I will discuss the production of Ulva sp. in photobioreactor systems, in particular for the production of interesting biochemical compounds for various applications. Results will be presented on Ulva growth in the reactors and their chemical composition from my own research and from the literature. Attention will be paid to dynamics in biomass, potential causes, microbiome of the algae, knowledge gaps (in particular with respect to collapses) and potential for upscaling.