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By using a newly constructed bench-scale hydrogen energy system with renewable energy, ‘Pure Hydrogen Energy System’, the present study demonstrates the operations of a metal hydride (MH) tank for hydrogen compression as implemented through the use solar thermal energy. Solar thermal energy is used to generate hot water as a heat source of the MH tank. Thus, 70 kg of LaNi5, one of the most typical alloys used for hydrogen storage, was placed in the MH tank. We present low and high hydrogen flow rate operations. Then, the operations under winter conditions are discussed along with numerical simulations conducted from the thermal point of view. Results show that a large amount of heat (>100 MJ) is generated and the MH hydrogen compression is available. [ABSTRACT FROM AUTHOR]

Abstract: We have been performing research on a Totalized Hydrogen Energy Utilization System (THEUS) which is composed of a Unitized Reversible Fuel Cell (URFC) and metal hydride tanks. THEUS is very similar to the regenerative fuel cell system located at the Savannah River National Laboratory (SRNL) but it utilizes the thermal energy from the system to improve the total system efficiency. AIST and SRNL started a collaborative research program on THEUS in 2010 under the Clean Energy Partnership Technology Program between METI and DOE. To initiate the project, a horizontal type metal hydride tank was developed. It had a double coil type heat exchanger and contained 50kg of AB5 type metal hydride alloy. Absorption and desorption of 6,350 NL of hydrogen was successfully attained at an absorption rate of 11.8 NL/min and a desorption rate of 8.1 NL/min. The experimental results of the heat exchanging performance were compared with the results of a vertical type metal hydride tank which was developed in AIST in 2008. This paper introduces the experimental results of the metal hydride tank which is tested in SRNL. [Copyright &y& Elsevier]

Abstract: We have been performing research on the Totalized Hydrogen Energy Utilization System (THEUS) which has applications to commercial buildings and a planned added function of supplying energy to stations for hydrogen and electric vehicles. In that case we will utilize liquid hydrogen transported from a hydrogen station and all Boil-Off Gas (BOG) will be recovered in THEUS’s metal hydride tanks. It is known that BOG is chiefly composed of para-hydrogen, which has different thermo-physical properties from normal hydrogen. It has been reported that some metal hydride alloys work as a catalyst to accelerate the para-ortho conversion and the conversion proceeds relatively fast in the case of La–Ni5. The conversion is considered to be an endothermic reaction. A misch metal (Mm)-Ni5 metal hydride alloy, which contained La and Ni, was used in our THEUS metal hydride tank. To examine the effect of the para-ortho conversion on the THEUS operation, we investigated the absorption/desorption characteristics of the metal hydride tank with BOG. We confirmed that the effect of the heat of conversion was very small and BOG could be treated as normal hydrogen for practical application. [Copyright &y& Elsevier]

Abstract: Experimental results for hydrogen storage tanks with metal hydrides used for load leveling of electricity in commercial buildings are described. Variability in electricity demand due to air conditioning of commercial buildings necessitates installation of on-site energy storage. Here, we propose a totalized hydrogen energy utilization system (THEUS) as an on-site energy storage system, present feasibility test results for this system with a metal hydride tank, and discuss the energy efficiency of the system. This system uses a water electrolyzer to store electricity energy via hydrogen at night and uses fuel cells to generate power during the day. The system also utilizes the cold heat of reaction heat during the hydrogen desorption process for air conditioning. The storage tank has a shell-like structure and tube heat exchangers and contains 50 kg of metal hydride. Experimental conditions were specifically designed to regulate the pressure and temperature range. Absorption and desorption of 5,400 NL of hydrogen was successfully attained when the absorption rate was 10 NL/min and desorption rate was 6.9 NL/min. A 24-h cycle experiment emulating hydrogen generation at night and power generation during the day revealed that the system achieved a ratio of recovered thermal energy to the entire reaction heat of the hydrogen storage system of 43.2% without heat loss. [Copyright &y& Elsevier]

