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.

    这是一个离谱的要求：在今后几十年里，世界需要逐步摆脱对化石燃料的依赖，显着减少温室气体。目前的技术只能让我们走到这一步了，我们需要拥有重大的技术突破。

    这些突破可能是些什么？本文列出了五项技术，如果成功，它们将会大大改变世界的能源格局。

    这些技术能带来巨大的机遇。例如，从太空获取能量的技术可能迅速催生全新的产业。从火电厂捕获和储存二氧化碳的技术可能会令较为老旧的电厂重获新生。

    当然，这些技术并不一定能取得成功，它们目前都面临着不少难题，一些技术需要在实验室创造的材料和或转基因植物方面实现一些重大突破。而且，创新的成本不能让能源变得太贵。如果能做到这一切，其中任何一项技术都可以改变游戏规则。

    太空利用太阳能

    30多年来，梦想家就一直设想在太阳永远能照耀到的地方──太空中──利用太阳能。如果我们能在环绕地球的轨道上安置巨大的太阳能电池板，将其中哪怕是一小部分的可用能源传回地球，它们可以向地球上的任何地方提供不间断的电力。

    这项技术听起来可能像是科幻小说，但其实很简单：在22,000英里之外的太阳能电池板将能源以微波的形式传回地球，然后转化为电力并进入到电网中。（低能量的光束被认为是安全的。）直径1英里的地面接收站可以提供约1,000兆瓦电力，足以供应平均约100万户美国家庭的使用。

    将太阳能收集器送至太空的成本是最大的障碍，因此有必要设计重量足够轻，可以减少发射次数的系统。已经有些国家和公司希望最早在未来10年内提供这种太空电力。

    高级汽车电池

    电动汽车可以降低石油消耗量，有助于空气清洁（如果电力来自于风能和原子能等低碳燃料的话）.但它需要使用更好的电池。

    笔记本电脑中常用的锂离子电池是下一代充电式混合动力车和电动车的理想之选。它们比其它汽车电池的电力更充足，但也更贵，不过充电后的行驶距离仍不够远；将于明年上市雪佛兰（Chevy） Volt混合动力车凭电池可行驶约40英里。理想情况下，电动车充电一次最好能行驶近400英里。尽管仍有改进的空间，但锂离子电池的潜力有限。

    作为一种替代产品，锂空气电池的性能是锂离子电池的10倍，可以提供与汽油同等的能量。锂空气电池从空气中吸收氧气充电，因此这种电池可以更小、更轻。不少实验室都在研究这种技术，但科学家认为，如果没有重大突破，要想实现商用可能还需要10年。

    电力储存技术

    所有人都在支持风能和太阳能技术，你怎能置身事外？但风能和太阳能是那种要么利用要么流失的资源。要改变现状，它们需要更好的储存技术。

    科学家正在从诸多角度应对这个问题，但各个方面都面临难题。举例来说，一项技术是通过风能将地下洞穴内的空气压缩产生电能；将空气输送至燃气涡轮机以提高燃烧功效。这其中面临的一个障碍是：要寻找到大空间以及可用的地下洞穴。

    类似的，还有能够吸收风能待日后使用的巨型电池，但当前的一些技术成本昂贵，其他技术则不是很有效率。尽管研究人员正在寻找新材料以提高性能，但要出现显着技术飞跃的可能性不大。

    锂离子技术可能是电网存储前景最好的技术，在这个领域内该技术不会面临像在汽车业中那样多的限制。随着性能提高和价格降低，公共事业机构可能会向电网边缘，较为靠近用户的地方输送小体积大容量的锂离子电池。

    这样，这些锂离子电池可以从可再生能源中存储多余的能源，有助于平抑电能供应的小波动，提高电网的效率，降低对备用火电厂的需求。公用事业机构可以利用汽车电池的研究成果。

    碳捕捉和储存技术

    继续将煤炭作为一种主要的能源意味着需要努力去降低碳燃烧生成的二氧化碳。这可能意味着要建设更高效的新发电厂。但从当前的电厂捕捉二氧化碳（每年大约为20亿吨）可能是一个真正能够改变游戏规则的技术。

    目前已经出现了小规模的二氧化碳捕捉技术，但如果将这些技术用于大型发电厂会导致发电量减少三分之一，并导致发电成本增长一倍。因此，科学家正在寻找既能够将碳排放量降低90%,又能限制成本增长的试验性技术。

    几乎所有技术目前都处于初步阶段，目前断言哪种方法能够最终胜出还为时过早。一个前景看好的技术是以金属氧化物的形式燃烧煤炭和纯净氧，而不是在空气中燃烧；这种方法会产生较容易捕捉的二氧化碳集中气流，几乎不会影响电厂的效率。这种技术已经在小规模试点项目中进行了展示，明年将用于一个装机容量为一百万瓦的试验电厂。但2020年之前，这种技术可能还难以投入商用。

    下一代生物燃料

    一个令我们逐步摆脱对石油依赖的途径就是研制出可再生的运输燃料。这意味着从非食品作物中研制出新一代的生物燃料。

    研究人员正在想办法将木材、作物废料、垃圾以及柳枝稷等不可食用植物转化为具有价格优势的燃料。但前景最为看好的新一代生物燃料来自于藻类。

    藻类生长迅速，会消耗二氧化碳，一英亩藻类每年可以生成超过5,000加仑的生物燃料，而一英亩玉米每年只能生产350加仑的乙醇。

    藻类燃料可以直接添加进当前的提炼和分销系统。理论上来说，美国可以生产大量的藻类燃料，足以满足美国所有的交通运输需求。

    但现在还为时过早。数十家公司已经开始了试点项目和小规模生产。但量产藻类燃料意味着要寻找到可靠的、价格低廉的养分和水资源，控制可能导致减产的病原体，研发和培育产量最高的藻株。