Novel Electrical and Thermochemical Energy Storage Systems based on Reversible Solid Oxide Cells and Redox Cycles
Speaker: Prof. Rob Braun from the Department of Mechanical Engineering in the College of Engineering & Computational Sciences at the Colorado School of Mines.
Abstract
Low-cost, high efficiency, energy storage is needed for the future electric grid which will include more variable energy resources, such as wind and solar. Substantial penetration of wind and solar resources into the electric power grid is challenged by their intermittancy, as well as the dynamic response limitations of central utility plants. Storing electric energy directly into batteries is one of the most efficient ways to preserve the energy generated from renewable resources, but capacity limitations of conventional batteries are too great at present to economically store enough energy at utility-scales. Energy storage for concentrating solar power (CSP) is also a critical enabling technology as it enables higher capacity factor power plants and unlike other renewables, its integration actually lowers the levelized cost of energy. However, in CSP plants, energy storage involves amassing thermal/thermochemical energy at high temperatures as a reserve for use during times when the sun is not shining. In this talk, two novel energy storage methods based on perovskite material sets are examined: intermediate temperature, ‘reversible’ solid oxide cells (ReSOCs) based on LSGM electrolytes and thermochemical energy storage based on redox cycling of doped calcium manganite (doped CaMexMnO3-δ) perovskite particles.
The ReSOC storage systems operate sequentially between fuel-producing electrolysis and powerproducing fuel-cell modes with intermediate tanking of reactants and products. By leveraging C-O-H reaction chemistry and operating at intermediate temperature (~600°C), the ReSOC is mildly exothermic in both operating modes, which simplifies balance-of-plant integration and thermal management. The roundtrip efficiency (< 74%), energy density (~90-100 kWh/m3), and capital cost tradeoffs (~250 $/kWh) of various configurations intended for distributed energy storage are quantified through computational modeling. The second portion of this talk will highlight work on redox cycles with reducible perovskite particles for direct high-temperature (up to 900°C) thermochemical energy storage (TCES) in a concentrated solar plant. The concept utilizes the fact that perovskite oxides (with chemical structure ABO3-δ) can undergo endothermic partial reduction to store solar heat at temperatures as high as 900°C. By providing excess reduced oxide during periods of high insolation, the combined thermochemical and sensible energy in the partially reduced perovskites can provide total storage of 750 kJ/kg or more such that < 1.5 m3 of particles can be re-oxidized to produce a MWh of electricity for a 50% power cycle. Strategies and progress towards enabling this concept are presented in the context of meeting U.S. DOE Sunshot targets of high temperature storage at <$15/kWht.
Biography
Dr. Robert Braun is Associate Professor of Mechanical Engineering at the Colorado School of Mines. He received a Ph.D. from the University of Wisconsin–Madison in 2002. From 2002-2007, Dr. Braun was at United Technologies Fuel Cell and Research Center divisions where he last served as project leader for UTC’s mobile solid oxide fuel cell (SOFC) power system development program. Dr. Braun has multi-disciplinary background in mechanical and chemical engineering and his research focuses on energy systems modeling, analysis, techno-economic optimization, and numerical simulation of transport phenomena within alternative energy systems. His industry experience encompasses development of low-NOx burners, CO2-based refrigeration, and fuel cell technologies. Dr. Braun’s current research activities focus on renewable energy pathways to synthetic fuel production and grid-scale energy storage, biorefinery systems modeling and analysis, and thermochemical energy storage systems for concentrating solar power plants. He has published over 25 journal papers, 3 book chapters, is a Link Energy Foundation Fellow, a member of ASME, ACS, and ASHRAE, and holds 4 patents.