Competitive algae biodiesel depends on advances in mass algae cultivation

[Display omitted] •Feedstock cost refers to some 9/10 of algae biodiesel production cost.•Light and O2 management are not yet mastered in algae mass cultivation.•Overnight respiratory loss of oil prolongs algae production.•Cost reduction in mass cultivation is the key to price competitiveness of algae biodiesel. The aim of this review was to study why, despite large investments in research and development, algae biodiesel is still not price competitive with fossil fuels. Microalgal production was confirmed to be a critical cost item (84 up to 93 %) for biodiesel regardless of the production technology. Techno-economic assessment revealed the main cost drivers during mass cultivation. It is argued that a breakthrough in the cultivation efficiency of microalgae is identified as a necessary condition for achieving price-competitive microalgal biodiesel. The key bottlenecks were identified as follows: (1) light and O2 concentration management; (2) overnight respiratory loss of oil. It is concluded that most of the research on microalgae biodiesel yields economically over-optimistic presumptions because it has been based on laboratory scale experiments with a low level of interdisciplinary overlap.