In this study, we significantly enhanced the performance of metal hydride (MH) tanks without incurring substantial costs by adopting commercially available heat exchangers, optimizing heat-medium flow paths, and incorporating structures to improve hydrogen diffusibility. The significance of this study lies in the fabrication of a practically sized MH tank that achieves high hydrogen absorption and release performance below 1 MPaG, using commonly available heat exchangers and TiFe-based MH. Even when the flow velocity through the heatmedium path of the exchanger was low, optimizing the flow path design enabled excellent absorption and release performance. Furthermore, the adoption of an original hydrogen diffusion structure within the MH tank improved hydrogen diffusibility, thereby enhancing absorption and release performance. The developed tank demonstrated the hydrogen absorption and release capabilities required for off-site hydrogen utilization. The tank was also successfully scaled up to a size capable of storing approximately 88 Nm3 of hydrogen. The findings of this study are significant both academically and practically, and the integration of the fabricated tank into buildings has the potential to contribute substantially to the decarbonization of urban areas.

Using off-site hydrogen can reduce CO2 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 (R), 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 Nm(3) 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 (R) can extend the operation time of fuel cells and significantly contribute to a reduction in CO2 emissions. Estimations indicate that gray hydrogen increases CO2 emissions, and CO2 emissions can be reduced to zero using a green-hydrogen supply of 300 Nm(3). The results indicate that the type and quantity of supply of off-site hydrogen are important for reducing the CO2 emissions of buildings.(c) 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

We have been developing hydrogen utilization systems for buildings using fuel cell, electrolyzer, and metal hydride hydrogen storage. This paper describes the reduction of CO2 emissions from buildings and assesses the hydrogen storage capacity required for using off-site hydrogen. We prepared a low- and a high-load-factor model to investigate the effects of off-site hydrogen deployment for different building uses. We confirmed that off-site hydrogen delivery contributes to reducing hydrogen storage capacity in the two models. We identified how hydrogen delivery planning can substantially reduce hydrogen storage capacity while achieving high CO2 emission reductions. The study also confirmed that hydrogen transportation is effective, even when parameters such as photovoltaic (PV) generation capacity are considered. The entire off-site hydrogen utilization system costs, including the cost of operating off-site hydrogen in a building, were evaluated to identify lower-cost operation conditions. The findings show that the cost of operating an off-site hydrogen system in a building can be managed through a well-designed hydrogen delivery strategy that does not increase the capacity required for hydrogen storage facilities.

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 CO2 reduction capability evaluation is based on the results. In all cases, the CO2 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 CO2 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.

After the end of the feed-in tariff (FIT) that promotes the introduction of renewable energy, the use of renewable energy is being discussed. We have developed a hydrogen utilization system which can store renewable energy. An energy simulation was performed when this system was applied to a building with the energy reduction rate as a constraint. As a result, we clarified the installed capacity when hydrogen utilization system can be selected economically, and found an effective equipment price factor.

To ensure the energy efficiency of renewable hydrogen energy systems, power conservation and thermal management are necessary. This study applies these principals to the operation of metal hydride tanks (MHTs) in a bench-scale hydrogen system, named Hydro Q-BiC (TM), comprising photovoltaic panels (20 kW), an electrolyzer (5 Nm(3)/h), MHTs containing a TiFe-based MH (40 Nm(3)), fuel cells (FC; 3.5 kW(power)/2.5 kW(heat)), and Li-ion batteries (20 kW/20 kWh). Here, we show that in a modified hydrogen production operation, with limited use of auxiliaries for cooling the MHTs, the power consumption of the MHTs was reduced by more than 99% compared to a typical operation. The thermal requirements for the MHTs were reduced by ceasing production in a pressurized state. During the hydrogen use operation, the power consumption was reduced to 1/4 and the FC heat output could be fully used; hence, the overall energy efficiency (power-to-hydrogen-to-power/heat) was as high as similar to 60% (43% for the typical operation). (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

In this study, cold start-up operations for a stationary hydrogen energy system utilizing metal hydride (MH) tanks, named Hydro Q-BiC (TM), 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 (double left right arrow 1.97 kWh) was sustained, overall, the procedure yielded an acceptable energy efficiency of 79%. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

