We have some good reasons to completely switch over to solar power.
我们有非常充分的理由完全的使用太阳能。
It's cheaper in many cases, and definitely more sustainable than our dependance on traditional power plants
从各方面来看，它比较便宜，并且毫无疑问的，比起其它我们所依赖的传统发电厂，要更加永续发展，
that use resources like coal, which will eventually run out.
这些发电厂使用如煤炭之类的资源，但煤炭终究会耗尽。
So why don't we replace these traditional plants with solar energy?
那么为何我们不以太阳能取代这些传统的发电厂呢?
Because there's one factor that makes solar power very unpredictable: cloud cover.
因为其中一个原因使得太阳能非常不好预测：那就是云的遮挡。
As the sun's rays move towards Earth, some get absorbed by the Earth's atmosphere,
当太阳光朝着地球照射时，有些会被地球的大气层所吸收，
some are reflected back into outer space, but the rest make it to the Earth's surface.
有些会反射回到外太空，而剩下的才会照射到地球表面。
The ones that aren't deviated are called direct irradiance.
那些没有被反射回的称做直射辐照度。
The ones that are deflected by clouds are called diffuse irradiance.
而那些因为云层而偏射的则称作散射辐照度。
And those rays that first get reflected by a surface, like a nearby building,
那些直接被表面反射的太阳光，例如旁边的高楼大厦，
before reaching the solar energy system are called reflected irradiance.
没能到达太阳能系统的称做反射辐照度。
But before we can examine how clouds affect the sun's rays and electricity production,
但是，在我们能够观测云层如何影响太阳光及电力的产生之前，
let's see how these solar energy systems work.
我们来看看太阳能系统的工作原理。
First up, we have solar towers.
首先，我们需要有太阳能塔。
These are made up of a central tower surrounded by a huge field of mirrors
这个高塔是由一个很大的、竖满了很多镜子的空地所围绕，
that track the sun's path and focus only the direct rays onto a single point on the tower, kind of like an eager beachgoer.
用来追踪太阳的轨迹及焦点，并且直接照射到塔上固定的一点，就有点像是一个非常热切的海滩游客一般。
The heat generated by these rays is so immense that it can be used to boil water
这些光线会产生非常巨大的热量，足以使水沸腾，
producing steam that drives a traditional turbine, which makes electricity.
并且产生水蒸气来推动传统的涡轮机而发电。
But when we say solar energy systems, we're usually talking about photovoltaics, or solar panels,
但当我们说太阳能系统时，我们通常是指光伏电池，或是太阳能面板，
which are the systems most commonly used to generate solar power.
这些也是非常普遍的太阳能发电系统。
In solar panels, photons from the sun's rays hit the surface of a panel,
在太阳能板里，从太阳光而来的光子打到面板表面，
and electrons are released to get an electric current going.
释放出电子并且产生流动的电流。
Solar panels can use all types of irradiance, while solar towers can only use direct irradiance,
太阳能板可以接受全部的辐射来源，而太阳能塔只能接受直射，
and this is where clouds become important because depending on their type and location relative to the sun,
这就是为什么云层变得如此重要，因为会非常依赖它们的种类及地点与太阳之间的关系，
they can either increase or decrease the amount of electricity produced.
它们可以直接增加或减少电量的产生。
For instance, even a few cumulus clouds in front of the sun
例如，只要有少量的积云挡在太阳前方，
can reduce the electricity production in solar towers to almost zero because of this dependence on direct rays.
就会减少太阳塔中电量的产生，甚至几乎为零，因为它非常倚赖直接照射的光线。

In solar panels, those clouds would decrease energy output as well,
太阳能板方面，这些云层也会减少能量的输出，
though not as much because solar panels can use all types of irradiance.
只不过没有这么多，因为太阳能板可以接收各类型的辐射。
However, all this depends on the clouds exact positioning.
不过，这全部都需看云层实际的位置而定。
Due to reflection, or a particular phenomeon called Mie scattering,
由于反射，或是称做米氏散射的特殊现象，
the sun's rays can actually be focused forward by clouds
太阳光其实可以在云层前端聚焦，
to create a more than 50% increase in the solar irradiance reaching a solar panel.
产生多于50%的太阳辐射增加量到太阳能板上。
If this potential increase isn't accounted for, it could damage the solar panel. Why does this matter?
如果没有考虑这些潜在的增加，可能会损坏太阳能板。这为什么重要呢？
Well, you wouldn't want this lesson to stop just because a cloud passed over the panel on your roof.
我想你应该不希望，因为云层通过顶楼的太阳能板使这堂课就这么结束了。
In solar towers, huge tanks of molten salt or oil can be used to store any excess heat and use it when needed,
在太阳塔中，有一个大缸子的熔盐或油，可以用来储存多余的热能，在需要的时候使用，
so that's how they manage the problem of fluctuating solar irradiance to smooth out electricity production.
所以这就是他们如何处理这个问题：利用照度的起伏不定来调整发电量。
But in the case of solar panels, there currently isn't any way to affordably store extra energy.
但在太阳能板这方面，目前没有任何可行的方法来储存多余的能量。
That's where traditional power plants come in because to correct for any fluctuations in these solar powered plants,
这就是为何传统发电厂要存在，因为这可以补足任何太阳能电厂的浮动，
extra electricity from traditional sources always needs to be available.
传统发电多余的电量来源必须保持随时可以供给的状态。
But then why aren't these tradtional power plants just used as a backup,
但是为何这些传统发电厂不用来当做备用，
instead of us humans depending on them as our main sources of energy?
而是人们却倚赖其成为主要能量来源呢？
Because it's impossible for an employee at a coal fired or a nuclear plant
因为对在火力发电厂或核能发电厂的员工而言，
to turn a knob to produce more or less electricity depending on how many clouds there are in the sky.
依据目前天空有多少云来调整应该输出的电量是不可能的。
The response time would simply be too slow.
反应时间会太慢。
Instead, to accommodate these fluctuations, some extra electricity from traditional power plants is always being produced.
相反，为了补足这些浮动，传统发电厂多余的电力是必须随时保持供应的。
On clear sky days, that extra electricity might be wasted,
天气晴朗时，多余的电力或许浪费了，
but when cloudy skies prevail, it's what fills the gap.
但当阴天来临，这就是派上用场的时刻。
This is what we currently depend on for a constant supply of energy.
这就是我们现在依赖一个能持续供给的能源。
For this reason, a lot of researchers are interested in forcasting the motion and formation of clouds
就这个理由看来，有很多的研究者对于预测云的动态和形成非常有兴趣。
through satellite images or cameras that look up at the sky to maximize the energy from solar power plants and minimize energy waste.
他们是利用卫星云图或是拍摄天空的相机来完成的，因为可以最大化使用太阳能发电厂并最小化能源的浪费。
If we could accomplish that, you'd be able to enjoy this video powered solely by the sun's rays, no matter what the weather,
如果我们可以完成这些，你也就可以纯以太阳能所供的电来享受这部影片，不论在任何天气状况下。
although if the sun is shining, you may be tempted to venture outside to go and do a different kind of cloud gazing.
但阳光灿烂时，你会想向外跑，去体会不同样的欣赏云层。