Energy

Prototype gravity-based energy storage system begins construction

Prototype gravity-based energy...
A concept image of the Gravitricity demonstrator facility, which should open for testing in early 2021
A concept image of the Gravitricity demonstrator facility, which should open for testing in early 2021
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A concept image of the Gravitricity demonstrator facility, which should open for testing in early 2021
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A concept image of the Gravitricity demonstrator facility, which should open for testing in early 2021

As renewable energy generation grows, so does the need for new storage methods that can be used at times when the Sun isn’t shining or the wind isn’t blowing. A Scottish company called Gravitricity has now broken ground on a demonstrator facility for a creative new system that stores energy in the form of “gravity” by lifting and dropping huge weights.

If you coil a spring, you’re loading it with potential energy, which is released when you let it go. Gravitricity works on the same basic principle, except in this case the springs are 500- to 5,000-tonne weights. When held aloft by powerful cables and winches, these weights store large amounts of potential energy. When that energy is needed, they can be lowered down a mineshaft to spin the winch and feed electricity into the grid.

Gravitricity says that these units could have peak power outputs of between 1 and 20 MW, and function for up to 50 years with no loss of performance. Able to go from zero to full power in under a second, the system can quickly release its power payload in as little as 15 minutes or slow it down to last up to eight hours.

To recharge this giant mechanical battery, electricity from renewable sources power the winches to lift the weights back to the top. In all, the system has an efficiency of between 80 and 90 percent.

Ultimately, this kind of system should be able to store energy at a lower cost than other grid-scale energy storage systems, such as Tesla’s huge lithium-ion battery in Australia. The concept sounds very similar to the one behind Energy Vault, which uses a crane to hoist concrete blocks into a tower.

That said, Gravitricity seems to be further ahead in development. The company is now in the early stages of constructing a demonstrator facility to test out the concept next year. The tower will stand 16 m (52.5 ft) tall, lifting and dropping two 25-tonne weights in order to generate 250 kW.

“In one test we’ll drop the weights together to generate full power and verify our speed of response,” says Miles Franklin, lead engineer at Gravitricity. “We’ll then run tests with the two single weights, dropping one after the other to verify smooth energy output over a longer period, alongside a program of other tests to demonstrate and refine the full capabilities of the system.”

The custom-built winches and control system are being constructed by Huisman in the Czech Republic, while Kelvin Power is fabricating the lattice tower in Leicester, UK. The separate pieces will then be shipped to the port of Leith in Edinburgh for construction of the demonstrator.

Testing of this facility is due to begin in (northern hemisphere) spring 2021, and a full-scale 4-MW project will begin later that year.

The Gravitricity system is described in the video below.

Latest Gravitricity Explainer - Extended Animation - Spring 2020

Source: Gravitricity

33 comments
Pio Tr
Potential energy of 25000kg at height of 16 m is roughly 1kWh. At least in Earth's gravity. Same energy can be stored in small box of 100 regular li-ion cells.
windykites
What goes down must come up! The weight must be pulled up by energy input, therefor the unit is out of use while this happens. Two shafts would seem to be necessary. I have other ideas, which I cannot divulge, so I will say no more!
Daishi
I used 25000kg @ 16m with a m/s of 9.81 (earths gravity) and got 3924000 Joules which is 1.09 kWh. I just used calculators I found on Google but I got the same result as @Pio Tr. Can anyone shed light on how gravitricity came up with 250 kW or fix my math/info?
Brian M
@Pio Tr
1kWh seems low Have you allowed for the x 3600 to convert kW/s to kWh? SI units are per second
(1 joule = 1 Watt for 1 second)
Captain Danger
This was made for imperial units - fitting that it takes place in Scotland ( James Watt defined horse power)
25000 KG = 55000 lb
to lift 550 lb 1 ft in 1 sec takes 1 hp
Shaft is 50 ft deep
Each weight can generate 100 HP (55000/550 ) for 50 seconds
.75 KW per HP = 75KW per weight (for 50 seconds)
2 weights
150 KW total for 50 seconds
If they drop it faster they can generate more power but over less time
I would be interested to see what the efficiency turns out to be.
Gary Gipson
Hmmm.....I got an idea, let nature store up energy for in the form of a liquid, maybe water, and then release it through a device tied to a generator. You could call it hydropower. You could also use wind and solar to pump the water back up again - but I think somebody already beat me to this idea.
Nobody
There is no doubt that it should work but I would question the 80-90% efficiency.
michael_dowling
This is not new,but other gravity systems would be cheaper to build,as they use towers to support their weights rather than digging a shaft if an old mine is not available. Of course,I assume erecting towers is cheaper than digging a shaft.
sam12
It’s just a demonstrator, 250 kW is probably just for 15 seconds. Where space is not a premium, this will scale better than lithium batteries and lasts longer too.
Chris Coles
The Eiffel tower has been doing this for more than a century; except that they use water to power all the lifts in the tower. So what is new?