Abstract: Numerical simulation of a hydrogen storage tank of a Totalized Hydrogen Energy Utilization System (THEUS) for application to commercial buildings was done to verify the practicality of THEUS. THEUS consists of a fuel cell, water electrolyzer, hydrogen storage tank and their auxiliary machinery. The hydrogen storage tanks with metal hydrides for load leveling have been previously experimentally investigated as an important element of THEUS. A hydrogen storage tank with 50 kg AB5 type metal hydride was assembled to investigate the hydrogen-absorbing/desorbing process, which is exothermic/endothermic process. The goal of this tank is to recover the cold heat of the endothermic process for air conditioning, and thus improve the efficiency of THEUS. To verify the practical effectiveness of this improved system, we developed a numerical simulation code of hydrogen storage tank with metal hydride. The code was validated by comparing its results with experimental results. In this code the specific heat value of the upper and lower flanges of the hydrogen storage tank was adjusted to be equal to the thermal capacity of the entire tank. The simulation results reproduce well the experimental results. [Copyright &y& Elsevier]

In this study, demonstration of a one-stage metal hydride hydrogen compressor (MH compressor) by using a BCC alloy was performed. It was estimated that V 40 Ti 22 Cr 38 could compress approximately 1.6 wt% of hydrogen from 1.0 to 10 MPa in 20–140 °C temperature range from equilibrium theory via pressure-composition-isotherm measurements. For demonstration of an actual MH compressor, a kg-scale experimental system was set up; V 40 Ti 22 Cr 38 (1.4 kg) was introduced into a 1-inch cylindrical vessel with a heat-medium flow tube outside. As a result, 1.0 MPa of hydrogen can be compressed into the hydrogen cylinder at >10 MPa by hydrogen absorption at 10 °C and desorption at 160 °C for 30 min each (1 cycle/h) to achieve a compression rate of 0.23 Nm3/h and indicate the potential of the practical MH compressors by using BCC alloy. • Thermodynamics of V 40 Ti 22 Cr 38 as MH compressor with H 2 ab/desorption was evaluated. • V 40 Ti 22 Cr 38 can compress 1.6 wt% of hydrogen from 1.0 to 10 MPa between 20 and 140 °C. • Demonstration of MH compressor with 1.4 kg of V 40 Ti 22 Cr 38 was performed. • Compression from 1.0 to >10 MPa at 0.23 Nm3/h was achieved between 10 and 160 °C. [ABSTRACT FROM AUTHOR]

In this study, the cycle durability and thermodynamic characteristics of V 40 TiCr and V 70 TiCr were examined to evaluate their performance as metal hydride compressors. The cycles of incomplete hydrogen absorption under low pressure increased the hysteresis in the higher hydrogen concentration region, wherein cycling was not conducted, thereby forming an unavailable region; however, the equilibrium absorption pressure recovered after several full cycles at higher pressure. Due to the thermodynamic evaluation after 300 full cycles, V 40 TiCr with 0.70, 0.53, and 0.44 of Ti/Cr ratio are expected to compress 1.2 wt% of hydrogen from 0.25 to 4.9 MPa, 1.96–22.2 MPa, and 5.97–46.8 MPa, respectively, between 40 and 150 °C. V 70 TiCr with a low Ti/Cr ratio (0.33) demonstrated good cycle durability and is expected to compress 1.7 wt% of hydrogen 10 times from 5.4 to 54.8 MPa between 35 and 155 °C. • VTiCr alloys are potential materials for hydrogen compression. • Cycles of incomplete hydrogen absorption forms unavailable region for VTiCr alloys. • V 40 TiCr can be adjusted as MH compressor over a wide pressure range. • V 70 TiCr with high Ti/Cr ratio shows worse cycle durability than that of V 40 TiCr. • V 70 TiCr is more suitable for compression in high pressure region than V 40 TiCr. [ABSTRACT FROM AUTHOR]

Using off-site hydrogen can reduce CO 2 emissions from urban buildings with limited renewable energy generation. We demonstrated the supply and usage of off-site green hydrogen using a pilot-scale hydrogen energy utilization system, Hydro Q-BiC®, for a commercial building. The off-site location supplied green hydrogen to the on-site system using high-pressure gas. By developing rapid-filling-type metal hydride tanks, we could safely fill 100 Nm3 of off-site hydrogen at <1 MPaG in approximately 1 h. The use of off-site green hydrogen in a 24 h operation of Hydro Q-BiC® can extend the operation time of fuel cells and significantly contribute to a reduction in CO 2 emissions. Estimations indicate that gray hydrogen increases CO 2 emissions, and CO 2 emissions can be reduced to zero using a green-hydrogen supply of 300 Nm3. The results indicate that the type and quantity of supply of off-site hydrogen are important for reducing the CO 2 emissions of buildings. • Utilization of off-site hydrogen can help reduce CO 2 emissions from urban buildings. • Hydrogen energy utilization system Hydro Q-BiC® developed for a commercial building. • Hydro Q-BiC® tested to demonstrate efficacy in reducing CO 2 emissions of a building. • Type and quantity of off-site green hydrogen influence reduction in CO 2 emissions. [ABSTRACT FROM AUTHOR]

