Microalgae have remarkable molecular pathways to generate biohydrogen, an environment friendly and sustainable energy source. For this reason, various studies for microalgal biohydrogen production have been carried out. The objective of the present study was to address the effect of environmental factors simulating outdoor conditions using D1 mutant strains and CC124 as control strain. The results showed that, in any cases D1 mutants were effective in terms of hydrogen generation capacity; however among them strain D239-40 has attractive in term of hydrogen output. The results are promising for further developments both in genetic and bioprocess aspect aiming scale up and commercialization for outdoor cultures. Copyright (c) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.