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.<p>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.<p>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.<p>[1] <a href="https://en.wikipedia.org/wiki/Pumped-storage_hydroelectricity" rel="nofollow">https://en.wikipedia.org/wiki/Pumped-storage_hydroelectricit...</a>
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.<p>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.<p>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!
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.<p>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.
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?<p>My physics is a little rusty, and I'm sure someone will come up with an answer before I figure it out.<p>EDIT:<p>If my math is right (using this [1] as reference),<p><pre><code> E = m * g * h (J)
</code></pre>
gives the energy E in joules. 1 watt hour is 3600 joules, so:<p><pre><code> E = m * g * h / 3600 (Wh)
</code></pre>
So, if this system were made up of 4 x 200kg weights suspended over a 50m well, it would hold<p><pre><code> E = 4 * 200 * 9.81 * 50 / 3600 = 109 Wh
</code></pre>
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.<p>[1]: <a href="http://physics.stackexchange.com/questions/39281/needed-energy-for-lifting-200-kg-weight" rel="nofollow">http://physics.stackexchange.com/questions/39281/needed-ener...</a>
Similar concept is already in use with hydroelectric power generation. It's called pumped-storage hydroelectricity: <a href="https://en.wikipedia.org/wiki/Pumped-storage_hydroelectricity" rel="nofollow">https://en.wikipedia.org/wiki/Pumped-storage_hydroelectricit...</a>
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.<p>About the only advantage is that with simple maintenance, this system should last indefinitely, while lead-acid batteries have a limited lifespan.<p>(Oh, and didn't web-sites that are nothing but one giant image go out of fashion around the turn of the century?)
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.
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.<p>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.<p>[1] <a href="https://en.wikipedia.org/wiki/Energy_density#Energy_densities_ignoring_external_components" rel="nofollow">https://en.wikipedia.org/wiki/Energy_density#Energy_densitie...</a>
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.<p>EDIT: See wikipedia link explaining it, with examples. <a href="http://en.wikipedia.org/wiki/Hydroelectric_energy_storage" rel="nofollow">http://en.wikipedia.org/wiki/Hydroelectric_energy_storage</a>
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.
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.
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.)<p>EDIT: thanks everyone, now I know that <i>that's</i> what a flywheel is. Had heard the name, never found out what one was.
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.<p>[1] <a href="http://www.indiegogo.com/projects/gravitylight-lighting-for-developing-countries" rel="nofollow">http://www.indiegogo.com/projects/gravitylight-lighting-for-...</a>