Biofuels such as biodiesel and alcohol fuel can be made from the oils in hemp seeds and stalks, and the fermentation of the plant as a whole, respectively. The energy from hemp may be high based on acreage or weight, but can be low based on the volume of the light weight harvested hemp.
It does, however, produce more energy per acre per year than corn, sugar, flax, or any other crop currently grown for ethanol or biodiesel.
Henry Ford grew industrial hemp on his estate after 1937, possibly to prove the cheapness of methanol production at Iron Mountain. He made plastic cars with wheat straw, hemp and sisal. (Popular Mechanics, Dec. 1941, "Pinch Hitters for Defense.")