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Is Lifting and Lowering Tons of Bricks the Best Storage Solution for Wind and Solar Intermittency

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Lifting and lowering tons of bricks: the best storage solution for Wind and Solar intermittency?

February 16, 2022 by James Conca

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We-Can-Store-Our-Excess-Renewable-EnergyIt’s a high capacity storage system that’s simplicity itself. Use excess wind and solar to raise heavy weights. Keep them at a height for as long as you like. Lower them to generate electricity. James Conca looks at a system being developed by Energy Vault and already being demonstrated in the Swiss national grid. At scale, a single “vault” with 10,000 bricks will have an annual output of 27 GWh, sitting on only 14 acres of land. The bricks are made from locally sourced soil, sand or waste. No cement. And importantly, no lithium or cobalt! The big problem with chemical batteries is, though 90% efficient, the key elements are in short supply. As for efficiency, the simplicity of the round trip of creating gravitational potential energy before releasing it as electrical power is 80 to 85% efficient. The LCOE of $65/MWh will be half that of Li-ion’s $128/MWh. The proposed big targets for wind and solar, globally, need to be met with complimentary at-scale and cheap storage. Conca thinks this could be the answer.

The Energy Vault stores excess electrical energy by efficiently transforming it into gravitational potential energy using 35-ton bricks that can be raised and lowered at will, and that can sit still storing the energy for any amount of time, before transforming the energy back to electrical energy when needed.

It is not a battery that can degrade over time. It does not need water or rare elements like Li or Co. It does not depend on the weather and is not affected by extreme weather. It can withstand Cat 4 hurricane winds and magnitude 8 earthquakes (tested at the California Institute of Technology).


An Energy Vault Resiliency Center (EVRC) supporting a large Solar Array similar to ones in the Middle East / SOURCE: Energy Vault

It uses common materials like dirt to make the bricks, even solid waste, that can be obtained locally and does not use cement to bind them together. It does not use ten times the steel and concrete that renewables use relative to nuclear or gas. And it has one of, if not the, lowest carbon footprints of any energy generation or storage system.

U.S. needs 830GW of storage by 2030

And this technology comes just in time. According to the U.S. Department of Energy’s Energy Storage Grand Challenge Market Report 2020, the World Energy Council, the U.S. Energy Information Administration, Bloomberg NEF and Lazard, the projected grid-related storage deployments between now and 2030 needs to be about 830 GWh. The cumulative investment in this grid-related storage required over this time period is about $270 billion.

I know that game-changer is an overused term, but this technology really is a game-changer. With it, we can achieve a low-carbon future by mid-century. And we don’t need to waste lithium.

Simple gravity

The Energy Vault is based on the science that most of us learned in Middle School – potential energy versus kinetic energy. When you climb the ladder of a water slide in the summer, your muscles are transforming the chemical potential energy you stored from your food into gravitational potential energy. The amount of that potential energy depends on your weight and the height above the pool.

When you release that potential by sliding down to the pool, the big splash is an indication of the kinetic energy you just deposited in the water.

Already proven… by hydroelectric dams

Gravitational potential energy is how a hydroelectric dam generates electricity. The potential energy of the water sitting a hundred meters or so above the downstream level is released as kinetic energy when the water falls, which turns the turbines that turn the generators, producing electricity.

It is no wonder that pumped hydro storage constitutes over 95% of our present energy storage capacity in the world. Pumped hydro basically creates an artificial dam high up near some body of water. Excess renewable energy pumps water up into the reservoir behind the dam, which lets out water to turn hydroelectric turbines when needed. It’s pretty efficient but requires a lot of concrete and a lot of water. And the public usually votes them down.

…but lifting bricks is much easier

The Energy Vault refines this process even further and requires little concrete and no water. Using the same well-understood fundamentals of physics and mechanical engineering as pumped hydro, the Energy Vault replaces water with non-cement custom-made composite blocks through an innovative use of local, low-cost materials and sophisticated material science.


