(266b) Potential for Solid-Oxide Fuel Cell Technologies to Minimize Water Use in the Electric Power Sector

Authors: 
Shuster, E., U.S. Department of Energy

The U.S. Department of Energy (DOE) provides a worldwide leadership role in the development of advanced fossil fuel-based energy conversion technologies, with a focus on electric power generation with carbon capture and storage (CCS). As part of DOE’s Office of Fossil Energy (FE), the National Energy Technology Laboratory (NETL) implements research, development and demonstration (RD&D) programs that address the challenges of reducing greenhouse gas emissions.  To meet this challenge, FE/NETL is interested in evaluating advanced power cycles that will maximize system efficiency and performance, while minimizing CO2emissions, water use, and the costs of CCS. 

Solid oxide fuel cell (SOFC)-based power cycles for utility-scale applications are an advanced technology currently undergoing research and development. Utilizing electrochemical conversion of the energy contained in the fuel instead of combustion as with conventional power generation technologies, SOFCs are very efficient (with successful development, better than 60% HHV - natural gas with 90% CO2capture) and have low pollutant emissions. A key feature of SOFCs is the ability to maintain the fuel and oxidant (air) streams physically separate, thereby facilitating carbon capture along with the capture and reuse of process water from the oxidized fuel stream (anode exhaust).  

The objective of this study is to investigate the potential for solid-oxide fuel cell (SOFC)-based electric power generation to enable projected growth in electricity demand while at the same time meeting water availability constraints in regions of the country that are both vulnerable to drought and have heavy competition for available water for other needs (e.g., municipal, agriculture, industry).  The approach is to select a specific river basin that is vulnerable to drought and carryout a case study to test the potential benefits that may be associated with the utilization of SOFC technologies to meet projected electricity demand while at the same time meeting projected water availability constraints in the area.  The Sandia National Laboratory (SNL) Western region Water Availability, Cost, and Use database[1]is used to provide estimates for water availability and demand from the agricultural, municipal, industrial, and thermoelectric power sectors along with other environmental demands.  The tasks that were carried out to develop the methodology included selection of a specific river basin; estimation of current water demand, supply, and availability through 2040; estimation of electric power demand through 2040, selection of power generation technology concepts, and their associated performance and cost, potentially used to meet the growth in electricity demand through 2040; and integration of the information into a system spreadsheet model.

The Lower and Middle Brazos River basin was selected to represent a region that already exhibits water stress and low water availability for new uses while also exhibiting projected increase in electricity demand.  It is hypothesized that solid-oxide fuel cell technologies could be deployed to meet increasing electricity demand while minimizing water use in the electric power sector for the area.  Three future water availability scenarios and eight electric power technology options were included in the study.

The analysis provides projections for the remaining water availability through 2040 for different water availability scenarios and electric power generation technology options.  The three levels of water availability are represented by increasing levels of drought: no drought/minor drought, a Sandia reference case, and a climate change case (in which severe drought was assumed).  The electric power technologies  represented in the analysis vary across scenarios, with one scenario being represented by  today’s natural gas combined cycle (NGCC) technology (current NGCC), a scenario with current NGCC and an advanced NGCC plants available in 2030 (current and advanced NGCC), a scenario with current NGCC and a shift to utility scale SOFC plants in 2030 (current NGCC and SOFC utility), and a final scenario with current NGCC until 2025 when SOFC distributed generation (DG) technology is assumed to be available (current NGCC and SOFC DG).  The results show the significant effect of the drought level and the selection of power generation technology on the projected water availability.  In the severe drought scenario, DG SOFC would allow for an increase in electricity demand while at the same time meeting water availability constraints.

Cost savings due to the implementation of SOFCs were estimated compared to the current generating fleet.  These savings were based on the cost of water shortfalls due to unavailable water from increased generation.  Costs were incurred from the cleanup of municipal wastewater and the diversion of water from agriculture.  Agriculture water diversion includes both the cost of transferring the water right from agriculture to electric power and the cost of lost agricultural sales estimated using data from the Census of Agriculture for the State of Texas.

Additionally, the impact of each scenario on CO2 emissions was evaluated.  It was found that the introduction of new electricity generation technologies provide the opportunity for significant reductions in the levels of CO2emissions associated with new electricity generation capacity for the various scenarios.

This analysis shows the beneficial role that SOFC technologies can play in water-stressed regions. For the Middle and Lower Brazos River region, the analysis shows that use of SOFC technologies allows the 2040 water balance to remain positive under more scenarios than the use of NGCC technologies only. Further, SOFC technologies offer additional benefits: cost savings and reduced CO2emissions.

The analysis provides a useful methodology and applied case study that identifies potential water availability issues at the watershed level. The methodology is useful for: a) assessing relative water availability across watersheds with relative degrees of availability indicating which watersheds are most likely to experience issues under specific scenarios; and b) exploring the relative impacts of different generation scenarios and technology choice combinations within a particular watershed.