to lift a weight through lower atmosphere by >= X required meters is waaaaay more efficient than displacing ((X required meters of height) * required storage surface area) volume of Earth crust.

Cheers. I must be missing something, but once the hole is dug, it’s dug, and i’d have thought it was pretty low maintenance and more structuraly sound than a crane. So over time, would the costs of maintenance provide a benefit?

You still need a crane to move the blocks from the bottom to the top and back. It might be a different type of crane, but I don't know that it would be any cheaper to maintain.

A few thoughts:

- Someone needs to watch the stacking process. If there is a single error the whole tower can collaps and do a lot of damage.

- You need a big (and expensive) foundation for a tower like this.

- Is the low-cost-concrete a strong enough building material?

- The generator needs cooling (in hydro pump it is cooled by the water flowing through)

> Someone needs to watch the stacking process.

Why do you say that? We have fully automated CNC machines and 3D printers that can make things to amazing tolerances without human intervention. Stacking blocks neatly isn't a hard AI problem like self-driving cars are.

> If there is a single error the whole tower can collaps and do a lot of damage.

My reading of it is that the whole thing is fenced off anyway, since it contains an autonomous crane. Just put it somewhere that land isn't too valuable. If it all does collapse, the worst that can happen is it damages itself. Most wind turbines are similarly situated in places where, if they fail, there's nothing else really there to damage anyway.

> Is the low-cost-concrete a strong enough building material?

Presumably so, or if it's not, then it won't be used. I'd leave that to the engineers.

> The generator needs cooling (in hydro pump it is cooled by the water flowing through)

Cooling is not a hard problem. There are much larger plants generating way more power that operate 24/7 that handle cooling just fine. This idea is only generating as much power as a tower crane typically uses anyway, so whatever a tower crane has for cooling its motors should be fine. Probably some kind of closed loop liquid cooling system going to a big radiator with fans, like for a typical automobile engine.

> CNC machines and 3D printers

Those are very controlled environments. Outside where there is weather and wind, anything can happen. Also if there is a bug in the software or some hardware fails in a CNC machine then you loose some material, not a big of a deal. If the concrete tower collapses you loose a skyscraper volume full of concrete, also it takes days or weeks to clean the area up.

I'm kinda surprised they're not talking about wrapping this thing in a cylindrical tower. Wouldn't add that much to the cost.

It seems pretty easy to verify the blocks are stacked properly.

First, make them out of a shape that naturally fits together.

Then, build them with a vertical hole (shaft) through them. Put a reflector under the bottom one. Before the crane releases a block, it shines a light down the hole and checks if it is reflected back. Misalignment will block the light. (Or, you can do something similar with electricity, connected contacts on the top and bottom, and a check that current flows through the entire stack.)

Slap a tiny solar-powered GPS unit and transmitter on each block. ~$10 of electronics is marginal compared to the $2000 of concrete for each block. If any break, you already have a crane that you can use to move the block out of the way for repair; just hand it over to an operator who can do the special-case operation by hand. If you get a beacon unit with a MTBF of 10 years and not awful clustering you might get one to five failing per stack per day, so you'd probably be able to handle a hundred stacks with a single operator dedicated to remote failure-handling.

Sounds good except what do you do about biology that decides to take up residence in the holes?

I suppose you'd have to clean it regularly. When the crane goes to pick up a block, it could do the optical continuity check then too. If it fails, that indicates that either the block was moved after it was stacked correctly (unlikely but possible) or it got dirty.

In that case, something comes along and cleans it. Maybe a rod-shaped brush (like a vacuum beater) that spins. Or a water jet.

Also, you can have more than one hole for redundancy. If one of them is clear, that should be good enough.

Hmm, or rather than holes through the middle, make them notches or grooves on the side and shine a laser through them.

That only works in theory. In practice the reflector, light, whatever gets dirty and you would have false alarms non-stop.

Everybody seems fixated on the stacking, but it's clearly not central to the system, merely an artifact of the demonstration-scale (and presumably demonstration-budget) implementation. They could just as easily be lifting a tremendously massive object a small distance and then letting it back down again with fixed hoists, which eliminates all of the structural problems this stack of barrels faces. Also, that would allow a single unit to sink and source power continuously instead of intermittently like this crane.

Yes, you could have 1 massive block, but the stresses and risks on the system would be much higher. Probably not achievable with current common tower cranes.

