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Une solution béton pour stocker l’énergie solaire à faible coût | André Gennesseaux | TEDxParisSalon


Translator: André GENNESSEAUX
Reviewer: Ivana Korom I found a means to solve
the energy problem with concrete! Yes, concrete! Not to build dams or install windmills, but concrete to power the grid, make light and heat. I am going to explain it to you. Did you know
that the cheapest energy today is solar energy? Thanks to the dramatic drop
in solar panel price, if you install now
a solar panel in a sunny place, you get a kilowatthour at 2 cents. It’s half the price
of classic polluting energies. In addition to being the cheapest,
solar energy is extremely abundant. The red square in Sahara,
roughly one quarter of France, represents the area of solar panels that can power
the whole planet with electricity! So, if solar energy is so cheap
and so abundant, why isn’t it our main energy source? Because there is a problem:
intermittence. In the day there is sun,
but in the night there is no sun. This bell curve shows that solar energy comes concentrated,
in the middle of the day, whereas our consumption is rather
constant: this is the white line. If we want to power the network
with a lot of solar energy, it is absolutely necessary
to store the excess of energy in the middle of the day, in yellow, to be able to use it
in the evening and the night. Storing energy is not
a technological problem, it’s an economical problem. Energy can be stored, in batteries. But energy cannot be stored
profitably with batteries. Batteries, like the lithium ones
of your phone, use a chemical reaction. After each charge-discharge cycle,
they wear, they lose some capacity. They need to be replaced
after a few years. And when you compute the cost
of storing energy in batteries, you find that it is very high. It is estimated to be
10 cents per kilowatthour, so that solar energy, when stored
in batteries, is no more interesting. It is not profitable:
it needs subsidies, it cannot develop. I am not a chemist,
I am a mechanical engineer. A few years ago, I was working for Total
and I went to Detroit Auto Show, and I see a startup willing to replace
electric car batteries with “wheels”. Not steering wheels for driving,
flywheels. A flywheel is a disc or cylinder
spinning at very high speed to store energy in a form called
kinetic energy. Flywheels have been made of steel. Recently some have been made
of carbon fiber. The very large advantage of flywheels
over batteries is their unlimited life. Unfortunately for electric cars,
flywheels proved to be too heavy. But I had the conviction that,
when weight is not a problem, flywheels have a tremendous potential
for storing renewable energies, and I founded my company. With my team of four, we made flywheels
with steel, then with cast iron. We were in the quest of the graal
that everybody is searching now: low cost storage. But these classical materials
are too expensive. We had to find something
completely different. Last year I had an intuition:
we had to test concrete. And I found that concrete is an extraordinary material
for energy storage. Concrete can store energy at a cost
ten times lower than classical materials. And I can tell you that,
in an engineer’s life, you don’t often make
such a large progress in so little time. Of course you will ask: if it’s so easy,
why did nobody think about it before? Because concrete is incompatible
with flywheels. Concrete does not resist traction:
if you pull on concrete, it breaks. When a flywheel spins,
there is a huge centrifugal force that creates intense traction. If you make a cylinder out of concrete,
it bursts as soon as you spin it. My solution consists
in compressing the concrete with a winding in traction all around so that concrete stays compressed
up to the maximum speed. To keep things simple, we can say
that we wrap it like a roast beef. This “Flywheel for Solar Energy Storage”,
we called it VOSS. How does it work? When there is an excess of solar energy,
needing to be stored, we use an electric motor
to spin the flywheel faster and faster, and store kinetic energy. Maximum speed is that of an airplane,
slightly less than 1,000 km/h. This is fast. But there is no air drag,
as we have removed the air – vacuum, so that we can keep energy for hours. To recover the energy,
the system is reversed, that is: the flywheel spins the motor, which produces electricity
like an alternator. Finally, with intuition,
a lot of reflexion and some concrete, we have found a means
to store energy at a low cost: The association of concrete flywheels
with photovoltaic panels produces a renewable energy,
available night and day, at a lower cost
than that of polluting energies. This technology is currently
under development. Our project in the short term
is to equip small networks: like Corsica, Guadeloupe, Réunion,
African villages… that are currently powered
by generating sets, in order to replace their fossil fuel
by solar energy. But our long term project,
in 4 to 5 years, is to create
large photovoltaic solar plants in highly sunny areas such as deserts, in order to power the global network with an energy that will be
clean and cheap: solar energy,
profitable without subsidies. Needless to say,
after all these years of research, I am impatient to see our technology
reach the energy market, and revolutionize it, because with such a low cost of storage, renewable energies will at last
be able to replace polluting energies. Thank you. (Applause)

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Bernard Jenkins

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