How we can turn the cold of outer space into a renewable resource | Aaswath Raman

翻译人员: Tianji (Homer) Li 校对人员: psjmz mz

Every summer when I was growing up,

在我小的时候，每到夏天，

I would fly from my home in Canada to visit my grandparents,

我都会从加拿大的家里飞去看望

who lived in Mumbai, India.

住在印度的祖父母。

Now, Canadian summers are pretty mild at best --

加拿大夏季的气候还算宜人——

about 22 degrees Celsius or 72 degrees Fahrenheit

温度通常在 22ºC （72ºF）左右，

is a typical summer's day, and not too hot.

并不算很热。

Mumbai, on the other hand, is a hot and humid place

然而，孟买是个闷热潮湿的地方，

well into the 30s Celsius or 90s Fahrenheit.

夏天的平均气温大概是 30ºC （90ºF）。

As soon as I'd reach it, I'd ask,

每次到了孟买，我都会好奇，

"How could anyone live, work or sleep in such weather?"

“人们怎么能在如此的天气 生活、工作和睡觉呢？”

To make things worse, my grandparents didn't have an air conditioner.

更糟糕的是， 我的祖父母家里没有空调。

And while I tried my very, very best,

但即使我用尽浑身解数，

I was never able to persuade them to get one.

也没能说服他们买一台。

But this is changing, and fast.

但是这种情况正在得到快速改善。

Cooling systems today collectively account for 17 percent

如今，冷却系统的耗能总共占到了

of the electricity we use worldwide.

全球电力供应的 17%，

This includes everything from the air conditioners

其中就包括我在暑假

I so desperately wanted during my summer vacations,

热切渴望拥有的空调系统，

to the refrigeration systems that keep our food safe and cold for us

在超市中保证我们的食品

安全新鲜的制冷系统。

in our supermarkets,

to the industrial scale systems that keep our data centers operational.

以及保证我们的数据中心 正常运行的工业级制冷系统。

Collectively, these systems account for eight percent

这些系统一共贡献了

of global greenhouse gas emissions.

全球温室气体排放量的 8%。

But what keeps me up at night

但是令我夜不能寐的是，

is that our energy use for cooling might grow sixfold by the year 2050,

我们用于冷却的能源 可能在 2050 年之前增加 6 倍，

primarily driven by increasing usage in Asian and African countries.

主要是由于亚洲以及 非洲国家能源消耗的增长。

I've seen this firsthand.

我亲眼目睹了这一切。

Nearly every apartment in and around my grandmother's place

我祖父母家周围的每个公寓

now has an air conditioner.

如今几乎都安装了空调。

And that is, emphatically, a good thing

这对生活在中高温地带的

for the health, well-being and productivity

居民的健康、幸福以及生产活动

of people living in warmer climates.

明显是有益的。

However, one of the most alarming things about climate change

但是，对于气候变化， 最应为我们敲响警钟的是，

is that the warmer our planet gets,

我们的地球越温暖，

the more we're going to need cooling systems --

我们对冷却系统的需求就越大——

systems that are themselves large emitters of greenhouse gas emissions.

而这些系统本身 又是温室气体排放的源头。

This then has the potential to cause a feedback loop,

这就有可能会引起反馈循环，

where cooling systems alone

在本世纪晚些时候，

could become one of our biggest sources of greenhouse gases

单单是这些冷却系统就会成为

later this century.

最大的温室气体来源。

In the worst case,

在最坏的情况下，

we might need more than 10 trillion kilowatt-hours of electricity every year,

到了 2100 年底，每年我们 用来冷却的电能就有可能

just for cooling, by the year 2100.

超过10 万亿千瓦时。

That's half our electricity supply today.

这是如今全球电力供应的一半，

Just for cooling.

还仅仅是用于冷却。

But this also point us to an amazing opportunity.

不过，这也为我们 提供了一个绝佳的机会。

A 10 or 20 percent improvement in the efficiency of every cooling system

把冷却系统的效率提升 10%-20%，

could actually have an enormous impact on our greenhouse gas emissions,

就会对温室气体排放 产生巨大的影响，

both today and later this century.

