The future is going to require us to make
some dramatic changes to the way we produce
and consume electrical power.
Climate change is happening whether we like it or not,
and switching to cleaner sources of energy is the main
way we’ll be able to keep it from getting worse.
And we’ll run out of fossil fuels eventually
anyway.
That’s why engineers are looking for ways to scale some
of the existing sources of energy that don’t rely on fossil
fuels, and maybe even find sources that are entirely new.
There are all kinds of promising candidates
– from nuclear fusion to plain old hydrogen to
…poop.
[Theme Music]
For at least the last 450 million years, another
form of life has been harvesting all it needs from the
sun without doing any harm to the planet.
I’m talking about plants.
The chlorophyll in a plant’s cells absorb light
and use its energy to combine carbon dioxide and
water to produce glucose and oxygen.
That’s photosynthesis.
Eliminating some carbon dioxide from the atmosphere
and producing the oxygen we breathe is already pretty
great, but there’s another useful aspect to this.
When the plants store some of that glucose,
it’s also storing chemical energy.
And where there’s energy, there’s an engineer
who will find a way to use it.
Biomass energy is a form of energy that relies
on burning biological matter, like plants, either
directly or by processing them into a fuel.
As it burns, the chemical energy stored in
the plant’s matter is converted into heat.
Like with many of the other energy sources
we’ve mentioned, the heat turns water into steam,
which in turn does work on a turbine;
in other words, it drives a heat engine.
A generator then converts the turbine’s
motion into electrical power.
About half of all biomass energy is delivered by
burning plant matter directly, which humans have
been doing long before the need for electrical power.
A wood burning stove can keep your house warm
in the winter, or it can be used as a heat source for
something else – to cook pizza, for example.
On a larger scale, scrap wood left over from wood processing or from waste produced by humans, along with food waste, can be burned in power plants more directly.
Most of the other half of biomass energy comes
from processing biological matter into biogas
or biofuel.
By pulping and chemically treating biomass
derived from crops and other plant matter,
it becomes easier for special proteins called
enzymes to chemically break it down into a
more readily usable fuel source.
One example of this is our old friend ethanol
– the type of alcohol you’ll also find in drinks.
Ethanol is produced from enzymes breaking
down crops such as wheat or corn.
That can then be turned into a liquid fuel
suitable for burning.
But it’s not just plants that we extract
energy from!
As certain types of agricultural waste, like
manure, decay, they can release what’s known
as biogas.
These are gases like methane that can be burned
as a source of fuel.
There’s also another small contributor to
biogas production: human waste.
When I said engineers will find a way to get
energy from everything, I meant everything.
Biofuels are already being used pretty widely.
In Brazil, 4 out of every 5 cars produced
have hybrid engines capable of burning both
ordinary gasoline and bio-ethanol.
To be clear, burning biomass fuels does
release carbon dioxide into the atmosphere,
just like fossil fuels.
But, because a nearly equivalent amount of
CO2 is captured from the atmosphere during
photosynthesis to store chemical energy,
on the balance of things, biomass energy is
what’s known as carbon neutral.
We can also always grow more plants, which
makes biomass more renewable than fossil fuels.
But given that plants absorb CO2 as they grow,
you could argue that we shouldn’t just release
it all back by burning them.
And processing biomass into biofuels often
requires some amount of energy input, which
indirectly releases more CO2.
Humans already use about a third of all the
CO2-absorbing plant matter on Earth.
Destroying even more of those plants to release
energy could be catastrophic for certain ecosystems.
And even though we could grow more plants, we’d
have to trade off the use of land, water, and chemical
resources between growing food or providing energy.
Demand for all of those resources is already high,
and projected to continue growing pretty quickly.
As with any other power system, there are
places where engineers can make better of
use of what’s already there,
like improving the design of those hybrid engines
that burn both ordinary gasoline and biofuels.
We also might be able to use different biomass
sources, like algae, or find more efficient chemical
reactions for processing biomass into fuel.
That might unlock new, more sustainable ways
to use biomass for power.
But there are other futuristic power sources
that don’t release any CO2 while being consumed.
Although as we’ll see, that doesn’t mean
they’re carbon neutral!
Hydrogen is the most abundant element in the
universe, which makes it pretty surprising that
pure hydrogen is very rarely found on Earth.
It consists of a single proton and electron, and
if you can produce it, it’s the perfect source of fuel
for the very aptly named hydrogen fuel cell.
Fuel cells of this kind use a chemical reaction
between hydrogen and oxygen to directly generate
electrical power.
And the only other byproduct of this
reaction is water.
Much better than carbon dioxide.
There’s a fairly big problem, though.
If hydrogen isn’t naturally produced on
Earth, how do you get it?
You can use the process known as electrolysis
to chemically separate water into hydrogen
and oxygen, and just store the hydrogen.
Except, performing electrolysis uses energy.
In fact, producing hydrogen fuel requires
more energy to produce than you get from using
it in a fuel cell.
Efficiency-wise, that’s not great.
But there are good arguments for having hydrogen
fuel cells in your power-producing arsenal.
