How Hundreds of 24-Ton Bricks Could Solve a Huge Renewable Energy Problem
Imagine a gigantic brick of highly compressed earth – as big as a van but, at 24 tonnes, about five times as heavy. An elevator powered by solar panels or wind turbines lifts him more than 300 feet up the side of a huge building, and a cart stows him inside. But it’s not the only one. An automated system lifts and stores hundreds of additional bricks, like giant Pez candies, as the sun shines and the wind blows.
Now imagine the building’s control system lowering those hundreds of bricks one by one, spinning electricity generators in the process. They decrease each evening when the demand for power reaches peaks, but the production of the solar panels fades.
In effect, the brick-filled building is a giant battery that stores energy by gravity instead of chemistry.
Gravity batteries are a potentially important solution to a critical problem in the green energy revolution: ensuring that electricity is available when we need it, not just during times when the sun and wind power it. .
And it’s not just an idea. With two sites under construction — one in Rudong, China, just north of Shanghai, and the other in Snyder, Texas, about 250 miles west of Dallas — startup Energy Vault will begin testing seriously the viability of gravity storage technology. An earlier pilot generated 5 megawatts of electricity, but these two facilities and expected successors will show whether gravity storage is economical and efficient enough to operate at scale.
Power when the sun goes down
You might think that putting solar panels on your roof will help fight climate change, but without some form of energy storage in your home or on the grid, you’ll probably rely on gas and oil-fired power stations. coal spewing carbon dioxide to run the lights in your house. , TV and dishwasher at sunset.
Energy Vault tested its technology on a smaller scale in Switzerland, where the 170-person company is headquartered. Its two EVx systems under construction are much larger. The Chinese system, built for waste management and recycling company China Tianying, is in a 400-foot-tall building and will have an energy storage capacity of 100 megawatt hours. That’s enough to power 3,400 homes for an entire day, and the system should be complete by June. The Texas system, in a 460-foot-tall (but narrower) building, will provide power company Enel with 36 MWh of capacity.
Solar panels and wind turbines now generate electricity at a lower cost than coal and natural gas plants, making them a clear choice in the drive to replace fossil fuels. Solar energy costs have fallen 83% from 2009 to 2023 and wind energy costs have fallen 63% over the same period, according to the investment advisory and management firm’s tracker. Lazard assets. But in many parts of the country, new solar panels often only provide a glut of electricity in the middle of the day without helping in the evening.
The mismatch between energy production and energy consumption is responsible for the infamous “duck curve”, a bird-shaped graph showing the growing disparity from year to year. This disparity makes it difficult for utilities to adapt to rapid changes in demand and means that fossil fuel-powered sources like natural gas “peaking plants” provide electricity in the evening.
“If we are ever going to wean ourselves more and more off fossil fuels and replace them with intermittent renewable generation, the only way to solve this problem is through storage,” said Robert Piconi, CEO of Energy Vault.
Energy Vault is not alone. Another startup, Gravitricity, has built a 250 kilowatt demonstration system and is planning a larger 4 MW to 8 MW system in an unused mine shaft.
The cost of energy storage is critical
Gravity storage is only one of the means of smoothing wind and solar surges. Big batteries like Tesla Megapacks — industrial-scale versions of the same batteries that power your phone or electric vehicle — are becoming more common on the power grid. “Pumped hydro,” an ancient form of gravity battery that pumps water to an upstream reservoir and then generates power when it comes back down, has been used for decades but is attracting new interest. Other methods include filling underground chambers with compressed air, storing hydrogen that will later power fuel cells, and developing different types of batteries, such as zinc batteries and flow batteries.
Cost will be a major factor in determining which storage technology prevails, including initial manufacturing and ongoing operations.
“Ultimately it will all come down to price,” said Selene Law, an energy analyst at consultancy Cleantech Group. And for gravity storage, questions about total cost persist, she said.
Indeed, a 2022 US Department of Energy study concluded that gravity energy storage is relatively expensive in small installations. Where it is most economical is in high capacity systems that generate electricity for relatively long periods of time – 10 hours or more.
