BACKGROUNDPhotobioreactors operated under sunlight require a temperature control system. Proposed cooling/heating systems increase the cost of the bioprocess due to their intensive energy utilization or the decrease in bioprocess efficiency they cause. In this study, a novel solar photobioreactor was developed in which phase change materials are employed for controlling the temperature without using external energy. The system was tested in outdoor conditions using Rhodobacter capsulatus as a model photosynthetic microorganism. RESULTSTests showed the considerable heat generation by bacteria in the photobioreactor, which makes the cooling system a must during the day. Compared with an uncontrolled photobioreactor, this design decreased the maximum temperature reached in the photobioreactor by 10 degrees C, in addition to decreasing the rate of temperature increase by 26%, the energy required for cooling by 52%, and the duration of the cooling by 9%. The design also decreased the heating requirements during the night slightly. CONCLUSIONThis research suggests that phase change materials such as capric acid and Glauber's salt can be utilized for controlling the temperature of photobioreactors that operate under sunlight to obtain significant energy savings by decreasing the requirements for both active cooling and heating. (c) 2014 Society of Chemical Industry