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Gravity batteries try to beat chemical ones with winches, weights, mine shafts

sciencemag.org

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Re: Gravity batteries try to beat chemical ones with winches, weights, mine shafts

#111

Post by imtringued »

accrual wrote: post #26

Higher materials density = higher energy density of the overall system. The more you're lifting (e.g. iron, steel, tungsten) the more you can get out in a smaller space. Kind of a cool way to increase the energy density.

Materials density is irrelevant, materials abundance and scalability is far more important. The more you spend on dense materials, the less money you have left to actually store energy.

We use pumped hydro because water is basically free and it is infinitely scalable depending on geography. Meanwhile the proposed system is limited by the size and existence of mineshafts. In other words this is a dead end.

Energy vaults is impractical but it at least tried to solve the scalability problem by taking advantage of the fact that the energy storage grows quadratically with the length of the crane arm. Assuming it is possible to actually build that system in a sealed tower to protect it from the elements (wind makes the control problem almost impossible). Given a large enough energy vaults system there will be a point where its advantages massively outweigh its downsides.

Going one step further, you could carve out a large cylinder of rock out of the landscape [0]. By using wiresaws you will only need to cut the surface area of the cylinder out. At this point your material costs are approaching 0. The only challenge is sealing the walls of the hole and sealing the walls of the cylinder to turn the system into a giant hydraulic cylinder. Storage scales with the fourth power of the radius. Considering the theoretical performance of a gravity storage system anything that is below r^2 scaling is just laughable, which is why the mineshaft idea will ultimately fail.

[0] http://eduard-heindl.de/energy-storage/energy-storage-system...

Re: Gravity batteries try to beat chemical ones with winches, weights, mine shafts

#112

Post by GuB-42 »

Not the first time I have heard of gravity batteries, and with the exception of dams, they all look unconvincing.

To make a comparison, there is a human-scaled variant of the concept in the GravityLight by Deciwatt. The concept is clever, it involves lifting a bag of rocks to get a bit of light for 20 minutes. But if you run the numbers, it is tiny. As the name of the company suggests, the generator outputs 0.1W, enough to power a 15lm LED. For 20 minutes you need to lift a 12.5kg bag 1.8m. That's around 0.03 Wh per lift. By comparison, a good 18650 battery is around 13 Wh, about 400x more.

As a niche product, GravityLight is not a bad idea, but it is telling that their new product, NowLight operates the same way, but they replaced the bag of rocks by... a 18650 battery.

Back to the topic, it looks like that "drop a weight in a mine shaft" idea does worse than what you can do with a single Tesla car, which have more energy storage and more power at the wheels. Plus, it is cheaper and you get a whole car with it.

Re: Gravity batteries try to beat chemical ones with winches, weights, mine shafts

#113

Post by fighterpilot »

rakoo wrote: post #48

As usual everyone is fixated on price when the real hurdle will be scale. If we're going to replace our existing fossil fuel plants we need at least as much capacity. A quick grep in the article tells me these guys have a plan for a 4MW plant that involves a 1km shaft. That's the same order of magnitude as a single wind turbine, which is already one of the worst ratio of power output per quantity of resource and land…

> As usual everyone is fixated on price when the real hurdle will be scale

If it's way too expensive (and there's no obvious way to reduce costs), then scalability is irrelevant, which is probably why people are fixated on it. We need both scalability and price to be favorable.

Re: Gravity batteries try to beat chemical ones with winches, weights, mine shafts

#114

Post by imtringued »

flal_ wrote: post #55
inasio wrote: post #45

Gravity and electromagnetic forces are somewhat similar, they both have infinite range, decay as 1/r, one key difference is that the electromagnetic force is 10^36 stronger than gravity [0]. Just for that reason I'm always immediately skeptical of projects of this type. [0] https://en.wikipedia.org/wiki/Fundamental_interaction

Yet, gravity is strong enough to initiate nuclear fusion at the core of stars, or create black holes... That 10^36 argument is non sensical to me.

Are you suggesting we should build a bigger planet?

