Image of the Gravitricity gravity energy storage battery (with a power of 250kw) located in the port of Edinburgh. (Gravitricity image credit).
These days, visitors to the port of Edinburgh may have come across a strange contraption the height of a four-story building, reminiscent of a bare elevator shaft. Only instead of a passenger cabin, what is suspended by steel cables is a green block weighing 50 tons.
From time to time, the electric motors are activated, lifting the enormous weight a few centimeters. In reality, all that elevated mass is a store of potential energy that can be released when needed. At a certain point, when the weight is about half the distance from its axis, the engineers responsible for the contraption decide to put it to the test and release the mass in a controlled way, so that the huge green block descends a few tens of centimeters.
At that time, the motors that had previously raised the mass, reverse their direction, becoming electrical generators capable of sending 250 kilowatts of power to the grid. If necessary, in times of very high electricity consumption, the weight could be completely released by initiating a descent that would take 11 seconds.
The company responsible for this “gravitational pile”, which is called Gravitricity, includes in its commercial name the British obsession with word games: “gravity plus electricity = gravitricity”.
This week, Gravitricity announced that its scale proof of concept (ie the four-story tall hulk) is operational, and that it is able to toggle between its “raise mass using grid energy” mode and its nemesis “release mass and deliver power to the grid ”in a matter of seconds.
If you remember, one of the main drawbacks of renewable energy sources is that they do not work on demand. The sun or wind speed appear and disappear randomly. It may be the case that a wind farm is generating energy at a good rate when the users of the electricity grid do not require it and quite the opposite. Unfortunately, storing energy is very complicatedSo much so that we have had to plunge into an unprecedented climate crisis to seriously consider the problem.
Since then, we have started to hear interesting projects aimed at storing surplus energy in the form of a vector (hydrogen), directly in chemical batteries, or – as we see in the Gravitricity initiative – in the form of potential energy. The idea in all cases is magnificent, to prevent that energy not consumed at the time can be recovered on demand, without polluting in the process.
In the end, the Scottish proposal is not at all new. The “lifelong” water dams that we all know not only serve as a reservoir of water, but also act as a store of potential energy that can be transformed into electrical energy due to gravity. The mechanism is identical, whether it is piped water falling on a turbine, or whether it is a 50-ton weight falling in a controlled way through a mine shaft.
The 122-meter-high crane would store concrete blocks concentrically according to energy demand. The idea would be to locate one of these in each wind turbine park to store the surpluses. (Image credit: Energy Vault).
I say this, because obviously it will be useless to have a gravity pile that descends 11 meters as we have seen in the port of Edinburgh. Gravitrici’s whole idea is enable old abandoned mines so that they become huge reservoirs of potential energy (see video above). The greater the distance and the greater the suspended weight, the greater the energy production that can be used when the consumption peaks arrive. (I hope that policy makers in Asturias read this for ideas, there could be a future for their abandoned coal mines)
And well, to be fair, the Scots have not been the first to propose the use of gravity as an energy store. In 2018, I read about the Californian Energy Vault initiative, in which something very similar was proposed. Install a storage tower consisting of a six-arm crane with a height of 122 meters, which would be stacking 35-ton concrete blocks when the energy generated in the neighboring wind farm, did not find demand in the electricity grid. Then the reverse process would generate electricity when demand increased and / or wind conditions changed.
Desalination plant plus hydroelectric power station in a single installation. The great idea of Vázquez Figueroa. (Image credit energeticafutura.com).
And without having to travel to California or Edinburgh, the Canarian writer Alberto Vázquez Figueroa has spent years trying to get the government to support his project for a desalination plant and gravity-based electricity generation. Figueroa’s idea is conceptually very simple. Pumping water from the sea to an elevated reservoir, using renewable energy for the process when it is not in demand. Then, in a total win-win, the writer proposes to release that water into a vacuum (as in a traditional hydroelectric power station) which would move a turbine generating electricity. But also, and here’s the genius, that salty water could fall on a semi-permeable membrane, so that it desalinated. Clean electricity and fresh water for the same price. Who gives more?
I found out by reading Science.