Microalgae represents a promising feedstock due to inherent advantages such as high solar energy efficiencies, large lipid fractions, and utilization of variouswaste streams including industrial flue gas. This study directly evaluates and compares the economic viability of biomass production from two different open cultivation platforms, 1) algal turf scrubbers and 2) open raceway ponds. Modular sub-process models were developed and leveraged for the economic comparison of the systems on the metric of harvested biomass. The system boundary was expanded to include downstream processing for the production of renewable diesel through thermochemical conversion for a comparison of the production platforms on a cost per gallon of fuel. Economic results of the two production pathways show a biomass production cost for the algal turf scrubber of $ 510 tonne(-1) and $ 8.34 per gallon for fuel. Open raceway pond results give a biomass cost of $ 673 tonne(-1) and a fuel cost of $ 6.27 per gallon. Sensitivity analysis show productivity and culture stability to be critical factors in the economic viability. Multiple scenarios are presented with baseline results directly compared to literature and highlight the need for robust growth modelling. (c) 2017 Elsevier B.V. All rights reserved.