Re: Gravity batteries try to beat chemical ones with winches, weights, mine shafts

#116

Post by polypodiopsi »

PeterisP wrote: post #69
o_p wrote: post #20

Earlier quoted context omitted.

This doesnt account the short duration of batteries, I have to replace them every time they go past their lifetime, so in the long term their cost is much higher

The heavy machinery with moving parts lifting thousands and thousands of tons is also going to need maintenance and wear&tear replacements. The problem with scale is that all these proposed gravity batteries need much, much more machinery than an equivalent pumped capacity pumped hydro or chemical battery plant.

Out of interest: do you have experience with mechanical engeneering or is this more of a common sense speculation?

Re: Gravity batteries try to beat chemical ones with winches, weights, mine shafts

#117

Post by arbitrage »

FooHentai wrote: post #73
rakoo wrote: post #48

As usual everyone is fixated on price when the real hurdle will be scale. If we're going to replace our existing fossil fuel plants we need at least as much capacity. A quick grep in the article tells me these guys have a plan for a 4MW plant that involves a 1km shaft. That's the same order of magnitude as a single wind turbine, which is already one of the worst ratio of power output per quantity of resource and land…

I did a bit of scratch math with the notion this might be more suited for individual, home power storage rather than grid supply - You need something in the order of a 5m tall tower bearing 73 tonnes to store 1 kilowatt hour (even then, ignoring conversion losses). So that's the weight of ~ten class-4 fully laden heavy trucks. Once you can get it up in the air then the higher you can go you're doubling your storage i…

I think you are drastically underestimating the density of bulk metal.

Trucks, while impressive as an illustration, are not quite dense enough to be practical or applicable in an energy-storage scenario.

Re: Gravity batteries try to beat chemical ones with winches, weights, mine shafts

#118

Post by lai-yin »

throwaway189262 wrote: post #100
rakoo wrote: post #48

As usual everyone is fixated on price when the real hurdle will be scale. If we're going to replace our existing fossil fuel plants we need at least as much capacity. A quick grep in the article tells me these guys have a plan for a 4MW plant that involves a 1km shaft. That's the same order of magnitude as a single wind turbine, which is already one of the worst ratio of power output per quantity of resource and land…

> as a single wind turbine, which is already one of the worst ratio of power output per quantity of resource and land use. This is just false. Every wind turbine I've ever seen uses 50 square feet on a farm or cattle ranch. Not once have I seen a wind farm where the land underneath isn't still used for it's previous purpose. And at least in US we have enough farmland to power entire US with wind. And that's not count…

Land AND resource use. Just because a single wind turbine takes up a small patch of land doesn't mean it's not extremely resource intensive. Case in point: https://twitter.com/extrachelle/status/986599367049179136?s=...

Re: Gravity batteries try to beat chemical ones with winches, weights, mine shafts

#119

Post by ClumsyPilot »

rakoo wrote: post #48

As usual everyone is fixated on price when the real hurdle will be scale. If we're going to replace our existing fossil fuel plants we need at least as much capacity. A quick grep in the article tells me these guys have a plan for a 4MW plant that involves a 1km shaft. That's the same order of magnitude as a single wind turbine, which is already one of the worst ratio of power output per quantity of resource and land…

Maybe our expectation that we can match generation to consumption with storage, is just plain wrong.

Maybe all we need is to have massive overcapacity of renewables - if we have 10x more solar than we need, even the most cloudy day will still provide power.

Re: Gravity batteries try to beat chemical ones with winches, weights, mine shafts

#120

Post by lai-yin »

throwaway189262 wrote: post #106
tarsinge wrote: post #102

Earlier quoted context omitted.

Resources are also construction material, that’s where wind get its bad ratio.

Construction material is a meaningless metric. If you compare coal or gas plants you need to consider the materials they consume and infrastructure needed for fuel transport. This is a big number, many times the material used for the plant itself. The only meaningful comparison is material used vs solar. Once these things are built they use near zero resources. For everything else you have to keep mining shitloads of…

Sorry but you don't get to discount wind turbines' ecological damage just because no more mining is involved post-construction.
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