A demonstration of the Hydro Q-BiC®, i.e., a pilot-scale green hydrogen energy utilization system consisting of 64.75-kW photovoltaic (PV) panels, a 5-Nm3/h water electrolyzer, 40 Nm3 of metal hydride hydrogen storage, 14-kW fuel cells, and 20-kW/20-kWh Li-ion batteries, is discussed here. We set up our hydrogen system in front of a market administration building with demands that differ from those of a typical business building. The purpose of this study is to demonstrate the practicability of the green hydrogen system. The demonstration tests include 24-h experiments with various weather conditions: clear, cloudy, and clear to rainy; the CO 2 reduction capability evaluation is based on the results. In all cases, the CO 2 reduction capability is shown to be better than that of the PV-only system. However, the utilization of grid power for hydrogen production is proven to be of concern in the event of drastic and unexpected changes in weather conditions. Simulating annual CO 2 emissions indicates that the Hydro Q-BiC® can reduce emissions by more than 50%. We believe our findings can develop the practical application of hydrogen energy systems for buildings. [Display omitted] • A green hydrogen energy utilization system was demonstrated in a commercial building. • System effectiveness and efficiency were evaluated under various weather conditions. • CO 2 reduction capability was compared to that of a photovoltaic panel (PV)-only system. • Our system was more capable of CO 2 emission reduction than the PV-only system. • Annual CO 2 emissions simulation results indicate a reduction of >50%. [ABSTRACT FROM AUTHOR]

In this study, cold start-up operations for a stationary hydrogen energy system utilizing metal hydride (MH) tanks, named Hydro Q-BiC™, are conducted for emergency power outages, i.e., when no power from both grid and renewable energy sources are available. Here, cold start-up refers to the heating of cold MH tanks and an increase in desorbing pressures to the minimum required for fuel cell (FC) operation to supply power and heat continuously. Our proposed procedure uses only the existing system components to generate power and heat. No external heat sources are used. Power was supplied from a Li-ion battery, and hydrogen was produced by the electrolyzer (ELY), stored in the MH tanks and used by the FC. Three internal heat sources were used to heat the MH tanks: ELY waste heat, MH reaction heat, and FC heat output. Two H 2 storage capacities were tested (75% and 50%) and both supplied ≥30 kWh electricity within 30 min. Although a minor energy loss of 5275 kJ (⇔ 1.97 kWh) was sustained, overall, the procedure yielded an acceptable energy efficiency of 79%. Image 1 • Cold start-up operations were conducted for emergency power outages. • Only existing system components are used to generate FC power and heat. • Results indicate an immediate and prolonged supply of FC power and heat. • Overall, the procedure yields an acceptable energy efficiency of 79%. • Proposed method is effective for a wide range of metal hydride applications. [ABSTRACT FROM AUTHOR]

We describe the operation of a bench-scale stationary hydrogen energy system comprising photovoltaic (PV) panels, a water electrolyzer (Ely), metal hydride tanks fabricated using an AB-type TiFe-based alloy (TiFe-based tanks), fuel cells (FC), and batteries under various weather conditions. The FC and TiFe-based tanks are thermally coupled to transfer heat when necessary to stabilize the output power, and automatic control is provided via a building energy management system (BEMS), which plans the operating schedule up to 48 h in advance based on the weather forecast and expected demands of the building. Experiments were conducted for 24-h operation on a fine day, 48-h operations on partly cloudy and partly cloudy days, and 48-h operations on partly cloudy and rainy days in order to verify the system. Each operation was performed as planned. Our results show that it is possible to operate the hydrogen system all year round without external heat sources. • We describe the operation of a bench-scale stationary hydrogen energy system. • The metal hydride tanks were fabricated using an AB-type TiFe-based alloy. • Thermal coupling between the fuel cells and tanks was provided. • The hydrogen system was validated under fine, partly cloudy, and rainy conditions. • The hydrogen system can be operated year-round without external heat sources. [ABSTRACT FROM AUTHOR]