How to make a city autonomous in energy | François Maréchal | TEDxGeneva

Nowadays, cities are responsible for more than 40% of greenhouse gas emissions. However, thermodynamics shows us that heating or cooling buildings should require only 10% of what they actually consume today. By using CO2 in an urban heating network, it is possible to heat and cool Geneva's city centre with 16% of the energy used today. With fuel cells, it is possible to convert gas into electricity and to capture CO2. With solar energy, CO2 and water combine to produce gas, and the waste that we produce every day can be converted into heat and electricity. By combining all of this, it is possible to make the city self-sufficient.

Of Belgian origin, François Maréchal is professor at the École Polytechnique Fédérale de Lausanne (Switzerland). He has always been passionate about the rational use of energy and systemic analysis. Internationally renowned engineer and researcher, François Maréchal leads a team of researchers whose aim is to help us make tomorrow’s energy systems more efficient, more reliable and more environmentally-friendly. Starting from the laws of thermodynamics, he will show us how to make cities more sustainable.

This talk was given at a TEDx event using the TED conference format but independently organized by a local community. Learn more at http://ted.com/tedx

Every individual needs energy to live
and to make his body work.

You, I, that refugee in Syria,
each of us needs energy.

The amount of energy that we need,

I can express it as a definite
quantity: 25 cl of petrol.

This is the energy equivalent
that we consume and need daily.

Our society, our civilisation
has developed a set of technologies

that enables us to guarantee our comfort
but actually consumes much more energy.

So, first, we produce waste:

each of us produces 2 kg of waste daily,
30% of which is organic waste,

that is, the residue of the food we eat,

the food that Nature gives us.

We consume energy: 5 litres of petrol
is the daily average in Switzerland.

The problem is that we burn it

and, as a result, it releases CO2:

14 kg every day.

Fourteen kilos per day,
imagine if it were solid,

you'd have to leave home each morning
with two packs of six bottles of water

and put them on the pavement.

Fourteen kilos per day ...
Luckily, it is a gas.

So it dissipates into the atmosphere,
we don't see it.

Too often we tend to forget

that it keeps on accumulating
in the atmosphere.

We ourselves don't feel it,

but Teddy-x here
is already seeing its effect.

We thought it was important
to save Teddy-x

and come up with a solution
to limit our CO2 emissions.

To do so, we need to study
the energy system.

So we took Switzerland and looked
where energy was consumed.

Forty-seven per cent
of Switzerland's energy consumption

is for keeping ourselves warm
and illuminating our buildings.

This energy consumption
occurs mainly in winter

when it's cold and we need to heat,
mainly in the form of heat.

Only 25% of our energy
consumption is electricity,

the rest is heat.

To this 47%, I'll add transport
which uses 36%,

and our society's driving force, industry,
which needs about 20%.

Each square here represents
100 litres of petrol per inhabitant,

and every red square
represents one CO2 emission.

When we observe cities, we see that
they tend to concentrate the population.

It is said that, in the future,

75% of the population will live in cities.

When it concentrates the population,
it takes up space.

In Geneva, each square metre of floor area

equals a square metre of heated area.

This means that energy is consumed.

The Swiss average
is 260 million litres per year

for the population
in Geneva's city centre.

It means that one million tons
of CO2 is emitted.

Cities also produce waste,

100,000 tons of solid waste
plus 40,000 tons of organic waste,

and they have opportunities.

In Geneva there's the lake
on the one hand,

and on the other hand, we have
the sun that shines on all our roofs.

If we convert the amount
of energy that we receive daily

into litres of petrol,

we can see that there are
620 million litres of petrol

that come to our roof each year.

We can see that there is
more energy available

than the energy that is consumed today.

So, together with some of my colleagues
and industrial partners,

we have asked ourselves
if we could make cities

really energy-autonomous.

'Energy-autonomous' means
ideally that we would no longer emit CO2,

we would not need to import energy,

that we would not have
to knock down all the buildings

to rebuild them later
but would use the city as it is,

and we would not bankrupt
ourselves, of course.

So, how did we do this?

As engineers, the first thing we do
is to look at the needs.

We don't need energy, and the best
would be precisely not to need it.

So we look at the minimum we need.

We call on science and thermodynamics.

