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.
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)
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!
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.
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.
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).
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".
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.
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.
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.
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.
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.
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.
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.
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.
[+] [-] kijin|12 years ago|reply
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...
[+] [-] Tloewald|12 years ago|reply
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)
[+] [-] ErikRogneby|12 years ago|reply
http://www.energycache.com/ http://www.youtube.com/watch?v=G3nz_kU604s&feature=youtu.be
[+] [-] hrjet|12 years ago|reply
I don't know how much loss does it amount to on a sunny day.
[+] [-] andrelaszlo|12 years ago|reply
[1] http://www.hydroworld.com/articles/print/volume-19/issue-3/a...
[+] [-] mrgriscom|12 years ago|reply
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!
[+] [-] puetzk|12 years ago|reply
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.
[+] [-] devrelm|12 years ago|reply
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),
gives the energy E in joules. 1 watt hour is 3600 joules, so: So, if this system were made up of 4 x 200kg weights suspended over a 50m well, it would hold 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...
[+] [-] maxerickson|12 years ago|reply
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).
[+] [-] mike_esspe|12 years ago|reply
[+] [-] zamalek|12 years ago|reply
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...
[+] [-] mxfh|12 years ago|reply
[+] [-] alextingle|12 years ago|reply
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?)
[+] [-] 1rae|12 years ago|reply
[+] [-] PeterisP|12 years ago|reply
[+] [-] jsmcgd|12 years ago|reply
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...
[+] [-] ash|12 years ago|reply
http://www.lightsail.com/
[+] [-] lylebarrere|12 years ago|reply
EDIT: See wikipedia link explaining it, with examples. http://en.wikipedia.org/wiki/Hydroelectric_energy_storage
[+] [-] Geee|12 years ago|reply
[+] [-] alextingle|12 years ago|reply
[+] [-] doctorwho|12 years ago|reply
[+] [-] praptak|12 years ago|reply
[+] [-] gum_ina_package|12 years ago|reply
[+] [-] jmelloy|12 years ago|reply
[+] [-] tehwalrus|12 years ago|reply
EDIT: thanks everyone, now I know that that's what a flywheel is. Had heard the name, never found out what one was.
[+] [-] wffurr|12 years ago|reply
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.
[+] [-] swayvil|12 years ago|reply
[+] [-] apendleton|12 years ago|reply
http://www.kickstarter.com/projects/1340066560/velkess-energ...
[+] [-] rxw|12 years ago|reply
http://en.wikipedia.org/wiki/Flywheel_energy_storage
[+] [-] brey|12 years ago|reply
http://en.wikipedia.org/wiki/Kinetic_energy_recovery_system
[+] [-] stephen_g|12 years ago|reply
[+] [-] achy|12 years ago|reply
[+] [-] ghh|12 years ago|reply
[1] http://www.indiegogo.com/projects/gravitylight-lighting-for-...
[+] [-] pkinsky|12 years ago|reply
I think you mean spun. Aside from that, very cool!
[+] [-] Gravityloss|12 years ago|reply
[+] [-] heeton|12 years ago|reply
[+] [-] stox|12 years ago|reply