The beauty of this idea is that these tower cranes are standardised and ubiquitous. So it could be implemented immediately in almost any city in the world.

I think the engineering there is more difficult because you need very strong cabling and pulleys that can deal with huge load.

Just use multiple attachment points.

I think the problem with the one big weight is that it'd require an extra structure (a gantry) to hold it, whereas this is really simple logistically. Easy to transport and assemble.

How big an expensive of a foundation do you think it would need? I can't even imagine that being a major cost driver, compared to other elements of the system.

A foundation like for a skyscraper and they can get pretty big if the ground isn't rock.

I don't think it would have anywhere approaching the kind of foundation a skyscraper would have. A quick google search and it looks like a tower crane sites on a 1.5m x 6.5m square footing. So 6 of those. Assuming the soil can handle it and the 'energy' weights act as their own foundations.

But skyscrapers are built in economically beneficial areas, whereas you can build this thing anywhere.

There is a similar idea using metal pellets fired from electromagnetic accelerators in a "space fountain". The energy would be stored there in the form of kinetic and potential energy, and it is relatively effortless to tap into that stored energy to even out something like the energy grid. Has the nice side effect of being able to launch things to space on it.


That page made my eyes bleed.

Looks like something hosted on Geocities. Just like with old paintings, when judging, you have to take into account the period it was produced in.

>Article added 2005

Chrome Mobile recognises this and suggests "simplified view" white background, black text.

when geeks try to do design....

What will happen to Earth's rotation if we start lifting objects on the side where the Sun shines, and dropping them on the other side?

Maybe the tech industry will pay them billions to adjust earth's rotation to eliminate leap seconds.

Good point. We know that large shifts in mass, like huge landslides caused by earthquakes, can measurably affect earth's rotation. What happens when we start using multi-gigaton masses for energy storage -- that are within a couple orders of magnitude of those landslides -- in a cyclic pattern? I wonder if we could even get resonant effects.

y'all remember we got tides right

Global Wobbling

You made me smile


Q: A big stack of concrete blocks seems to be almost purpose built for the wind (or a gigantic mutant toddler/cat) to push over. Cranes are also extremely susceptible to wind. I suppose the blocks could be engineered to interlock, but the pictures show cylinders. How do they plan to counteract the wind?

Huh? A big stack of concrete blocks weighing 35 tonnes each seems to me exactly the opposite of being purpose-built for the wind. Maybe if you built it out of feathers then it'd be purpose-built for the wind, but gigantic concrete blocks don't get blown around a lot.

This seems like it'd be much more resistant to wind than buildings, which are hollow.

To me the most fascinating stability question is seismic. Wind is mostly predictable (apart from unusual events like microbursts). It would be easy enough to stack up a storm-stable shape before major predicted storms hit. Seismic stability would need to be considered throughout the stacking / unstacking process.

The cylinders have got to go, however. Stable stackable shapes are a thoroughly solved problem (bricks!), and stack at higher densities as well. Scaling up a press release model from the barrels they used for a real life demo saves very little time or money and implies an absence of familiarity with structural engineering, which will be this concept's #1 critical problem.

As far as the crane goes, the article indicates that "Wind could cause the block to move like a pendulum, but the crane’s trolley is programmed to counter the movement." That actually seems like the most interesting part of this system.

I'm sure they've accounted for winds they expect to encounter on a yearly basis, but "century" storms do happen, just ask Houston TX.

"Houston is experiencing its third ‘500-year’ flood in 3 years. How is that possible?" - https://www.washingtonpost.com/news/wonk/wp/2017/08/29/houst...

They aren't worried about the wind's effect on the stacked blocks, just the ones suspended. If a century storm comes, just shut it all down for a day, everything is stable.

Moving average. Climate change.

Huston got unlucky, but the real worry is the new 100+ year storm, because that will be even more brutal in the changed climate.

Surround it with a hyper-dense mesh of windmills. Now it can generate energy when demand is high, and store energy when demand is low.

The wind problem seems tractable and quite fun to think of different ways to solve it.

Could you dig it down?

By putting it indoors?

That would almost certainly price it well out of the range of even lithium ion storage.

Why not stack or lift heavy lead-acid batteries? 2 for 1 deal on energy storage.

Or make a fly wheel out of batteries and lift that

With a mirrored surface, so it could contribute to a concentrated solar farm.

Stacking flywheels reminds me of that NES robot attachment. https://en.m.wikipedia.org/wiki/R.O.B.

