其實人類一年活動所需能源，等同於太陽照射地球一小時所產生的所有能量。因此，以目前科技來說，人類發展太陽能，還有很大進步空間。而葉子行光合作用轉換太陽能、產生氧氣、水和葡萄糖的過程，指引了重要方向。
若能複製出如綠葉般充份轉換太陽能量的系統，順利將水(H2O)分解成氧與氫，就能進一步利用氫，發展乾淨能源將大有可為。其實現在已有相關分解水的技術，但所費不貲，且需嚴格控制實驗環境，過程不易。
若計劃主持人詹姆斯‧巴伯與研究團隊，能成功運用人工造葉系統、轉換太陽能量的10%，評估人類能源使用量，未來只需地表面積0.16%的大小，能源供應到2030年前都沒有問題。而這項人工造葉系統也能擺置在廣大沙漠地區，減少與人爭地的困擾。
其他科學家，如巴伯的同事詹姆斯‧杜蘭，美國麻省理工學院的丹‧諾索拉，也在研究如何製造出穩定、造價低的催化劑，協助分解水、得到氫。美國、荷蘭也有類似的太陽能計劃。其中，美國投入一年3500萬美元(約新台幣10億)，荷蘭則是4000萬歐元(約新台幣18億)。
MIT's artificial leaf is ten times more efficient than the real thing
The device is an advanced solar cell, no bigger than a typical playing card, which is left floating in a pool of water. Then, much like a natural leaf, it uses sunlight to split the water into its two core components, oxygen and hydrogen, which are stored in a fuel cell to be used when producing electricity.
Nocera's leaf is stable -- operating continuously for at least 45 hours without a drop in activity in preliminary tests -- and made of widely available, inexpensive materials -- like silicon, electronics and chemical catalysts. It's also powerful, as much as ten times more efficient at carrying out photosynthesis than a natural leaf.
With a single gallon of water, Nocera says, the chip could produce enough electricity to power a house in a developing country for an entire day. Provide every house on the planet with an artificial leaf and we could satisfy our 14 terrawatt need with just one gallon of water a day.
Those are impressive claims, but they're also not just pie-in-the-sky, conceptual thoughts. Nocera has already signed a contract with a global megafirm to commercialise his groundbreaking idea. The mammoth Indian conglomerate, Tata Group has forged a deal with the MIT professor to build a small power plant, the size of a refrigerator, in about a year and a half.
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| Due to deforestation, new type of energy is needed for human |
This isn't the first ever artificial leaf, of course. The concept of emulating nature's energy-generating process has been around for decades and many scientists have tried to create leaves in that time. The first, built more than ten years ago by John Turner of the US National Renewable Energy Laboratory, was efficient at faking photosynthesis but was made of rare and hugely expensive materials. It was also highly unstable, and had a lifespan of barely one day.
For now, Nocera is setting his sights on developing countries. "Our goal is to make each home its own power station," he said. "One can envision villages in India and Africa not long from now purchasing an affordable basic power system based on this technology."
( Note 註 : Global Deforestation Estimates 全球森林砍伐預估, In his excellent Deforesting the earth: from prehistory to global crisis, Williams estimates that humans have cleared some 1.8 billion hectares over the past 5,000 years, or an average net loss of 360,000 hectares per year. So it is difficult to find an energy system without generating CO2, only Artificial Leaf can avoid to generate more of other kind of air components not meet with the need of long term of human living environment )
