Solid Oxide Cell Technology for Supply, Recovery, and Storage Energy

Abstract

Fuel Cell Energy, Inc. (FCE) is advancing the current state of Solid Oxide Fuel Cell (SOFC) technology towards commercial deployment for efficient and nonpolluting generation of electric power from natural gas and biomass derived fuels. Additionally, FCE is utilizing the same solid oxide cell and stack technology in electrolysis of steam for production of hydrogen from renewable sources and other electric power sources, such as nuclear power plants during the curtailment periods. Additionally, FCE’s SOFC technology has shown to be a viable technology for storage of energy by cyclic charge and discharge operation.FCE’s SOFC technology is based on anode supported thin electrolyte planar cell platform chosen for its higher power density at reduced operating temperature (700-800°C). Traditional materials, such as Ni/YSZ anodes, YSZ electrolytes and perovskite cathodes have been utilized in a basic cell structure. Research and development focus has been placed on developing better electrochemical functional areas at both cathode/electrolyte and anode/electrolyte interfaces. This was achieved through material advancements, microstructure optimization, and manufacturing process integration.The solid oxide stack is comprised of planar solid oxide fuel cells with glass ceramic seals and sheet metal, bipolar plate interconnects; and has a mix of internal and external gas manifolds. Each cell is a 0.30 mm thick annular (donut shaped), cell with 81 cm2 active area made in a process consisting of tape casting, screen printing, and firing cell components. The full height stack consists of 350 repeat units and a set of non-repeat parts. A repeat unit includes one ceramic cell, inner and outer seals, and a metallic interconnect which incorporates flow fields for both fuel and oxidant. Non-repeat parts include the end plates, manifolds, and compression components. The stack is capable of producing 7kW power when fueled with natural gas, biogas, hydrogen, or other fuels. The same stack is capable of operating at higher power density in electrolysis mode, producing 25 kg/day hydrogen with 36 kW power input.FCE’s SOFC system design philosophy is based on using factory-assembled stack building blocks, which in turn may be used to fabricate larger multi-stack modules for applications in centralized natural gas and coal fueled power plants. An attractive pathway to deployment of SOFC systems is through near-term market opportunities in natural gas fueled distributed generation (DG) applications. FCE is planning to take the advantage of the scalability, modularity, and fuel flexibility of the SOFC technology to transition the technology from small (sub-MW) systems to megawatt class power plants for distributed generation, and ultimately (through aggregation of fuel cell modules) to large stationary power plants for base-load utility applications using coal and/or natural gas fuel.FCE has recently designed, fabricated, and tested a 200kW natural gas fueled packaged system. This autonomous unit is an outdoor rated power system with capabilities for both grid-connection as well as island operation.Electricity storage is a growing need given the increasing penetration of intermittent renewable sources of solar and wind. Traditional battery storage technology uses rare materials that could pose sourcing challenges and depletion with widespread adoption. Hydrogen based energy storage is the only practical way to store the GWh of energy that will need to be stored to enable significant penetration of intermittent renewable energy on the electricity grid. Another advantage of hydrogen based energy storage is that once hydrogen is stored it can be used to make power, or exported for another use such as vehicle fueling or industrial uses.