The ever-ascending heights of its high-rise building stock potentially positions Toronto to produce and store gravitational energy. The concept is still theoretical, but researchers with the International Institute for Applied Systems Analysis (IIASA) suggest elevators could present an option for generating a small but steady supply of sustainable power to augment battery storage and intermittent renewable sources.
In a recently published paper in the academic journal, Energy, they sketch out the broad elements of what they’ve dubbed lift energy storage technology (LEST). Gravitational energy is most commonly a source for centralized hydroelectric generation, where above-dam reservoirs are the storage receptacle. LEST is decentralized and on a much smaller scale, but embodies the same basic principle in which energy is stored within a mass as it is lifted upward and then released from the mass as it falls downward.
As envisioned, it would rely on: a regenerative braking system in elevators; up and down transport of containers holding a dense storage material such as sand or stone; storage areas at the top and bottom of the building; robots to transport the storage containers; and a software-based operating system. The greater the distance between the top and bottom storage areas, the greater and more cost-effective the system capacity.
IIASA researchers project the global storage potential at 30 to 300 gigawatt-hours and tap Toronto as one of a handful of North American cities, along with New York, Chicago, Los Angeles, Philadelphia and Seattle, where it would be most feasible. They estimate the cost of installed capacity energy storage at USD $128 per kilowatt-hour (kWh) where the distance between the top and bottom storage areas is 50 metres. That drops to USD $62/kWh if the distance stretches to 100 metres and USD $21/kWh at 300 metres.
Among qualifications, the upper area would have to bear the load of the weighty storage containers. “It is rather unlikely that buildings in the past have been designed with the idea that they might serve as energy storage facilities in the future,” the paper acknowledges.
However, the researchers suggest that robots would have the capability to manoeuvre the containers to counterbalance swaying in high winds or earthquakes. As for the potential disruption of robots moving the containers in and out of elevators, IIASA researchers frame it as an opportunity for building owners to derive value from an existing structural component that frequently isn’t in use.
“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,” urges Behnam Zakeri, a coauthor of the study and a researcher with the IIASA’s Integrated Assessment and Climate Change Research Group. “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.”
