Shin'ya Obara

Contribution of a hydrogen storage-transportation system to the frequency regulation of a microgrid

This work addresses the dynamical contribution of a hydrogen storage-transportation system to the frequency quality of a microgrid containing large amounts of variable-output wind and solar generation which make the task of energy balance more demanding. Hydrogen has recently emerged as a promising energy carrier and in this respect the method of organic chemical hydride (OCH) offers advantages in the transportability and handling, over the traditional methods of compression and storage of hydrogen. This study is regarded as necessary for a clear understanding of how this type of storage system can contribute to the effective energy demand-supply balance, since the power absorption and injection processes are performed by different devices with different time constants. Two broad scenarios are considered: first, the dynamics is evaluated for a step increase of the solar radiation, which imposes a need for rapid power absorption by the water electrolyzer, and secondly, a step decrease in the wind speed, which requires that the loss in power generation be compensated by the injection of power by the fuel cell. The study is performed by modelling and simulation of a microgrid located in a cold region, in the northern part of Japan. The injection and absorption of energy by these two devices can contribute to improve the frequency profile under variable load and generation conditions. However, the maximum possible variations should be carefully taken into account in order to, if necessary, properly set other faster storage devices to provide support in the task of keeping the frequency variation within prescribed values.

Analysis of the overall efficiency of a PEFC with a bioethanol-solar-reforming system for individual houses

Abstract The development of a bioethanol reforming system for fuel cells (FBSR) using sunlight as a heat source was investigated. The FBSR was introduced into standard individual houses for numerical analysis. In this paper, operation of the system was analyzed by introducing two-dimensional heat diffusion equation of the catalyst layer. The supply electric power and heat were investigated using the energy-demand characteristic in a standard house in March and August in Sapporo, Japan. The overall efficiency of the production of electricity and heat power was determined by examining its thermal output characteristic. The amount of hydrogen production, the production-of-electricity characteristic, and the thermal output characteristic were examined using meteorological data in March and August. The overall efficiency of the system, defined as the rate of power and heat output compared to the amount of solar heat collected, was measured on the representative days.

Power generation efficiency of photovoltaics and a SOFC-PEFC combined micro-grid with time shift utilization of the SOFC exhaust heat

The operation plan of a solid-oxide fuel cell (SOFC) and a proton -exchange membrane fuel cell (PEFC) with time shift utilization of the SOFC exhaust heat is developed. The proposed system in this paper consists of a SOFC-PEFC combined system and a photovoltaic system as the energy supply to a micro grid of 30 residences in Sapporo, Japan. The operation plan of the system has three cases: without solar power, with 50% and with 100% of solar output power. Furthermore, three types of system operation of using the SOFC independent operation, PEFC independent operation and SOFC-PEFC combined system are used to supply the demand side. A comparative study between the types of system operation is presented. The power generation efficiency is investigated for different load patterns: average load pattern, compressed load pattern and extended load pattern. This paper reported that the power generation efficiencies of the proposed system at different load patterns are 27% to 48%.

Study on a Power Generation System as Distributed Power Supplies in Consideration of the High-Pressure Dissociation Characteristics in the Small Difference in Temperature of CO2 Hydrate

A fluid mixture of gas and water, pressurized and cooled to a certain pressure and temperature, gas hydrate is produced. By heating the gas hydrate after the formation, extremely high pressure gas can be obtained by hydrate dissociation. This study aims the pressure obtained by dissociation of gas hydrate, drives a high-pressure gas engine generators as distributed power. Gas hydrate has a function of the energy storage capabilities and the working fluid. However, the actuator using the expansion properties dissociation of gas hydrate does not have any examples for previous discussion. This paper focuses on CO2 hydrate. Then the expansive energy dissociation of CO2 hydrate formation rate of hydrates storage capacity is investigated. As a result, it is proved an electric power corresponding to approximately 45% of the daily power consumption (4.5 kWh of generator outputs) of an individual house is stored, when 1 m3 of water is used to generate CO2 hydrate for 480 minutes.

Study on the Operation Analysis of a Compound Energy System using Orthogonal Array-GA Hybrid Analyzing Method

Generally, the output characteristics of the energy apparatus are nonlinear. Furthermore, because multiple power sources are used in microgrids, many variables must be considered to optimize the system. Although the operation of energy systems has been optimized before, nonlinear problems with many variables have been approximated by linear formulas with mixed-integer-programming. Moreover, the conjugate gradient method and genetic algorithm (GA) were also used. In this study, a method of searching for the optimal solution with GA is reported. Any method for obtaining the optimal solution will require a longer time if the number of variables is increased or a higher accuracy is required in the analysis. Otherwise, only quasi-optimal solutions and unsatisfactory solutions of the energy balance equations are obtained. Therefore, orthogonal array used to experimental design are employed in this presentation to reduce the complexity of the problem to plan the optimal operation method of a compound energy system. The initial values of design parameters of the system near the optimum operation method are determined using result of orthogonal array experiment and the factorial effect figure. Next, the optimal solution is obtained by introducing this result as initial values of GA. An example is given in this presentation to explain the orthogonal array (L18)-GA hybrid analyzing method. The proposed analysis method can be utilized to improve the design parameters and the accuracy of the performance analysis. The trial number of times of GA largely decreases. By analysis results, the orthogonal array-GA hybrid analyzing method needs some technique for the setting of each design parameters. This method is available for improvement of the analysis precision by the increase of the number of gene models and the increase of the design parameters. Therefore, proposed analyzing method was overcame weak points of the optimal calculation of conventional simple GA.

