×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
• Keyword Search
Favorite Forums
• Automated Signatures
• Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

#### Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

# Gravity Battery

## Gravity Battery

(OP)
I am trying to figure out how the energy density of a gravity battery (Energy Vault) would be calculated ?

I know the formula is energy/unit volume, but with a system that uses cranes or large lifts, would you use the full volume of the height the mass as lifted to ?

Thanks

Scott

### RE: Gravity Battery

why ? what would it mean ?

I think it'd be more meaning to say the maximum energy capacity of the facility.
Then possibly the maximum energy storage per sq.ft ?

### RE: Gravity Battery

If the swept volume of the lift excludes anything else being there, then I would use that as the reference volume claimed.

### RE: Gravity Battery

I would do total lift height minutes 1/2 the height of the stack multiplied by area to get your potential volume.

The 1/2 stack height is the average height of the stack if always going from full stack to full empty.

### RE: Gravity Battery

Consider the analogy of an IC engine as a system. The fuel has an energy density, but fuel volume is consumed during operation. But the fuel tank stays the same size in most cases.

Batteries, of course, stay mostly the same size (but they do swell).

Consider also efficiency -- energy in vs energy out. I'd wager the mechanical system has better returns, but this is before conversion to electricity.

### RE: Gravity Battery

Look for "Energy Vault" on Youtube, a number of videos, pro and con.
I haven't studied the issue, but I suspect wear and tear and maintenance of mechanical equipment of any kind would outweigh the benefit of the storage.

### RE: Gravity Battery

funny how often futile projects and suckers find each other.

### RE: Gravity Battery

Enery density is not the correct term to use for gravity storage systems.

Think of a pumped water storage system. How can you say the water has any "energy"?

Only thing you could do is calculate total energy stored for the mass of water or concrete used in the store maybe, but really not sure what you could use it for.

What you want to know is how much energy can it store and what is its power output?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

### RE: Gravity Battery

Oh, wait ....

The Energy Vault MBAs have finally hired an engineer !!! (there are hundreds of MBAs already on staff)

Are you the poor b*astard that is supposed to make everything work ?

You seem like a nice polite guy Scott .... but

I strongly suggest that you read all the way through this thread

And please give us more background on what you are trying to accomplish and your overall evaluation of this industry

Best Regards, sir

MJC

MJCronin
Sr. Process Engineer

### RE: Gravity Battery

The new version now looks more like a large factory where they lift the blocks all the way to the top out of the wind and then store them in racks / rows at the top.

So they have addressed a key issue which was wind and also that the lower blocks stored less energy than the high ones.

So they are a bit coy as to how it works but looks like you store all the blocks in rows at the bottom, push them horizontally to the end, lift them up ~100m? 200m? then store them in a rack at the top. Then the reverse back out. Then cover the steel frame to prevent wind issues.

CAPEX for the building is HUGE and all the blocks, but once the are there in some desert where space is free, running costs are pretty low, don't really need replacing and are inert.

I worked out with 100% efficiency you need 180, 20 tonne blocks to store 1MWhr. Hmmmm

https://www.energyvault.com/gravity and scroll down for the animation. This is a much better design than the crane block thing, but needs a lot of steel. Think it might be a long payback time in carbon terms.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

### RE: Gravity Battery

there's one lifter per row (the blue structures) ?

and some "magical" way of moving the blocks laterally at the top and at the bottom ?

marginally less silly then the original crane. but more complicated ... each row has it's own "charging" and "discharging" electrical sub-system ?

### RE: Gravity Battery

So 3600 tonnes for just the weights not counting the structure to support them, to store 1 MWh (i.e. 1000 kWh)?

For comparison, the (roughly) 0.1 MWh battery in a modern electric car weighs (roughly) 0.5 tonnes. The whole car weighs (roughly) 2 tonnes.

YES, stationary batteries can afford the use of heavier but cheaper and more available battery chemistries, and they need not have the power density, and they can afford temperature control strategies that an automotive one can't, which opens up some options ... sodium-sulfur, for example. 100 kWh/tonne seems in the ballpark for those. 1 MWh = 10 tonnes of batteries.

Chemistry wins.

### RE: Gravity Battery

Watch the animation. one motor / generator per row.

The bricks move horizontally on rails (kind of by magic on the animation mind) but clearly some small motors moving them along the rails.

So each row will be independent but if you program them so that you always have say 7 out of 10 moving down then the other 3 are moving a lot faster to get back to the top empty to pick up the next one you should have some fairly even power out put.