For starters, because hydrogen is the lightest
element, hydrogen fuel is incredibly lightweight, which
makes it great for transport, like on spacecraft.
And unlike solar-powered devices, if you
have hydrogen fuel at the ready, fuel cells don’t
require recharging like batteries.
So they’re great for indoor vehicles like
forklifts, where releasing lots of fumes could
be problematic,
but you also need to use them pretty much
continuously, which makes batteries less practical.
Finally, if we can efficiently produce hydrogen
fuel by electrolysis from the surplus energy
provided by solar power on especially sunny days,
hydrogen fuel could give us a carbon 
neutral way of storing electricity.
On a larger scale, there is a power producing
process you’ve already heard of that’s already used
to provide a good deal of energy – 10% in the US –
while releasing comparatively tiny amounts
of CO2: nuclear fission.
In fission, an atom splits in two, releasing
a lot of energy in the process.
Nuclear power releases the same amount or
even less of those greenhouse gases than most
renewable energy sources.
But don’t be fooled, it’s a non-renewable
source of energy!
The main fuel used in nuclear fission, uranium 2-3-5,
is a limited resource that has to be mined and purified
from the ground, much like fossil fuels.
The way we get power from uranium is by
assembling rods of uranium parallel to one another
and setting up a chain reaction.
The nucleus, or core, of a uranium atom is
made up of protons and neutrons.
If a fast moving neutron hits a uranium atom at
just the right energy, it can split the uranium in two.
The uranium splits into atoms of other elements,
like krypton and barium.
But three of the neutrons from the nucleus
will fly off, carrying some energy with them.
Those neutrons can then collide with another
uranium atom, causing fission that releases
even more neutrons, and so on.
Meanwhile, the cascade of splitting atoms
gives off gamma radiation and heat, heating
up the reactor.
So fission turns a nuclear reactor into a
heat source for a power plant.
Unfortunately, once you’ve used up all the useful
uranium in the rods, you’re left over with the biggest
setback of nuclear power: nuclear waste.
Nuclear waste consists of radioactive material that
emits highly energetic particles that can be extremely
dangerous for any living thing, including humans.
Dealing with it safely is the sort of issue
nuclear engineers can help with.
They also design nuclear power plants to
carefully control fission to stop it turning into
a runaway process.
If that happens, it can lead to disasters
like the kind that happened in Chernobyl or
Fukushima.
As for nuclear waste, nuclear engineers aim
to find as safe a way as possible for disposing
of it.
Most of the time, used-up uranium rods are put into
thick steel containers and buried in deep underground
vaults far from any people,
or kept in tanks near the nuclear power
plants themselves.
Neither of these solutions is ideal, and engineers
may find a better way of handling the problem
in the future.
But it would be better if we could find a
way of generating nuclear power that produces
no radioactive fuel as waste at all.
Which is where nuclear fusion comes in.
It’s the same energy-releasing process that
occurs in the sun.
So naturally, getting it to happen here on
Earth is something many engineers are looking
into!
In fact, the National Academy of Engineers in the US
has declared the goal of providing energy from fusion
one of its grand challenges for the 21st Century,
in addition to the improved solar power we
talked about last time.
The major setbacks to providing energy from
fusion are the intense amounts of heat and
pressure that atoms need to fuse.
Without the gravitational strength of the sun on hand,
nuclear physicists and engineers have to design some
of the world’s most powerful magnets to contain plasma:
an extremely hot gas made up of ions, or
atoms with an electric charge.
Unfortunately, the magnets require energy to operate,
so fusion has to deliver more power than the magnets
consume for it to be useful.
And we haven’t figured out how to do that
yet.
In 2018, a test reactor in the U.K. announced they’d
reached temperatures of 15 million °C in a plasma –
well on the way to a sustainable fusion reaction.
And currently under construction in the South
of France is what will be the world’s biggest
fusion plant, called ITER.
The design is still experimental, but the hope is that it will be capable of delivering the first ever self-sustaining fusion process capable of generating more power than the magnets consume.
Engineers have already contributed to the
effort by designing more efficient magnets
and contributing to the design of ITER itself.
But if fusion ends up being a suitable power
source, they’ll have a lot more work left to do
to scale it for wider use.
Between the sources like solar and wind power
we talked about last time,
and less-developed tech like nuclear fusion, there
are lots of different ways we can change the future
of energy for a world less reliant on fossil fuels.
No matter what, we’ll need a new power infrastructure
to support the cleaner energy world of the future.
And that infrastructure, that future, will
be built by engineers.
In this episode we looked at alternative energy
sources.
We saw how biomass can be burned as a fuel
source, how hydrogen can be used in a fuel
cell to generate electrical power,
and how nuclear fission provides power to the grid.
Finally, we saw how nuclear fusion might someday
do the same without any radioactive waste.
Next time, we’ll be looking at ways of storing
all that power when we look at energy storage
and batteries.
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Crash Course Engineering is produced in association
with PBS Digital Studios.
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Dianna Cowern explains the physics behind puzzling
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Crash Course is a Complexly production and this
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