The plant is a major source of food energy and a major food security crop.

VOA: special.2010.06.08

Glucose has to get into cells, that's the main source of energy source that cells use, metabolism of glucose.

但葡萄糖又必须进入细胞,因为它是细胞能量的主要来源,即通过葡萄糖代谢产生能量

耶鲁公开课 - 生物医学工程探索课程节选

It seems Pandora is the only place in the galaxy with deposits of a valuable new energy source worth untold millions back on Earth.

VOA: standard.2009.12.19

The shutdown is bad news for the recession-hit country partly because it will lose a source of cheap electricity and be forced to import more expensive energy.

VOA: standard.2010.01.01