不论是在今天，还是几十年后。

And it could help us avert that worst-case feedback loop.

并且，还能帮助我们 避免最坏情况下的反馈循环。

I'm a scientist who thinks a lot about light and heat.

我是一名科学家，致力于研究光和热，

In particular, how new materials allow us to alter the flow

尤其是新材料如何能够

of these basic elements of nature

以我们一度难以想象的方式

in ways we might have once thought impossible.

改变这些自然基本元素的流动方式。

So, while I always understood the value of cooling

所以，虽然我非常清楚 冷却系统在炎热的暑期

during my summer vacations,

所扮演的重要角色，

I actually wound up working on this problem

但我之所以对这个问题非常感兴趣，

because of an intellectual puzzle that I came across about six years ago.

是因为六年前我遇到的一个智力题。

How were ancient peoples able to make ice in desert climates?

古代人是怎么 在沙漠气候中制造出冰的？

This is a picture of an ice house,

这是一座冰屋的照片，

also called a Yakhchal, located in the southwest of Iran.

也叫做“冰坑”， 坐落于伊朗的西南部。

There are ruins of dozens of such structures throughout Iran,

伊朗境内遍布着几十处这样的废墟，

with evidence of similar such buildings throughout the rest of the Middle East

中东的其他地方也有 类似建筑存在的证据，

and all the way to China.

并且一直延伸到中国。

The people who operated this ice house many centuries ago,

几世纪前操作冰屋的人

would pour water in the pool you see on the left

会在傍晚太阳落山的时候，

in the early evening hours, as the sun set.

将水倾倒在图中左侧的水池里。

And then something amazing happened.

随后，神奇的一幕发生了。

Even though the air temperature might be above freezing,

即使周围空气的温度可能在冰点以上，

say five degrees Celsius or 41 degrees Fahrenheit,

比如 5ºC （41ºF），

the water would freeze.

水依然会结冰。

The ice generated would then be collected in the early morning hours

人们会在黎明时分收集生成的冰，

and stored for use in the building you see on the right,

储存在图片右侧的建筑中备用，

all the way through the summer months.

整个过程一直重复到夏天结束。

You've actually likely seen something very similar at play

如果你在空气温度 高于冰点的晴朗的夜晚

if you've ever noticed frost form on the ground on a clear night,

注意过地面上的霜，

even when the air temperature is well above freezing.

你就会发现二者的相似之处。

But wait.

但是，等等——

How did the water freeze if the air temperature is above freezing?

水是怎么在零点以上结冰的呢？

Evaporation could have played an effect,

蒸发可能在其中起到了一定的作用，

but that's not enough to actually cause the water to become ice.

但是还不够导致水变成冰。

Something else must have cooled it down.

一定有些别的东西 降低了它的温度。

Think about a pie cooling on a window sill.

想象在窗台上有一块 正在冷却的馅饼。

For it to be able to cool down, its heat needs to flow somewhere cooler.

想让它冷却，它自身的热量 需要传递到凉爽些的地方，

Namely, the air that surrounds it.

也就是它周围的空气中。

As implausible as it may sound,

听起来可能难以置信，

for that pool of water, its heat is actually flowing to the cold of space.

那一池水的热量实际上 扩散到了寒冷的太空中。

How is this possible?

这怎么可能呢？

Well, that pool of water, like most natural materials,

就像大多数天然材料， 这一池的水也会

sends out its heat as light.

以光的形式散发它的热量。

This is a concept known as thermal radiation.

这个概念被称作热辐射。

In fact, we're all sending out our heat as infrared light right now,

实际上，我们现在都在以红外光的形式 向彼此以及我们周围的环境

to each other and our surroundings.

散发自身的热量，

We can actually visualize this with thermal cameras

我们实际上可以利用 热成像仪观察到这一现象，

and the images they produce, like the ones I'm showing you right now.

并生成像这样的图像。

So that pool of water is sending out its heat

所以，那一池水把自身的热量

upward towards the atmosphere.

