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Since plants with a high biomass conversion efficiency of light energy consume less energy and require shorter cultivation periods, it is expected that plant factories can have more output with less energy. However, there have been few studies on the biomass conversion efficiency of light energy in various cultivated plants, and this agricultural engineering field is still unexplored. If the amount of energy consumed by a plant factory can be obtained from the biomass conversion efficiency of light energy, the plant types that can be grown in a plant factory and the economic efficiency of the plant factory can be clarified. In this study, we determined the amount of light energy required for plant cultivation by measuring the wavelength distribution of sunlight and plant-growing light-emitting diodes. Also, we investigated the light to biomass conversion efficiency (LBE) from the amount of heat generated by the biomass of cultivated plants. The LBE was also used to analyze the payback period of plant factories so as to estimate the profitability of various cultivated plants. However, since the market price of plants varies with the selling season, it is necessary to clarify the biomass conversion efficiency while taking into account the annual air conditioning energy consumed by plant factories. The biomass conversion efficiency by light and air conditioning energy (BELA) is the energy conversion efficiency based on the input values of light energy and air conditioning energy and the output value of the biomass calorific value of cultivated plants. In this study, a new method for economically determining the plant types that can be cultivated using BELA was proposed.

In this study, we clarify the effect of cyclopentane (CP), which is a formation reaction promoter and shifts the phase equilibrium curve to high temperature and low pressure, on the energy storage density of the proposed CO2 hydrate power generation system. The phase change should be shifted to a higher temperature for expanding the operating conditions of the power generation systems. In addition, the formation of hydrates is facilitated by the repeated formation and dissociation of gas hydrates (the memory effect). Although the memory effect mechanism during hydrate formation has not yet been clarified, its occurrence has been reported in many studies, where the reformation of each gas hydrate began more quickly when compared with the initial case. Hydrate formation and dissociation were conducted at least once in a day in the proposed power generation system. Therefore, the power generation cycle can be repeatedly performed in a short time period if the memory effect is effectively applied. Hence, we conducted experiments in the presence or absence of CP and with respect to the time duration of the dissociation state in the formation and dissociation cycles. Furthermore, we calculated the hydrate amount and the time required for its formation under each condition. Subsequently, the energy storage density of the proposed power generation system can be estimated based on the calculation results. The conducted experiments and calculations reveal that a CO2 hydrate power generation system containing CP is more beneficial when compared with a pure CO2 hydrate power generation system in terms of the energy storage density and the time required for storing energy.

In order to make an electric power of renewable energy source increase, development of a new transmission network is effective. However, it is because installation of a new transmission network takes a huge investment, operating technique regarding improvement of the utilization factor of a transmission network is investigated. On the other hand, stabilization of distribution electric power by hydrogen energy careers, such as ammonia or methyl-cyclohexane (MCH) is expected to contribute to the drastic increase in utilization factor of the transmission network. Moreover, because these hydrogen energy careers can store electric power, it is effective in making the reliability of the transmission network increase. The energy flow of the system accompanied by use of each energy career of ammonia or MCH is clarified, the examination method of the utilization factor of the transmission network with the electric power leveling by the hydrogen career was proposed. The proposal analysis method is applied to a transmission network of Wakkanai, the relation between the amount of introduction of renewable energy and the utilization factor of the transmission network, and the utilization factor of the transmission network using a hydrogen career were clarified.

In this research, we investigated an energy supply system based on hydrogen derived from renewable energy. We modeled the energy flow and efficiency of a system using the MCH-toluene-hydrogen reaction cycle (MTHR) by methylcyclohexane (MCH, C6H11CH3) and toluene (C6H5CH3). Electric power storage by the MTHR and energy transport by a hydrogen infrastructure were investigated using numerical analysis. The energy flow of the whole system was investigated by cooperation of the numerical model of each component. The rate of input and output based on the calorific value of hydrogen defines the efficiency of each component and the system. When the electric power output of the renewable energy source was set to 100%, the maximum energy efficiency based on the calorific value of the hydrogen supplied from the hydrogenation facilities was 53.6%. Conversely, the electric power and thermal efficiency based on the rating of the dehydrogenation facilities were 29.9% and 6.8%, respectively. The maximum total power generation efficiency of the MCH-toluene-hydrogen reaction cycle was 16.0%; however, when thermal power was taken into account this rose to 16.7%. A case study was also conducted using a 1 MW wind farm combined with MTHR for Hokkaido in Japan.

