It's a tall order: Over the next few decades, the world will need to wean itself from dependence on fossil fuels and drastically reduce greenhouse gases. Current technology will take us only so far; major breakthroughs are required.

    What might those breakthroughs be? Here's a look at five technologies that, if successful, could radically change the world energy picture.

    They present enormous opportunities. The ability to tap power from space, for instance, could jump-start whole new industries. Technology that can trap and store carbon dioxide from coal-fired plants would rejuvenate older ones.

    Success isn't assured, of course. The technologies present difficult engineering challenges, and some require big scientific leaps in lab-created materials or genetically modified plants. And innovations have to be delivered at a cost that doesn't make energy much more expensive. If all of that can be done, any one of these technologies could be a game-changer.

    SPACE-BASED SOLAR POWER

    For more than three decades, visionaries have imagined tapping solar power where the sun always shines -- in space. If we could place giant solar panels in orbit around the Earth, and beam even a fraction of the available energy back to Earth, they could deliver nonstop electricity to any place on the planet.

    The technology may sound like science fiction, but it's simple: Solar panels in orbit about 22,000 miles up beam energy in the form of microwaves to earth, where it's turned into electricity and plugged into the grid. （The low-powered beams are considered safe.） A ground receiving station a mile in diameter could deliver about 1,000 megawatts -- enough to power on average about one million U.S. homes.

    The cost of sending solar collectors into space is the biggest obstacle, so it's necessary to design a system lightweight enough to require only a few launches. A handful of countries and companies aim to deliver space-based power as early as a decade from now.

    ADVANCED CAR BATTERIES

    Electrifying vehicles could slash petroleum use and help clean the air （if electric power shifts to low-carbon fuels like wind or nuclear）. But it's going to take better batteries.

    Lithium-ion batteries, common in laptops, are favored for next-generation plug-in hybrids and electric vehicles. They're more powerful than other auto batteries, but they're expensive and still don't go far on a charge; the Chevy Volt, a plug-in hybrid coming next year, can run about 40 miles on batteries alone. Ideally, electric cars will get closer to 400 miles on a charge. While improvements are possible, lithium-ion's potential is limited.

    One alternative, lithium-air, promises 10 times the performance of lithium-ion batteries and could deliver about the same amount of energy, pound for pound, as gasoline. A lithium-air battery pulls oxygen from the air for its charge, so the device can be smaller and more lightweight. A handful of labs are working on the technology, but scientists think that without a breakthrough they could be a decade away from commercialization.

    UTILITY STORAGE

    Everybody's rooting for wind and solar power. How could you not? But wind and solar are use-it-or-lose-it resources. To make any kind of difference, they need better storage.

    Scientists are attacking the problem from a host of angles -- all of which are still problematic. One, for instance, uses power produced when the wind is blowing to compress air in underground chambers; the air is fed into gas-fired turbines to make them run more efficiently. One of the obstacles: finding big, usable, underground caverns.

    Similarly, giant batteries can absorb wind energy for later use, but some existing technologies are expensive, and others aren't very efficient. While researchers are looking at new materials to improve performance, giant technical leaps aren't likely.

    Lithium-ion technology may hold the greatest promise for grid storage, where it doesn't have as many limitations as for autos. As performance improves and prices come down, utilities could distribute small, powerful lithium-ion batteries around the edge of the grid, closer to customers.

    There, they could store excess power from renewables and help smooth small fluctuations in power, making the grid more efficient and reducing the need for backup fossil-fuel plants. And utilities can piggy-back on research efforts for vehicle batteries.

    CARBON CAPTURE AND STORAGE

    Keeping coal as an abundant source of power means slashing the amount of carbon dioxide it produces. That could mean new, more efficient power plants. But trapping C02 from existing plants -- about two billion tons a year -- would be the real game-changer.

    Techniques for modest-scale CO2 capture exist, but applying them to big power plants would reduce the plants' output by a third and double the cost of producing power. So scientists are looking into experimental technologies that could cut emissions by 90% while limiting cost increases.

    Nearly all are in the early stages, and it's too early to tell which method will win out. One promising technique burns coal and purified oxygen in the form of a metal oxide, rather than air; this produces an easier-to-capture concentrated stream of CO2 with little loss of plant efficiency. The technology has been demonstrated in small-scale pilots, and will be tried in a one-megawatt test plant next year. But it might not be ready for commercial use until 2020.

    NEXT-GENERATION BIOFUELS

    One way to wean ourselves from oil is to come up with renewable sources of transportation fuel. That means a new generation of biofuels made from nonfood crops.

    Researchers are devising ways to turn lumber and crop wastes, garbage and inedible perennials like switchgrass into competitively priced fuels. But the most promising next-generation biofuel comes from algae.

    Algae grow fast, consume carbon dioxide and can generate more than 5,000 gallons a year per acre of biofuel, compared with 350 gallons a year for corn-based ethanol.

    Algae-based fuel can be added directly into existing refining and distribution systems; in theory, the U.S. could produce enough of it to meet all of the nation's transportation needs.

    But it's early. Dozens of companies have begun pilot projects and small-scale production. But producing algae biofuels in quantity means finding reliable sources of inexpensive nutrients and water, managing pathogens that could reduce yield, and developing and cultivating the most productive algae strains.

