More Ideas for Gravity Storage

If there is anything more basic than sunlight, it has to be gravity.  I mean, the sun itself is powered by gravity.  So yeah. 

These days there are quite a few ideas for storing power using gravity.

The basic idea is to use “excess” electricity, e.g., the sunlight at mid day, to move things uphill.  Then, when power is needed later, e.g., at night, the things are released to “fall” downhill, generating electricity.  Ideally, you can get almost all the input energy back out again. Thus, the energy is stored in the form of the potential energy of “up”.

This principle can be realized with water, with blocks, or, heck, with dirt.  One key technology is the duality of electric motors, which can reversed to generate electricity.  A simple example is an elevator that lifts its load, and then regenerates electricity from braking as it lowers the load.  Basically, the elevator is storing part of the energy used to lift, and releasing it on the return trip.

This spring researchers at the International Institute for Applied Systems Analysis outside of Vienna describe some new concepts for gravity storage based on regenerative braking [3].

One idea is to use the elevators in high rise buildings as an energy store [1].  So, during low use times the elevators can lift mass—say buckets of sand—to the roof.  Later on, the mass can be lowered down again, generating electricity from the braking system.

This idea has the advantage that it is a retrofit on existing infrastructure.  I’ll note that buckets of sand on the roof are certainly more fireproof than a lot of battery technology, so that’s another plus.  The economic feasibility depend a lots on the cost of alternative storage such as batteries.

Now, retrofitting a building to safely accommodate significant additional mass on the roof may or may not be cheap and easy.  There may also be issues with noise and vibration in residential buildings.  Running the elevators all night might not be popular if they disturb the tenants.

A second idea in this same vein is to use electric trucks to haul heavy loads—e.g., sand—up a mountain [2]. The energy is release by coasting down the road with regenerative brakes on.   

This also builds on existing infrastructure.  The economics depend on the coast of trucks, which is falling, so that is a good point. 

This will only work in the right geography, and the perfect spot would be somewhere with a usable road already built, but not inhabited (e.g., a disused section of a mine or quarry pit).  Building new roads in pristine terrain is neither cheap nor desirable.  In addition to aesthetic considerations (roads, dust, big piles of sand), there may be safety issues.  This would not be a great thing to do on a busy, multi-use road, or where there is a lot of local and pedestrian traffic.

Altogether, these concepts seem pretty marginal to me. They are on the edge of economic feasibility and have potential side effects. interesting, but not likely to be widely deployed.

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1. Julian David Hunt, Andreas Nascimento, Behnam Zakeri, Jakub Jurasz, Paweł B. Dąbek, Paulo Sergio Franco Barbosa, Roberto Brandão, Nivalde José de Castro, Walter Leal Filho, and Keywan Riahi, Lift Energy Storage Technology: A solution for decentralized urban energy storage. Energy, 254:124102, 2022/09/01/ 2022. https://www.sciencedirect.com/science/article/pii/S0360544222010052
2. Julian Hunt, Jakub Jurasz, Behnam Zakeri, Andreas Nascimento, Paweł Dąbek, Roberto Brandao, Nivalde Castro, Paulo Schneider, Walter Filho, and Keywan Riahi, Electric Truck Gravity Energy Storage, a solution for long-term energy storage. SSRN Electronic Journal, 1  04/06 2022. http://dx.doi.org/10.2139/ssrn.4076988
3. Prachi Patel, Skyscrapers—A Gravity Energy Storage Boon, in IEEE Spectrum – Energy, June 16, 2022. https://spectrum.ieee.org/gravity-energy-storage-elevators-skyscrapers