Storing energy in blocks: How gravity may solve green power’s problem

Mimicking the broad attributes of pumped hydroelectric plants, which use moving water to store and discharge power, Energy Vault’s proprietary ‘EVx’ platform utilises gravity and a mechanical elevator system to stack 25-tonne blocks made of a composite material at the top of a towering structure.

When the electricity demand is low, the elevator uses surplus electricity from the grid or electricity generated by renewable plants, to raise these blocks and line them up at the top of the structure. When electricity demand picks up, the blocks are then lowered one by one, releasing kinetic energy that is used to rotate a motor and generate electricity, which can then be pumped back to the grid.

While it does have similarities to a high school science project, this type of energy storage could be an innovative solution for countries, including India, that are transitioning to clean energy, as it can solve the biggest impediments to wider deployment of renewable generation — the ability for power companies to store energy for use by consumer when the sun is not shining or the wind is not blowing.

The NYSE-listed company, dual-headquartered in Westlake Village, California, and Lugano, Switzerland, is currently in the process of installing its EVx long-duration gravity-based energy storage solutions in China and the US. It is in talks with NTPC Ltd, India’s biggest generation utility, Mumbai-based Tata Power and green energy company ReNew Power for collaborations.

From a focus on long-term storage, the company has shifted sights on short-term storage too, alongside a focus on utilising eco-friendly materials with the ability to integrate waste materials for beneficial reuse, that could facilitate the shift to a circular economy while ensuring clean energy transition, Robert Piconi, Chairman, Co-Founder and CEO, Energy Vault told The Indian Express. Alongside its gravity-based systems, it is also offering battery storage for short-term storage use, and green hydrogen energy storage technologies in the longer term.

NTPC had signed an MoU last year for a long-term strategic partnership for the deployment of Energy Vault’s EVx energy storage technology and software solutions. Piconi said that Energy Vault’s mission “is to make sustainable, carbon free energy a reality”, and so an expansion into India, one of the largest global markets for energy, was inevitable. He also said that India’s push for deployment of largescale renewable power makes storage a prerequisite to support this expansion. The company is in the process of establishing a base in Bengaluru.

While attempts are being made to repurpose lithium-ion batteries to meet some of the need for storage, including Tesla’s famed Powerwall prototype, largescale deployment of these batteries for energy storage poses multiple problems. So entrepreneurs around the world have been looking for alternatives, which, apart from the innovation by Energy Vault, include ongoing work on reversible sulfur power-plants, projects involving water being pumped underground, and leveraging cryogenic technology – all with the objective of storing surplus renewable energy. But most of these are in the early prototype stage or still on the drawing boards.

Currently, about 96 per cent of the world’s energy storage comes from pumped hydro — a hydroelectric project where excess energy on the grid is used to pump water uphill to a high elevation reservoir and when there is energy demand, the water is released, driving a turbine as it flows into a reservoir below.

In India, grid managers are already grappling with the challenge of operationally sustaining a massive monthly addition of an average 1,000 megawatt – almost five times the amount of power a 250 MWe nuclear plant produces – from renewables to the electricity grid.

Policy makers are of the view that New Delhi needs to expeditiously work on developing viable energy storage options in a country that is the world’s third largest producer of renewable energy; nearly 40 per cent of installed electricity capacity comes from non-fossil fuel sources. This green push has resulted in a 24 per cent reduction in emission intensity of GDP between 2005 and 2016, but it has also thrown up challenges of a grid being increasingly powered by renewables.

There are two alternatives being considered by the government for now: hydrogen and hybrid generation models blended with off-stream pumped storage. In 2023, as the hidden challenges of the renewable energy transition are likely to manifest more concretely, the government is making a renewed push on both technologies.

In September, Union Power Minister R K Singh said the government will soon accept bids for the construction of a 100MW round-the-clock clean energy system, backed by storage. A policy for stepping up green hydrogen production and tapping into its potential as a fuel was cleared by the Cabinet last year. The Union Power Ministry had also wrapped up a survey of all pumped hydro sites, and hydro PSUs had been given a target of taking up pumped hydro schemes. The ministry had also written to the Union Coal Ministry to consider the option of opencast mines as potential sites for pumped hydro in the future.