As renewable energy operations continue to expand worldwide, governments and energy companies are racing to develop battery storage capacity to ensure that people have access to clean energy at all hours of the day and night. The inconsistency of many renewable energy sources has made the need for battery storage greater than ever, which has spurred a huge amount of investment into new battery technologies around the globe. Now, gravity batteries may help us harness the power of wind and solar farms even when the wind isn’t blowing and the sun’s not shining.
Gravity batteries work by using power from renewable energy projects to lift a heavy weight into the air or to the top of a deep shaft. As energy is required, winches are used to lower the weight, producing electricity from the movement of the cables. This means that energy from renewable projects, which cannot produce consistent power – such as wind and solar farms, can be stored in an alternative way from traditional battery power for use during peak demand times.
These mechanical batteries build upon the concept of pumped hydroelectric power storage, which uses dams to pump water up and down a hill to produce electricity as needed. Several of these projects are already underway, with the U.K. seeing the potential for 700 hydroelectric power sites, which could provide as much as 7 GW of energy storage. It is not surprising, therefore, that engineers have been inspired to adapt this idea to battery storage.
But are gravity batteries different or better than lithium-ion batteries? The current market leader, lithium-ion batteries are made up of an anode, cathode, separator, electrolyte, and two current collectors (positive and negative). The anode and cathode store the lithium. The electrolyte carries positively charged lithium ions from the anode to the cathode and vice versa through the separator. The movement of the lithium ions creates free electrons in the anode which creates a charge at the positive current collector. The electrical current then flows from the current collector through a device being powered, such as a laptop, to the negative current collector. The separator blocks the flow of electrons inside the battery. While the battery is discharging and providing an electric current, the anode releases lithium ions to the cathode, generating a flow of electrons from one side to the other. When plugging in the device, the opposite happens: Lithium ions are released by the cathode and received by the anode.
To continue manufacturing enough lithium-ion batteries to power our electrical devices and fuel the green transition, the world will need to vastly expand its lithium mining operations to provide enough of the metal to produce these batteries. In contrast, gravity batteries are mechanical instruments, which can be used repeatedly with simple reparations, with a lifespan of around 50 years. Asmae Berrada, an energy storage specialist at the International University of Rabat in Morocco, explains, comparatively, "Lithium-ion cells degrade, which means their storage capacity drops irreparably over time.”
In addition to being longer lasting, Berrada’s research suggests that the lifetime cost of lithium batteries may be twice that of mechanical alternatives. Gravity batteries may also reduce our reliance on the minerals and metals required to produce chemical batteries, alleviating the burden on the environment.
Some projects are already underway trialing gravity batteries. In the U.K., Gravitricity has been testing a prototype gravity battery in the port of Leith, Edinburgh. The company used a 15-meter-high steel tower to raise two 25-tonne weights on steel cables, using solar power. When the power is needed, the weights are lowered, allowing the motors to be used as generators to produce electricity. The firm’s senior test and simulation engineer, Jill Macpherson, said that the test was a success, stating “The demonstrator was rated at 250kW – enough to sustain about 750 homes, albeit for a very short time. But it confirmed that we can deliver full power in less than a second, which is valuable to operators that need to balance the grid second by second. It can also deliver large amounts more slowly, so it’s very flexible”.
However, despite recent developments in the sector, companies face a myriad of challenges in the expansion of this technology to be used on a larger scale. Several companies have made bold claims about the potential of their gravity battery operations, with Gravtricity stating it can power around 63,000 homes through an hour of operation of its 20 MW facility, and GravitySoilBatteries believing it can provide up to 30,000 kWh of storage at a system efficiency of 85 percent. Yet these advances have yet to be seen and may be just a pipedream.
As engineers and scientists continue to think outside the box to find the next big green energy solution, more ideas like gravity batteries are being explored. While not every idea may pan out, this is likely to be the way that we will find the new best renewable energy or battery storage option. For now, gravity batteries are in their nascent stage, and only time will tell whether the startups developing the technology will succeed in the scaling of operations.
By Felicity Bradstock for Oilprice.com
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We don't know what the round-trip efficiency is or what the losses are in the system to heat.
Plus, the kinetic energy used to bring the weight to speed has to be recaptured with a regenerative braking system. Additionally, for these systems to be useful, they have to be tall.
So we now know that is a dead end. They are also very risky and volatile sources as the russian war has elucidated clearly.
As far as grid scale storage is concerned, lithium or sodium batteries don't seem to scale due to supply issues.
Pumped hydro storage works reliably well and has been used for well over a century to store vast amounts of power, even allowing seasonal shift.
The roundtrip efficiency is around 70%.
Unfortunately they require specific geology. A lower and upper dam or lakes, an adequate water supply, and all that somewhat near where the power is produced or needed.
Energy Vault is another outfit that is pretty far along with commercial availability of their gravity "battery" though.
They claim that it is completely scalable, have a roundtrip efficiency of over 80% and expect to have the first grid connected project online by the end of Q2/23 at prices competitive to lithium ion batteries.