Hydrogen is one of the future energy carriers that is distributed from a renewable energy surplus, and does not discharge CO2 and other air pollutions onsite. However, it must be handled carefully in order to be used safely and prevent negative economic and societal impacts when implemented as an energy source. For these reasons, the technologies of “carbon dioxide Recycling (CO2 Recycling)” are receiving much attention in Japan and Europe. The advancement of technologies regarding verylow temperature and high-pressure compression is expected to lead an important role in realizing a hydrogen-implemented society in the sense of three aspects: 1) Energy storage, 2) Carbon capture and recycling, and 3) Energy portability.
Toyota announced the “Toyota Environmental Challenge 2050” in 2015. The CO2 target for new cars in 2050 is a 90% reduction compared to the CO2 level in 2010. In order to reach that target, we are focusing our efforts on developing electric vehicles. We began developing fuel cells in 1992, accumulating a long development history of more than 20 years. We launched the MIRAI passenger vehicle in 2014 and have sold a total of approximately 9,000 to date. Fuel cells produce only water during operation, and fuel-cell vehicles (FCVs) have the features of a long driving range and short refueling time. This paper also explains the wide-ranging fuel cell applicability, from small vehicles such as FC forklifts to large vehicles such as FC buses and FC trucks.
To develop basic technologies for the marine transportation of hydrogen energy, a liquid hydrogen experiment facility (LHEF) has been designed and constructed at the Fukae campus of Kobe University. This LHEF consists of an experiment room, a measurement room, a H2 gas vent line, a vacuum pumping line, high-pressure gas security equipment, etc. A liquid hydrogen (LH2) optical cryostat equipped with a vacuum jacket, a liquid nitrogen space (15 L) and LH2 space (20 L) has been installed in the experiment room. This paper explains the details of constructing the LHEF, including countermeasures for high-pressure gas security and experimental results using LH2 obtained so far.
This article introduces techniques to ensure sufficient hydrogen metering performance, which is a technical aspect for determining things such as guidelines, regulations, and standards for measurement management at hydrogen refueling stations. Measurement management aims to protect the users of fuel-cell vehicles and to promote voluntary appropriate measurement by the companies operating the refueling stations. The gravimetric equipment equipped with scales and high-pressure containers and the master meter equipped with a flowmeter are calibrated using national standards, and were developed for the metering performance inspection of hydrogen dispensers. The number of hydrogen refueling stations that have been subjected to metering performance inspections of their dispensers using the gravimetric equipment has exceeded more than 200 in total. Those include not only initial verification, but also in-service inspections. Continuous and periodical inspections are needed for identifying influential factors and investigating secular changes with regards to measurement accuracy. The public and private sectors have to work together to achieve the target of hydrogen refueling stations becoming an independent business by the late 2020s.
We propose a “hybrid energy storage system composed of electric and hydrogen energy storage systems” and perform verification tests for demonstrating that the hybrid energy storage system proposed is effective for improving the utilization rate of renewable energy and can be used for large-capacity emergency power sources that do not require external fuel procurement. Predicting the difference between solar power generation output and load power consumption using the Kalman filter, short-period fluctuation compensation using the power storage device, and long-period fluctuation compensation using the hydrogen storage system were effective for compensating the precise fluctuation of solar power generation output and load power consumption. The hydrogen release rate from a hydrogen storage alloy was improved by installing a buffer tank between a fuel cell and the hydrogen storage alloy. During 72-hr continuous operation tests assuming a long-term blackout due to a large-scale natural disaster, it was demonstrated that the DC bus voltage fluctuation due to sudden fluctuations in solar power generation output and load power consumption was suppressed to approximately 1.5% or less of the reference voltage (380 V).Therefore, it was proven that the hybrid energy storage system proposed is useful as a large-capacity emergency power source for water purification plants, and enables long-term highly accurate fluctuation compensation and a highly stable power supply.
