4.3 Other energy crops
Starchy and sugary crops
The major biomass energy component of these crops, examples of which are shown in Figure 7, is their sugar or starch, which can be fermented to produce ethanol. Their supporting cellulosic tissues may also be used in the same way as the mainly cellulose crops. Globally, the most important crops for bioenergy purposes are sugar cane and maize.
Another sugar-rich crop of interest in Europe is sugar beet, where the roots contain 15–20% sugar. Sugar-cane bagasse (the sugar cane’s fibrous residue) and the straw from maize and other cereals can also be used for energy, in the same way as for cellulosic crops.
Sunflowers, oilseed rape and soya beans are grown widely for the oil in their seeds, while in tropical areas, oil palm (Elaeis guineensis) is a major crop.
The oils from these crops can be converted to a diesel substitute known as biodiesel. As with the starchy/sugar crops considered above, there is a residue left from these processes that is currently often used as animal feed, but which could be a bioenergy feedstock.
The oil from all these crops has a vast number of uses, for example in foods and cosmetics/ However, there are widespread misgivings about the conversion of mature forests to palm oil plantations in South-East Asia and elsewhere. The use of palm oil for bioenergy could lead to an increase in such problems.
Some types of algae can also be used to produce energy, as they too photosynthesise. You’ll look at this in the next section.