If you think about something like a robot driven warehouse it shows it can be done and this only has one thing it is moving.

Now how you service it all and fix problems up in the lattice work is another issue.

This version actually seems feasible, but the crane thing is a complete waste of money.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

### RE: Gravity Battery

They traded positional inaccuracy for lots of frictional losses, it seems to me.

As for the OP's energy density, it's not unreasonable to calculate it as described, and you can then compare it with, say, a rack of batteries, although you'd have to account for the net mains power to be comparable.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

### RE: Gravity Battery

Brian - Yes that sounds about right to me - I get about 4,200 to 4,500 tonnes assuming 100m lift for 1MWh depending on what you take to be overall efficiency.

They claim of course you can use loads of waste materials for your weights, but it does seem rather extreme, even if the weights should last for 2-3 times longer than the batteries, plus you don't need expensive / in short supply minerals etc.

I'm like you I think in that it doesn't seem to work financially, but at least from an engineering and operation perspective it is at least a lot more feasible than the crane and blocks idea and you get to use the full height first rather than having to build from the bottom up.

So i guess this is why they still want to find investors to build one of these things.

The energy density thing is density of what though? difficult to compare something which uses kinetic and static energy vs stationary batteries.

But I suppose kWh per tonne isn't too bad a way, just you need to assume the height storage ( so maybe use 100m?) So 0.25kwH/tonne versus 100kW/h /tonne for a battery

but if cost of the tonne of battery is 100 times the tonne of ??(insert waste product here) then you're looking at 25 versus 100 in terms of kWh/ \$

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

### RE: Gravity Battery

Hmm. Any chemical battery will degrade in capacity over time due to corrosion of the cathode/anode. Wag the average battery life at around 10 years, depending on chemistry. Sure the dead loads being lifted have potentially infinite lifetime, but the mechanical system (lifting cables and motors) have finite life...a quick google search suggests cables in elevators get replaced at around a 10-15 year frequency, so not seeing a huge benefit for this.

### RE: Gravity Battery

Perhaps, but the average elevator gets used a lot more often than once a day, which is the maximum that a 'gravity battery' would be cycling their loads.

John R. Baker, P.E. (ret)
Irvine, CA
Siemens PLM:
UG/NX Museum:

The secret of life is not finding someone to live with
It's finding someone you can't live without

### RE: Gravity Battery

and elevators carry people, so higher safety expectations ??

### RE: Gravity Battery

Scott P Jr,

The energy contained in a gravity battery is the lifted weight, times the elevation. If I lift a big chunk of (hopefully) depleted uranium, there will be less elevation and less mechanical volume for a given amount of energy. Is this what you mean by energy density?

--
JHG

### RE: Gravity Battery

JB - To be "efficient" the energy storage should be working at least 75% of the time - so storing say Solar energy during the day then releasing at night so pretty constant operation of the cables.

but cables should be relatively cheap. It's how long the motor generators and the switch gear for all this stop start reverse action its getting.

The main structure and weights though should last a long time. not so sure out the wheels on the weights, but again, maybe not a big renewal cost once you've built the thing.

Just needs oodles of space. and money.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

### RE: Gravity Battery

Switchgear? This system should operate very similar to the electric motor in a car with regenerative breaking. In fact, a compact electric car motor and controller would probably be just the right size for this project because that's about the same amount of power raising and lowering each weight is going to produce.

### RE: Gravity Battery

.... well, .... I feel better....

As long as this machine is based on a firmly established, and tested technology, I have no problem investing in it..

It's those half-assed fever dreams of MBAs, Project Management Institute Grads, entrepreneurs and investment bankers that you have to watch out for ....

But I have been told that I am not a "team player" before ..

MJCronin
Sr. Process Engineer

### RE: Gravity Battery

really ? "surely" this is so capital inefficient as to be unviable ?

unless it's used for carbon trading !? Look, we've created so much Carbon-free power storage that we can offset our other coal burning power stations ??

### RE: Gravity Battery

Can't see it working with all the sideways moving. Why not just use one winch per block. Up/down in a building?

Keith Cress
kcress - http://www.flaminsystems.com

### RE: Gravity Battery

Come on you guys, so many nay-sayers? They are going to make the energy storage blocks out of solid lithium, they heard that’s pretty good for energy storage batteries.

### RE: Gravity Battery

There is undoubtedly a lot of energy just itching to get out of solid lithium

- Andrew

### RE: Gravity Battery

Climate change means it's never going to rain again. Without humidity I see no problems using solid lithium. Just don't lick it.

#### Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

#### Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

#### Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a partâ€™s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

# Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!