It’s too bad South Dakota doesn’t have more skyscrapers. If we did, we could support renewable energy and energy independence by installing gravity batteries in high-rise buildings. Researchers from Austria, Germany, Poland, and Brazil have just published a paper contending that using the lifts (that’s elevators for us Yanks) to carry containers of wet sand or other dense materials up to store energy and down to release energy.
When elevators go up, the energy they use translates into potential energy in the people and objects they lift. We give up that energy when gravity brings us back down; regenerative brakes in elevators can capture that energy on the way down and turn it into electricity. The researchers propose Lift Energy Storage Technology (LEST), a system of robots wheeling heavy containers in and out of elevators and empty spaces at the tops and bottoms of skyscrapers:
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 (upper storage site). Energy is stored as potential energy by elevating storage containers with an existing lift in the building from the lower storage site to the upper storage site. Electricity is then generated by lowering the storage containers from the upper to the lower storage 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 (upper or lower, respectively)…. The autonomous trailer has visual sensors to avoid hitting people when entering or leaving the lift and carrying the containers around the building…. As the energy requirements to move the containers horizontally with the autonomous trailer are small, they were not included in this estimate. The horizontal energy consumption will depend on the trailer, the wheels, and the flooring. Carpet flooring will significantly increase horizontal energy consumption. The storage system will record the position of the containers and run software to optimize the available storage capacity in the upper and lower storage sites. The building administration can choose to have the system operate only during periods of low lift demand to minimize the impact of the LEST system’s operation on the building occupants. The lift system can vary the speed of the lift depending on the energy storage power requirements. If the power requirements are high, the lift can increase its speed; however, this will reduce the system’s overall efficiency. …[W]hen the lifts are not being used, such as during the night, the autonomous trailers can fill the lift with containers, and the lift can be used to provide ancillary services to the power grid by lifting and descending the mass continuously on grid requirements [Julian David Hunt, Andreas Nascimento, Behnam Zakeri, et al., “Lift Energy Storage Technology: A Solution for Decentralized Urban Energy Storage,” Energy, vol. 254, part A, final version posted online 2022.05.25].
The authors estimate that the 22,600 skyscrapers worldwide, buildings ranging from the 53.25-meter Wills Eye Hospital Walnut Towers in Philadelphia to the 828-meter Burj Khalifa in Dubai, could support conservative LEST systems with 5,000 sand containers and ten robot haulers and provide 30 gigawatthours of energy storage. The 6,000-plus skyscrapers in the U.S. could provide 8.6 GWh of storage. According to the U.S. Energy Information Administration, large-scale battery storage in the U.S. in 2019 was 1.7 GWh.
The average capital cost of existing battery storage in the U.S. in 2019 was $589 per kilowatthour. LEST would cost between $21 and $128 per kilowatthour, depending on the height of the building (the taller the building, the cheaper the storage).
Of course, if Lift Energy Storage Technology uses elevators, why not install LEST on South Dakota’s great skyscrapers, our grain elevators? Instead of robots in residential and commercial buildings carrying big buckets of wet sand sharing the people movers and then rolling around looking for empty apartments, offices, and corridors to store their loads, South Dakota could add lifts dedicated to energy storage containers on the outside of grain elevators with railed racks for those containers ringing the grain storage bins on the ground and at the top. Plug the grain elevators into the nearest wind turbines or solar farm, and presto! South Dakota stores grain and green energy in the same place.
Dang, if only they hadn’t taken down the Zip Feed Tower.
Help me out here, at first blush wouldn’t the net energy gain be zero or less? Energy to lift minus energy generated by lowering? Or does this system rely on lifting with low spot price grid power and generating power when grid spot prices are high?
Nick, we always lose some energy. But I think the idea is that when the wind and solar farms are generating more energy than the grid needs, we store that energy in gravity batteries. We naturally lose some energy running the elevators and the robots, but it’s not the total loss that happens without any storage option.
