Efficiency is crucial in such cells if they are ever to be a substitute for existing methods of mass power-generation, such as coal and gas.

对于这些太阳能电池来说，要想取代现有的大规模发电方法，如煤炭和天然气，最关键的是效率。

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China has a technological lead in turning coal into gas. It has been using the technology widely to make petrochemicals and fertilizers as a substitute for pricier natural gas.

中国在煤气化领域拥有技术领先优势，已在石化及化肥生产领域用到了这一技术，用以替代更为昂贵的天然气。

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The closest substitute for coal in electricity generation is natural gas.

与煤炭最相近的发电替代品就是天然气。

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It produces less carbon dioxide for a unit of energy than coal or oil, so the climate will benefit to the degree that gas replaces either of those: it will mostly substitute for coal, though some oil too, especially if gas-powered trucking becomes widespread.

ECONOMIST: Natural gas

China is already investing billions of dollars to substitute hydropower (which counts as a renewable energy source) for coal and gas in electricity generation.

FORBES: Pollution And Prosperity

Cheap US gas is already driving down the price of the biggest substitute for generating electricity, coal, freeing it up for export to Europe, where it is displacing Europe's relatively highly-priced gas.

BBC: Burning issues for the world's future