Bioenergy with CCS (BECCS)
Another method discussed in the context of CCS is the cultivation of fast-growing plants that take up CO2 from the atmosphere. The biomass can be converted to biofuels and combusted for energy with the CO2 released upon combustion being captured and permanently stored. This is referred to as bioenergy with CCS (BECCS). Suitable crops include miscanthus, poplar, willow and eucalyptus species. All of these produce large quantities of biomass very quickly. Combining biomass power plants with CCS would allow the CO2 released during combustion to be removed from the environment. Unlike direct air capture, this method has the advantage of generating energy rather than just consuming it. In contrast to direct air capture, however, BECCS takes up large areas of land and may also need additional water and fertiliser to cultivate the energy crops, thus placing it in conflict with other land uses such as food production. One alternative may be to use algae as the input for BECCS, as this would partly solve the land-use conflict.
Potential and scale
BECCS plays a decisive role in the IPCC emissions scenarios for attainment of the climate targets and has been hotly debated as a key negative emission technology (NET) since the Paris Climate Agreement. Current energy scenarios assume that BECCS could meet at most up to 20 percent of global energy needs, although estimates vary substantially. According to various scientific studies, if BECCS technology were to be developed in the years ahead, between 2.4 and eleven billion tonnes of CO2 a year could be removed from the atmosphere worldwide from 2050. However, this depends on geological storage capacity being established quickly enough and on a sufficient scale – something that is currently hard to imagine in Germany – at least given the strong resistance from policymakers and the public.
Reducing CO2 by the quantity just mentioned would require about one to four million square kilometres of land for the cultivation of energy crops, equating to up to a third of today’s global arable land.
Another major problem with BECCS is that, as with afforestation, planting energy crops conflicts with the cultivation of food crops in terms of land, water and fertilisation needs. In view of global population growth and rising food demand, it is now doubted that BECCS can be used as a CDR method on a large scale.
Application readiness and research needs
There are many open questions surrounding the cultivation of energy crops for BECCS, including to what extent large-scale cultivation would increase the pressure on the Earth’s remaining natural land regions, deplete biodiversity and contribute to the extinction of animal and plant species. It is also unclear how far such cultivation can be justified in terms of competition for land and water (with regard to food production and natural regions). This is because massive expansion of irrigated plantations could drastically exacerbate water shortages in some parts of the world. The use of BECCS also depends on geological storage capacity for CO2 being established at a sufficient scale. It is not foreseeable that such capacity will be available in the near future. Attempts are currently being made to more precisely quantify the economic viability of large-scale BECCS projects.