161–170 of 222 posts
If we had a dyson sphere around something heavy then the crank part could be in space with the weight dangling into the atmosphere: https://en.wikipedia.org/wiki/Dyson_sphere
How about the Moon? :D
Intelligent people on HN are pointing out huge holes with this idea but some people are still defending their Nigerian princes, because... they want it to be true?
The warning signs here are huge. It's an incredibly simple idea, if it was possible it'd be already done. Nothing here really seems to rely on scale either.
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You don't need to be a carpenter to tell if a house is built poorly.
You don't need to be a carpenter to tell if the doors are hung straight. You DO need to be one to actually assess the overall build and structure.
Anyone can tell if a really really shoddy building is NOT structurally sound.
What is hard to tell is if a building IS structurally sound. That is why engineers exist. Not for the previous.
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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.
Other materials, like lead and antimony? http://en.wikipedia.org/wiki/Abundance_of_elements_in_Earth%... Lithium: 33 Lead: 37 Antimony: 62
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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…
Actually 1/2 the shaft filled by weights is optimal independently of material, considering only raw energy. (E=p A h(H-h), respectively density, area, payload height and shaft height, Eopt=p A H^2/2 ). Pretty surprising to me that the energy increases quadratically with depth.
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Not really. Electrical engines and generators are incredibly efficient. It's not the transition there that is the problem. In fact, if it was only for that loss the efficiency would be more like 97%. The problem is the friction in the mechanical parts; the wires, gears and so on.
Dang, that's impressive. I had no idea electrical mechanical conversion was so efficient.
By contrast anything that qualifies as a "heat engine" (including internal combustion) is limited by Carnot's law to be low-efficiency. If it weren't for the extraordinary energy density of combustible fuels they wouldn't be competitive.
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.
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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 rai…
Earlier quoted context omitted.
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 rai…
That implies that you want a weight orders of magnitude more than a train (or many trains per charge "cycle" with a stockyard at each and of the mountain to store them) You're now going to need a very tough track and wheelset. They're also going to wear quickly. Probably enough to make it impractical to build and operate.
Can one use potential energy to, well, store energy? Duh. This, however, is the wrong way to do it.