The flywheels would make it more stable as you lift it, too!

This is neat.

We are also facing a global sand shortage crisis due to increased demand for concrete.


Great film.

I wanted to get a sense of the economics of the entire thing.

They said mining for sand could be more profitable than mining for gold.

I presume that means extracting a truckload of sand will yield more profit than a truck of ore containing rock?

I’m also now curious about sand alternatives.

That was interesting to watch. Thanks for sharing :-)

Apparently using desert sand, which is abundant, isn’t feasible and beach / river sand has been the only solution.

A team has recently created a concrete alternative from desert sand, however, that has half the carbon footprint and is made from abundant materials.


One crane can store 20 megawatt hours. The wholesale price of a megawatt hour varies between US$-40 and US$120, normally being around US$60; if you manage to hit those peaks and valleys, which usually happen once a day, you make US$160. If you manage to do this 20 days a month, you make US$3200 a month or US$38400 a year. Given saulrh's comment https://news.ycombinator.com/item?id=17790442 that each tower crane requires US$500 a month in parts to keep it running, it seems plausible that this could be economically viable.

If this became a real thing, can the employees who operate the cranes be called "Sisypheceans?"

Per the article, the cranes are automated. Having paid operators would probably kill all the cost advantages and then some.

At least give that name to the cranes.

What an "absurd" proposition! :)

I wonder what religious purpose future archeologists will think this served :)

Does anyone have a sense of what maintenance for a system like this would look like relative to maintenance for a dam? It seems expensive as hell.

Are you serious? A crane vs corrosive water?

The cranes also encounter corrosive water from outside the weather - and the dam of a pumped hydro station doesn't need a full replacement after a couple of decades; a crane does after 15-20 years at the most.

Well, rains or winter temperatures.

I would think storing energy using compressed air would be more practical. Excess electricity pumps air into a compressed air tank. When electricity supply is low, the compressed air is released turning a turbine to generate electricity. It's basically the same principle as the pumped hydro mentioned in the article but using compressed air. The advantages are size, cost, and availability. You can put it anywhere and scale when necessary.

I do not know much about engineering this sort of things, but it seems to me that working against gravity is easier than working against elastic force (as you propose), because the force of gravity is independent of the amount of energy stored, while the elastic force depends on the amount on energy stored (when the air is already pressurized it is much harder to push in some new one). And in general I believe that it is more difficult to build a motor or a generator that are efficient independently of the force they have to work against/with.

Just random thoughts, though...

There are systems like that:

* old empty mine in Germany. They pump air into the mine and then heat it to get extra energy when letting it out.

* big underwater bags next to wind turbines. Wind turbine directly pumps air into nearby bags. When there is no wind, the air is used to rotate the same electric generator that the wind turbine uses.

Compressed air has been around for centuries, but:

""" While pumped hydropower storage has a charge/discharge efficiency of 70-85%, and chemical batteries reach 65-90%, the CAES plants in operation in Germany and the US have an electric-to-electric efficiency of only 40-42% and 51-54%, respectively """


The disadvantage is that you have made a huge compressed air bomb in the event of failure. The concrete blocks would fail in a more local way by just falling down.

The compressed air would be located in deep inside abandoned mines. The volume and thus energy storage potential of such places is vast.

The idea has been around for decades, but no one has been able to really do it yet.

Rock isn't necessarily airtight more so in mines. A fractured host material for the ore is very desirable as it means less explosives and higher ore production numbers.

There are substantial thermodynamic challenges to scaling compressed air energy storage. You either need to perfectly insulate the pressure vessel or perfectly cool/heat the air as you compress/decompress it via passive radiators.

The compressed air systems anger the thermo gods though

Doesn't seem to have worked out so well for Lightsail Energy... http://energystoragesense.com/uncategorized/lightsail-anothe...

Think spent natural gas fields. Proven airtight, vast capacity.

This is an area of active and relatively promising research. Adibiatic heating and cooling is a concern.

Compressed air storage is less efficient. I think practically they have an efficiency of about 50 %, due to thermal losses (e.g. compressing air creates heat).

Doesn't dropping a weight on a cable cause heat? What's the difference?

The article says that they can achieve an efficiency of 85 %. Which puts them in the ball park of hydro storage or lithium ion batteries. The problem with compressed air storage is that you are fighting with the fundamentals of thermodynamics i.e. compressing and decompressing air. The laws of thermodynamics try to ruin every good idea.

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