Energy Vault did not disclose the cost of the two systems under construction, but agrees that the technology offers benefits for long-duration power needs.
Longevity is a cost factor over the lifetime of the plant. Batteries lose capacity with use, similar to how your phone won’t last as long after a few years of ownership, but gravity storage components like pulleys and generators can be saved.
“Key to our value proposition is zero storage media degradation,” said Marco Terruzzin, mechanical engineer and commercial product manager for Energy Vault. “We offer a warranty on the system for at least 35 years.”
Although Energy Vault has only taken its first steps in proving the value of the technology, two customers have concluded that it is worth paying today. And the 100 MWh system in China is only the first there, the company said. The country plans to finance an additional capacity of 4 GWh to 6 GWh later, an increase of 40 to 60 times the initial plant.
How Energy Vault’s EVx Works
Energy Vault’s Gravity EVx storage system is a giant rectangular building that operates largely automatically. Here’s how it works.
The bricks at the heart of the system each measure 3.5 by 2.7 by 1.3 meters (about 11 by 9 by 4 feet) and weigh 24 metric tons. They are made of 99% earth compressed with water and a mixture of polymers to stabilize it using a recipe from the Mexican building materials company Cemex. They are 2.4 times denser than water and much like concrete.
The bricks are stored side by side inside the building, like dominoes stuck together. Before they are raised or lowered, a trolley system lifts each brick and transports it to the elevator.
The bricks are housed on the upper eight levels of the building to store energy and descend to the corresponding lower eight levels to generate energy. Each brick, descending at 1.9 meters per second (6.23 feet), produces about one megawatt, Terruzzin said. That’s about enough to power 2,000 refrigerators.
Once each brick reaches the bottom, it is robotically transferred to the trolley system and moved to the center of the building.
The lengthening of the building, with longer carriage tracks, means more bricks can be stored for more hours of power generation. Making the building wider, with more elevators, means the system can generate a higher peak power rate.
When it comes to efficiency, Energy Vault guarantees that EVx systems will generate at least 80% of the energy needed to lift bricks and move them, including factors such as friction. This overall efficiency is comparable to that of pumped hydroelectricity.
Key to the Energy Vault business is the control system that decides when and where to position the bricks for optimal storage and even energy production.
“As we decelerate one down, the next one loads up and starts to accelerate,” Bill Gross, CEO of Idealabs and co-founder of Energy Vault, told the Techonomy Climate conference in March.
The maximum power will be 25 MW on the Chinese system and 18 MW on the Texas system.
Overcoming Gravity Storage Challenges
Energy Vault decided on its current design after evaluating several other options – gravel in carts, water in tanks, concrete blocks suspended from cranes.
The EVx is designed to overcome the problems associated with these designs. It is weatherproof, which means that the bricks do not get wet or blown away, for example.
Energy Vault does not put all of its Energy Storage Eggs into the Gravity Basket. A contract with Pacific Gas and Electric of California could result in a system to power the city of Calistoga for up to 48 hours with a combination of hydrogen fuel cells and batteries. Hybrid systems with gravity and battery storage also make sense because batteries can react very quickly to scale up or down, Terruzzin said.
As the Energy Vault factories come into production, we should start to get a better idea this year of how gravity storage actually works. “This will be a pivotal year for Energy Vault,” said Cleantech Group’s Law. “The proof will be in the pudding.”
The company is unprofitable, posting a net loss of $78 million for 2022 on revenue of $146 million. And its stock has fallen 89% in the past year, a fate many startups have suffered with economic hardship and skeptical investors.
Energy Vault’s Piconi is confident, however, that the company is on the right track to making energy storage more economical.
“Wind and solar are so much cheaper than fossil fuels now… The problem is that storage is typically 10 to 15 times higher,” Piconi said. “We have to get there.”
Fix, 9:26 a.m. PT: An earlier version of this story misrepresented Energy Vault’s 2022 financial results. It reported a net loss of $78 million on revenue of $146 million.
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