Research on gravity energy storage has mostly focused on its use in restoring abandoned mines and quarries, but is there any possibility that this cutting-edge technology can be used to transform high-rise buildings into storage systems?
Gravity energy storage is similar to pumped-storage hydroelectricity. Pump-storage hydropower works by adjusting the water level. In a scenario with surplus electricity production, the electric water pump will be driven to transport water to a reservoir at a higher elevation. When the demand for electricity increases, the reservoir will discharge water, allowing it to flow back to the initial location as water flows from high to low elevations. The resultant water potential can then prompt turbines along the channel to regenerate electricity. The only difference between pumped hydropower storage and gravity energy storage is that the former considers water the source of electricity generation, while the latter relies on other objects.
The International Institute for Applied Systems Analysis (IIASA) holds that as electricity generation and energy storage can be achieved through elevation difference, elevators in buildings can be utilized using the same principle, leading to the development of lift energy storage technology (LEST). After all, compared to trouble with gravity battery construction in mines, quarries and other places, using the existing equipment is possibly more cost effective and convenient.
（Source：IIASA）
As the IIASA team proposes, remote control of a LEST system can be achieved by using autonomous trailers that can tow weights into and out of an elevator. First, the weights are moved from the bottom to the top of the building through elevators. When there is excess renewable energy, the weights are sent back to the bottom, whereby the energy can be transferred back to power grids.
To avoid overload, the team suggests that a program be developed to detect the presence of overload in elevators or determine the most appropriate times for energy storage. A study revealed that when being fully loaded and descending in optimal conditions, a permanent-magnet synchronous gear-motor smart elevator can work impressively at a nearly 92% efficiency.
The IIASA believes that the greatest strength of LEST is its ability to take full advantage of the existing facilities, which helps save a large amount of storage costs. However, a LEST system will not work as fast as its counterparts based on large-battery energy storage. Instead, it is more suitable for long-term energy storage that can be useful during a prolonged power outage or the change of seasons.
The cost of lift energy storage depends on the building height, which is around $21–128/kWh. The price gap is wide, but the LEST system is much cheaper than any battery energy storage systems. According to a study compiled by the National Renewable Energy Laboratory in 2020, the cost of 4-hour battery energy storage systems averaged $345/kWh. Even under the most positive assumptions, such cost would not be lower than $100/kWh in the post-2040 period.
Despite being considerably cost-effective, LEST is faced with multiple challenges, including questions concerning load at the upper end, modification cost and places for weight storage, all of which must be solved as per the building and site in question.
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