The interior of an EVRC, showing rows of individual hoists and bricks, each able to store and regenerate about 10 MWh of energy on a repeating daily cycle / SOURCE: Energy Vault

The technology uses motors to raise those massive composite bricks, motors powered by wind or solar energy when the wind and the sun are producing more energy than can be used at the time, like in California during mid-day. Raising the bricks changes this excess renewable energy into gravitational potential energy that can just sit there until needed.

When you need energy, like when the sun has set or the wind stops blowing, you lower those massive bricks and the attached cables spin a motorised generator that generates electricity back to the grid. Typically, the bricks move at 2.0 meters per second (about 6.6 ft/s), but can be accelerated or slowed via artificial intelligence computerised control to allow for faster or slower electricity discharge. One brick raised 100 meters in less than a minute, stores almost 10 MWh of electricity.

Typically, the system cycles once per day. With five days of downtime per year, a 75 MWh Vault with 10,000 bricks will have an annual output of 360 x 75,000 MWh = 27 GWh, and will sit on only 14 acres of land.

The blocks are combined with proprietary system design and machine vision, and AI-enabled software that operates specially designed lifts which autonomously orchestrate the lifting and lowering of the blocks, thus storing the potential energy at height and then discharging electricity as the blocks are lowered (see figure above).

Bricks are made from locally sourced soil, sand or waste

Importantly, the bricks are made from locally sourced soil, sand or waste materials, including waste products of fossil fuel production, such as coal bottom ash, and end of life energy components, such as wind turbine blades, specially shredded for this purpose (see figure below).


A simple onsite brick-making facility making the 35-ton bricks in as green a way as possible – with local waste material or dirt, and no cement / SOURCE: Energy Vault

Lithium and Cobalt: efficient, but in short supply

There is a reason that batteries have not grown to more than 3% of our present storage capacity, which is itself only 3% of our storage needs. We have seen that there isn’t enough Li or Co to make sufficient ion batteries, although their round trip efficiency (RTE) is 90%. Flow batteries like vanadium flow batteries, thermal storage, liquefied air and aqueous batteries just have not caught on and only have efficiencies between 50% and 70%. All of these have narrow discharge durations.

Bricks: 80 – 85% efficient, wide discharge duration, LCOE of $65/MWh

The Energy Vault has measured RTE of between 80 – 85% and has a wide discharge duration from minutes to days, and longer if needed. As to cost, according to Bloomberg NEF June 2020 Energy Storage Review, it’s LCOE of $65/MWh will be half that of Li-ion’s $128/MWh, and lower than any other storage technology. There are no safety hazards to Energy Vault outside those of ordinary construction operations, and there is no risk of fire or release of hazardous gasses as for Li-ion manufacturing facilities.

Their standard Energy Vault Resiliency Center (EVRC image, above) can be modularised, but its standard storage capacity presently sits at 500 MWh. Such a centre, backing up a 1,500 MW solar array or wind farm, can replace a large coal plant.

Demonstration unit in Switzerland

Energy Vault’s first 5MW/35MWh Commercial Demonstration Unit achieved mechanical completion in July 2020, concurrent with its connection to the Swiss national utility grid (see figure below). The architecture is modular and can be built out in 10MWh increments that can scale to multi-GW-hour storage capacity.

CEO Robert Piconi explained that the system typically takes 9 to 12 months to build, with the major constraint being the fabrication time of the brick composites.  “We could do it faster with two brick machines instead of one if the customer wants a system delivered faster.”

Solving Wind and Solar intermittency

This technology does not address all the issues with wind and solar. It does not change the huge physical footprint needed by wind and solar nor the large amounts of steel and concrete required for their construction. It does not increase their low capacity factors. It does not change the relatively short life-span of solar and wind units.

But it does remove the worst aspects of their intermittency and allows wind and solar to be more useful when needed. In other words, it addresses the Duck Curve.


A Commercial Demonstration Unit moving blocks in Switzerland after being hooked up to the Swiss grid / SOURCE: Energy Vault

Avoiding the blackouts in the U.S.

