4.4 Biomass energy from plants
Energy crops – plants grown specifically to provide bioenergy – have attracted increasing attention in recent years.
From Table 2, you’ll see that these plants can be categorised broadly according to the physical and chemical nature of the biomass involved.
Table 2 A broad generalized classification of primary bioenergy sources
|Category||Major energy-rich components||Structural stength/resistance to natural decay||Examples||Typical yields of dry matter /t ha1 y1|
|Woody biomass||Lignin/lignocellulose (complex carbohydrates)||High||Trees (deciduous or hardwoods)||10 (temperate) to 20 (tropics)|
|Cellulosic biomass||Cellulose/lignocellulose (complex carbohydrates)||Medium||Grasses (e.g. miscanthus), water hyacinth, seaweeds||10 (temperate) 60 (tropical aquatics)|
|Starch/sugar crops||Simpler carbohydrates||Low||Cereals (maize. sugar cane, wheat||10 (temperate cereals to 35 (sugar-cane)|
|Oily crops||Lipids (i.e. oil/fats)||Low||Oilseeds (rape, sunflower, oil palm, jatropha)||8 to 15|
|Micro organisms||Oil||Low||Microalgae||Unkown - still speculative|
These categories overlap to a considerable extent, so some crops may be grown primarily for their sugar or starch content but their supporting lignocellulosic (woody) structural materials may also be used for other purposes