Leveling Intermittent Renewable Energy Production Through Biomass Gasification-Based Hybrid Systems

The increased use of intermittent renewable power in the United States is forcing utilities to manage increasingly complex supply and demand interactions. This paper evaluates biomass pathways for hydrogen production and how they can be integrated with renewable resources to improve the efficiency, reliability, dispatchability, and cost of other renewable technologies. Two hybrid concepts were analyzed that involve co-production of gaseous hydrogen and electric power from thermochemical biorefineries. Both of the concepts analyzed share the basic idea of combining intermittent wind-generated electricity with a biomass gasification plant. The systems were studied in detail for process feasibility and economic performance. The best performing system was estimated to produce hydrogen at a cost of $1.67/kg. The proposed hybrid systems seek to either fill energy shortfalls by supplying hydrogen to a peaking natural gas turbine or to absorb excess renewable power during low-demand hours. Direct leveling of intermittent renewable electricity production is accomplished with either an indirectly heated biomass gasifier, or a directly heated biomass gasifier. The indirect gasification concepts studied were found to be cost competitive in cases where value is placed on controlling carbon emissions. A carbon tax in the range of $26–40 per metric ton of CO₂ equivalent (CO₂e) emission makes the systems studied cost competitive with steam methane reforming (SMR) to produce hydrogen. However, some additional value must be placed on energy peaking or sinking for these plants to be economically viable. The direct gasification concept studied replaces the air separation unit (ASU) with an electrolyzer bank and is unlikely to be cost competitive in the near future. High electrolyzer costs and wind power requirements make the hybridization difficult to justify economically without downsizing the system. Based on a direct replacement of the ASU with electrolyzers, hydrogen can be produced for $0.27 premium per kilogram. Additionally, if a non-renewable, grid-mix electricity is used, the hybrid system is found to be a net CO₂e emitter.