Carnot, a French scientist
specialised in thermodynamics,

showed that in order to heat
a building up to 21°C

when the environment is at 0°C,

we need to buy one unit of energy
to deliver 10 of it.

This is an important element
because it can guide and motivate us.

Where is the motivation?

If I look at the amount of energy
I spend using a very good boiler

that has 90% efficiency, uses gas
and so burns and produces CO2,

I realise that for the same amount
of heat, that is 10 units,

I must buy 11 units.

Here emerges a new question:

why do we consume 10 times more

than the minimum
indicated by thermodynamics,

while producing CO2 on top of it?

The answer is to be found
in the heat pump.

What is a heat pump?

You all have a fridge at home.

This fridge works on the following principle:

you take electricity,

you extract heat to cool
the inside of the fridge,

and in doing that you heat your room.

The heat pump does exactly the same:
it takes the outside heat

and with the help of electricity
it increases the temperature

in order to provide you with heat.

Thermodynamics tells us two things.

The first is that

the lower the temperature
at which you have to heat,

the less energy you have to spend.

That's why the recommendation

is to install low temperature
heating systems

and not high temperature ones.

Thermodynamics also tells us

that the higher the source temperature,
in other words the environment, the better.

The problem is finding that source.

Cities are dense ;
there are buildings everywhere,

so it is very difficult to make
only one heat pump.

So we thought of splitting
the heat pump into two:

On one side, we will use a heat pump

that will find the good heat sources
in the environment.

For example, if I have water in the lake,
a river or underground,

I can extract this heat
and carry it where I need it.

Then I can use a second heat pump

which gives me exactly
the temperature that I need.

You have a heating system
at low temperature,

so you will pay less than someone
who has a high temperature heating system.

In order to carry the heat,
the idea is to use the CO2.

What we can do is use two tubes:

one tube with CO2 in the liquid state,
one tube with CO2 in the vapour state.

We can take the steam, condense it,

and in this way we can deliver heat,

and we can use a heat pump
to reach the temperature we need.

Now, if someone wants to be cooled,
I can take the liquid and boil it off.

I can then cool my buildings
down directly.

Because they are connected with a pipe,

I can also cool the building
that needs to be cooled

with the building that needs to be heated.

This ultimately allows me
to save a good amount of energy.

Then, on the way, we can identify
all the good heat sources that we have.

For example, the waste water
that leaves your house at around 20°C

can be used to heat the buildings.

as well as the water in the lake,

or the water that leaves the water
treatment plant, or geothermal energy.

So now, I have a system
that enables me

to exchange energy
between the different users.

Another important element
is that I use CO2.

CO2 has a high energy density
which means we don't need large pipes.

We can insert pipes in the pavement

and don't have to bury them
because CO2 doesn't freeze.

We don't have to go very deep.

Therefore we can manufacture
precast pavement

that enable us to transport
the energy that you need.

So, here is a complex system
that, thanks to a heat pump,

allows us to warm up,
to be directly cooled,

that also enables refrigeration
in shopping centres, for example,

where fridges or freezers are needed,

that also enables us to recycle
the heat of our waste when we burn it,

and that uses all the opportunities
that the environment has to offer.

Now the question is:

is it more efficient
than the traditional system?

To get the answer, we did a case study:

an area in Geneva
where there are offices,

appartments, banks, shops -

for those who know it,
it is the "Rues Basses" area.

We calculated the amount of energy

that is needed and used today
to provide heating and cooling

and we saw that we need 12 energy units,

10 in the form of heat and natural gas
and two in the form of electricity.

We also saw that the natural gas
is mainly used in winter,

while electricity is used
in summer for cooling.

The same system with the CO2 network
only needs two units.

We made a factor of six
in our energy consumption.

We only need 16% of the energy
that we consume today

without changing the buildings.

Obviously, if we insulate the buildings
we will save even more.

Of course, everybody said,
'Yes, but it's going to be too expensive'.

And the answer is: 'Yes,
it's very expensive at present.

But in fact, the system we propose
will cost less and will be profitable,

while today's system is not profitable'.

Now. I've almost achieved my goal,

but I still need to provide
electricity to the system

so I am not quite self-sufficient yet.

I have to provide electricity in winter,
so now the question is:

how do we make electricity in winter?

We can import electricity from outside

but then, we will emit a lot of CO2
and so lose many benefits.

I can also use new technologies
such as the gas combined cycle

which has a better efficiency

and emits far less CO2
because it uses natural gas.

