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. It shows typical yields and the energy content of the crop produced by burning various biological materials. The heat content combines the calorific value of biofuels produced from the crop and the heat content of the residue that can be burned. A wide variation both in crop yield and energy content may be seen, though clearly tropical areas such as Brazil and Indonesia have significantly greater biomass potential per unit area than temperate climes such as Europe.
Table 2 Typical yields and heat energy content produced per unit area of various forms of biomass. Adapted from (Long et al., 2015)
|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. oils/fats)||Low||Oilseeds (rape, sunflower, oil palm, jatropha)||8 to 15|
|Micro organisms||Oils||Low||Microalgae||Unknown - 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.