Gravity takes centre stage: Storing renewable energy with height

A new race is on.

Skidmore, Owings & Merrill LLP (SOM), the architecture design house behind the world's tallest tower, Burj Khalifa, is reportedly developing ways to turn buildings into batteries.

They’re currently exploring ways to lift massive blocks with motors, storing energy that converts to electricity when lowered. 

So, could some of the world's most iconic skyscrapers produce their own power by harnessing gravity?

Not a new idea

That’s the whole idea. And it’s not new. The concept of harnessing gravity for energy storage started more than a century ago.

Pumped-storage hydroelectric (PSH) plants actually utilise this principle. It's a type of water storage system that acts like a giant battery. Water is pumped uphill during low-demand periods,

When electricity is needed, the water flows back down, generating power through turbines. It's already widely used (97 per cent of energy storage) and is a clean, renewable source as the water gets reused.

This technique started in the 1890s. Today, they produce about 180 GW of power generating capacity (out of the 8.9-terawatt global energy generating capacity).

Now, imagine replacing water as potential energy, with something solid.

Massive solid blocks (like concrete or heavy iron pistons) are pumped up using excess solar or wind power. When extra energy is needed, the blocks are released in software-controlled sequence from the upper level into the lower level, generating energy along the way.

This means gravity power can be generated almost instantly and at any time.

Gravity batteries: A modern twist

So it seems, the future of energy storage is pumped-up… with weights (instead of water). Last month (May 2024), a company known as Energy Vault debuted its “gravity battery” behemoth near Shanghai.

The colossus can hoist and hold enough power to keep the lights on for hours. But they're not the only game in town. Innovative companies are exploring gravity's potential in abandoned oil wells and mines, proving that going green can mean going down – or up.

Modern gravity batteries come with greater flexibility. This form of energy, and its ability for long-duration storage, is critical because it means having a reliable energy supply even during times when the wind doesn't blow or the sun doesn't shine.

And instead of relying on specific geographical features like mountains and water, gravity batteries can utilise existing infrastructure – including high-rises – or even repurpose abandoned mines.

How gravity batteries work

The core principle is to convert excess electricity into potential energy by lifting a mass – and then converting it back to electricity when needed by lowering the mass.

This mass can be:

Concrete blocks: Raised and lowered by cranes within a tower (e.g., Energy Vault)

Water tanks: Filled at high points in buildings using surplus energy, then released through turbines (high-rise water storage)

Heavy weights: Lifted within abandoned mineshafts using winches (e.g., Gravitricity)

Benefits of gravity batteries

High efficiency: Reaching up to 90 per cent efficiency, compared to solar power's 25 per cent.

Clean and sustainable: Minimal environmental impact.

Long-lasting storage: Can store large amounts of energy for extended periods.

Faster response: Can provide power during peak consumption periods in less than a second.

Scalability: Capacity can be adjusted to specific needs.

Cost-effective: Lower deployment and operating costs compared to lithium-ion batteries.

Location-agnostic: Can be deployed almost anywhere, unlike PSH plants with strict geographical requirements.

High-rise buildings as batteries?

This innovative concept utilises the height of buildings for energy storage. One idea is for elevators to be retrofitted to lift heavy weights or water tanks during off-peak hours.

These weights are then lowered during peak hours, converting potential energy back into electricity through a system of pulleys and actuators to harness gravity and drive turbines, using regenerative braking systems.

From prototypes to reality

The first commercially operational gravity battery system, built by Energy Vault, recently joined the Chinese power grid. Other companies like Gravitricity of the UK are testing prototypes in disused mines.

Following are some of the challenges and considerations:

Retrofit costs: Upgrading existing buildings can be expensive.

Maintenance: Ensuring the efficiency and safety of mechanical systems requires regular maintenance.

Energy loss: Some energy is inevitably lost during conversion processes.

Structural integrity: High-rise buildings need to be assessed for handling the additional weight and strain.

Game-changer?

The century-old concept has already proven its worth with the pumped-storage hydroelectric. It's now being reimagined, or repurposed.

Gravity batteries are defying expectations: They leverage existing infrastructure, promote sustainability, and provide efficient energy storage, making them a significant player in the future of clean energy.

They offer a potential game-changer in the fight for clean energy. While the technology is still young, its potential for cost-effectiveness and flexibility could see it become a major player in the global energy mix.

So, will our future batteries be reaching for the sky or burrowing underground? Only time will tell, but one thing's for sure: the future of energy storage is looking anything but down-to-earth.