This paper considers the transient stability enhancement of a power system containing large amounts of solar and wind generation in Japan. Following the Fukushima Daiichi nuclear disaster there has been an increasing awareness on the importance of a distributed architecture, based mainly on renewable generation, for the Japanese power system. Also, the targets of CO2 emissions can now be approached without heavily depending on nuclear generation. Large amounts of renewable generation leads to a reduction in the total inertia of the system because renewable generators are connected to the grid by power converters, and transient stability becomes a significant issue. Simulation results show that sodium-sulfur batteries can keep the system in operation and stable after strong transient disturbances, especially for an isolated system. The results also show how the reduction of the inertia in the system can be mitigated by exploiting the kinetic energy of wind turbines.

To level the fluctuations in electric power sourced from renewable energy, the transmission network can be spread over a wide area, but this is expected to dramatically increase the renewable energy rate. Therefore, this paper proposes an algorithm that analyzes the maximum amount of renewable energy in the network, and hence optimizes the type of electric power source connected to the transmission network, and the arrangement and capacity of each power source. The proposed algorithm is based on a genetic algorithm, which effectively processes many nonlinear variables concurrently. Accounting for the power interchange in the transmission network and the energy storage in electric heat pumps and heat storage tanks, the objective function plans the arrangement of the electric power sources that maximizes the economic efficiency of the system. The developed algorithm is applied to a renewable-energy network in Hokkaido, Japan. In this area, the introductory rate of renewable energy was 39.5% of the total electricity production. Moreover, the cost of a distributed power-supply network was 9.99 × 1010 USD. The proposed system is equivalent to 1.88 years of Hokkaido's energy consumption.

Direct current systems that lack an inertial force, such as fuel cells or photovoltaics, are expected to be used for electrical power in advanced sustainable cities. A small-capacity transmission network (microgrid) without inertial force has difficulties for converging short-term electric power fluctuations. Consequently, the frequency of transmission on such networks frequently diverges. Therefore, the electric power fluctuation due to cyclic fluctuation of an interconnected system of clean and renewable power sources (namely a solid oxide fuel cell (SOFC)-hydraulic generator, photovoltaics, and a wind-power generator) is investigated by numerical analysis in this study, together with means of controlling it. The characteristics of this fluctuation are clarified, and the setting range required to control the cyclic fluctuation of the transmission network is illustrated based on the relation between the inertial force of the hydraulic generator and battery (lithium ion) capacity.

The Fukushima nuclear disaster in 2011 changed Japan's strategy for reducing CO2 emissions. The government is now placing more emphasis on the development of nonCO2-emitting distributed generation systems such as wind, solar, and tidal power to reduce greenhouse gas emissions and guarantee electricity supply in the case of a natural disaster. This paper proposes a strategy for the exploitation of wind, solar, and tidal resources in a cold region in Japan by utilizing surplus energy from the summer and spring during winter. It also aims to determine the most favorable energy mix of these renewable sources and storage system types. The study is performed by calculating hourly demand and renewable energy supply for the city in one year, which is based on actual data of demand, solar irradiation, wind speeds, and tidal current speeds. The costs of the components of the renewable power plants and storage systems are considered, and different proportions of generation outputs are evaluated with different types of storage systems. According to results, the configuration containing the hydrogen storage system using organic chemical hydride methylcyclohexane (OCHM) is the most economical but is still more expensive than one using a conventional generation system. Moreover, we confirm that the cost of CO2 emissions is the key element for leveling the playing field between conventional and renewable generation from an economic perspective. The cost of CO2 emissions to public health as well as those costs related to the interruption of services during a catastrophe must be carefully calculated with other issues from conventional power projects to perform a precise comparative evaluation between both types of generation systems.

This paper presents an operation strategy for a power system supplied from 100% renewable energy generation in Kitami City, a cold region in Japan. The main goal of this work is the complete elimination of the CO2 emissions of the city while keeping the power frequency within prescribed limits. Currently, the main energy related issue in Japan is the reduction of CO2 emissions without depending on nuclear generation. Also, there is a need for the adoption of distributed generation architecture in order to permit local autonomous operation of the system by the local generation of power. As a solution, this paper proposes a strategy to eliminate CO2 emissions that considers digital simulations using past hourly meteorological data and demand for one year. Results shows that Kitami City can be supplied entirely by renewable generation, reducing its CO2 emission to zero while keeping the quality of its power grid frequency within permitted limits.

