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Gravitricity

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Re: Gravitricity

#81

Post by fractalsea »

malandrew wrote: post #80
apsec112 wrote: post #61

Let's do out the math on this... A subway tunnel might have a diameter of about 6 meters, so cross section = 3 * 3 * pi = 28 square meters. Digging subway tunnel through rock costs about $100M per kilometer. On the one hand, these holes would be vertical, which is harder than horizontal; on the other hand, they wouldn't need ventilation and train tracks and stuff. Let's handwave and say it's $100M for a 1 km deep hol…

What's the math look like for the side of a mountain or hill, where you pour a concrete channel and put wheels on the weight so it can be rolled up and down the hill. I'm just wondering if there are places like in the Rockies where this idea would be viable.

I don't understand why they need to dig holes to do this. Why not build something equivalent onto the side of a cliff?

Re: Gravitricity

#82

Post by [deleted] »

mikeyouse wrote: post #30
troymc wrote: post #17

Earlier quoted context omitted.

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.

In 2011, we mined 0.2% of known lithium reserves.. This would provide over 350 years worth of lithium at current rates. Obviously usage is dramatically increasing but so will our known reserves as the overall level of demand increases. This is also without developing a method to pull the relatively abundant lithium from sea water and without recycling any lithium we're currently disposing of. Ambri is interesting fro…

[deleted]

Re: Gravitricity

#83

Post by tomp »

apsec112 wrote: post #61

Let's do out the math on this... A subway tunnel might have a diameter of about 6 meters, so cross section = 3 * 3 * pi = 28 square meters. Digging subway tunnel through rock costs about $100M per kilometer. On the one hand, these holes would be vertical, which is harder than horizontal; on the other hand, they wouldn't need ventilation and train tracks and stuff. Let's handwave and say it's $100M for a 1 km deep hol…

How are you going to hang a 280 000 ton weight, and more importantly, how are you going to move it up and down?

Re: Gravitricity

#84

Post by [deleted] »

msandford wrote: post #74
cperciva wrote: post #69

Earlier quoted context omitted.

Digging subway tunnel through rock costs about $100M per kilometer. On the one hand, these holes would be vertical, which is harder than horizontal I would have thought that a better comparison would be oil wells, which cost about $500 per ft of depth, or $1.5M per km. our total volume of mass will be about 25 m^2 1000 m = 25,000 cubic meters. If the weights are made from lead, that's a total mass of ~280,000 tons* Y…

Oil wells are also only a foot in diameter. Makes the economics worse, really.

[deleted]

Re: Gravitricity

#85

Post by delinka »

Stately wrote: post #77

I'm far from being even slightly knowledgeable in this topic, but would it be possible to build this in very deep waters? Like a massive column containing a tunnel? Seems cheaper than digging a 1km hole.

You'd be anchoring a buoyant tube to the ocean floor, trapping all that energy. Instead, float a barge in deep enough water, drop a weight to generate power, raise it to store.

Re: Gravitricity

#86

Post by lotsofmangos »

Coincoin wrote: post #59
mikeyouse wrote: post #30

Earlier quoted context omitted.

In 2011, we mined 0.2% of known lithium reserves.. This would provide over 350 years worth of lithium at current rates. Obviously usage is dramatically increasing but so will our known reserves as the overall level of demand increases. This is also without developing a method to pull the relatively abundant lithium from sea water and without recycling any lithium we're currently disposing of. Ambri is interesting fro…

"The greatest shortcoming of the human race is our inability to understand the exponential function."

Increases in known reserves can also be exponential.

The known reserves are 13 million tonnes. However lithium is the 25th most abundant element and you get 20mg of it for every kg of crust, so there is a lot more to find.

Re: Gravitricity

#87

Post by [deleted] »

wklauss wrote: post #75
andrewliebchen wrote: post #58

Good thing HN wasn't around durning the development of most of humanity's great inventions. "So your telling me I'm going to have to hold my food over this fire for 15 minutes before I eat it? No thank you, I'd stick with my raw meat."

A lot of bad ideas happen in between humanity's greatest inventions. When you look at the past, you are only looking to the successful stories. Maybe a lot of people with unrealistic or bad ideas would have benefited from HN.

[deleted]

Re: Gravitricity

#88

Post by ChuckMcM »

tempestn wrote: post #70
marcosdumay wrote: post #68

Earlier quoted context omitted.

Now that you mentioned a mountain... Why again is a hole needed? Edit: I mean that an inclined rail could be just as good as a hole, and way cheaper.

For the gravity-based design, you need to lower a weight directly up and down in a controlled manner (ie without swinging etc.) That basically requires a shaft in the ground. If you have a mountain and a lake handy, pumped storage would be more economical, but the advantage of this design - as I understand it - is it can be deployed in places that don't have those things.

Actually an inclined plane and a hole in the ground are identical in terms of their energy storage, both are a function of their highest and lowest points. Which suggests a very simple implementation which is to run a pair of rails up the side of a mountain and but the winder/generator at the top and tie it off to the end of a rail car filled with rocks. Sure you would give up some efficiency with the friction of rail on steel but it would be pretty cheap to implement. On some of the alluvial fans in the Mohave it would make for an interested 'excess energy' storage mechanism for solar.

That said, how are those gravity fed porch lights doing? That seems like it would be an interesting proxy here.

Re: Gravitricity

#89

Post by sskates »

andrewliebchen wrote: post #58

Good thing HN wasn't around durning the development of most of humanity's great inventions. "So your telling me I'm going to have to hold my food over this fire for 15 minutes before I eat it? No thank you, I'd stick with my raw meat."

Here's an interesting reference, Drew Houston showing Dropbox to HN: https://news.ycombinator.com/item?id=8863

Definitely more negative comments on HN these days (although it's always been a skeptical audience).

Re: Gravitricity

#90

Post by revelation »

Zikes wrote: post #4

I look forward to Elon Musk's proposal for unconventional energy storage, because he wouldn't dare call it anything other than Eccentricity.

This is just a pun, but of course his proposal for energy storage already exists, and (surprise surprise) its lithium ion batteries. Significant parts of the projected gigafactory capacity are reserved producing cells for SolarCity home energy storage appliances and other storage systems.

In fact, right now the Tesla factory has 4GWh of lithium ion batteries installed for smoothing energy demands and they are actively building 400kWh storage units:

http://www.greentechmedia.com/content/images/articles/straub...

I'm sure that the end game idea in his mind is using the 85kWh+ batteries of Teslas everywhere for distributed energy storage.

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