Growth of algal biomass in laboratory and in large-scale algal photobioreactors in the temperate climate of western Germany

[Display omitted] •Chlorella growth was studied in laboratory and in 3 large scale photobioreactors.•Mathematical model shows how algal growth depends on light and cell density.•Growth was light-limited in the photobioreactors with relevant culture densities.•Less light shading and more modularity and robustness are key to high yields. Growth of Chlorella vulgaris was characterized as a function of irradiance in a laboratory turbidostat (1L) and compared to batch growth in sunlit modules (5–25L) of the commercial NOVAgreen photobioreactor. The effects of variable sunlight and culture density were deconvoluted by a mathematical model. The analysis showed that algal growth was light-limited due to shading by external construction elements and due to light attenuation within the algal bags. The model was also used to predict maximum biomass productivity. The manipulative experiments and the model predictions were confronted with data from a production season of three large-scale photobioreactors: NOVAgreen (