Economic analysis of energy and matter generation from microalgae : an environmental LCC model for hydrogen and biogas production from Chlamydomonas reinhardtii

Abstract: Environmental life cycle costing has been applied to determine the economic viability of exclusive biogas production and coupled hydrogen and biogas production from microalgae in a photobioreactor (PBR). Exclusive biogas production consists of the production steps photoautotrophic biomass production and anaerobic digestion. Coupled hydrogen and biogas production considers the steps photoautotrophic biomass production, photobiologically hydrogen production and anaerobic digestion of the residual algal biomass. This study especially evaluates the economic performance of a novel staggered PBR design with an appearance of interconnected roofs. The novel PBR design aims at minimizing energy consumption and at providing optimal light conditions for the growth of the microalgae species Chlamydomonas reinhardtii and for hydrogen generation. Membrane aeration through diffusion instead of air sparging is a difference to conventional PBRs. In a German production setting for 2011, environmental life cycle costs for exclusive biogas production amount to 0.99 Euro/MJ. For coupled production, costs of 0.81 Euro/MJ biogas and 12.17 Euro/MJ hydrogen could be determined. These costs considerably exceed the market prices of 0.02 Euro/MJ biogas and 0.04 Euro/MJ hydrogen. Operating costs amount to 72 percent of life cycle costs for biogas and to 69 percent for hydrogen respectively. Major cost contributors to operating costs are personnel and overhead costs with a share of more than 70 percent. The investment costs consist to about 92 percent of those for the PBR, of which 61 percent are material costs for the membrane. In the given setting, the choice of a production location such as Spain with higher incident solar irradiation and mainly lower personnel costs compared to Germany results in a reduction of life cycle costs by about 50 percent for a similar production system. A future projection with experience curves for Germany has shown that hydrogen life cycle costs would be expected to amount to about 80 times the market prices by 2030 under consideration of technology learning. Biogas production for a German setting is expected to amount to about 15 times of the projected market price by 2030.