散播到了上方的大气中。

The atmosphere and the molecules in it

大气以及其中的分子

absorb some of that heat and send it back.

吸收并反射回了部分的热量。

That's actually the greenhouse effect that's responsible for climate change.

而导致气候变化的温室效应 就是这样发生的。

But here's the critical thing to understand.

但很重要的一点在于，

Our atmosphere doesn't absorb all of that heat.

我们的大气不会吸收所有的热量。

If it did, we'd be on a much warmer planet.

如果吸收了，我们将会 住在一个更温暖的星球。

At certain wavelengths,

在某些波长下，

in particular between eight and 13 microns,

尤其是在 8 和 13 微米之间的波长下，

our atmosphere has what's known as a transmission window.

我们的大气相当于一个“传输窗口”。

This window allows some of the heat that goes up as infrared light

这个窗口允许某些热量 以红外光的形式上升，

to effectively escape, carrying away that pool's heat.

或者说逃逸，同时带走水池的热量。

And it can escape to a place that is much, much colder.

并且它会逃逸到十分冷的地方。

The cold of this upper atmosphere

从上层大气

and all the way out to outer space,

到外太空的这段区域，

which can be as cold as minus 270 degrees Celsius,

温度可以低至 -270ºC，

or minus 454 degrees Fahrenheit.

或者 -454ºF。

So that pool of water is able to send out more heat to the sky

所以这一池水向天空释放的热量

than the sky sends back to it.

比天空反射回来的热量要多。

And because of that,

因此，

the pool will cool down below its surroundings' temperature.

这池水会冷却到低于周围的环境温度。

This is an effect known as night-sky cooling

这种效应被称作 “夜空冷却”，

or radiative cooling.

或者“辐射冷却”。

And it's always been understood by climate scientists and meteorologists

这一自然现象的重要性早已被

as a very important natural phenomenon.

气候学家及气象学家所熟知。

When I came across all of this,

当我了解到这些时，

it was towards the end of my PhD at Stanford.

我在斯坦福的博士研究已经接近尾声了。

And I was amazed by its apparent simplicity as a cooling method,

我为如此简单的冷却方法所震惊，

yet really puzzled.

但也十分的困惑。

Why aren't we making use of this?

为什么我们还没有 充分利用这一现象呢？

Now, scientists and engineers had investigated this idea

在过去的数十年中， 科学家和工程师已经对这一想法

in previous decades.

展开了研究。

But there turned out to be at least one big problem.

但是他们发现，至少还需要 解决一个大问题。

It was called night-sky cooling for a reason.

这个现象被称作“夜空冷却”是有原因的。

Why?

为什么呢？

Well, it's a little thing called the sun.

因为有种小东西叫做太阳。

So, for the surface that's doing the cooling,

当地球表面正在冷却时，

it needs to be able to face the sky.

它需要朝向天空。

And during the middle of the day,

在中午时分，

when we might want something cold the most,

在我们最需要冷却什么东西的时候，

unfortunately, that means you're going to look up to the sun.

很遗憾，这些东西也需要面朝太阳。

And the sun heats most materials up

而太阳会将大多数材料加热，

enough to completely counteract this cooling effect.

足以完全抵消这种冷却效果。

My colleagues and I spend a lot of our time

我和同事花费了很多时间

thinking about how we can structure materials

思考如何打造

at very small length scales

一种微型材料——

such that they can do new and useful things with light --

它的尺寸比光本身的波长更小—— 从而利用阳光

length scales smaller than the wavelength of light itself.

做一些新奇且实用的事情。

Using insights from this field,

利用这个领域的知识，

known as nanophotonics or metamaterials research,

即纳米光子学，或超材料研究，

we realized that there might be a way to make this possible during the day

我们首次发现了在白天

for the first time.

让这个构想成为现实的方式。

To do this, I designed a multilayer optical material

为了实现这个目的， 我设计了这张显微图片中的

shown here in a microscope image.

多层光学材料，

It's more than 40 times thinner than a typical human hair.

它比人的头发丝细 40 多倍，

And it's able to do two things simultaneously.

