
Gravity Battery Concept - vrepsys
http://gravitybattery.info/
======
kijin
At larger scales, these are called pumped-storage hydroelectric plants. There
are currently more than 100 GW of pumped-storage capacity in the world, with
efficiency ranging from 70% to 87% [1]. They are, in fact, some of the largest
batteries we've ever built.

They store electricity by pumping thousands of tons of water uphill when
demand is low, and letting it fall back down past a bunch of turbines when
demand is high. Water is much easier to handle than a solid block of steel,
and it's much more scalable as well. You just need a hill and some water,
possibly an already existing reservoir. Pumps can be turned on and off almost
instantly to meet fluctuating demand. There's one about 10 minutes' drive from
where I live. It's marvelous, and the two artificial lakes (one at the top,
one at the bottom) also make nice parks for the public to enjoy.

Since pumped-storage plants seem to work so well, I wonder if there will be
any need to install smaller versions in each home. It's probably going to be
difficult to match the efficiency of much larger units. Maybe these will be
more useful as backup batteries.

[1] [https://en.wikipedia.org/wiki/Pumped-
storage_hydroelectricit...](https://en.wikipedia.org/wiki/Pumped-
storage_hydroelectricity)

~~~
Tloewald
I suspect that the big problem with this concept (vs. the hydroelectric
example) is going to be the amounts of energy involved. Let's suppose the
shaft is 500m deep and a 100kg battery -- potential energy is simply F * z, so
F = 980N and z is 500, which gives you 490kJ. A wH is 3.6 kJ (you'll need
~10-20 of these to run an iPad for an hour). You're going to need a really big
weight and a really big shaft.

This shouldn't be surprising -- with a fairly small motor and good gearing you
could raise a remarkably large weight a remarkably long distance with
relatively little energy.

Also note that with a hydroelectric dam, the storage mechanism also happens to
be the power generation mechanism (dam + turbine) so you aren't incurring huge
additional construction and maintenance costs relative to just building the
power source, so even if you replaced the weights with a giant tank of water,
the entire storage mechanism is extra capital investment and maintenance on
top of the solar panels.

If the fundamental problem you're trying to solve is baseline power, it's
probably more efficient to bring power in from somewhere the sun is shining
(8000 miles away, say):

"As of 1980, the longest cost-effective distance for Direct Current
transmission was determined to be 7,000 km (4,300 mi). For Alternating Current
it was 4,000 km (2,500 mi), though all transmission lines in use today are
substantially shorter than this." (Wikipedia)

~~~
sp332
_A wH is 3.6 kJ (you 'll need ~10-20 of these to run an iPad for an hour)_

I'm pretty sure a whole iPad battery only contains ~7 Wh (1,900 mAh * 3.7v)
and it can run for 10 hours.

Edit: OK I was looking at completely the wrong device for these numbers.
Thanks miahi!

~~~
andrewcooke
if an ipad has a 40Wh battery and can run for 10 hours then it consumes 4Wh
per hour so runs at 4W or 4J/s. 100kg dropping 1m releases 1kJ so will supply
an ipad for 1000/4 = 250s = 4min. so a 100kg weight needs to drop 15m to power
an ipad for an hour.

i don't completely understand the parent comment - what are "these"? but you
do not need multiple weights and shafts to run an ipad for an hour. a single
100kg weight and a 15m shaft is sufficient.

~~~
renekooi
"these" are the Wh's

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mrgriscom
I'm really sick of hearing about this idea. At least this one doesn't make the
same mistake of suggesting it should be human powered, but the energy density
of gravity is ridiculously low compared to practically any other technology we
have. It works for hydroelectric plants because they have HUGE reservoirs to
supply them.

Assume one of these gravity batteries uses a 100m deep shaft with a
counterweight the mass of a Cadillac Escalade. The energy stored is 100m *
2700kg * 9.8m/s^2 = 2.6 MJ.

The first deep-cycle battery I found through google (retail price $260) is
90Ah * 12V * (assume 80% discharge cycle) = 3.1 MJ. It just doesn't add up!

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puetzk
The problem is the poor density: power stored is just mass * gravity * height.
So if we want to store 1kWh, using a hole 500m deep (about the max for
elevator cables, which seems analogous) this would need a 750kg weight.

