An Energy Crop is any crop grown specifically for its energy value. In general there are two approaches to energy crops: growing plants specifically for energy use, or using the residues from plants that are grown primarily for another purpose.

Energy Crops entail either short rotation woody crops, which are fast growing hardwood trees ready for harvest 5-8 years after planting, or herbaceous crops, including both annuals and perennials. Short rotation trees exhibit the potential to be grown as energy crops if they produce large amounts of biomass quickly and can continue to grow after being cut off close to the ground, a feature called "coppicing." Herbaceous energy crops are typically grown for either carbohydrates or cellulose, both of which can be burned and converted to ethanol, but some annuals are grown to produce oil which can also be used to make fuels.

Traditionally capturing energy from biomass required burning the biomass; however, a number of non-combustion methods are available for converting biomass to energy. These processes convert raw biomass into a variety of gaseous, liquid, or solid fuels that can then be used directly for energy generation. The carbohydrates and cellulose in biomass can be broken down into a variety of chemicals, some of which are useful fuels. This conversion can be done in three ways:

• Thermochemical: When plant matter is heated to approximately 55°C in thermophilic digestion systems, (the process typically lasting 12-14 days), it breaks down into various gases, liquids, and solids. These products can then be further processed and refined into useful fuels such as methane and ethanol. Biomass gasifiers capture methane released from the plants and burn it in a gas turbine to produce electricity. This method offers higher methane production, faster throughput, better pathogen and virus ‘kill’, but requires more expensive technology, greater energy input and a higher degree of operation and monitoring.

• Biochemical: Bacteria, yeasts, and enzymes also break down carbohydrates and cellulose. Fermentation, the process used to make wine, changes biomass liquids into ethanol, a combustible fuel. When bacteria break down biomass, methane and carbon dioxide are produced; this methane can be captured and burned for heat and power; while the CO2, and instead of releasing carbon into the air that has been stored for millions of years, does not increase the carbon dioxide content of the atmosphere. The digestion process takes place in a warmed, sealed airless container which provides the oxygen-free conditions required for the bacteria to ferment the organic material. The container is heated to 30-35°C and the feedstock remains in the digester typically for 15-30 days. Gas production is less, larger digestion tanks are required but the process tends to be more robust and tolerant

• Chemical: Biomass oils can be chemically converted into a liquid fuel similar to diesel fuel, and into gasoline additives. Oil can be extracted mechanically with an oil press, an expeller, or even with a wooden mortar and pestle. Presses range from small, hand-driven models that an individual can build to power-driven commercial presses. Expellers have a rotating screw inside a horizontal cylinder that is capped at one end. The screw forces the seeds or nuts through the cylinder, gradually increasing the pressure. The oil escapes from the cylinder through small holes or slots, and the press cake emerges from the end of the cylinder, once the cap is removed. Crude oils are easy to produce and, in principles, they can be used in engines but, to be employed, they require engines with a pre-combustion chamber or ad-hoc designed engines.

There are advantages associated with producing energy from perennial biomass yielding crops. Perennials reduce soil erosion as well as the release of soil carbon, both of which are disadvantages related to annual tillage. They achieve this by removing CO₂ from the atmosphere and incorporating it into their plant tissue, especially below the ground in their roots, by what is known as carbon sequestration. Exposure to wind and water erosion occurs primarily during establishment of annual crops and is minimized with perennials. Perennials possess deep root systems that enable them to access more soil moisture and survive frequent droughts that decimate annual crops thereby significantly reducing water requirements Perennials can provide N fixation and provide windbreaks.