并且能够同时实现两种功能。

First, it sends its heat out

首先，它可以恰到好处的

precisely where our atmosphere lets that heat out the best.

散发出大气能够向外传导的热量。

We targeted the window to space.

我们把这扇窗开向宇宙。

The second thing it does is it avoids getting heated up by the sun.

其次，它不会被太阳加热，

It's a very good mirror to sunlight.

而是可以像镜子一样 高效的反射太阳光。

The first time I tested this was on a rooftop in Stanford

我第一次测试这种材料 是在斯坦福的楼顶，

that I'm showing you right here.

就在图片里的这个位置。

I left the device out for a little while,

我将这个设备放置在室外，

and I walked up to it after a few minutes,

几分钟后，当我走上前查看，

and within seconds, I knew it was working.

就立刻知道它凑效了。

How?

我是怎么知道的呢？

I touched it, and it felt cold.

它摸起来挺凉快的。

(Applause)

（掌声）

Just to emphasize how weird and counterintuitive this is:

为了强调这多么的违反直觉：

this material and others like it

把类似这样的材料

will get colder when we take them out of the shade,

放置在阳光下，

even though the sun is shining on it.

它们的温度反而会降低。

I'm showing you data here from our very first experiment,

这是我们第一次的测试数据，

即使把它放在太阳光下，

where that material stayed more than five degrees Celsius,

or nine degrees Fahrenheit, colder than the air temperature,

材料表面的温度始终维持在 比周围大气温度

even though the sun was shining directly on it.

还要低 5 ºC （9 ºF）的水平。

The manufacturing method we used to actually make this material

我们用来制造这种材料的方法

already exists at large volume scales.

实际上已经规模化了。

So I was really excited,

这让我激动万分，

because not only do we make something cool,

因为我们不仅做出了很酷的东西，

but we might actually have the opportunity to do something real and make it useful.

并且很可能有机会 实现大规模的实际应用。

That brings me to the next big question.

这也引出了下一个大问题。

怎么通过这个想法来节约能源？

How do you actually save energy with this idea?

Well, we believe the most direct way to save energy with this technology

我们相信，这项技术最直接的节能方式

is as an efficiency boost

是提高当今

for today's air-conditioning and refrigeration systems.

空调和制冷系统的效率。

To do this, we've built fluid cooling panels,

为了做到这一点，我们 已经建造了流体冷却板，

like the ones shown right here.

正如图片中展示的一样。

These panels have a similar shape to solar water heaters,

这些节能板看起来很像 太阳能热水器，

except they do the opposite -- they cool the water, passively,

却有着截然相反的功能—— 使用我们发明的材料

using our specialized material.

被动的冷却水。

These panels can then be integrated with a component

然后，这些面板可以与一个

almost every cooling system has, called a condenser,

几乎每个冷却系统 都拥有的部件，冷凝器

to improve the system's underlying efficiency.

进行结合，以提高该系统的潜在效率。

Our start-up, SkyCool Systems,

如图所示，我们的初创公司 SkyCool Systems

has recently completed a field trial in Davis, California, shown right here.

如今已经在加利福尼亚州的 戴维斯市完成了实地测试。

In that demonstration,

在这项演示中，

we showed that we could actually improve the efficiency

我们证明了可以将现场

of that cooling system as much as 12 percent in the field.

冷却系统的效率提高最多 12%。

Over the next year or two,

在未来的一两年内，

I'm super excited to see this go to its first commercial-scale pilots

我非常期待这项技术 能够在空调和制冷领域

in both the air conditioning and refrigeration space.

开展第一个商业规模的试验。

In the future, we might be able to integrate these kinds of panels

在未来，我们也许能够将这类面板

with higher efficiency building cooling systems

与更高效的建筑冷却系统相结合，

to reduce their energy usage by two-thirds.

从而减少三分之二的能源消耗。

And eventually, we might actually be able to build a cooling system

最终，我们也许能够打造

that requires no electricity input at all.

