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Gravitricity

gravitricity.com

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Re: Gravitricity

#31

Post by tinco »

troymc wrote: post #17
elektropionir wrote: post #10

The energy density for gravity is just immensely small, that's why you need dams holding back rivers to use them to generate electricity. For a 1km hole (that's in the middle of their 500m - 1500m range) you have an energy density of 10kJ/kg of the weight that stores the energy. The energy stored in a Tesla roadster battery pack is around 50kWh which is 180MJ. This means that you need a 18,000kg weight in a 1km deep…

That's true. Unfortunately, current Tesla battery packs use lithium, which isn't super-abundant in Earth's crust. That's why companies like Ambri are looking at using other materials in the batteries they're developing for grid energy storage.

He's not suggesting that we use lithium battery packs. He's suggesting the idea is just plain ludicrous.

Re: Gravitricity

#32

Post by vinkelhake »

jostmey wrote: post #28
elektropionir wrote: post #10

The energy density for gravity is just immensely small, that's why you need dams holding back rivers to use them to generate electricity. For a 1km hole (that's in the middle of their 500m - 1500m range) you have an energy density of 10kJ/kg of the weight that stores the energy. The energy stored in a Tesla roadster battery pack is around 50kWh which is 180MJ. This means that you need a 18,000kg weight in a 1km deep…

Okay, so what if you built a huge artificial dam way above sea level? To store energy you would pump water uphill. Usable work could then be extracted when the water is allowed to travel back downhill.

This is what is currently done.

http://en.wikipedia.org/wiki/Pumped-storage_hydroelectricity

Re: Gravitricity

#33

Post by jccooper »

jostmey wrote: post #28
elektropionir wrote: post #10

The energy density for gravity is just immensely small, that's why you need dams holding back rivers to use them to generate electricity. For a 1km hole (that's in the middle of their 500m - 1500m range) you have an energy density of 10kJ/kg of the weight that stores the energy. The energy stored in a Tesla roadster battery pack is around 50kWh which is 180MJ. This means that you need a 18,000kg weight in a 1km deep…

Okay, so what if you built a huge artificial dam way above sea level? To store energy you would pump water uphill. Usable work could then be extracted when the water is allowed to travel back downhill.

Well known as "pumped storage". They're competing with it, but dry and upside down. Is it more economical? Maybe. Is it safer? See http://en.wikipedia.org/wiki/Taum_Sauk_Hydroelectric_Power_S...

At least if this contraption breaks, there's nothing important below it.

Re: Gravitricity

#34

Post by Retr0spectrum »

slashnull wrote: post #23
Animats wrote: post #13

OK, a typical mine hoist is about 10 metric tons. 10 metric tons descending at 1m/sec is very close to 100KW. So a 1000 meter deep hole can deliver 100KW for 1000 seconds, or 27 KWH. That's about $3 worth of electricity, and about 1/3 of the battery capacity of a Tesla Model S with the large batter option. Numbers not looking reasonable for this concept.

I don't know how heavy are the planned weights, but it sure as hell will be heavier than 10 tons.

Even if it was 1000 tons, it would still only be about $300 worth of power.

Re: Gravitricity

#35

Post by tasty_freeze »

Although I think the idea isn't workable (energy density is too low, cost of boring the hole is tremendous), most of the other commenters here seem to think they'd just have one weight, whether it is 1000 KG or 50,000 KG.

Any sane plan would be to have more than one weight. When the first weight hits the bottom, it would release from the cable and another weight up top would grab the cable and start dropping. To store energy, the top weight would get winched up, and when it hit the top it would lock into place somehow and the next weight at the bottom of the shaft would engage the lifting cable, etc. The cable would have to follow a circular track, rather than having 1KM of cable for each weight.

Re: Gravitricity

#36

Post by adaml_623 »

awjr wrote: post #24
elektropionir wrote: post #10

The energy density for gravity is just immensely small, that's why you need dams holding back rivers to use them to generate electricity. For a 1km hole (that's in the middle of their 500m - 1500m range) you have an energy density of 10kJ/kg of the weight that stores the energy. The energy stored in a Tesla roadster battery pack is around 50kWh which is 180MJ. This means that you need a 18,000kg weight in a 1km deep…

It becomes viable when you use a 500,000kg weight...about 1.2MWh This is not unachievable with some lifting systems currently exceeding this lifting weight.

Also lifting 500 tons is a lot easier when you don't have to move it horizontally. 1.2MW isn't as much as a wind turbine though which is a pity because they conceivably could be a good pairing.

Re: Gravitricity

#37

Post by [deleted] »

bsilvereagle wrote: post #22
grondilu wrote: post #21

Earlier quoted context omitted.

I suppose they plan on using a transmission mechanism that will turn one meter down to as many turns as you want anyway, so I guess the depth of the hole is at least partially determined by how good a transmission mechanism you can afford. But since they explicitly say the hole will be the most expensive part, I'm not so sure.

You're losing torque with every gear reduction, and I believe that current out of a generator is a function of torque. So there's some happy medium between hole depth & transmission ratio for the amount of power they want to generate.

[deleted]

Re: Gravitricity

#38

Post by _greim_ »

elektropionir wrote: post #10

The energy density for gravity is just immensely small, that's why you need dams holding back rivers to use them to generate electricity. For a 1km hole (that's in the middle of their 500m - 1500m range) you have an energy density of 10kJ/kg of the weight that stores the energy. The energy stored in a Tesla roadster battery pack is around 50kWh which is 180MJ. This means that you need a 18,000kg weight in a 1km deep…

This doesn't make sense. Gravity doesn't have an energy density. The energy density of this system is going to be directly related to the density of the material being raised/lowered.

Re: Gravitricity

#39

Post by pbhjpbhj »

So basically clock-type counterweights. PSH seems like it would be far more efficient - there's surely a lot of mechanical losses in the sort of system in the OP?

If the hole could be used for some sort of heatpump too then maybe that would weigh off [no pun intended!] some of the problems.

Re: Gravitricity

#40

Post by schoen »

bsilvereagle wrote: post #12
KaiserPro wrote: post #6

So how many joules can it contain? I mean, technically I can get a super cap the size of jam jar to kick out 1 kw, just not for very long. A watt is a unit of how much energy is expended in a second, not how much energy is stored. There is a reason why hydrostations in wales use lakes to store energy, because you need a lot of mass at great height to be of any use.

Work = Force*distance, so theoretically the number of Joules would be mgh^2.

Your units got messed up there -- it's just mgh. There's no reason to square the distance.

  $ units
  Currency exchange rates from 2013-07-11 
  2562 units, 85 prefixes, 66 nonlinear units
  
  You have: 1000 kg gravity 1 km
  You want: J
 	* 9806650
 	/ 1.0197162e-07
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