Tatsuya Kodama’s research while affiliated with Niigata University and other places

In order to produce electricity beyond insolation hours and supply to the electrical grid, thermal energy storage (TES) system plays a major role in CSP (concentrated solar power) plants. Current CSP plants use molten salts as both sensible heat storage media and heat transfer fluid, to operate up to 560°C. To meet the future high operating temperature and efficiency, thermochemical storage (TCS) emerged as an attractive alternatives for next generation CSP plants. In these systems, the solar thermal energy is stored by endothermic reaction and subsequently released when the energy is needed by exothermic reversible reaction. This review compares and summarizes different thermochemical storage systems that are currently being investigated, especially TCS based on metal oxides. Various experimental, numerical, and technological studies on the development of particle reactors and materials for high‐temperature TCS applications are presented. Advantages and disadvantages of different types heat storage systems (sensible, latent, and thermochemical), and particle receivers (stacked, fluidized, and entrained), have been discussed and reported. This article is categorized under: Sustainable Energy > Solar Energy Emerging Technologies > Energy Storage Emerging Technologies > Materials

To perform solar thermochemical conversion, by utilizing high-temperature solar heat as an energy source and redox metal oxide particles as a chemical source, fluidized bed reactor has been developed to produce clean fuels. In this study, an Euler-Lagrange model has been developed for the simulation of particulate and gas flows in fluidized bed reactor for hydrogen production, by two-step water splitting cycles, using solar beam down concentrating system. The solid phase is modelled by Discrete Element Method (DEM) using soft-sphere approach and the gas phase is modelled as continuum by Navier-Stokes equations. The flow behavior of newly developed fine ceria particles has been analyzed for various conditions using the 30 kWth fluidized bed reactor prototype. The effect of particle size on the flow-dynamics at the spout, fountain periphery and annulus of the internally circulating fluidized bed has been examined. The results indicate that the particle size distribution should be minimized as much as possible to avoid the segregation behavior of different size particles.

Solar thermochemical energy storage systems, utilize the entire spectrum of solar radiation to drive endothermic chemical reactions, have received great interest in concentrated solar power applications during the past years. Storing solar radiation as chemical energy during the day can be utilized at night times and cloudy days. In these solar thermochemical processes, chemically reactive and radiatively participating multiphase flows in various regimes are frequently encountered. Numerical modeling of multiphase flows assists to optimize the processes of solar thermochemical reactors by reducing the time-consuming experimental testing and cost. In this study, an Euler-Euler two phase model has been developed to investigate the fluidization behavior of 2:1 iron-manganese oxide redox and spinel particles for thermochemical and sensible heat storage systems respectively. In order to validate the model, a pseudo 2D experimental set up has been made. Experimental and numerical results have been compared for various conditions. The effect of gas flow rate on the fluidization behavior has been analyzed.

The effects of doping manganese ions into a cerium oxide lattice for a thermochemical two-step water-splitting cycle to produce oxygen and hydrogen and new synthesis methods were experimentally investigated. In order to comparison of oxygen/hydrogen producing performance, pristine CeO2, a coprecipitation method for Mn-CeO2, and a direct depositing method for Mn-CeO2 with different particle sizes (50~75, 100–212, over 212 μm) and doping extents (0, 5, 15 mol%) were tested in the context of synthesis and fabrication processes of reactive metal oxide coated ceramic foam devices. Sample powders were coated onto zirconia (magnesium partially stabilized zirconia oxide, MPSZ) porous foam at 30 weight percent using spin coating or a direct depositing method, tested using a solar reactor at 1400 °C as a thermal reduction step and at 1200 °C as a water decomposition step for five repeated cycles. The sample foam devices were irradiated using a 3-kWth sun-simulator, and all reactive foam devices recorded successful oxygen/hydrogen production using the two-step water-splitting cycles. Among the seven sample devices, the 5 mol% Mn-CeO2 foam device, that synthesized using the coprecipitation method, showed the greatest hydrogen production. The newly suggested direct depositing method, with its contemporaneous synthesis and coating of the Mn-CeO2 foam device, showed successful oxygen/hydrogen production with a reduction in the manufacturing time and reactants, which was lossless compared to conventional spin coating processes. However, proposed direct depositing method still needs further investigation to improve its stability and long-term device durability.

