parties to the United Nations

2015年12月 国連の 気候変動枠組条約締約国会議が

Framework Convention on Climate Change

ある同意にこぎ着けた

reached a landmark agreement.

ほぼすべての国と言える195ヵ国が―

One hundred and ninety-five nations,

公式に気候危機と闘うことを宣言

practically every country in the world,

これが“パリ協定”よ

were going to officially fight against the climate crisis.

この協定の目的は 地球の気温上昇をセ氏２度以内に抑えること

This is now known as the Paris Agreement.

地球を気温上昇から救うには―

And the main goal of that treaty

毎年 数十億トンの二酸化炭素の除去が必要よ

is to limit global temperature rise

[番組ホスト　マレン･ハンスバーガー]

to well below two degrees Celsius.

そのため各国はネガティブエミッションや 低炭素化技術に投資

But in order to save the Earth from rising temperatures,

インフラも強化している

we need to remove billions of metric tons of carbon

この劇的な変化の中 太陽エネルギーは最先端

from our atmosphere every year.

この地球上で最も豊富なエネルギー資源だからよ

To help accomplish this,

ではソーラーパネルとは何か どんな仕組みになっているのか？

countries have been investing in negative emissions

太陽電池セルから説明するわ

and low-carbon technologies,

これが日光を変換する太陽電池セル

as well as adding infrastructure to support them.

太陽電池セルは 単に“太陽電池”とも呼ばれ―

And solar energy is already at the forefront

１つのセルは 切手より小さく 髪の毛より薄い

of this renewable revolution.

１つの電池で 生成できるのは0.5ボルト

Why? Because the sun is the most abundant

出力を増やすには セルをつなげて 太陽電池モジュールを作り―

energy resource we have on our planet.

より大きなソーラーパネルを作る

But how much do you know about solar panels

パネルの大きさや その原材料 利用できる日光の量に応じ―

and how exactly do they work?

パネルの出力は変化する

Well, let's start with photovoltaic cells.

パネルが生み出すエネルギー量は キロワット時で測定

These cells are what convert sunlight into electricity.

１時間で100ワットを生成するなら―

A single photovoltaic cell, also called a solar cell,

100ワット時または0.1キロワット時となる

can be smaller than a postage stamp

モジュールやパネルをさらにつなげて 太陽電池アレイも作れる

and thinner than a human hair.

太陽光発電住宅や宇宙船でも 使われている構造物よ

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

アレイを１ヵ所に集中させれば 太陽光発電都市さえ造れる

So, to increase this energy output,

アレイで覆われた一帯を見たことはあるはず

you can combine these solar cells

“ソーラーファーム”や “ソーラーパーク”と呼ばれる

to create solar modules

最大規模は インドのパヴァガダ･ソーラーパーク

and even slightly-bigger solar panels.

面積は53平方キロ以上で ２ギガワットの電気を生成できる

Depending on their size

70万世帯の電気を供給できるの

and the materials they're made of,

2018年末までに世界中の太陽電池の出力量は 480ギガワットを超え―

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

風力に次ぐ 第２位の再生可能エネルギーとなってる

the power output of solar panels can vary.

すでに豊富なエネルギー源ではあるけど 研究者によると2050年までには―

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

世界の太陽光発電量は 8,500ギガワットを超えるらしい

is measured in kilowatt-hours.

パリ協定の削減目標を達成するのに 必要な技術拡張よ

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

いまだに太陽光発電が 世界に浸透していないのは―

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

技術に制限をもたらす３つの要素があるため

But you can combine modules and panels even further

費用と効率性 そして信頼性

to create solar arrays.

効率性とは １枚のパネルが どの程度の太陽エネルギーを生成できるか

These structures are what are used to power homes

費用については次のとおり

and even spacecraft.

太陽電池の製造 配送 および設置コストに対して―

And if you gather enough solar arrays in one place,

何ワットの電力を見返りとして生み出せるのか

you can even power cities.

そして最後に 晴れでも曇りでも 太陽電池が発電しなければならない

You may have seen swaths of land

思ったより難しいわ

covered in solar arrays.

近年では技術が進み―

These are often called solar farms or solar parks.

私たちのような一般人も 太陽光技術を利用できる

The largest solar park built to date

ワールドソーラーチャレンジへの参加も可能

is the Pavagada Solar Park in India.

太陽は光子というエネルギーを作るの

It spans over 53 square kilometers

[スタンフォード　コーリ･ブレンデル]

and can produce two gigawatts of electricity,

この光子がアレイやパネルに当たり―

which is enough to power 700,000 households.

