By | April 24, 2023
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The Energy Vault start-up, based in Switzerland, develops electrical energy storage solutions, including a patented gravity storage solution based on composite blocks. To assess the effectiveness of this large-scale approach, it began construction of two storage sites in Texas and China. This technology aims to strengthen the reliability of the electricity network and allow the integration of renewable energies, all at a reduced cost.

Electricity storage is mainly carried out using three techniques: electrochemically via batteries, and mechanically via pumped transfer stations (STEPs) and compressed air storage. WWTPs are gravity storage solutions: they consist of two water reservoirs, located at different heights, connected by pipes; when the demand for electricity is lower, a pumping system transfers water from the lower basin to the upper basin. When demand is greater, the facility operates as a hydroelectric power station.

The solution proposed by Energy Vault is inspired by the principle of STEPs. No need for water here: the system works by lifting/lowering blocks weighing several tons. The system hoists these blocks to the top of a huge structure to accumulate electricity (in the form of gravitational potential energy), then “drops” the blocks to supply electricity (the blocks driving cables connected to an alternator ). A pilot installation, on a reduced scale, is already operational not far from the company’s headquarters in Switzerland. Energy Vault now wants to prove that its concept works on a larger scale.


A storage capacity of 100 megawatt hours

To reduce the dependence of utilities on fossil fuels (natural gas, coal, oil) and encourage the adoption of renewable energies, it is essential to develop efficient storage solutions, said Robert Piconi, CEO of Energy Vault, at CNET. Indeed, the availability of renewable energies is not continuous, and yields necessarily fluctuate according to the vagaries of the weather. This is the reason for the long-term storage solution offered by Energy Vault.

As with WWTPs, the principle is to accumulate electricity produced by renewable energy sources during periods of excess production – a system powered by solar panels or wind turbines then lifts hundreds of 24-ton blocks – then release the energy — by releasing blocks — when demand is high and production is low.

The blocks are stored inside a huge rectangular building; each measures 3.5 x 2.7 x 1.3 meters and weighs 24 tons. They consist of 99% compressed earth, mixed with water and polymers to stabilize it, and are ultimately almost as dense as concrete. A system of rails transports them to and from an elevator: each block descends at a speed of about 2 m/s, producing about one megawatt, according to Marco Terruzzin, mechanical engineer and director of commercial products for Energy Vault.

A system of trolleys on rails transports the 24-tonne blocks to an elevator that hoists them hundreds of meters high. © EnergyVault

The pilot system, installed in Arbedo-Castione has been operational since 2020; connected to the Swiss electricity grid, it can generate a power of five megawatts. Sites under construction in Snyder, Texas, and north of Shanghai, will test whether the technology is economical and efficient enough to operate at scale. The Texas site, 140 meters high, is designed to supply a neighboring electricity company with a capacity of 36 megawatt hours.

Chinese installation is even more imposing: about 120 meters high and wider than Snyder’s, it will offer a storage capacity of 100 megawatt hours. According to CNET, that’s the amount of electricity needed to power 3,400 homes for an entire day. It will be used to supply a waste management and recycling company, China Tianying Group. Construction is expected to be completed by June.

A profitable and sustainable solution, at competitive costs

This storage solution “offers revolutionary storage capacity ranging from 2 to 18 hours, with competitive costs and an efficiency of more than 80% over the entire lifetime”, specifies the company on its site ; the overall efficiency announced is comparable to that of pumped hydroelectricity (STEP). To increase the storage capacities, it is enough to design even longer buildings, with more elevators, allowing to accumulate even more blocks.

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Energy Vault’s technology has several advantages. For starters, the company emphasizes that it uses local materials to build the blocks and relies on industry-standard components, sourced from predictable regional supply chains. In addition, its approach eliminates the risk of fire due to thermal runaway associated with chemical technologies — allowing reliable operation in hot or humid environments.

Finally, one of its major advantages is its lifespan: while the batteries lose their capacity as they are used, the Energy Vault system is guaranteed for at least 35 years. ” Key to our value proposition is zero storage media degradation “, said Marco Terruzzin.

If the concept proves successful in practice, it could therefore enhance the resilience and sustainability of the power grid while reducing the cost of energy storage. The latter will be a major factor in choosing the preferred technology. Energy Vault, however, did not disclose the cost of the two systems under construction.

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