A copper–germanium alloy (Cu–Ge alloy) was examined as a phase change material, at temperatures exceeding 600°C, for latent heat storage in solar thermal applications. First, the thermo-physical properties of the Cu–Ge alloy were examined using differential scanning calorimetry, thermomechanical analysis, and laser flash analysis. Second, to evaluate the thermal response and reliability of the Cu–Ge alloy, the cyclic properties of thermal charge/discharge were examined under various thermal conditions. The alloys obtained after the tests were examined for their chemical compatibility with the stainless steel container using an electron probe micro analyzer. The elemental distribution of each Cu–Ge alloy was evaluated using cyclic performance tests. Finally, the chemical compatibility of the Cu–Ge alloy was evaluated using a high-temperature test with candidate materials of a phase change material container vessel [stainless steel (SUS310S), Inconel625, silicon carbide (SiC), and alumina (Al2O3)]. The Cu–Ge alloy exhibited significant potential as a latent heat storage material in next-generation solar thermal power plants because it demonstrates various advantages, including a superior storage capacity at a temperature of 644°C, temperature coherence to the phase diagram, a quick thermal response, satisfactory cyclic behavior of charge/discharge modes, a thermodynamically stable metallographic structure, and non-reactivity with container ceramic materials (SiC and Al2O3).

In this paper, the effect of doping of Manganese on to Cerium oxide for thermochemical two-step water splitting cycle for produce the hydrogen was experimentally studied. In order to compare the oxygen/hydrogen productivity, pure CeO2, coprecipitation method applied Mn-CeO2, and direct doping calcination method adopted Mn-CeO2 were used to thermo-chemical two-step water splitting cycle tests. The synthesized sample powders were coated on the reticulated porous foam device and tested in the fixed bed type reactor for the temperature of 1400 °C for thermal reduction step, and 1200 °C for water decomposition step through 5 cyclic tests. The redox reactive foam devices were irradiated by 3kW sun-simulator, and all samples recorded successful oxygen/hydrogen production. Among the 3 sample devices, the 15 mol% Mn-CeO2 foam device which synthesized by direct doping calcination method shows highest hydrogen production amount and H2/O2 conversion ratio.

A thermochemical two-step water-splitting cycle using perovskite oxide of La0.7Sr0.3Mn0.9Cr0.1O3 was examined for hydrogen production from water using concentrated solar radiation. The impact of the thermal reduction temperatures of 1000–1350 °C on oxygen/hydrogen productivity and repeatability was examined for hydrogen production at a water decomposition temperature of 1200 °C. The sample displayed relatively high evolution rates of oxygen at TR temperatures of 1350-1300°C, and showed similar rate at TR temperatures of 1000-1200 °C. After the sample was subjected to the TR step at temperatures of 1350-1300 °C, the obtained samples were superior hydrogen production rate to the others. On the other hand, the sample provided relatively good reactivities and repeatabilities for oxygen release and hydrogen production with a small production level without coagulation or sintering during the TR temperatures of 1000-1200 °C.

A thermochemical two-step water-splitting cycle using perovskite oxide of La0.7Sr0.3Mn0.9Cr0.1O3 was examined for carbon monoxide production from CO2 using concentrated solar radiation. Previously, the authors proved the perovskite oxide can thermochmically split H2O via two-step process into oxygen and hydrogen in an individual step. In this study, a thermochemical two-step CO2 splitting cycle using the perovskite oxide was examined for the reactivity and repeatability of redox reaction at CO2 spitting temperatures of 1000-1200 °C. The reactivity and repeatability for two-step CO2 splitting was compared to those for H2O splitting operating at the same temperature level.

Latent heat storage technology in CSP plant has been studied to enhance the dispatchability of solar energy in order to meet fluctuating electricity needs. A novel concept using metal alloys as latent heat storage material gives way to achieve this technology. In this paper, we analyzed the structural and thermal properties of Cu-Ge alloy to evaluate the potential of metallic PCM for high temperature TES application. Containment options for metallic PCM were explored and the materials are selected for long term operation. Compatibility tests of stainless steel, alumina and SiC ceramics under inert atmosphere were performed at high temperatures (800°C) for a duration of 1 month (720 h) in order to develop a suitable container material for thermal energy storage system.