The present disclosure concerns methods, apparatus, compositions and systems relating to closed bioreactors for algal culture and harvesting. In certain embodiments, the system may comprise bags with various layers, including a thermal barrier layer, that may be used to contain the algal culture and/or to thermally regulate the temperature of the algal culture. The system may comprise various mechanisms for moving fluid within the sytem, such as a roller type mechanism, and may provide temperature regulation by compartmentalization of the fluid to regulate absorption of solar radiation and/or conductive or emissive heat loss and gain. Various mechanisms may be used to harvest and process the algae and/or to convert algal oil into biodiesel and other products.