Cost breakdown indicates that biochar production from microalgae in Central Europe requires innovative cultivation procedures

• algae biochar is agronomically similar to biochar made of terrestrial plants. • flocculation can reduce algae harvest cost by 29 %. • harvesting from an Open-pond followed by (bio)refining bring multiple synergies. In most current academic thinking, the prevailing consensus underscores the potential of algae as a promising biochar feedstock. Nevertheless, a significant gap exists in the literature, as most assertions conducted outside tropical and subtropical regions lack substantiation through comprehensive analyses on a comparison of the economic benefits and the costs associated with the application of algae biochar is mostly missing. This study reports a meticulous breakdown of production costs for algae biochar derived from 6 various cultivation systems via 2 harvesting techniques under the conditions characteristic of central Europe. The findings revealed that the production costs of the algae biochars always greater than 110 €.kg −1 that is much higher than the selling prices of the most common biochars on the market including the most expensive biochars made of hard woods. To achieve social acceptability, it is recommended to prefer higher value-added applications for algae and to implement biochar production as the final stage of the refining process.