Thermodynamic, Environmental, and Economic Analysis of Electrosynthesis of Hydrogen Fuel with State-of-the-Art Solid Oxide Electrolyzers
Authors: Colella Whitney Goldsborough 
Published: February 2020

Gaia Energy Research Institute (Gaia) presents results for (1) a life cycle analysis (LCA) and (2) a technoeconomic analysis (TEA) of a state-of-the-art solid oxide electrolyzer (SOE) for electrosynthesis of hydrogen fuel. The significance of this work is that it quantifies potential reductions in greenhouse gas emissions (GHGs) and other environmental impacts with the use of SOEs. The significance of this work is that it also quantifies the potential future cost of producing extremely pure hydrogen using SOEs in dollars per kilogram of hydrogen ($/kg H2).

1: Life cycle analysis

LCA results indicate that GHGs from the SOE can be lower than GHGs from steam methane reforming (SMR) of natural gas (the most prevalent technology for making hydrogen). To obtain this result, Gaia builds on the existing DOE models, including, but not limited to, the Argonne National Laboratory full life-cycle model, GREET (Greenhouse gases, Regulated Emissions, and Energy use in Transportation.) SOE GHG emissions are also evaluated through single-variable sensitivity studies and Tornado charts. Model results indicate that some of the input variables that are most impactful to GHGs include, but are not limited to, (1) the SOE stack and system electricity usages (kWh_electric/kg H2), (2) the SOE stack and system heat usages (kWh_thermal /kg H2), (3) the carbon footprint of the electricity input source to the SOE (kg carbon /kWh_electric), and (4) the carbon footprint of the thermal input source to the SOE (kg carbon /kWh_thermal). Also quantified are potential future changes in GHG emissions that result from further SOE technology advancements. These results are plotted in Waterfall Charts. In addition to GHGs, this analysis also considers life cycle air pollution emissions and solid waste streams.

2: Technoeconomic analysis

TEA results indicate that the SOE is estimated to produce hydrogen at less than $2/kg H2, which is the DOE Fuel Cell Technologies Office’s (FCTO) H2 production cost target. To obtain this result, Gaia builds on existing DOE FCTO H2 production analysis modelling tools, including the H2A tools, and the existing FCTO SOE case studies and Excel-based models. Gaia deploys the FCTO's Hydrogen Analysis tools, including the H2A Production and H2A Delivery Scenario Analysis Model (HDSAM) models, to estimate the levelized cost of (1) producing, (2) delivering, (3) compressing, (4) storing and (5) dispensing H2 ($/kg H2). The levelized cost of producing H2 from SOEs is also analyzed using single-variable sensitivity studies and Tornado charts. (An important caveat is that H2A model results do not indicate optimal results for engineering design parameters or market conditions.)

Model results indicate that some of the input variables that are most impactful to the levelized cost of producing H2 from SOEs include, but are not limited to, (1) the electricity price, (2) the purchase price for external heat going into the SOE stack, (3) the SOE stack and system capital costs, (4) the SOE stack and system electricity usages, (5) the SOE stack and system heat usages, (6) SOE stack and system lifetimes, and (7) the operating capacity factor. System costs include both stack and balance of plant costs. Also quantified are potential improvements in the levelized H2 production that result from further SOE technology advancements. These results are plotted in Waterfall Charts.

Both current and future cases were analyzed for H2 generation with state-of-the-art SOE electrolyzers using the DOE’s H2A Production Model. For the state-of-the-art SOE system design analyzed here, uninstalled SOE system capital costs are expected to decline from $840/kWe to $640/kWe between current and future cases. Electricity usage is expected to decline from 37.61 kWh_e/kg H2 to 35.1 kWh_e/kg H2 between current and future cases. The current case reflects a ~$3 /kg levelized H2 production cost, based on an average cost of electricity of 2.5¢/kWh. The future case reflects a <$2 /kg levelized H2 production cost, based on an average cost of electricity of 2¢/kWh. Capital costs are the primary cost driver in current and future cases. The secondary cost driver is electricity costs. Between the current and the future case, the estimated levelized H2 production cost declines due to expected decreases in (1) SOE system capital costs (primarily at the stack), (2) indirect capital costs and replacement costs, (3) system energy consumption, (4) electricity price, and (5) fixed operations and maintenance costs. The LCA shows a 79% to 100% reduction in GHGs for hydrogen from the state-of-the-art SOE system analyzed here, compared with hydrogen from natural gas SMR.