The equipment and operation planning of a compound energy system (microgrid) with renewable energy sources is a dynamic, multivariate, nonlinear problem. Genetic algorithms (GA) provide a facile method for solving such problems and can be easily adapted to complicated energy systems; however, conventional GAs require a long runtime when the microgrid contains numerous energy sources and the solution must be highly accurate. This work introduces a preliminary step in which experimental design techniques, namely, an orthogonal array experiment and a factorial-effect chart are used to find an operation method that is close to the optimal solution for the energy system. The optimal operation solution is determined by using the operation method obtained from the orthogonal array experiment as the initial generation of chromosomes for the conventional GA. This proposed method does not find a strictly mathematical optimal solution, but the quasi-optimum solution is far more accurate than that from convention GAs and can be used industrially. The characteristics of the output power sources are found to strongly affect the analytic accuracy for the example of a microgrid.

The utilization of alternative energy is being strongly promoted in order to prevent the progression of climate change due to the increase in greenhouse gas emissions. Therefore, in our previous study, the carbon dioxide (CO2) hydrate engine generator (CHEG), which converts unutilized energy to electrical energy, has been proposed as a way to produce alternative energy. CHEG uses the heat cycle of a CO2 hydrate which is generated by a small temperature difference using heat from such unutilized energy sources as low-temperature exhaust heat from home heating appliances, difference in temperature between day and night, geothermal heat, etc. In previous works, the theoretical validity of the CHEG as an alternative energy for homes has been analyzed. However, the control method of power output for changing heat source temperature and power load has not been investigated. Therefore, the dynamic model of the CHEG is constructed to investigate the dynamic characteristics of the control method of power output.

Investigation of a plant shoot configuration is used to obtain valuable information concerning the received light system. Additionally, analysis results concerning a plant shoot configuration interaction with direct solar radiation were taken from a past study. However, in order to consider a plant shoot as a received sunlight system, it is necessary to understand the received light characteristics of both direct solar radiation and diffused solar radiation. Under a clear sky, the ratio of direct solar radiation to diffused solar radiation is large. However, under a clouded sky, the amount of diffused solar radiation becomes larger. Therefore, in this paper, we investigate the received light characteristics of a plant shoot configuration under the influence of diffused solar radiation. As a result, we clarify the relationship between the amount of diffused solar radiation and the amount of received light as a function of the characteristics of the plant shoot configuration. In order to obtain diffused solar radiation, it is necessary to correspond to the radiation of the multi-directions. In the analysis, the characteristic of the difference in arrangement of the top leaf and the other leaf was obtained. Therefore, in analysis, leaves other than the top were distributed in the wide range.

Plant shoot configurations evolve so that maximum sunlight may be obtained. The objective of this study is to develop a compact light-condensing system mimicking a plant shoot configuration that is applicable to a light source from a large area. In this paper, the relationship between the position of a light source (the sun) and the rate at which light is absorbed by each leaf was investigated in detail for plant shoot models of a dogwood (simple leaf) and a ginkgo tree (lobed leaf). The rate of light quantum received in each leaf model is reported to an analysis program that uses cross entropy (CE). The analyses showed that the peak amount of light received in the plant-shoot-light-condensing system was during February (vernal equinox) and October (autumnal equinox). Similarly, the rate of light quantum received in each leaf was measured with the CE. The results found that the plant-shoot-light-condensing system that maximizes the amount of light received has differences in the light received in each leaf. Furthermore, the light-condensing characteristics of the ginkgo biloba model are better than the dogwood model. The light-condensing characteristics of a leaf are influenced by the size, a lobe, shape, and the length of the branch.

