Comment by saulrh | Hacker News Reader

Comment by saulrh | Hacker News Reader

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.

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.

> 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.

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:

https://commons.wikimedia.org/wiki/File:Port_crane_of_Mammoe...

[1] video of a self erecting crane:

https://www.youtube.com/watch?v=pqSFxZV6OvY

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

https://www.youtube.com/watch?v=RB91Sm-kGJ8

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.

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.

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

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.).

http://documents.worldbank.org/curated/en/739881515751628436...

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.

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

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.

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.

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.

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.

https://www.nature.com/articles/ngeo2840.epdf

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?

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?

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.

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.

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.

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

Right

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.

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.

< 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)

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

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.

"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" ;)

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?

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?

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.

http://www.authorstream.com/Presentation/heindl-958931-hydra...

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