by Akshat Rathi
Thanks to the modern electric grid, you have access to electricity
whenever you want.
But the grid only works
when electricity is generated in the same amounts as it is consumed.
That said, it's impossible to get the balance right all the time.
So operators make grids
more flexible by adding ways to store excess electricity for when
production drops or consumption rises.
About 96% of the world's energy-storage capacity comes in the form
of one technology: pumped hydro. Whenever generation exceeds demand,
the excess electricity is used to pump water up a dam.
When demand exceeds
generation, that water is allowed to fall - thanks to gravity - and
the potential energy turns turbines to produce electricity.
But pumped-hydro storage requires particular geographies, with
access to water and to reservoirs at different altitudes. It's the
reason that about three-quarters of all pumped hydro storage has
been built in only 10 countries.
The problem with pumped hydro storage
is that it’s highly dependent on the geography of a country,
with access to large rivers a necessity.
This is why nearly three-fourths of global energy storage
is located in only 10 countries.
The trouble is the world
needs to add a lot more energy storage, if we are to continue to add
the intermittent solar and wind power necessary to cut our
dependence on fossil fuels.
A startup called Energy Vault thinks it has a viable alternative to
Instead of using
water and dams, the startup uses concrete blocks and cranes. It
has been operating in stealth mode until today (Aug. 18), when
its existence will be announced at Kent Presents, an ideas
festival in Connecticut.
On a hot July morning, I
Biasca, Switzerland, about two hours north of Milan,
Energy Vault has built a demonstration plant, about a
tenth the size of a full-scale operation.
The whole thing - from
idea to a functional unit - took about nine months and less than $2
million to accomplish.
If this sort of low-tech,
low-cost innovation could help solve even just a few parts of the
huge energy-storage problem, maybe the energy transition the world
needs won't be so hard after all.
The science underlying Energy Vault's technology is simple.
When you lift something
against gravity, you store energy in it. When you later let it fall,
you can retrieve that energy. Because concrete is a lot denser than
water, lifting a block of concrete requires - and can, therefore,
store - a lot more energy than an equal-sized tank of water.
Bill Gross, a long-time US entrepreneur, and Andrea Pedretti, a
serial Swiss inventor, developed the Energy Vault system that
applies this science.
Here's how it works:
A 120-meter (nearly
400-foot) tall, six-armed crane stands in the middle.
In the discharged state,
concrete cylinders weighing 35 metric tons each are neatly stacked
around the crane far below the crane arms.
When there is excess
solar or wind power, a computer algorithm directs one or more crane
arms to locate a concrete block, with the help of a camera attached
to the crane arm's trolley.
Simulation of a large-scale
Once the crane arm locates and hooks onto a concrete block, a motor
starts, powered by the excess electricity on the grid, and lifts the
block off the ground.
Wind could cause the
block to move like a pendulum, but the crane's trolley is programmed
to counter the movement. As a result, it can smoothly lift the
block, and then place it on top of another stack of blocks - higher
up off the ground.
The system is "fully charged" when the crane has created a tower of
concrete blocks around it. The total energy that can be stored in
the tower is 20 megawatt-hours (MWh), enough to power 2,000 Swiss
homes for a whole day.
When the grid is running low, the motors spring back into action -
except now, instead of consuming electricity, the motor is driven in
reverse by the gravitational energy, and thus generates electricity.
The innovation in Energy Vault's plant is not the hardware.
and motors have been around for decades, and companies like ABB and
Siemens have optimized them for maximum efficiency.
efficiency of the system, which is the amount of energy recovered
for every unit of energy used to lift the blocks, is about 85% -
comparable to lithium-ion batteries which offer up to 90%.
Pedretti's main work as the chief technology officer has been
figuring out how to design software to automate contextually
relevant operations, like hooking and unhooking concrete blocks, and
to counteract pendulum-like movements during the lifting and
lowering of those blocks.
Energy Vault keeps costs low because it uses off-the-shelf
Surprisingly, concrete blocks could prove to be
the most expensive part of the energy tower. Concrete is much
cheaper than, say, a lithium-ion battery, but Energy Vault would
need a lot of concrete to build hundreds of 35-metric-ton blocks.
