A process for cultivating photosynthetic microbes comprising Closed Systems for continuous cultivation and Open Systems for batch cultivation, in which (a) the Closed System Area occupies no more than 20% of the Total Land Area of the cultivation facility (b) batch cultures in the Open Systems are initiated with an inoculum from the Closed Systems containing a cell biomass of no less than 5% of the carrying capacity of said Open System (c) the doubling rate of said photosynthetic microbe is no less than once every 16 hours and (d) the residence time of the batch culture in said Open System is no more than a period of 5 days.
