Energy crops are low-cost and low-maintenance crops grown solely for renewable bioenergy production (not for food). The crops are processed into solid, liquid or gaseous fuels, such as pellets, bioethanol or biogas. The fuels are burned to generate electrical power or heat.
The plants are generally categorized as woody or herbaceous. Woody plants include willow[1] and poplar, herbaceous plants include Miscanthus x giganteus and Pennisetum purpureum (both known as elephant grass). Herbaceous crops, while physically smaller than trees, store roughly twice the amount of CO2 (in the form of carbon) below ground compared to woody crops.[2]
Through biotechnological procedures such as genetic modification, plants can be manipulated to create higher yields. Relatively high yields can also be realized with existing cultivars.[3]: 250 However, some additional advantages such as reduced associated costs (i.e. costs during the manufacturing process[4]) and less water use can only be accomplished by using genetically modified crops.