発生した電子が太陽電池の バンドギャップ間を飛び移り

By the end of 2018,

回路を流れる

the world's installed capacity of solar cells

これが電子の流れ

reached over 480 gigawatts,

現在 太陽電池に最もよく使われる 半導体物質が

representing the second largest

シリコンよ

renewable electricity source after wind.

結晶シリコンを詳しく見ていくと―

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

結晶した原子が結びつき 結晶格子ができている

but researchers are projecting that by 2050

シリコンは原子内の負帯電粒子で結びついてるの

the world's solar cell capacity

この粒子がシリコンを完全に結びつけ―

could reach over 8,500 gigawatts.

格子の構造を生み出している

This is the kind of expansion we need

太陽電池内にシリコンの層は２つ

to reach the carbon-cutting goals

n型には負の電荷が集まり―

of the Paris Agreement.

もう一方のp型には正の負荷が集まる

The big reason why photovoltaic cells

エネルギーを生むには両方の電荷が必要となる

haven't taken over the world yet

そのためには シリコンに他の要素を加えることで―

is because the technology is still limited

余分な電子を生むか 電子で満たす穴を作らないといけない

by three important factors.

負の電荷は シリコン層にリンを混ぜると発生する

Cost, efficiency and reliability.

これで余分な電子ができ 格子内を自由に移れるようになる

Efficiency basically just means

正の負荷は p層にホウ素を混ぜることで発生し―

how well a solar panel is able

“ホール”を生み出す

to convert sunlight into electricity,

２つの層の境界はpn接合といい―

and cost can be defined by, well,

この付近は空乏層と呼ばれている

how much goes into making a solar cell

次は楽しい話よ

like materials, manufacturing,

太陽光がこれらの層に当たると 光子のエネルギーが電子を分解

distribution, installation,

各層に逆の電荷がかかり―

relative to how much wattage is generated

電子がn層からp層へ移動して ホールを満たすためよ

in return for that investment.

電子はセルの間に電位差を生み出す

And lastly, we have to make sure a solar cell

そこで電気回路を追加すると 電子はその中を移動し―

can generate power on sunny and cloudy days,

デバイスに電力を与えてp層へ行き着く

which is tougher than you might think.

太陽電池が どうやって太陽光を 電気に変えるかの説明は以上よ

In recent years, advances to solar energy technology

通常の結晶シリコン型太陽電池は―

have helped it become more accessible

日光量の18～22％しか電気に変えられない

to the average person like you and me,

明らかに足りない

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

より多くの対象へ電力を供給するには 効率性を上げる必要がある

So, basically, the sun provides energy

ワールドソーラーチャレンジでは―

in the form of photons.

そのための先進的な材料を使用している

And when those photons will hit your solar ray

通常の太陽電池はシリコン製であり

when it hits your solar cells,

[デレク･ミューラー]

the photons excite electrons

この車はシリコンパネルで覆われている

and those will jump across the band gap

最大で４平方メートルまで使える

inside your solar cell

ただ 最近の車は 動力源を切り替えている

and they'll basically flow through your circuit.

GaAs太陽電池という 大変 効率的なものだ

So, you get this flow of electrons.

ガリウムヒ素は半導体の材料で―

Today, the most popular semiconducting material

ガリウムとヒ素でできている

used in solar cells is silicon.

単一の電池としての効率性では GaAs太陽電池が世界一で―

Diving in even deeper,

そのエネルギー変換率は約28.8％

we'll see that crystalline silicon cells

では なぜ広く使われていないのか？

are made of silicon atoms connected to one another

ガリウムヒ素のウェハは シリコンウェハより費用が高いの

to form a crystal lattice.

ガリウムヒ素のアレイは3.56平方メートル

Silicon bonds are made of electrons,

これにかかる費用は約10万ドル

the negatively-charged particles in an atom.

４平方メートル分をカバーする必要がある

These electrons allow it to perfectly bond

シリコン製なら3,000ドルで より広い面積をカバーできる

to its silicon neighbors,

コストが安く 効率性に優れた太陽電池を―

creating this perfectly organized

研究者は今も考え続けている

lattice structure.

ワールドソーラーチャレンジは―

In a solar cell,

太陽エネルギーの可能性を探り続けていく

there are two layers of silicon.

ソーラーパネルや太陽光発電が理解できたら―

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

レースカーへの太陽光技術の応用を見てね

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.