Renewable raw materials and energy crops

Willows and poplars are among the fast-growing tree species that may be grown on arable land. They have their strongest biomass growth in the first years after planting or harvesting and can therefore be harvested in "short rotation", i.e. repeatedly every 3-6 years. During harvesting, the entire tree is cut off about 15 cm above the ground and the trunks and branches are either laid down to dry or directly processed into chaff. The harvested biomass contains about 45% cellulose and 15% lignin. This makes it particularly suitable for paper production or for heat generation through combustion.

After planting, perennial grasses can be harvested annually for up to 10 years, such as switchgrass, or 20 years, such as miscanthus. Both miscanthus and switchgrass belong to the heat-loving grasses and are characterised by a very high biomass yield. The biomass contains about 40% cellulose and 20% lignin. In China, where miscanthus occurs naturally, it is processed into paper or building materials. In Germany, miscanthus is currently used mainly as a fuel for heat generation. In the future, however, it will also be used in other ways, for example as a biogas substrate and animal bedding or for the production of ethanol, composite materials and lightweight concrete.

The flower-rich, Cup plant is native to North America and was already studied in Russia in the mid-20th century as a fodder plant for ruminants, but was found to be useless because it did not taste good to the animals. In the last two decades, however, it has been found that the taste does not matter to biogas plants and Cup plant is therefore well suited as a biogas substrate. Cup plant provides high annual biomass yields from the second year of establishment and provides plenty of food for pollinating insects during flowering. Cup plant has also been recognised as a greening measure since 2018. This means that farms that cultivate Cup plant are "rewarded" with about 60 € per hectare and year.

Biogas wild plant mixtures (WPM) contain annual, biennial and perennial flowering and predominantly wild plant species that are suitable for use as biogas substrates but have not yet been used as such. The WPM can significantly reduce tillage intensity over five to seven years. No pesticides are applied, with the possible exception of herbicides in the year of sowing. Even with lower annual biogas yields of WPM compared to maize, WPM can thus break up maize-emphasised crop rotations and enhance them from many social and ecological aspects (food for pollinator insects, habitat for small game, groundwater protection, landscape).