Support for Cost Analyses on Solar-Driven High Temperature Thermochemical Water-Splitting Cycles

The Department of Energy (DOE) is currently investigating approaches for producing hydrogen via solar-driven high temperature thermochemical processes (i.e., “solar thermochemical hydrogen” (STCH) production) towards an eventual goal of commercializing STCH production. The DOE has established cost targets for commercialized STCH production of $6 per kg hydrogen (2015 H2 production cost), and $2 to $3 per kg hydrogen (2025 target for delivered H2). In support of this effort, DOE has funded independent research teams to perform applied research on specific processes. To help compare technologies on a consistent basis, DOE engaged TIAX to provide independent expert chemical and mechanical engineering and cost analyses support to the project teams to evaluate the cost of promising technologies. Individual process teams used chemical process flowsheet analysis to identify process conditions, major capital equipment, materials and utilities usage rates, and to estimate equipment sizes. A combination of capital equipment cost databases and bottom-up cost analysis were used to estimate costs of major capital equipment. These assumptions were applied together with a consistent set of input financial and operating assumptions that were developed jointly by TIAX and DOE to develop near-term (2015) and longer-term (2025) STCH hydrogen production cost projections. During the course of this effort, eight different STCH production processes were supported by TIAX: hybrid-sulfur (HyS), copper chloride (CuCl), thin-film nickel ferrite (“ferrite”), sulfur-ammonia (S-A), zinc oxide (ZnO), manganese oxide (MnO), sulfur-iodine (S-I), and cadmium oxide (CdO). The resulting cost projections are summarized in Table A-1. While several of the cycles that were evaluated appear likely to achieve the near-term DOE target of $6/kg hydrogen (production only), achieving the long-term goal of $2 to $3/kg hydrogen (delivered) appears to be a very challenging prospect. Of the cycles evaluated, only one (the thin film ferrite cycle) was projected to achieve the target using base case assumptions. Even in this case, achieving the long-term target requires significant technological development along multiple dimensions, as well as demonstration and scale up of novel chemical plant concepts. Single-variable sensitivity analysis indicates that several other processes could also approach this target if more favorable economic or operational assumptions are used. While specific sensitivities vary between cycles, the plant’s capacity factor, the specific economic assumptions used, cycle efficiency, and the direct capital cost were all shown to have a large effect on plant economics for each of the cycles. Heliostats costs are the primary cost driver for all of the processes that were analyzed. As such, measures that increase plant efficiency (i.e., reduce the plant thermal requirement and hence the size of the solar field) or decrease the heliostat unit cost offer a high return on investment. Table A-1: 2015 and 2025 STCH Cost projections Year Hy-S CuCl Ferrite S-A ZnO CdO MnO S-I 2015 $5.68 $6.83 $4.06 $7.78 $6.07 N/A $5.62 $5.01 2025 $3.85 $5.39 $2.42 $4.65 $4.18 N/A $4.63 $4.68 i Validated CdO cost analysis was not completed ii 2025 MnO results reflect only lower heliostat costs compared to the 2015 case iii Preliminary estimate based on scaled nuclear case 3 Copyright 2011, TIAX LLC TABLE OF CONTENTS ............................................................................................... 3 Abstract 1 ............................................................................................................................. 6 Introduction 2 ........................................................................................................................... 8 Methodology 2.1 ......................................................................................................................... 8 Overview 2.2 .................................................................................................. 8 Economic Assumptions 2.3 ........................................................................................................................ 9 Efficiency 2.4 ............................................................................................... 10 Cost Estimation Sources 2.5 ...................................................................................................... 11 Sensitivity Analysis 3 ................................................................................................................................... 12 Results 3.1 ................................................................. 12 Overview of Solar Thermal Water Splitting 3.2 ....................................................................................... 13 Hybrid-Sulfur STCH Process 3.3 ....................................................................... 20 Copper Chloride (CuCl) STCH Process 3.4 ................................................................................................... 27 Ferrite STCH Process 3.5 ......................................................................... 34 Sulfur Ammonia (S-A) STCH Process 3.6 ................................................................................. 39 Zinc Oxide (ZnO) STCH Process 3.7 ..................................................................... 46 Manganese Oxide (MnO) STCH Process 3.8 ........................................................................ 52 Cadmium Oxide (CdO) STCH Process 3.9 ................................................................................ 57 Sulfur-Iodine (S-I) STCH Process 4 ........................................................................................................................... 59 Conclusions 4.1 ................................................ 59 Summary of STCH Process Results and Critical Paths 4.2 ........................................................................................... 64 Cross-Cutting Conclusions References..................................................................................................................................... 68 Appendix A: STCH H2A Assumptions........................................................................................ 71 Appendix B: STCH Solar Field Efficiency Analysis Guidelines ................................................. 74 Appendix C: Electrolyzer Cost Basis ........................................................................................... 75 4 Copyright 2011, TIAX LLC