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. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Nearly 40% of the total greenhouse gases (GHGs) are emitted from the energy consumption in buildings in Japan, which should be reduced to address global warming. A hydrogen energy utilization system with renewable energy (RE) was designed by MATLAB/Simulink simulations for realizing a zero emission building (ZEB), comprising a hydrogen-producing electrolyzer, a hydrogen storage tank, fuel cell, and battery for short-term power storage with estimated specifications of 3.0 Nm(3)/h, 36 Nm(3), 4.2 kW, and 10 kW/17 kWh, respectively. We identified a small low-rise building (total floor area: similar to 1000 m(2), demand: similar to 5 kW) as the planned ZEB to construct and operate a bench-scale system. A 20-kW photovoltaic (PV) system was selected as the RE source. Two hydrogen production processes (constant power of 10 kW or with excess PV power) were evaluated by simulating 48-h operations on fine and cloudy days, where the former showed higher efficiency. The results with excess power on a fine day agreed well with that of actual operation, validating our simulation models. Further, the constant case was suitable for practical application. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Since the output of photovoltaic (PV) generation includes power fluctuations caused by natural conditions, the installation of PV on a large scale is expected to affect load frequency control of the power grid. One method of compensating power fluctuations is the use of energy storage (ES), such as batteries and capacitors. A power fluctuation compensation system composed of an electrical double layer capacitor energy storage system (ESS) and a Li-ion battery energy storage system is considered. The power loss characteristics of both ESSs during power fluctuation compensation are modeled by equivalent circuits based on ES impedance spectra. The models are validated by experiments simulating power fluctuation compensation. Using these ES models, simulations were carried out to determine the power fluctuation dispatch method between the two ESSs and the capacity of the ESSs in consideration of power loss minimization.

We have developed control system for micro-grid in which a battery compensates fluctuation by solar generation and electrical load. This paper describes an evaluation of control parameters (compensated band, output's initial value) for battery control to obtain peak demand reduction by the micro-grid. We show that by applying this method, amount of peak demand reduction has little influence of prediction error and reliability of this method is verified by two kinds of demand profiles in summer and winter. These results show that the method has applicability to the micro-grid operation.

In this paper, the use of heat pump air-conditioning system (HPACS) for power fluctuation compensation is focused. Verification experiments have been carried out using a model microgrid system with gas engine, battery energy storage system (BESS), HPACS, photovoltaic cells, and loads. The BESS's necessary energy capacity for power fluctuation compensation and the microgrid system's ability to suppress power fluctuation is analysed by use of experimental results. It is clarified from the analysis that control of HPACS is effective for reduction of BESS's necessary energy capacity without deterioration of microgrid's ability to suppress power fluctuation. Furthermore, the temperature of the rooms that use the HPACS is calculated by a room temperature calculation model. The results show that the temperature fluctuation caused by control of HPACS is negligible small.

Microgrid is one of the solutions to supply stable electrical power with a large amount of intermittent renewable sources. However, efficiency of DGs and ESSs in microgrid might drop to a lower value because of microgrid operation, and there is a possibility that the convenience of a consumer may be spoiled. This paper shows a load forecast method and an optimized operation planning for DGs and ESSs in microgird to solve this problem. It is possible to estimate high accuracy electrical load by using a pattern data of power consumption not including power consumption of heat sources and an operation planning of the heat sources which run according to heat load prediction. The operation planning of DGs and ESSs consider direct-current characteristics of ESSs. As a result, error of SOC between planning and real-time operation decreases.

To reduce the necessary capacity of energy storage systems(ESSs) for power fluctuation compensation, the concept of load control has been proposed. In this paper, heat pump air conditioning unit is treated as controllable load. Verification experiment of heat pump power consumption control has been conducted using model microgrid with gas engine(GE) and Nickel Metal Hydride(NiMH) battery. The fastest part of the power fluctuation is compensated by NiMH battery, and the slowest part of the power fluctuation is compensated by GE. The heat pump is used for compensation of mid-range power fluctuation. The control system was designed to keep the tie line power flow of the microgrid to a constant value. In the experiment, the fluctuation of the tie line power flow was small compared to that of load demand in microgrid. The result of the experiment suggests that heat pump has enough response speed and control of heat pump's power consumption as controllable load is effective for power fluctuation compensation.

The power consumption control of hat pump air-conditioning system (HPACS) is expected to be an effective method to reduce energy capacity of energy storage systems (ESSs) that is necessary to compensate power fluctuation caused by renewable energy sources. In this research, experiments to control HPACS's power consumption directly has been conducted using real machine. The input signal of the HPACS has been calculated by microgrid control simulation. The heat output of the HPACS has been measured and thermal comfort of the room that is air-conditioned by the HPACS has been analyzed using room temperature calculation model. The results of the experiments and analysis show that by implementing appropriate temperature control loop, the HPACS can compensate power fluctuation in frequency range between 0.005Hz and 0.01Hz without affecting thermal comfort of the users.