Texas and California could have really used the Energy Vault in the last two years when this exact intermittency problem caused their blackouts during unusually cold and unusually hot weather.

California has 12,000 MW from solar. For the last few years, the State has curtailed, or thrown away, over 300,000,000 kWh of solar energy in individual months, over 2 billion kWh in 2021 alone. That is the magnitude of energy lost that could be stored with Energy Vaults. With about 10% of that stored, the blackouts of 2020 would not have occurred.

Similarly for Texas in the middle of the cold-induced blackouts of February 2021. The State has over 30,000 MW of wind capacity, most of which was unable to generate during the cold spell. That this was expected does not alter the fact that wind cannot respond to extreme weather conditions. Natural gas in Texas was not able to fill the gap, as it usually does, because of diversion to heat homes and insufficient pipeline supply.

From noon on February 14 to noon on February 15 in Texas, the amount of offline wind capacity climbed to 18,300 MW. During the same period, the amount of offline natural gas capacity jumped 25,000 MW. Both were at fault. And the problem has still not been addressed.

If about 30 million kWh had been stored in Energy Vaults, no blackout would have occurred. Over $130 billion would not have been lost. Many fewer lives would have been lost.

But such problems are not confined to Texas or California. New England is also looking forward to rolling blackouts this winter. Their energy use is of the same order as California and Texas. They also are becoming more dependent on gas without sufficient pipeline supply, and just assume Canada will send them sufficient hydro when needed, something unlikely in the coming decades as that source is being tapped by many northern states, and by Canada itself, as they decarbonise their grids.

U.S. future energy mix

As discussed previously, any Low-Carbon Plan in America will require some form of the following mix (calculated by achievable build rates) dominated by renewables and backed up by significant nuclear and hydro:

– 500,000 new MW of wind turbines (1.75 trillion kWhs/year)

– 200,000 MW new nuclear reactors (1.58 trillion kWhs/year)

– 300,000 new MW of new solar (0.92 trillion kWhs/year)

– 120,000 new MW of hydro w/80,000 MW existing (0.77 trillion kWhs/yr)

…and will cost over $9 trillion between now and 2050 of which $4 trillion is capital investment. This does not include related grid or transmission infrastructure, just building the power plants.

Although new nuclear designs and hydro are excellent for load-following renewables, as good as natural gas, this much renewable production needs a lot of buffering. And we’ll never have enough batteries. But sufficient 500 MWh EVRCs, about 1,000 for the above mix assuming a maximum renewable curtailment of 20%, can provide the back-up needed in the time frame required.

Yes, this does sound like a game-changer.


James Conca is an earth and environmental scientist and a regular contributor to Forbes magazine


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It should be part of the solution since you want diversity in sources.  Batteries have short duration , use toxic materials, and fail in extreme heat or cold and are not part of the solution. Batteries also do not produce dynamic reactive power using electronics.   One could use a DC pony motor to drive a generator.  Pumped hydro can have  serious problems with leakage in the lake bottom. Lake Powell  for example loses enough water due to leakage to supply the City of Los Angeles. And that does not include evaporation losses.  Lake Meade is bottomed in solid granite  so it doesn't leak.   Hydro can't be put just anywhere and we have made bad choices in the past.  The coal fly ash brick is not a 100% cure all since you would have a radioactive waste dump but it would be a good partial filler to keep the thorium and uranium levels low. Mix it with the waste fiberglass and other difficult to recycle materials.  To be able to reenergize the grid after a black out, you will need something like  hydrogen /oxygen gas turbine to set frequency and provide initial dynamic reactive power. That has the side benefit of providing 100% clean uncontaminated  water  as you only find in the comets  and Ort cloud in deep space.

This is solid engineering and should be part of the the solution.  Used with wind and solar, this  has a negative Delta T when storing excess electricity.  That means it cools the atmosphere instead of heating it as a cooling tower does; the reverse of any steam driven (or supercritical CO2 ) plant. 

Edited by nsdp
additiional sentence.

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