So, is it possible that one day the world could be completely reliant on solar energy?

有沒有可能有一天全世界只依賴太陽能？

To answer that question, we first need to examine how solar panels convert solar energy to electrical energy.

要回答這個問題，我們需要先瞭解太陽能板如何將太陽能轉換成電能。

Solar panels are made up of smaller units called solar cells.

太陽能板是由太陽能電池的小單元組成。

The most common solar cells are made from silicon, a semiconductor that is the second most abundant element on Earth.

最常見的太陽能電池是矽元素組成的，是地球上第二豐富的半導體元素。

In a solar cell, crystalline silicon is sandwiched between conductive layers.

在太陽能電池中，晶體矽被夾在導電層之間。

Each silicon atom is connected to its neighbors by four strong bonds, which keep the electrons in place so no current can flow.

每個矽原子以四個鍵結互相鍵結，讓電子固定而沒有電流產生。

Here's the key: a silicon solar cell uses two different layers of silicon.

關鍵點在於：矽太陽能電池會用到不同的兩層矽。

An n-type silicon has extra electrons, and p-type silicon has extra spaces for electrons, called holes.

N 型矽有多餘的電子，P 型矽有多餘的電子空間，稱為孔洞。

Where the two types of silicon meet, electrons can wander across the p/n junction, leaving a positive charge on one side and creating negative charge on the other.

當這兩種矽會合，電子可以通過之間的 P/N 連結讓其中一邊帶正電，而另一邊帶負電。

You can think of light as the flow of tiny particles called photons, shooting out from the Sun.

你可以把光想成小粒子的流動，稱為光子，從太陽發射過來。

When one of these photons strikes the silicon cell with enough energy, it can knock an electron from its bond, leaving a hole.

當光子用了足夠能量撞擊矽電池，可以撞走鍵結上的一個電子，並留下一個洞。

The negatively charged electron and location of the positively charged hole are now free to move around, but because of the electric field at the p/n junction, they'll only go one way: the electron is drawn to the n-side, while the hole is drawn to the p-side.

帶負電的電子和帶正電的孔洞現在可以自由活動，但由於在 P/N 連結的電場，它們只會往一個方向走：電子被拉去 N 端而孔洞被拉去 P 端。

The mobile electrons are collected by thin metal fingers at the top of the cell.

移動電子被電池上方的薄金屬收集。

From there, they flow through an external circuit, doing electrical work, like powering a lightbulb, before returning through the conductive aluminum sheet on the back.

它們從那裡流至一個外部電路運作電力，像電燈泡發亮一樣，再經導電的鋁板回到後面。

Each silicon cell only puts out half a volt, but you can string them together in modules to get more power.

每單位矽面板只提供半伏特，我們可以把它們串連成模組，得到更多能量。

Twelve photovoltaic cells are enough to charge a cellphone, while it takes many modules to power an entire house.

12 個光伏電池夠幫一支手機充電，而要有許多模組才能供應整棟房子的用電。

Electrons are the only moving parts in a solar cell, and they all go back where they came from. There's nothing to get worn out or used up, so solar cells can last for decades.

太陽能電池中的電子僅做小部分移動，然後回到原本的位置，不會有任何耗盡或是磨損，所以太陽能電池的壽命能達十年以上。

So, what's stopping us from being completely reliant on solar power?

那為什麼我們不完全依賴太陽能呢？

There are political factors at play, not to mention businesses that lobby to maintain the status quo.

除了有政治因素在其中，更別提既得利益者想要維持現狀。

But for now, let's focus on the physical and logistical challenges, and the most obvious of those is that solar energy is unevenly distributed across the planet—some areas are sunnier than others.

不過現在，讓我們專心討論物理和邏輯上的挑戰，其中最明顯的是，太陽能並不是均勻的分佈在地球——有些地方獲得較多光照。

It's also inconsistent. Less solar energy is available on cloudy days or at night.

它也是不一致的，像是在陰天和晚上能取得的太陽能也比較少。

So a total reliance would require efficient ways to get electricity from sunny spots to cloudy ones, and effective storage of energy.

所以要完全依賴太陽能，需要一個能在陰天晴天都可有效獲得電力的方法，並有效的儲存能量。

The efficiency of the cell itself is a challenge, too.

電池本身的效能也是一個挑戰。

If sunlight is reflected instead of absorbed, or if dislodged electrons fall back into a hole before going through the circuit, that photon's energy is lost.

如果陽光被反射多於吸收，或可能脫落電子在形成電路前又回到洞裡，光子產生的能量就損失了。

The most efficient solar cell yet still only converts 46% of the available sunlight to electricity, and most commercial systems are currently 15-20% efficient.

即使是效能最好的太陽能電池，也只能將 46% 陽光轉成電力，一般商業用的系統更只有 15-20% 轉換率。

In spite of these limitations, it actually would be possible to power the entire world with today's solar technology.

儘管有著這些限制，還是有可能用太陽能科技提供全世界能源。

We'd need the funding to build the infrastructure and a good deal of space. Estimates range from tens to hundreds of thousands of square miles, which seems like a lot, but the Sahara Desert alone is over 3 million square miles in area.

我們需要資金來建設和理想的空間環境，估計要幾萬或幾十萬平方英里，看起來好像很大，但其實光是撒哈拉沙漠就有超過三百萬平方英里的面積。

Meanwhile, solar cells are getting better, cheaper, and are competing with electricity from the grid, and innovations, like floating solar farms, may change the landscape entirely.

同時，太陽能電池變得效能更好、更便宜，足以跟現在的電力系統競爭，再加上不斷創新，像是漂浮太陽能農場，可能完全改變能源生態。

Thought experiments aside, there's the fact that over a billion people don't have access to a reliable electric grid, especially in developing countries, many of which are sunny.

在實驗之外，實際上有上億人口沒穩定的電力可以使用，尤其是開發中國家，其中許多國家都氣候晴朗。

So in places like that, solar energy is already much cheaper and safer than available alternatives, like kerosene.

所以像是這樣的地方，太陽能比起其他能源是較便宜和安全的，舉例來說，像是煤油。

For say, Finland or Seattle, though, effective solar energy may still be a little way off.

不過，像是芬蘭或西雅圖這樣的城市，離有效的使用太陽能可能還有點遙遠。