一个完全不需要 电力供应的冷却系统。

As a first step towards that,

作为迈向这一目标的第一步，

my colleagues at Stanford and I

我和斯坦福的同事

have shown that you could actually maintain

已经证明了，通过更好的工程设计，

something more than 42 degrees Celsius below the air temperature

我们可以让材料维持在比气温

with better engineering.

低 42ºC 以上的温度。

Thank you.

谢谢。

(Applause)

（掌声）

So just imagine that --

不妨想象一下——

something that is below freezing on a hot summer's day.

在炎热的夏天，拥有一些 低于冰点的东西。

So, while I'm very excited about all we can do for cooling,

我对于冷却技术的 巨大潜能感到十分激动，

and I think there's a lot yet to be done,

并且我认为仍然有 许多事情需要完成。

as a scientist, I'm also drawn to a more profound opportunity

作为科学家，我也被 这项工作所凸显的

that I believe this work highlights.

意义深远的机会所吸引。

We can use the cold darkness of space

我们可以利用寒冷的黑暗太空

to improve the efficiency

加速地球上每一个

of every energy-related process here on earth.

与能源相关的过程。

One such process I'd like to highlight are solar cells.

我想强调的其中一个工程 就是太阳能电池。

They heat up under the sun

它们会在太阳光下被加热，

and become less efficient the hotter they are.

但随着温度升高，效率会逐渐下降。

In 2015, we showed that with deliberate kinds of microstructures

在 2015 年，我们展示了 在太阳能电池的顶部

on top of a solar cell,

加上一些精心设计的微观结构，

we could take better advantage of this cooling effect

就可以更好的利用冷却效果

to maintain a solar cell passively at a lower temperature.

来使太阳能电池被动的保持低温。

This allows the cell to operate more efficiently.

这保证了电池更高的操作效率。

We're probing these kinds of opportunities further.

我们正在探索更多类似的机会。

We're asking whether we can use the cold of space

我们想知道，是否可以 使用太空中的低温

to help us with water conservation.

来帮助我们节约用水，

Or perhaps with off-grid scenarios.

又或者在离网的状态下实现。

Perhaps we could even directly generate power with this cold.

也许，我们甚至可以 直接利用这种低温来发电。

There's a large temperature difference between us here on earth

地球表面与寒冷的太空之前

and the cold of space.

存在着很大的温差。

That difference, at least conceptually,

至少在概念上，这种差异

could be used to drive something called a heat engine

能够被用来启动所谓的“热力发动机”

to generate electricity.

进行发电。

Could we then make a nighttime power-generation device

我们能不能制造 一个夜间发电装置，

that generates useful amounts of electricity

当太阳能电池不工作的时候，

when solar cells don't work?

来产生大量的替代电能？

Could we generate light from darkness?

我们能不能从黑暗当中产生光？

Central to this ability is being able to manage

这种能力的核心在于

the thermal radiation that's all around us.

管理我们周围的热辐射。

We're constantly bathed in infrared light;

在我们的四周，红外线辐射无处不在；

if we could bend it to our will,

如果我们能够让它为我们所用，

we could profoundly change the flows of heat and energy

就可以彻底改变遍布在我们身边的

that permeate around us every single day.

热量和能量流动。

This ability, coupled with the cold darkness of space,

这种能力，再加上 宇宙的寒冷黑暗，

points us to a future where we, as a civilization,

能够指引我们的未来—— 作为一个文明，

might be able to more intelligently manage our thermal energy footprint

我们或许能够 在非常大的尺度上更智能的管理

at the very largest scales.

我们的热能足迹。

As we confront climate change,

在面对气候变化时，

I believe having this ability in our toolkit

我相信，在我们的工具箱中 拥有这样一种能力

will prove to be essential.

将被证明是至关重要的。

So, the next time you're walking around outside,

因此，下一次你在户外散步，

yes, do marvel at how the sun is essential to life on earth itself,

在惊叹太阳对地球的生命 如此重要的同时，

but don't forget that the rest of the sky has something to offer us as well.

也不要忘记，天空的其他部分 也可以为我们提供一些东西。

Thank you.

谢谢。

(Applause)

（掌声）