Skyscrapers could be turned into massive ‘gravity batteries,’ study suggests

Scientists have developed a new energy storage concept that could turn skyscrapers into giant batteries, an advance that may lead to improved power quality in urban settings.

In the new study published last month in the journal Energy, scientists propose a novel gravity-based concept that uses lifts and the vertical height of tall buildings to store energy.

The idea, called Lift Energy Storage Technology (Lest), stores energy by lifting wet sand containers or other high-density materials, which are transported remotely in and out of a lift with autonomous trailer devices.

“Lest links two storage sites, one located on the bottom of a tall building (lower storage site) and the other at the top of the same building,” scientists explained.

Energy is then stored as potential energy by elevating storage containers with an existing lift in the building from the lower site to the top.

In the concept, robots load heavy ballasts into lifts, or elevators, in the building when demand for power is low and store them at the top site.

“The loading and unloading of the containers into the lift is performed by an autonomous trailer that retrieves the containers from the storage site (lower or upper), enters the lift, moves up or down, leaves the lift and deposits the container in the other storage site,” researchers explained.

Then as energy usage peaks, these weights would be added back to the elevators and lowered back down, generating more energy.

Since lifts are already installed in such tall buildings, there would be no need for additional investment or space occupancy, said the researchers from the International Institute for Applied Systems Analysis (IIASA).

They estimated that there are at least 18 million lifts in operation globally, adding that many of these spend a significant amount of time sitting still.

Instead, they say the Lest technology would use what is already there in a different way to create additional value for the power grid and the building owner.

While there are many challenges in making a gravity energy storage solution viable, mainly the power capacity cost, researchers say the most important benefit of Lest is that the power capacity is already installed in lifts with regenerative braking systems.

However, they said the technology idea needed to be further refined before the system can be deployed.

Scientists said this includes finding room to store the weights the system needs at the top of the building when the system is fully charged, and at the bottom of the building when the system is discharged.

Empty apartments or corridors could be viable options.

Since the energy storage potential is proportional to the building height, researchers estimate that a skyscraper like Burj Khalifa could potentially store up to 9MWh to 90MWh. They estimated that the combined Lest storage potential of all tall buildings in the US could be up to 6.5GWh to 65GWh, and around 7.3GWh to 73GWh in China.

In comparison, a battery pack used in the Tesla electric vehicle stores about 0.1MWh at a time.

Citing some limitations of the study, scientists said the ceiling bearing capacity of existing buildings could be a concern, adding that buildings and their floors need to be designed to serve specific purposes.

However, researchers believe the ability of this system to store energy where electricity is mostly consumed, such as in cities, would greatly benefit the energy grid.

They said Lest can provide affordable and decentralised supporting energy storage services that could improve the power quality in an urban setting.

“Environmentally friendly and flexible storage technologies like Lest are set to become more and more valuable to society in a future where a large share of its electricity comes from renewables,” study co-author Behnam Zakeri said.

“Therefore, policymakers and power system regulators need to adopt strategies to incentivize end users, in this case, high-rise buildings, to share their distributed storage resources, such as Lest, with the central grid. The coordinated utilisation of such distributed resources alleviates the need for investment in large-scale central storage systems,” he added.