Storing the same amount of energy in a lead-acid battery would only take 21kg,
a LiFePO battery only ~10kg. And those don't require digging out a 500m hole,
or the supporting equipment to winch a car up and down a skyscraper.

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devrelm
Has anyone worked out how much energy this could actually theoretically store
given the number of weights as n, the mass of each weight as m, and the height
of each well as h?

My physics is a little rusty, and I'm sure someone will come up with an answer
before I figure it out.

EDIT:

If my math is right (using this [1] as reference),

    
    
      E = m * g * h (J)
    

gives the energy E in joules. 1 watt hour is 3600 joules, so:

    
    
      E = m * g * h / 3600 (Wh)
    

So, if this system were made up of 4 x 200kg weights suspended over a 50m
well, it would hold

    
    
      E = 4 * 200 * 9.81 * 50 / 3600 = 109 Wh
    

109 Wh. That's hardly enough to run a few high-efficiency light-bulbs for an
hour. I don't mean to be a naysayer, but this doesn't seem very efficient at
small scales.

[1]: [http://physics.stackexchange.com/questions/39281/needed-
ener...](http://physics.stackexchange.com/questions/39281/needed-energy-for-
lifting-200-kg-weight)

~~~
maxerickson
It's just mass * gravity * height.

So, for instance, 1000 kg with a working height differential of 1000 meters
can store a theoretical maximum of 2.72 kilowatt hours (9.8 million joules).

~~~
seniorsassycat
You would have to factor the efficiency motors that raise the weights, and the
generator that lowers them to get a more accurate estimate.

~~~
maxerickson
That's why I used a kilometer. There's little need for an accurate estimate,
capacity for such a system is very expensive, either in dealing with huge
masses or huge distances.

By way of comparison, a thousand dollars of lead acid batteries would have
more capacity (and despite the issues with lead, such batteries are quite
recyclable...).

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mike_esspe
Similar concept is already in use with hydroelectric power generation. It's
called pumped-storage hydroelectricity: [https://en.wikipedia.org/wiki/Pumped-
storage_hydroelectricit...](https://en.wikipedia.org/wiki/Pumped-
storage_hydroelectricity)

~~~
zamalek
Indeed, I was about to point this out. I visited the Drankensberg one[1] in
South Africa a few years back. It's amazing how big the complex was for such a
simple concept (if memory serves me correctly the turbines were 50 or so
stories underground).

I'm very interested to see if graphene supercapacitors may eventually have a
role to play here. Using gravity seems a bit "primitive".

[1]:
[http://en.wikipedia.org/wiki/Drakensberg_Pumped_Storage_Sche...](http://en.wikipedia.org/wiki/Drakensberg_Pumped_Storage_Scheme)

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alextingle
This is a terrible idea. It would cost a fortune to build a "battery" that
stores no more energy than a simple lead-acid deep cycle battery.

About the only advantage is that with simple maintenance, this system should
last indefinitely, while lead-acid batteries have a limited lifespan.

(Oh, and didn't web-sites that are nothing but one giant image go out of
fashion around the turn of the century?)

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1rae
In Johannesburg we have a whole lot of deep mine shafts that are no longer
being used, and one of the main ideas for reusing them is to turn them into
hydroelectric power stations. During the night when the electricity is
cheaper, the water will be pumped up to the top, and during peak hours the
water will be allowed to fall back down and provide power if necessary. It's a
similar concept but on a much larger scale.

~~~
PeterisP
Are they really that big? Stored-hydro stations are efficient because of lake-
sized reservoirs, and it takes uncountable miles of tunnels to have the same
volume as a medium-sized lake.

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jsmcgd
I (like many people) have had this idea an energy storage mechanism.
Unfortunately gravity batteries have an extremely low energy density for
weight [1] or volume and so are only really a valid choice for something that
operates at the scale of a hydroelectric dam.

Heat batteries make more sense for energy storage at a household level,
whether it's heating or cooling. They're smaller, can require almost no
maintenance and have a much higher energy density.

[1]
[https://en.wikipedia.org/wiki/Energy_density#Energy_densitie...](https://en.wikipedia.org/wiki/Energy_density#Energy_densities_ignoring_external_components)

~~~
ash
LightSail Energy system uses heat and compressed air to store energy:

[http://www.lightsail.com/](http://www.lightsail.com/)

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lylebarrere
Using potential energy to store electricity is nothing new. Many hydroelectric
damns pump water to a high reservoir when there is excess electricity
generated to store it, and let it fall to a low reservoir when more is needed.

