Jorquera and colleagues compared the energy life-cycle analysis for the production of microalga Nannochloropsis sp. in flat-plate photobioreactors (FPPR), tubular photo­bioreactors (TPR), and raceway ponds (RP) [485] . The NER of these systems was estimated and compared as total energy produced (energy of biomass) over the energy content of the materials, energy required for construction, and the energy required for operation. A preliminary analysis (including energy costs for pumping, mixing, and gas transfer) showed that the NER value of biomass production in the TPR is 0.2. Consequently, the energy demand is larger than the energy content of the produced biomass in the TPR. The estimated NERs for biomass production in the FPPR and RP are 4.51 and 8.34, respectively [485] . The authors also performed a detailed energy life-cycle analysis using the GaBi program and achieved NER values 4.33 and 7.01 for the FPPR and RP, respectively. This result is in agreement with data achieved for the production of Dunaliella biomass where raceway ponds were found to be more efficient [486]. Indeed, the production of C. vulgaris in raceway bioreactors is more environ­mentally sustainable compared to the production in air-lift tubular reactors [487].