    這是一個離譜的要求：在今后幾十年里，世界需要逐步擺脫對化石燃料的依賴，顯著減少溫室氣體。目前的技術只能讓我們走到這一步了，我們需要擁有重大的技術突破。

    這些突破可能是些什么？本文列出了五項技術，如果成功，它們將會大大改變世界的能源格局。

    這些技術能帶來巨大的機遇。例如，從太空獲取能量的技術可能迅速催生全新的產業。從火電廠捕獲和儲存二氧化碳的技術可能會令較為老舊的電廠重獲新生。

    當然，這些技術并不一定能取得成功，它們目前都面臨著不少難題，一些技術需要在實驗室創造的材料和或轉基因植物方面實現一些重大突破。而且，創新的成本不能讓能源變得太貴。如果能做到這一切，其中任何一項技術都可以改變游戲規則。

    太空利用太陽能

    30多年來，夢想家就一直設想在太陽永遠能照耀到的地方──太空中──利用太陽能。如果我們能在環繞地球的軌道上安置巨大的太陽能電池板，將其中哪怕是一小部分的可用能源傳回地球，它們可以向地球上的任何地方提供不間斷的電力。

    這項技術聽起來可能像是科幻小說，但其實很簡單：在22,000英里之外的太陽能電池板將能源以微波的形式傳回地球，然后轉化為電力并進入到電網中。（低能量的光束被認為是安全的。）直徑1英里的地面接收站可以提供約1,000兆瓦電力，足以供應平均約100萬戶美國家庭的使用。

    將太陽能收集器送至太空的成本是最大的障礙，因此有必要設計重量足夠輕，可以減少發射次數的系統。已經有些國家和公司希望最早在未來10年內提供這種太空電力。

    高級汽車電池

    電動汽車可以降低石油消耗量，有助于空氣清潔（如果電力來自于風能和原子能等低碳燃料的話）.但它需要使用更好的電池。

    筆記本電腦中常用的鋰離子電池是下一代充電式混合動力車和電動車的理想之選。它們比其它汽車電池的電力更充足，但也更貴，不過充電后的行駛距離仍不夠遠；將于明年上市雪佛蘭（Chevy） Volt混合動力車憑電池可行駛約40英里。理想情況下，電動車充電一次最好能行駛近400英里。盡管仍有改進的空間，但鋰離子電池的潛力有限。

    作為一種替代產品，鋰空氣電池的性能是鋰離子電池的10倍，可以提供與汽油同等的能量。鋰空氣電池從空氣中吸收氧氣充電，因此這種電池可以更小、更輕。不少實驗室都在研究這種技術，但科學家認為，如果沒有重大突破，要想實現商用可能還需要10年。

    電力儲存技術

    所有人都在支持風能和太陽能技術，你怎能置身事外？但風能和太陽能是那種要么利用要么流失的資源。要改變現狀，它們需要更好的儲存技術。

    科學家正在從諸多角度應對這個問題，但各個方面都面臨難題。舉例來說，一項技術是通過風能將地下洞穴內的空氣壓縮產生電能；將空氣輸送至燃氣渦輪機以提高燃燒功效。這其中面臨的一個障礙是：要尋找到大空間以及可用的地下洞穴。

    類似的，還有能夠吸收風能待日后使用的巨型電池，但當前的一些技術成本昂貴，其他技術則不是很有效率。盡管研究人員正在尋找新材料以提高性能，但要出現顯著技術飛躍的可能性不大。

    鋰離子技術可能是電網存儲前景最好的技術，在這個領域內該技術不會面臨像在汽車業中那樣多的限制。隨著性能提高和價格降低，公共事業機構可能會向電網邊緣，較為靠近用戶的地方輸送小體積大容量的鋰離子電池。

    這樣，這些鋰離子電池可以從可再生能源中存儲多余的能源，有助于平抑電能供應的小波動，提高電網的效率，降低對備用火電廠的需求。公用事業機構可以利用汽車電池的研究成果。

    碳捕捉和儲存技術

    繼續將煤炭作為一種主要的能源意味著需要努力去降低碳燃燒生成的二氧化碳。這可能意味著要建設更高效的新發電廠。但從當前的電廠捕捉二氧化碳（每年大約為20億噸）可能是一個真正能夠改變游戲規則的技術。

    目前已經出現了小規模的二氧化碳捕捉技術，但如果將這些技術用于大型發電廠會導致發電量減少三分之一，并導致發電成本增長一倍。因此，科學家正在尋找既能夠將碳排放量降低90%,又能限制成本增長的試驗性技術。

    幾乎所有技術目前都處于初步階段，目前斷言哪種方法能夠最終勝出還為時過早。一個前景看好的技術是以金屬氧化物的形式燃燒煤炭和純凈氧，而不是在空氣中燃燒；這種方法會產生較容易捕捉的二氧化碳集中氣流，幾乎不會影響電廠的效率。這種技術已經在小規模試點項目中進行了展示，明年將用于一個裝機容量為一百萬瓦的試驗電廠。但2020年之前，這種技術可能還難以投入商用。

    下一代生物燃料

    一個令我們逐步擺脫對石油依賴的途徑就是研制出可再生的運輸燃料。這意味著從非食品作物中研制出新一代的生物燃料。

    研究人員正在想辦法將木材、作物廢料、垃圾以及柳枝稷等不可食用植物轉化為具有價格優勢的燃料。但前景最為看好的新一代生物燃料來自于藻類。

    藻類生長迅速，會消耗二氧化碳，一英畝藻類每年可以生成超過5,000加侖的生物燃料，而一英畝玉米每年只能生產350加侖的乙醇。

    藻類燃料可以直接添加進當前的提煉和分銷系統。理論上來說，美國可以生產大量的藻類燃料，足以滿足美國所有的交通運輸需求。

    但現在還為時過早。數十家公司已經開始了試點項目和小規模生產。但量產藻類燃料意味著要尋找到可靠的、價格低廉的養分和水資源，控制可能導致減產的病原體，研發和培育產量最高的藻株。