EDIT: See wikipedia link explaining it, with examples.
[http://en.wikipedia.org/wiki/Hydroelectric_energy_storage](http://en.wikipedia.org/wiki/Hydroelectric_energy_storage)

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Geee
Better would be to use your whole house as the weight. And store the energy in
angular momentum.. That's limitless energy storage :D

~~~
alextingle
Wheeeee.....!!

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doctorwho
This is just a large physical battery. The only way to win is if storing the
energy in a weight system is more efficient or has more capacity than storing
it in a chemical battery. It's certainly not as scalable as a chemical battery
and requires a lot of infrastructure to pull off.

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praptak
Any reasonable estimates of (investment, maintenance) costs per joule of
capacity?

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gum_ina_package
I'd be curious to see the immediate/longterm ROI for something like this. It
seems like there would be an incredible amount of resources spent on initially
building a powerhouse like the one in the picture.

~~~
jmelloy
There's one in England that's mainly for tea kettles after major television
events, like Eastenders. They're one of the power storage options that has the
quickest ability to change their output.

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tehwalrus
I've always imagined a frictionless spinning top instead of a long shaft
(using permanent magnets, perhaps with some copper coils for stabilisation).
You don't need a big geometry, and you can go faster and faster, up to
relativistic speeds if required, without any inefficiency. (of course, it must
be in a vacuum tube.)

EDIT: thanks everyone, now I know that _that 's_ what a flywheel is. Had heard
the name, never found out what one was.

~~~
wffurr
You mean a flywheel:
[http://en.wikipedia.org/wiki/Flywheel_energy_storage](http://en.wikipedia.org/wiki/Flywheel_energy_storage)

They're in use for a number of applications, namely in datacenter UPS systems.

The main downside is a catastrophic failure mode. Lots of mass, spinning at
high speed. Just apply imagination.

Their energy density is pretty good relative to batteries, which is to say
terribad compared to hydrocarbons. Good ones are pretty expensive, and they
require periodic servicing for bearings, gaskets (for vacuum sealed systems),
etc. Generally limited to niche applications for now, but there are various
pilot projects to look at them for train system energy recovery and grid
storage.

~~~
tehwalrus
yeah, my thought process had some pretty complicated failure systems. The
thing is, with magnetic suspension, you can "catch" the thing using it's own
energy. With a good and fast enough controller, you could catch the thing
where it is and flood the tube with air to slow it down. since all you're
doing is dissipating energy, you can use it to soften the crash.

In terms of energy density, you can just *keep increasing the speed can't you?

~~~
pbhjpbhj
> _In terms of energy density, you can just increasing the speed can 't you?_
> //

In which case you only need a tiny mass to start with ...

The speed limitation is presumably going to come in with the rate at which you
can alter the magnetic field to still accelerate the mass. Also you'll get
drag as it impinges on local fields (Earth's magnetic field) and there'll
presumably be eddy currents and local electrical fields to cope with too which
will become more significant at higher flux rates.

~~~
tehwalrus
:( you're probably right, the universe always finds a way to ruin all the good
ideas.

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achy
A pretty illustration of a terrible idea. Gravity just isn't that strong of a
force. Electrostatic forces in chemical bonds on the other hand...

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ghh
GravityLight[1] applied this concept at small scale: to power a white led in
e.g. rural areas without power, a bag of dirt is suspended from a dynamo.

[1] [http://www.indiegogo.com/projects/gravitylight-lighting-
for-...](http://www.indiegogo.com/projects/gravitylight-lighting-for-
developing-countries)

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pkinsky
>(H) Generator & CPU > The generator axis gets spinned

I think you mean spun. Aside from that, very cool!

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Gravityloss
I have another idea: just throttle the hydro and nat gas plants?

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heeton
I refuted a few of his points and got banned from commenting ;)

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stox
The ghost of Storm King rises again.

