? Skyscraper elevators to store and exploit “gravitational” energy: soon a reality
In demand for energy transition to free itself from fossil fuels, the world is turning, among other things, to renewable energies. This global conversion trend has led to a rapid reduction in the cost of producing green energy. To be able to meet current demands and anticipate future ones, there is a growing need for storage technologies today. The International Institute for Applied Systems Analysis (IIASA) in Vienna proposes a sci-fi movie solution, where skyscraper elevators would power and operate “gravitational batteries”. Although they are far from being able to satisfy energy consumption in real time, these new batteries would constitute a non-negligible support in cities,
For most of us, renewable energy is considered a healthy and easily accessible resource. Over the past decade, the world's capacity to produce green energy has grown steadily, and it is expected to increase another 60% by 2026. Total production is then expected to be equivalent to that of fossil power plants and nuclear combined. According to estimates by the International Energy Agency, renewable energy will account for almost 95% of the increase in global energy capacity, more than half of which will come from solar energy.
In addition to the still largely untapped solar and wind energy potential, other interesting renewable resources exist, such as tidal energy (energy from ocean waves and currents), geothermal energy, etc.
In a new study published in the journal Science Direct , researchers propose to exploit potential energy (vulgarized "gravitational") in order to convert it into electrical energy. This is an innovative storage solution already offered in the past, which could in particular come from elevators in large buildings.
The exploitation of the potential energy accumulated by altitude change is already used in hydroelectricity for example, storage by pumping as well as in float systems. The new concept proposed by the researchers however, dubbed Lift Energy Storage Technology (LEST), accumulates energy by lifting containers of wet sand (or other high-density material) outside and inside lifts with autonomous trailers.
" The concept of LEST came to me after spending a lot of time going up and down an elevator since I recently moved into an apartment on the 14th floor ," says Julian Hunt, lead author of the study and researcher in IIASA's Sustainable Service Systems Research Group.
A system with many advantages
The main advantage of the LEST storage system is that the elevators are already pre-available and do not require specific investments in space. The “power available” is also already established in elevators with regenerative braking systems (recovery of kinetic energy). In addition, nearly 18 million elevators are in service worldwide, and some of them remain idle for a long time. Those that don't carry anyone could then be used to store electricity.
The (heavy) loads would be moved to the top of a building to 'load' a skyscraper, then released using existing regenerative braking systems in recent elevators to recover the energy. :copyright: IIASA
According to the Austrian researchers, smart elevators with synchronous gear motors and permanent magnets are 92% efficient when fully loaded and set to descend at an optimal level of energy-producing speed. If more energy is needed, it would suffice to configure the elevators so as to begin their descent more quickly. The whole system could be even more efficient with cableless magnetic lift systems.
Moreover, this new “gravitational battery” system would also be advantageous in terms of costs. The LEST system energy storage price is estimated to be between $21 and $128 per kilowatt hour, depending on the height of the building. By comparison, battery systems from the National Renewable Energy Laboratory cost around $345 per kilowatt-hour in 2020.
The IIASA researchers also estimate that the tallest buildings could produce and store between 30 and 300 gigawatt hours, which is more than enough to power all of New York for about a month.
Challenges to overcome
But this new system has to overcome a few challenges before it can be applied. In particular, it does not yet have the capacity to meet the current peaks in demand for electrical energy.
However, an energy storage in the middle of the city will still be able to support the main electricity network, by filling the gaps or by intervening in the event of breakdowns. " Coordinated use of these distributed resources mitigates the need to invest in large-scale central storage systems ," says Behnam Zakeri, study co-author and researcher with the Integrated Assessment Research Group. and climate change from IIASA.
It is also still necessary to establish and identify the space required for the storage of storage loads, at the top of the buildings when the system is fully charged and at the bottom when it is unloaded. The maximum weight that the ceilings of the building can support must also be considered.
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