Energy Vault—Storing Energy by Stacking Concrete Blocks

Pumped storage hydroelectric power is a mature technology for storing excess electrical power from generating plants at times of low demand and then releasing it back to the grid when demand is high, allowing base load generation to run at maximum efficiency and avoiding the need to start expensive intermittent “peaking” plants at times of high load. The first such facility was built in Switzerland in 1907, and a total of more than 100 gigawatts of capacity is installed worldwide today. Pumped storage provides a means of banking energy from intermittent sources of power such as wind and solar energy and using it as more of a base load source than otherwise would be possible.

A pumped storage plant usually requires two things: a mountain and abundant water, and so it’s not surprising that Switzerland leads the world in deploying the technology, with 32.6% of total generating capacity coming from pumped storage (neighbouring Austria is second, at 18.7%). In the U.S., the number is just 2.1%. But what if you don’t have mountains, or water?

A Swiss company, Energy Vault, is developing a system to store and release energy by stacking and unstacking concrete blocks massing around 35 tonnes each. The demonstration unit in Arbedo-Castione, Switzerland has a capacity of 18 megawatt hours and output power of 5 megawatts. Commercial units under design scale to 500 megawatt hours.

As crazy as this sounds, the company claims it is 85% efficient (energy out compared to energy in), while typical pumped storage hydro plants are around 75% efficient.

Of course, they are going public in the U.S. via a SPAC.




Hmmm! When is stored energy an explosive? For example, nuclear aficionados love to point out that many more human beings have died due to the accidental release of the stored energy in hydro-power plants than in accidents at nuclear power plants.

More seriously – system boundaries! Aficionados of “renewable power” tend to ignore what it takes to build whatever system they are proposing. Making a vast number of 35 ton concrete blocks is going to release a massive amount of CO2, as is manufacturing the steel for the structure and the wire cables (which will need to be replaced regularly). That needs a lot of fossil fuels.

That said, the Edinburgh project involving a massive weight installed in an abandoned vertical mine shaft sounds like a really neat idea. Like it!

Another issue that often eludes the enthusiasts is that economic large-scale power storage offers a major potential to improve the efficiency of regular nuclear, gas, coal power stations. If those stations can be run at constant output instead of having to continuously vary power production with power demand (with the energy storage system handling the diurnal swings), the cost of power from regular sources will go down – leaving the “renewables” further behind in the race for economic competitiveness.


This has been almost the entire rationale for pumped storage over its history. Switzerland had very little intermittent energy sources over the period its infrastructure was being built, and pumped storage was a way to optimise use of base load generation and avoid expensive peaking sources.


That was a particularly ingenious solution for that epoch - i.e. in an increasingly-industrializing society and before the era of worship of the ‘environment’. Just ingenious, sensible and economically prudent.