The sustainable use of energy crops for biogas is a possible solution to reduce the contribution to climate change of human activities. Power based on biomass, in particular biogas, is increasing, with a concomitant increase in the need for energy crop production.
In response to global warming and the expectation of reduced fossil energy resources, many countries have created regulations or incentives in favor of renewable energies including bioenergy from agricultural resources. Several countries implemented various instruments like tax exemption, quotas, or direct subsidies to stimulate the use of agricultural resources as renewable energies. In Germany the Renewable Energy Sources Act, which came into force in 2000, triggered a boom in the use of agricultural resources as feedstock for biogas plants to produce electrical energy. Since the introduction of the Renewable Energy Sources Act the number of biogas plants increased to about 5000 in Germany in 2009, covering more than 1% of the electrical energy consumption. The acreage used for energy crops amounted to 530,000 ha in the year 2009, or 4.4% of the total arable land.
The dominant crop used for biogas production in most countries is corn, which makes up more than 75% of the crops planted for biogas production. The environmental benefits of using biogas primarily stem from the substitution of fossil energy and the mitigation of emissions which occur in the supposed reference system.Furthermore, biogas plants which use manure from animal husbandry mitigate emissions from the storage of that manure. However, for each impact category, the credits gained due to the substitution of fossil energy use have to be balanced against the emissions generated during the production and processing of the feedstock.
Nevertheless, corn production occupies most areas suited for food production. Energy crops are intended for marginal areas to not disrupt food and livestock production and have environmental benefits.
Some examples of technology available has been developed in Germany.
Manure and many other residues can be used and combined with specific crops that require some knoledge on the best quality of biomass to achieve through management. Harvest optimum periods, varieties/species selection and cultivation techniques as well as logistic optimization is needed for many interesting species as energy crops to complement the bioenergy chain. Biogas production systems and business require energy crops to reduce risks and have long term contracts with farmers in the region.
Several studies have analyzed the environmental impacts of biogas use providing a great range of results depending on the feedstock used, the reference system which is replaced, accounting rules and system boundaries, feedstock transport distances, and others. Perennial crops have been suggested to be used in several studies to introduce soil benefits in rotations and have low environmental impact.
Accordingly, the estimates on GHG mitigation potentials cover a very wide range. For example, some studies found that the use of biogas to produce electrical energy resulted in 7–23% of the GHG emitted when electrical energy is produced with the reference fossil-based gas. Others have found a contribution to climate change of between 60 and 90% of the reference system if energy crops were anaerobically fermented to produce gas to be injected into the natural gas grid in Luxembourg. The diversity of processes involved and feedstock used make it difficult to apply the results from existing environmental analyses to other specific situations. Furthermore, the use of agricultural feedstock as an energy resource may induce a direct or indirect land use change resulting in high so-called carbon debts due to the conversion of native ecosystems to bioenergy providing systems, casting doubt on the environmental benefits of bioenergy based on agricultural feedstock.
An specific explanation about biogas from grasses shows functioning and benefits in this video.
In many countries the conversion of grassland to arable land may contribute to substantial GHG emissions since the soils below grasslands, especially on organic soils, have a considerably higher carbon content than those of arable lands.
Explanations on technology for biogas can be also found in this good video.
A new look on bioenergy crops need take place looking for more sustainable patterns to produce highly efficient systems. Now, technology and farming combined solutions can be used to provide energy to small communities in tropical, temperate and even semiarid regions with large social, economic and environmental benefits. Applications are many and business units with promising results could be develop in many regions of the world, and both small and larger enterprises are possible.
Biogas systems in desertified areas with huge potential to be integrated to livestock systems (goats, sheeps and many other possibile livestock) are viable options. Perennial grasses and energy crops should be considered as feedstock and several evaluations are possible and required to be sure the bioenergy chain is optimized and have benefits for the environment.
Some good sources of information, presentations and articles can be found here: