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Gravitricity

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Re: Gravitricity

#131

Post by imaginenore »

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…

18,000 kg is just 1.58 cubic meters of lead.

You can have a much much heavier weight.

Re: Gravitricity

#132

Post by jamesaguilar »

photon137 wrote: post #125
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.

Peak-power output would be less for an inclined rail (vs the vertical shaft solution).

Yeah, but if they're a quarter as efficient and cost a tenth as much, then we might have a winner.

Re: Gravitricity

#133

Post by jmadsen »

I love how every Tom, Dick & Harry with a bit of math & engineering thinks he can "dispel the myth" of HN Idea X with two minutes of off-the-top-of-his-head equations.

Read about these two: http://www.gravitricity.com/#people

Do they seem like complete morons? Do you think they haven't studied this just a little bit more than you have? It doesn't mean their idea is good or will work - just that you aren't going to rip it apart with two hastily written paragraphs.

People who ask questions about the costs, process, etc. are in the right spirit. People who think they can show off how clever they are really make me /facepalm

Re: Gravitricity

#135

Post by krschultz »

Keep in mind, we currently remove entire mountains to extract coal. If there is one thing we can do at scale it's dig holes, move concrete, and make steel cable.

Re: Gravitricity

#136

Post by pbreit »

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.

I would think you could find an elevated lake that replenishes naturally to avoid pumping the water up. But then maybe that is just "energy".

Re: Gravitricity

#137

Post by jpau »

abdullahkhalids wrote: post #79

The key figure of merit for comparing energy storage is not $/KWh, but rather $/KWh*Number of cycles. Li-ion only has about a 1000 cycles. Assuming one cycle per day (solar charge during day+discharge during night) in 50 years there are 18000 cycles. The figure of merit for Li-ion is 250x1000=2.5e5. My estimate (and those of others) is that this costs up to about $2000/KWh. So the figure of merit for this is 1000x180…

I did some quick analysis comparing the proposed project against Li-ion, adjusting for storage and lifespan, and the result is very hopeful. I used values for $/KWh and lifespan from abdullahkhalids' comment. The analysis shows that if you can get more than one cycle per day out, the proposal offers fantastic value.

Model visible here - http://imgur.com/KmQPb8P

Finance uses something called 'equivalent annual cash flows' (EACFs) to compare projects of different lifespans. Using EACFs makes this analysis very simple.

Using abdullahkhalids' figures and assuming a single cycle per day, the equivalent annual cash flows per KWh are equal when the cost of capital is about 4.35%.

Something magical happens when you assume can get more than one cycle per day. At two cycles per day, your funding costs could be 10% and the project still feasible! At four cycles per day and with a 5% cost of capital, Li-ion costs almost four times as much as the proposed project.

Could someone shine some light on how many cycles per day is realistic for both Li-ion & the proposal?

PS if you find this sort of analysis interesting and want to hit me up to talk about such things, feel free to send me an email (available in my profile).

Re: Gravitricity

#138

Post by unchocked »

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."

"The greatest shortcoming of exponential forecasting is the S-curve."

Re: Gravitricity

#139

Post by bduerst »

jmadsen wrote: post #133

I love how every Tom, Dick & Harry with a bit of math & engineering thinks he can "dispel the myth" of HN Idea X with two minutes of off-the-top-of-his-head equations. Read about these two: http://www.gravitricity.com/#people Do they seem like complete morons? Do you think they haven't studied this just a little bit more than you have? It doesn't mean their idea is good or will work - just that you aren't going to ri…

You don't need to be a carpenter to tell if a house is built poorly.

Re: Gravitricity

#140

Post by joering2 »

I have this idea in my mind for a while now and it seems great subject to share it with you.

Imagine an elevator going kilometers into the oceans dept. A huge tank is mounted on the top of it. It gets filled in with pressurized air. Because its heavy it sinks to the bottom. Then an air is released. Air travels into the surface but on its way it is actually captured into a little traps. When enough air is trapped, the entire structure built from hundreds of traps is lifted into the surface, together with the tank. of course during this trip, it triggers friction and the dynamo mounted on the surface translates this movement into electricity.

Once on the surface, the tank is filled in with air, and the process starts all over.

With long enough elevator in deep enough ocean, the electricity produced thanks to the travelling elevator would be greater than electricity used to put air into the tank.

If you ignore the rules of gravity and that trapped air travels to the surface of a water, this could be a perpetuate mobile.

What's wrong with my idea?

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