But I can also say,

'Why not use renewable energies
to make my heat pumps work?'

The problem is that renewable energies
are mainly available in summer.

The sun shines a lot in the summer,
far less in the winter.

We can also use
a different kind of technology.

The EPFL has patented a new concept

that combines a fuel cell
and a gas turbine,

that has 80% electrical efficiency,

much higher than the best
gas power plant,

and that separates CO2 for free.

So now, I have some CO2 in a tube,

and that's perfect
since I already have a tube.

I have residual heat because I'm at 80%.

I still have 20% left which is great

since I have the means
to carry it towards my users.

So now, my system enables me
to produce electricity,

to catch CO2 and to meet my heat needs.

But I’m still using fossil fuel
because I’m using natural gas.

So here, we must go back
to look into History

and see what gifts
Mother Nature has given us.

In fact, Nature has given us two things.

On the one hand, we have a treasure.

The treasure is something
that never gets refilled.

It is there and we can only use it,
and this is what we do:

we take a part of the treasure
and burn it to produce CO2.

And Teddy-x is not very happy actually.

What you can observe
is that the reservoir has run out

and nobody is refilling it.

That means our children will have less
than what we've received from our parents.

We can also look at Nature’s
current and savings accounts

which are renewable energies
that come in different forms.

We have the sun, the wind,
the water and the biomass.

The biomass is much like the savings
account because it is stored.

I can therefore take the biomass
and convert it into gas.

Organic and chemical processes exist

that enable us to convert
the biomass into gas.

When the process is not efficient,
it generates heat

and I have a tube to use that heat
so it's great when I need heat.

As for the gas, I can use it
in fuel cells.

I’m also trying to learn from Nature.

If I think carefully, I need energy,
where do I find it?

I find it in food which is stored energy.

I don’t feel variations
like I do with the sun

that changes from hour to hour
and from season to season.

How did Nature do that?
By photosynthesis.

It took CO2 from the atmosphere,

used the photons coming
from the sun, used water,

and created carbohydrates
that make up my food

and the trees as well.

We can do the same
with a technical system.

I can take the sun,

transform it into electricity
with photovoltaic cells,

then I can take these, CO2
and water, and create methane.

And what I'm going to do
is to take the CO2 I stored

and create methane in the
liquid state to store as well.

It's going to become
quite a complex system

because, in the summer,
I'll take liquid CO2

to make liquid methane
by means of the shining sun,

and in the winter, I'll take
the liquid methane

and feed it into the fuel cell

to produce the electricity that I need
for heating and lighting,

then, I'll capture the CO2,

bring it back into my tube
and convert it into liquid CO2.

By doing so, I’ll have a system
that seems very complicated,

but don’t forget that you have many tubes
coming into your houses every day.

You have the electrical cable,
the Internet cable,

and also the drinking water
and the waste water leaving your home.

So adding a new tube is not necessarily
as difficult as it seems.

It's a system that enables us
to warm up, to cool down, to refrigerate,

to add value to all of our waste,

and to store the solar energy produced
during the summer on our roofs

to make it available during the winter.

If I can do that, I'll have a system
entirely autonomous in energy.

The system I had before

burnt a large quantity of energy
to meet my needs,

emitted a lot of CO2,
and emptied my treasure.

Today, with an investment -
the installation of new infrastructure

with heat pumps, fuel cells and storage -

I will be able to fulfil the same needs.

I don't need to change the buildings
or to change your comfort,

you will still have the same
temperature in all your rooms.

You will simply have
solar panels on your roof,

You will have fuel cells

that generate electricity from the methane
produced during the summer.

You will recycle the heat from the hot
water poured in the sewer

because you will be able to use it
in your heat pumps.

You will recycle energy from your waste,

and in the end, in fact,
you're going to export electricity,

an electricity available on request.

That means that you'll be able
to decide when to export it

when you have too much,
and it'll be stored as methane.

As a point of interest,

the storage space required for this
is 10 times smaller

than the amount of tanks
we would need in all the buildings

if we heated everything with fuel oil.

And that's my conclusion.

Anyway, Teddy-x can thank us,

because if you are able
to transform cities

into independent electricity producers
without CO2 emissions,

he may have the opportunity
to find a more secure block of ice.

Thank you very much.

(Applause)