Energy efficiency (netenergy gain or energy ratio) of corn-based ethanol as a substitute for fossil fuel is an important criteria for assessing its sustainability.
玉米燃料乙醇作为化石燃料的替代品，能量效率(净能量或能量比)是评价其可持续性的一个重要标准。
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The ratio of net radiation over rainfall for a given period of time is a measure of excess energy relative to available water and is therefore a measure of drought hazard.