Thinking like this: shouldn’t it be called TRUE conservatism instead of liberal leftist green which it will be called of course. Using ALL the potential of something existing instead of building more and more to have more and more makes sense. Especially when it benefits the rest of society. in efficiency and less resources used. Conservatism as it exists today is too given over to making riches off others needs. Thanks Cory, I had no idea such a method of energy production was available, but it surely makes sense.
Correct, Cory vis a vis Nick’s question. It’s not so much a matter of a zero sum game but of energy storage at times when demand is low, releasing it when needed at other times. Some very elaborate designs and variations have been proposed, and each has its own set of disadvantages.
https://www.wired.com/story/energy-vault-gravity-storage/
Just a follow-up to say that Nick is on the right track in both respects: (1) one never can harvest all the energy put into any system—some is always lost (known as entropy, or increasing disorder resulting in useless energy dissipation, be it heat or otherwise), (2) the concept is indeed to use unused energy excesses at low demand times to store energy for energy use later.
As a simple analogy to the elevator storage concept, consider: If one drops a ball from a given height, upon impact with the ground it will bounce up, but will not return to the same height from which it was dropped. The ball at a certain height had stored potential energy. Impact with the ground causes that energy to be released and the ball rebounds upward–but not to its original height. In other words, some of the stored potential energy is lost (we say the ball is ‘lossy’ for that reason). (How far upward the ball rebounds depends is quantifiable by the ‘coefficient of restitution’).
Thus, a partially deflated beach ball will not rebound very poorly: much of the stored energy will be irretrievably lost.
A superball, by contrast, will rebound remarkably well when dropped from a given height (has a much greater coefficient of restitution than a beach ball): more of the stored energy is retained and recovered. But why? Consider the energy cost to make inventor Norman Stingley’s original vulcanized polybutadiene rubber superball: it requires some 3,500 psi for manufacture to create such a dense material. This greater cost of energy input to create the ball results in more energy output—although one can’t break even. Note: I am norming to *dropping* the ball in each case from a given height, not to throwing it down with force, although even in this latter case one can’t get out the full amount of energy one puts in.
The entropy of a given system may be decreasing while the entropy of the system and its surroundings is always increasing, as expressed by the second law of thermodynamics.
So Nick is correct that (1) the stored energy one can get out of a system is always less than the energy stored (or we could have perpetual motion machines but entropy prevails), and his “or” caveat is also correct, (2) apportionment of energy to storage at times when energy is plentiful and in excess, using that energy at other times.
Batteries and capacitors are the among the better solutions we can currently have, and much work is needed to improve on them, an issue of on-going scientific concern.
You can read my paper on novel novel polycarbonate films we developed for wound-film capacitors. This work was funded by the US NAVY for capacitors for use on all-electric naval vessels including energy demands for all-electric weaponry: https://www.researchgate.net/publication/256701884_Electrical_properties_of_a_novel_fluorinated_polycarbonate also
https://www.researchgate.net/publication/258805803_Dielectric_Properties_of_Bisphenol_A_Polycarbonate_and_Its_Tethered_Nitrile_Analogue
How does the weight of water or sand falling spin a generator?
Edwin Arndt
How does a rope spin a pulley? How does a fan belt mediate the spin of an alternator?
Gentlemen. Mr. Ardnt and others are lawyer-type-fellows, but the answer lies #4Science.
They tell me, like our old friend of the blog Mr. Gibilisco would say, it is physics.
Laws, those linguistically articulatef constructs which attempt to map the territory of what is possible, therefore allowable, and what is not, ie., what is forbidden, whether it be in nature or in culture.
Conservatives appear to err on the side of what they wish to be immutable and absolute while progressives err on the side of thinking nothing is absolute and everything is subject to change. Both are correct at some level while at another level both are wrong.
The emergent dialect is a matter of emphasis more than a matter of any inherent truth which might pertain to either side.