To realize the practical application of Superconducting Magnetic Energy Storage (SMES) systems cooled by liquid hydrogen, MgB2 is promising as a material for SMES coils in terms of reducing cost in the future and enabling high critical temperature above the temperature of liquid hydrogen. Major technological development issues to realize the application of SMES coils are fabrication of the Rutherford superconducting cable with a kA-class current capacity and fabricating the coils using both Wind and React (W&R) and React and Wind (R&W) methods. Since there is little data regarding the allowable bending strain of the MgB2 strand before heat treatment, an experiment was conducted and it was determined to be approximately 4 % before the fabrication of the cable. The Rutherford cable was designed and developed based on analysis of the space curve theory because the complex bending strain is exposed to the MgB2 filaments during the cable and coil fabrication processes. However, the critical currents measured using cables developed according to the design were degraded approximately 30%. This degradation can be explained as being due to local deformation of the strands caused by compression at the cross-over point between the strands of the conductor. The broken sections of the Nb barrier, which were observed by reviewing SEM images of the strand cross-section, can cause degradation of the critical current. Two double pancake coils, which were primarily wound using the Rutherford cables and manufactured applying both the R&W and W&R methods for the purpose of comparing fabrication processes, were connected in series to excite the coils. As a result, an operating current of 600 A was successfully achieved.
A hydrogen based energy infrastructure, where liquid hydrogen (LH2) is one of the important energy carriers, has recently been being developed in support of a future carbon-free society. Effective utilization of LH2 cold energy is one of the key issues. We have been developing a hydrogen-cooled energy apparatus under a grant from the Japan Science and Technology Agency (JST). LH2 has good physical properties for cooling, including a low boiling point, a high latent heat, a high specific heat and low viscosity properties. Moreover, its low boiling point (20.3 K) is advantageous in view of the excellent electromagnetic properties of high-critical-temperature superconductors, such as YBCO, BSCCO and MgB2, which have been under development for many years. It is important to understand the heat transfer characteristics of LH2 in order to design LH2 cooled superconducting devices. For this purpose, we have designed and constructed basic experimental facilities, such as a thermal-hydraulics experimental system for LH2, in order to carry out systematic investigation of the forced-flow heat transfer, set up experiments for investigating the electro-magnetic properties of superconductors or superconducting magnets, and introduced an LH2 supply and exhaust test system for superconducting rotating machines. Using these facilities, we have conducted systematic experiments relevant to LH2 cooling properties, and LH2-cooled superconductor and superconducting magnet properties, and hence, have accumulated operational experience for handling LH2 safely throughout over 25 test events.
A new Active Magnetic Regenerator (AMR) cycle has been proposed and tested. We developed a four-unit AMR (fAMR) driving cycle consisting of four AMR units and two magnets. f-AMR operates a pair of magnetization and demagnetization processes in an AMR cycle simultaneously, and as a result, four AMR cycles can be continuously operated. The merits of the fAMR cycle are: four times larger cooling capacity, reducing the thermal loss of heat transfer fluid, a simple mechanism to provide a larger temperature span, feasibility as a thermal device, and expandability of the AMR unit number. Experimental results at room temperatures showed unique properties of f-AMR. Using a weak 0.75 T permanent magnet, the largest temperature span reached to 20 deg. using Gd spheres with a 0.4 mm diameter and COP was larger than 1.0 for a temperature span of 10 deg. We have started to use the f-AMR cycle for a hydrogen re-condensation system at 20 K. A hybrid cooling system using f-AMR and GM cycles will be able to pursue a target of 15% Carnot for hydrogen re-condensation liquefiers.
In this paper, we investigated the influence of AC loss in a high-temperature superconducting (HTS) coil and the parallel number of HTS coils on the power transmission characteristics (i.e., receiving power, charging time, and transmission efficiency). We clarified the design guidelines for the wireless power transmission (WPT) system of railway vehicle using HTS coils. We also designed a full-scale WPT system for railway vehicle using the HTS coils. As a result, we found that the WPT system for railway vehicle using HTS coils enables fast charging with high operating efficiency at low frequency. This result shows that the WPT system for railway vehicle using HTS coils can realize faster charging and higher operating efficiency at a lower frequency than a system with copper coils.