Negative carbon intensity of renewable energy technologies involving biomass or carbon dioxide as inputs

Conventional fossil fuel-based energy technologies can achieve efficiency in energy conversion but they are usually completely inefficient in carbon conversion because they generate significant CO2 emissions to the atmosphere per unit energy converted. In contrast, some renewable energy technologies characterized by negative carbon intensity can simultaneously achieve efficiency in the conversion of energy and in the conversion of carbon. These carbon negative renewable energy technologies can generate useful energy and remove CO2 from the atmosphere, either by direct capture and recycling of atmospheric CO2 or indirectly, by involving biofuels. Interestingly, the deployment of carbon negative renewable energy technologies can offset carbon emissions from conventional fossil fuel-based energy technologies and thus reduce the overall carbon intensity of energy systems.The current review analyzes two groups of renewable energy technologies involving biomass or CO2 as inputs. The discussions focus on useful techniques which enable to achieve negative carbon intensity of energy while being technologically promising in near-term as well as cost-effective. These analyzes include advanced carbon sequestration concepts such as soil carbon sequestration and CO2 recycling to useful C-rich products such as fuels and fertilizers. The 'drop-in' of renewable energy is achieved by allowing bioenergy and renewable energies in the form of renewable electricity, renewable thermal energy, solar energy, renewable hydrogen, etc. The carbon negative renewable energy technologies are analyzed and perspectives and constraints of each technology are expounded.