Researchers at the University of Waterloo in Canada have designed a solid gravity energy storage system that could be used to store renewable energy in high-rise urban buildings.
The rope-hoist-based system is designed to operate in combination with photovoltaic facades installed on the south, east, and west walls, as well as small rooftop wind turbines and lithium-ion (Li-ion) batteries.
In the proposed configuration, the gravity-based system serves as the primary energy storage unit, while the batteries are used only for fast-response storage during hours of significant production surplus or shortage. The system harnesses the energy generated by the PV facades and wind turbines to lift a heavy mass within a shaft during the charging phase. This stored potential energy is then released to rotate an electric generator during discharge.
The system comprises a motor-generator unit, hoisting ropes, transmission gears, and steel or concrete blocks. It functions similarly to conventional elevators in city buildings, operating at nearly the same speed.
“This design is technically viable and has also been proven commercially recently,” the research's lead author, Muhammed A. Hassan, told pv magazine. “Specifically, Gravitricity has demonstrated a 15-m high, 250-kW prototype system at Leith Harbor in Edinburgh, with two 25-ton suspended weights and two generators connected to the grid. The same company also started two full-scale commercial projects with capacities of 4 MW and 8 MW since 2021.”
The researchers modeled the system across 625 generic building designs, considering factors such as the façade area-to-volume ratio, length-to-width ratio, and height-to-footprint area ratio. They also employed a multi-objective genetic algorithm (MOGA) to assess both the levelized cost of electricity (LCOE) and each building’s dependency on grid electricity.
The analysis indicated that this hybrid system could achieve LCOE values ranging from $0.051/kWh to $0.111/kWh, and grid electricity costs between $0.195/kWh and $0.888/kWh. These results are reported to be consistent with those of similar building-integrated renewable energy systems located in Canada and other regions with limited renewable energy resources.
“Higher buildings with large floor areas tend to achieve lower LCOE but higher grid electricity costs,” the researchers explained, noting that the capacity of the gravity storage system must increase as a building’s energy-use intensity rises.
Modeling results also showed that the gravity storage system could achieve payback periods of 9 to 17 years, and discounted payback periods below 25 years in most cases.
“This confirms its long-term financial viability,” said Hassan. However, he emphasized that industry consensus remains crucial on several fronts, including operational complexity, upfront costs, and the need to demonstrate 24/7 reliability through years of real-world operation.
“While the mechanical principles are proven, the challenge will be scaling engineering, securing competitive capital costs, and integrating within grid or industrial environments. Therefore, market adoption still depends on proving that these systems can outperform battery, chemical, and other gravity alternatives over their expected operational life, especially for applications needing multi-hour to day-long energy delivery without capacity fade,” he added.
“Independent analyses suggest that commercial maturity in terms of bankable, mainstream deployment in developed markets outside China is likely around the late 2020s, pending a few years of operational data from current flagships,” he went on to say. “At present, above-ground gravity storage is commercially proven at initial scale, but not yet at volume-discounted mass adoption. Sustained contracts and reliability performance over the next three years should move the status to full commercial maturity.”
The system was introduced in “Building geometry-aware lifecycle optimization of hybrid renewable energy systems with solid gravity storage,” published in Applied Science.
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Hmmm. I did the math, and it appears that the immense weight (25 metric tonnes) and approximately 49 feet of elevation drop will produce 250 KW for 2.38 minutes. This total energy is about 10 KWH.
The four LFP batteries in my garage store that much and occupy a small wire rack. And weigh less than 200 lbs. What’s wrong with this picture?
Buildings are not designed to carry these weights. Is there analysis showing that they could?
How about putting heavy slabs on carts and pulling them ski slopes, using skids in winter and wheels when enough snowpack is not there. Generate power by releasing them back down the slope.
Or hang heavy weights off cliffs that are not popular with climbers.