So Pedretti found another solution.
He's developed a machine that
can mix substances that cities often pay to get rid off, such as
gravel or building waste, along with cement to create low-cost
The cost saving comes from having to use only a
sixth of the amount of cement that would otherwise have been needed
if the concrete were used for building construction.
Rob Piconi (left)
The storage challenge
The demonstration plant I saw in
Biasca is much smaller than the
planned commercial version.
It has a 20-meter-tall,
single-armed crane that lifts blocks weighing 500 kg each. But it
does almost all the things its full-scale cousin, which the company
is actively looking to sell right now, would do.
Robert Piconi has spent this summer visiting countries in Africa and
Asia. The CEO of
Energy Vault is excited to find customers for its
plants in those parts of the world.
The startup also has a
sales team in the US and it now has orders to build its first
commercial units in early 2019.
The company won't share
details of those orders, but the unique characteristics of its
energy-storage solution mean we can make a fairly educated guess at
what the projects will look like.
Energy-storage experts broadly categorize energy-storage into three
groups, distinguished by the amount of energy storage needed and the
cost of storing that energy.
First, expensive technologies, such as
lithium-ion batteries, can be
used to store a few hours worth of energy - in the range of tens or
hundreds of MWh.
These could be charged
during the day, using solar panels for example, and then discharged
when the sun isn't around. But lithium-ion batteries for the
electric grid currently cost between $280 and $350 per kWh.
Cheaper technologies, such as
flow batteries (which use high-energy
liquid chemicals to hold energy) can be used to store weeks worth of
energy - in the range of hundreds or thousands of MWh.
This second category of
energy storage could then be used, for instance, when there's a lull
in wind supply for a week or two.
The third category doesn't exist yet.
In theory, yet-to-be-invented,
extra-cheap technologies could store months worth of energy - in the
range of tens or hundreds of thousands of MWh - which would be used
to deal with interseasonal demands.
For example, Mumbai hits
peak consumption in the summer when air conditioners are on full
blast, whereas London peaks in winters because of household heating.
Ideally, energy captured
in one season could be stored for months during low-use seasons, and
then deployed later in the high-use seasons.
Piconi estimates that by the time Energy Vault builds its 10th or so
35-MWh plant, it can bring costs down to about $150 per kWh.
That means it can't fill
the needs of the third category of energy-storage use; to do that,
costs would have to be closer to $10 per kWh. In theory, at the
current capacity and price point, it could compete in the second
category - if it could find a customer that wanted Energy Vault to
build dozens of plants for a single grid.
Vault's best bet is to compete in the first category.
That said, some experts told Quartz that the cost of lithium-ion
batteries, the current dominant battery technology, could fall to
about $100 per kWh, which would make them cheaper even than Energy
Vault when it comes to storing days or weeks worth of energy. And
because batteries are compact, they can be transported vast
Most of the lithium-ion
batteries in smartphones used all over the world, for example, are
made in East Asia.
Energy Vault's concrete blocks will have to be
built on-site, and each 35 MWh system would need a circular piece of
land about 100 meters (300 feet) in diameter.
Batteries need a fraction
of that space to store the same amount of energy.
Batteries do have some limitations. The maximum life of lithium-ion
batteries, for example, is 20 or so years. They also lose their
capacity to store energy over time. And there aren't yet reliable
ways to recycle lithium-ion batteries.
Energy Vault's plant can operate for 30 years with little
maintenance and almost no fade in capacity. Its concrete blocks also
use waste materials.
So Piconi is confident that there's still a
niche that Energy Vault can fill:
Places that have abundant access
to land and building material, combined with the desire to have
storage technologies that last for decades without fading in
Meanwhile, whether or not Energy Vault succeeds, it does make a
strong case for the argument that, while everyone else is out
looking for high-tech, futuristic battery innovation, there may be
real value in thinking about how to apply low-tech solutions to
Energy Vault built a
functional test plant in just nine months, spending relative
It's a signal of sorts
that some of the answers to our energy-storage problems may still be
sitting hidden in plain sight.