Inventory data of microalgal-based energy production systems are based on models or extrapolation of lab-scale or pilot-scale data. This is a clear source of uncertainty and variabil­ity between studies. Consequently, it is important that each new study clearly sources its data and provides detailed inventory data for each process of the production. Hence, a mass and energy balance of each process should be provided, with specific attention to the flow of fossil and biogenic carbon.

13.6.2.1 Input

It is a common practice when performing an LCA of a first — or second-generation biofuel to exclude infrastructures. Indeed, in these systems, it has been shown that their impact was negligible, and the inventory of every element of the infrastructure could be a tedious task. On the contrary, algal biomass production requires the construction of culture facilities, either raceways or photobioreactors. These two options differ from each other by the type of infrastructure they require, and they also differ from a usual crop by the need for a heavy culture infrastructure. As a consequence, LCAs of algae-based systems that exclude the infrastructure do not allow a fair comparison between options for algae culture and between algal-based and terrestrial plant-based biofuels.