parties to the United Nations

Framework Convention on Climate Change

reached a landmark agreement.

One hundred and ninety-five nations,

practically every country in the world,

were going to officially fight against the climate crisis.

This is now known as the Paris Agreement.

And the main goal of that treaty

is to limit global temperature rise

to well below two degrees Celsius.

But in order to save the Earth from rising temperatures,

we need to remove billions of metric tons of carbon

from our atmosphere every year.

To help accomplish this,

countries have been investing in negative emissions

and low-carbon technologies,

as well as adding infrastructure to support them.

And solar energy is already at the forefront

of this renewable revolution.

Why? Because the sun is the most abundant

energy resource we have on our planet.

But how much do you know about solar panels

and how exactly do they work?

Well, let's start with photovoltaic cells.

These cells are what convert sunlight into electricity.

A single photovoltaic cell, also called a solar cell,

can be smaller than a postage stamp

and thinner than a human hair.

On its own, a solar cell can generate about half a volt.

So, to increase this energy output,

you can combine these solar cells

to create solar modules

and even slightly-bigger solar panels.

Depending on their size

and the materials they're made of,

as well as the amount of sunlight that's available,

the power output of solar panels can vary.

This output, or the amount of energy a panel produces,

is measured in kilowatt-hours.

So, if a panel generates 100 watts in one hour,

that would be 100 watt-hours or 0.1 kilowatt-hours.

But you can combine modules and panels even further

to create solar arrays.

These structures are what are used to power homes

and even spacecraft.

And if you gather enough solar arrays in one place,

you can even power cities.

You may have seen swaths of land

covered in solar arrays.

These are often called solar farms or solar parks.

The largest solar park built to date

is the Pavagada Solar Park in India.

It spans over 53 square kilometers

and can produce two gigawatts of electricity,

which is enough to power 700,000 households.

By the end of 2018,

the world's installed capacity of solar cells

reached over 480 gigawatts,

representing the second largest

renewable electricity source after wind.

Now, this may seem like a lot of energy already,

but researchers are projecting that by 2050

the world's solar cell capacity

could reach over 8,500 gigawatts.

This is the kind of expansion we need

to reach the carbon-cutting goals

of the Paris Agreement.

The big reason why photovoltaic cells

haven't taken over the world yet

is because the technology is still limited

by three important factors.

Cost, efficiency and reliability.

Efficiency basically just means

how well a solar panel is able

to convert sunlight into electricity,

and cost can be defined by, well,

how much goes into making a solar cell

like materials, manufacturing,

distribution, installation,

relative to how much wattage is generated

in return for that investment.

And lastly, we have to make sure a solar cell

can generate power on sunny and cloudy days,

which is tougher than you might think.

In recent years, advances to solar energy technology

have helped it become more accessible

to the average person like you and me,

and to the teams taking part in the World Solar Challenge.

So, basically, the sun provides energy

in the form of photons.

And when those photons will hit your solar ray

when it hits your solar cells,

the photons excite electrons

and those will jump across the band gap

inside your solar cell

and they'll basically flow through your circuit.

So, you get this flow of electrons.

Today, the most popular semiconducting material

used in solar cells is silicon.

Diving in even deeper,

we'll see that crystalline silicon cells

are made of silicon atoms connected to one another

to form a crystal lattice.

Silicon bonds are made of electrons,

the negatively-charged particles in an atom.

These electrons allow it to perfectly bond

to its silicon neighbors,

creating this perfectly organized

lattice structure.

In a solar cell,

there are two layers of silicon.

One layer, n-type, has a negative charge,

and the other layer, p-type, has a positive charge.

Now, each charge needs to be enhanced

to create the energy we're looking for.

And to do that, researchers will dope

or add other elements to the silicon material,

giving it extra electrons,

or creating empty holes for electrons to fill.

The negative charge is usually achieved

by mixing the layer of silicon with phosphorus.

This adds extra electrons to the mix,

allowing more electrons

to roam freely in the lattice.

A positive charge for that p-layer

is achieved by doping that layer with boron,

causing those spaces called holes.

The boundary between the two layers

is called the p-n junction,

while the area around it

is known as the depletion region.

So, now for the fun part.

When light from the sun hits those layers,

the energy from the photons knocks electrons loose.

Because the layers are oppositely charged,

the electrons want to travel

from the n-type layer to the p-type layer

to fill its empty holes.

The electrons create a voltage difference

between either end of the cell.

So, by adding an electric circuit to one end,

the electrons can travel through that circuit,

powering devices along their way

and end up in the p-type layer.

[EXHALES] Okay, we did it.

We made it through the molecular explanation

of how solar cells convert sunlight into electricity.

But typical crystalline silicon PV cells

only convert 18 to 22% of sunlight

into electricity.

And that's clearly not enough.

We want solar cells to be as efficient as possible

so they can power as many things as possible.

And the teams competing in the World Solar Challenge

are already using an advanced material to do so.

The typical material to make solar cells out of is silicon,

and this is a car covered in silicon panels.

They're allowed up to four square meters.

But recently a lot of cars air switching over

to a different material, gallium-arsenide cells,

and they're significantly more efficient.

Gallium-arsenide is a semi-conducting material

made from the elements gallium and arsenic.

Gallium-arsenide solar cells

now hold the world efficiency record

for a single junction solar cell,

with a conversion rate of just around 28.8%.

So what's stopping us from using that in everything?

Well, making a wafer of gallium-arsenide

is considerably more expensive than making a silicon wafer.

The size of the gallium-arsenide array

was 3.56 square meters,

and to cover that size array, you need about 100 grand,

um, to cover the same amount of area,

actually to cover about four square meters.

So even a larger area of silicon,

you'll need about 3 grand,

so there's a huge price difference.

So researchers are still trying to find that perfect solar cell

that is both cost effective and full efficiency.

Innovations like those used in the World Solar Challenge

are going to continue to push the boundaries

of renewable solar technology.

And now that you have a solid grasp

on how solar panels and photovoltaics work,

let's take a closer look at how we can apply

all of this solar tech to a race car.