Would a giant orbital gravity battery be a good future power source?

[Maximum7]

Gravity batteries intrigue me. We are starting to develop them now. We currently are able to drop cement blocks and harness the energy that the kinetic energy releases. We are considering them as an alternative energy source to help the environment. Here’s a link for those unfamiliar with it. https://en.m.wikipedia.org/wiki/Gravity_battery
So what do you think of this idea? In the future build a giant ball or square metal structure attached to a space elevator in orbit that can be dropped down. Would it be a feasible energy source?

 

[anorlunda]

A battery, even a gravity battery is never an energy source. It is an energy storage device. The energy must come from someplace else.

What do you think the efficiency would be of lifting a weight to orbit with a rocket, than letting it come down running a gravity battery? Think of the energy in the rocket fuel.

 

[sophiecentaur]

Summary: Question about feasibility of giant gravity battery

Would it be a feasible energy source?

Not a source but a form of storage.
But you have taken things further and introduced the idea of a space elevator. Such an elevator would not be a source of energy. If it could ever be built, it would be a much more efficient method of getting things into orbit because there would be none of the losses associated with rockets. But that's another issue.
But, back to gravity batteries. The basic idea is very old indeed - old long case clocks used energy stored in a heavy weight on a chain, wound up once a week. I don't think there are economies of scale associated with such mechanical storage, compared with the efficiency improvements when using bigger and bigger heat engines.

 

[anorlunda]

I don't think there are economies of scale associated with such mechanical storage, compared with the efficiency improvements when using bigger and bigger heat engines.

A major exception to that is pumped hydro electric power. Pump uphill at night when prices are low. Generate downhill during the day when prices are high. Round trip efficiency about 80%. But you see the scale of the weight we are talking about; the weight of water in a good size lake such as Henninfield Reservoir.

 

[sophiecentaur]

A major exception to that is pumped hydro electric power.

You are right up to a point. But the number of places where there is a combination of high valleys that are easily dammable (?) and lowland reservoirs is actually quite limited.

 

[russ_watters]

Summary: Question about feasibility of giant gravity batterySo what do you think of this idea? In the future build a giant ball or square metal structure attached to a space elevator in orbit that can be dropped down. Would it be a feasible energy source?

I suppose you could run your space elevator only at night, and lower the hoist during the day, but otherwise I'm not seeing a particular value in this idea. Why do you think it would be beneficial?

 

[gmax137]

Someone linked to this awhile back
https://www.aresnorthamerica.com/grid-scale-energy-storage

The facilities are highly scalable in power and energy ranging from a small installation of 100MW with 200MWh of storage capacity up to large 2-3GW regional energy storage system with 16-24GWh energy storage capacity.

 

[anorlunda]

Someone linked to this awhile back

Ah yes. You're correct, I heard of ARES years ago but forgot about it. It sounds like it would work, and that it would be scale-able to huge size.

The market for utility-scale storage is red hot right now. Yet I've never heard of ARES being implemented in real life. There must be a reason why not.

 

[CB_FC]

Y'all aren't thinking big enough.

If you can efficiently bring an asteroid to Earth and slow it down enough to tether it to a space elevator, you could then start to drop the asteroid down and generate energy on the way down.

And when it reaches the ground, slowly because you've been sapping the PE on a slow descent, you can then mine the thing for valuable metals.

 

[sophiecentaur]

Y'all aren't thinking big enough.

Unfortunately, we'all have a certain amount of realism. You'd have to present more than an arm waving description and produce some numbers if you want a proper discussion of this.

 

[russ_watters]

Y'all aren't thinking big enough.

If you can efficiently bring an asteroid to Earth and slow it down enough to tether it to a space elevator, you could then start to drop the asteroid down and generate energy on the way down.

And when it reaches the ground, slowly because you've been sapping the PE on a slow descent, you can then mine the thing for valuable metals.

Arright, I guess that's true. But that idea is predicated on two really, really big "ifs".

 

[russ_watters]

Unfortunately, we'all have a certain amount of realism. You'd have to present more than an arm waving description and produce some numbers if you want a proper discussion of this.

Yep, realism sucks. It's boring, expensive and extremely limiting.

 

[gmax137]

so maybe @CB_FC can sketch out the business plan. mass of asteroid, cost to grab one, how much energy returned by dropping it to the surface? what's it made of, return on the mining?

 

[Andrew Blakers]

We found 616,000 pumped hydro sites around the world with combined energy storage potential of 23 million Gigawatt hours, about 100 times more than required to support a global 100% renewable electricity system.

http://re100.eng.anu.edu.au/global/index.php

[moderator: edited to make it clear that the text is quoted from the linked site.]

 

[russ_watters]

Welcome to PF!

This may warrant it's own thread...

We found 616,000 pumped hydro sites around the world with combined energy storage potential of 23 million Gigawatt hours, about 100 times more than required to support a global 100% renewable electricity system. Zoomable maps in great detail are available at http://re100.eng.anu.edu.au/global/index.php

Does "we" mean you are on the team that produced that study?

That's a really large number of sites, so they couldn't have all been individually evaluated by a human. Did you use an algorithm that finds land depressions on at least 3 sides and just measure the volume/depth of every one? Did it consider any practical considerations or was it totally a geometry exercise?

I'm skeptical, but I'll have a read when I get more time.

 

[anorlunda]

We found 616,000 pumped hydro sites ...
http://re100.eng.anu.edu.au/global/index.php

The same article also says this:

The commercial feasibility of developing these sites is unknown. As with all major engineering projects,

Nevertheless, I commend @Andrew Blakers for introducing numbers rather than adjectives into the discussion. Even if almost all of those sites prove to be unattractive, energy storage is a red hot topic and pumped hydro feasibility should be reexamined.

When I toured Norway, I was struck by the huge flat areas bordering fjords 1000 m or more above sea level. Being a power engineer, my thoughts immediately turned toward pumped hydro. (Irony: Norway already has so much hydro power and North Sea oil/gas, that it is one place where energy storage is least needed.)

 

[anorlunda]

http://re100.eng.anu.edu.au/global/index.php

I looked more at that article. For mysterious reasons, the map shows zero sites at latitudes higher than 59 degrees north. That excludes Alaska, Yukon, much of Russia, and much of Scandinavia. I can't think of a good reason for that.

 

[CB_FC]

so maybe @CB_FC can sketch out the business plan. mass of asteroid, cost to grab one, how much energy returned by dropping it to the surface? what's it made of, return on the mining?

Would be hard to give you numbers without an actual target object. Unknown mass, orbit, and resource makeup, as the object is hypothetical. The questions you ask are not really relevant to the hypothesis, and don't discredit it.

It would have to be one that doesn't cost that much energy to (at minimum) capture into orbit (could use a part of the asteroid's own mass as reaction mass to change orbit, maybe not as fuel though), including costs of putting hardware into space, etc. Presumably it would be a NEO.

I understand this is hypothetical and futurism and whatnot. But the OP asked about a "giant orbital gravity battery," so I don't get why my answer is inappropriate, except that I am entertaining the hypotheticals here.

 

[gmax137]

I never said it was inappropriate, I'd just like to see some numbers. Maybe start with the scale: an asteroid of MM kilograms, orbiting at YY kilometers would present a potential energy of JJ joules... there are NN asteroids of this mass...