Study on the Polymer Membrane-Type Fuel Cell and Hybrid Hydrogenation Engine System Considering Improvement of Efficiency for Partial-Load Operation

Power demand patterns, such as for houses, fluctuate sharply. Therefore, if fuel cell cogeneration is installed in a house, partial-load operations with low efficiency frequently occur On the other hand, if the hydrogen rate of hydrogenation gas-engine generation is increased at the time of low load, emission cleanup and brake thermal efficiency improve. So, in this paper, a hybrid cogeneration system that combines a hydrogenation gas engine and a solid polymer membrane-type fuel cell is proposed. So, operation of a fuel cell or a gas engine with the threshold value of load is investigated. In this paper, four systems were investigated by numerical analysis: independent hydrogenation gas-engine operation, solid polymer membrane-type fuel cell independent operation, that operates a fuel cell or a gas engine with the threshold value of load, and operation using a fuel cell to a base load. As a result, the operating method corresponding to a base load in polymer membrane-type fuel cell had the highest total efficiency. In this case, gas-engine generator (NEG) is operated corresponding to load fluctuation. Moreover, in the comparison results of carbon dioxide emissions, the hydrogenation operation of NEG achieved the best result.

The Distribution Design of PEM Fuel Cell Cogeneration

The capacity reduction of a solid-polymer-membrane-type fuel cell (PEFC) with a reformer by load leveling and by improving the efficiency of part-load operation of the reformer is considered. When electric power demand of the building is small, a part of electric power generated by the fuel cell is supplied to a water electrolysis device, and hydrogen and oxygen gases are generated. And time is shifted and gases are supplied to a fuel cell. Consequently, compared with the conventional system, reduction of 40% of fuel cell capacity is expected. As the 2nd review, route planning program of hot water piping of a fuel-cell-energy-network for fuel cell central system and distributed system was developed. The hot-water piping route planning program of fuel cell network was developed by using genetic algorithm based on the view of TSP (traveling salesman problem)

Development of the control system for gas-hydrate power generation systems

When CO2 hydrate of 273 K is heated by 283 K, the pressure difference of nearly 3 MPa can be obtained by expansion of dissociated gas. Moreover, the heat cycle of generation of CO2 gas-hydrate and gas dissociation can use low temperature exhaust heat and the outdoor air temperature in a cold district. When an actuator is operated using the pressure difference of this heat cycle, the power generation system with a low environmental impact can be obtained. However, there is no example of examination until now regarding the control method of the gas-hydrate power generation system. Therefore, the gas-hydrate power generation system is modeled. The optimal control system is examined taking notice of the electric-power quality of the model described in the top. The proposed system which consists of various loads is assumed, the details of the control method which the stable supply of electric power can realize were clarified.

Development of a small temperature difference generator by using the dissociation and expansion characteristics of a CO 2 hydrate

The introduction of distributed generation systems using renewable energy has been advancing in Japan mainly driven by the influence of the Fukushima Daiichi nuclear accident. In this work, a distributed energy system which exploits the unique state-change property of a CO2 hydrate through a heat cycle is proposed. The proposed system is environmentally friendly because no fossil fuel is burnt and no carbon dioxide is emitted to the atmosphere. Furthermore, the inputs of heat energy are supplied by renewable sources such as the outdoor cold air and the geothermal heat, as cold and hot mediums, respectively. In this study, we determined the characteristics of the output of the proposed generation system by experiments performed in a prototype constructed in our laboratory. As a result, a maximum power output of 30W and a maximum efficiency of 2.15% were obtained.

A study on installation planning for interconnected renewable energy facilities in Hokkaido, Japan

In this paper, to optimize the kind and capacity of renewable energy which is installed in each area, an optimization program was developed by using a simple genetic algorithm (GA). The most efficient and economical system could be identified by applying the model in a random computer search. In the case study, a solar power installed only in seven cities, while a wind power in many cities in Hokkaido, Japan. Through the use of algorithm, the system planning requirements for the interconnection of these renewable energy facilities in a large area were optimized. On the basis of these results, the kind and capacity of renewable energy considered to be the most economically advantageous in that region has been identified and evaluated. The optimization of algorithm for planning and design, an efficient, economical, and interconnected system of electrical power could be realized from renewable energy in the over large area.