The distribution of solar cell modules is planned by referring to the configuration of plant shoots. The object is to develop a solar power generation system with low directivity and a small installation space. In this paper, the amount of insolation that reaches a plant shoot in an arbitrary period was investigated using the “Light received analysis algorithm of a plant shoot” (LAPS) described in a previous report. Based on the analysis, the optimal configuration of the shoot to maximize the amount of light received was determined. The position of the light source on a representative day in summer has a wide range of elevation angles and directions, and has a narrower range in the winter. This paper mainly examines the condensing system of low directivity using the plant shoot of a simple leaf. Based on the relation between the characteristics of these light sources, the shoot configuration for the summer season is optimized by a solar position at 12:00, with considerable solar radiation. The shoot configuration for winter, meanwhile, is arranged so that half the total leaves may absorb solar radiation at a small elevation angle. When the amount of light received by the leaves arranged horizontally and the optimized plant shoot configuration for every month is measured, the difference is found to be modest during the period from March to September. However, a greater amount of light is received in the plant shoot arrangement in January, February, and October to December, based on an optimal solution that is superior to that with the leaves arranged on the level surface.

It is thought that plants have evolved to modulate the amount of light received by the leaves in order to raise the photosynthetic rate. By investigating a plant condensing system, it is small and a directive low condensing system may be able to develop. A compact condensing system with low directivity may be able to be developed by investigating the condensing method by a plant. This paper presents the results of an investigation into light reception characteristics using the numerical-analysis program (LAPS), with emphasis on a kenaf plant (Hibiscus cannabinus) with division leaf of diversity. From this analysis, the relationship between the range of movement for the light source (sun) and the shoot configuration of a kenaf plant were clarified. There is a suitable shoot configuration, and the shoot configuration has a strong influence over the efficiency of light reception. The summer season is characterized by wide oscillations of the light source, and it is therefore necessary for the kenaf plant to adjust its shoot configuration in order to improve light reception.

A micro-grid with the capacity for sustainable energy is expected to be a distributed energy system that exhibits quite a small environmental impact. In an independent micro-grid, “green energy,” which is typically thought of as unstable, can be utilized effectively by introducing a battery. In the past study, the production-of-electricity prediction algorithm (PAS) of the solar cell was developed. In PAS, a layered neural network is made to learn based on past weather data and the operation plan of the compound system of a solar cell and other energy systems was examined using this prediction algorithm. In this paper, a dynamic operational scheduling algorithm is developed using a neural network (PAS) and a genetic algorithm (GA) to provide predictions for solar cell power output. We also do a case study analysis in which we use this algorithm to plan the operation of a system that connects nine houses in Sapporo to a micro-grid composed of power equipment and a polycrystalline silicon solar cell. In this work, the relationship between the accuracy of output prediction of the solar cell and the operation plan of the micro-grid was clarified. Moreover, we found that operating the micro-grid according to the plan derived with PAS was far superior, in terms of equipment hours of operation, to that using past average weather data.

The bioethanol reforming system (FBSR) using sunlight as a heat source is a fuel production system for fuel cells with little environmental impact. However, because solar radiation and outside air temperature are unstable, it is difficult to predict operation of the system with accuracy. Therefore, an operation prediction program of the FBSR using a layered neural network (NN) with the error-correction learning method has been developed. We developed a method of analyzing the operation of a natural energy system with sufficient accuracy. The weather pattern (the amount of global solar radiation and the outside air temperature) and energy-demand pattern for the past one year are inputted into the NN. Moreover, training signals are calculated by a genetic algorithm (GA). The training signals are given to the NN, and the operation pattern of the FBSR is made to learn. Operation of the FBSR on arbitrary days can be predicted by inputting the weather pattern and the energy-demand pattern into this learning NN. In this paper, the operation prediction program of the FBSR is developed, and details of the analytic accuracy are clarified. As a result of analyzing using the developed algorithm, when ±20% or less of power load fluctuation occurred, the operation plan was analyzable in 14% or less of error span. On the other hand, in operation prediction when ±50% or less of fluctuation is added to the outside temperature and global solar radiation, there was 16% or less analysis error.

The combustion exhaust heat of woody biomass engine using Stirling cycle is high temperature. This exhaust heat is used for the city gas reforming reaction of a proton exchange membrane fuel cell (PEM-FC) system. The woody biomass engine generator has the characteristic that the greenhouse gas amount of emission with power generation is greatly reducible. In this paper, the micro grid system that introduces PEM-FC/woody biomass engine hybrid cogeneration (PWHC) is proposed. It depends on the dynamic characteristics of the grid for the power quality at the time of load fluctuation being added to the micro grid. Especially, the dynamic characteristics of the independent micro grid are important on security of power quality. So, in this paper, the response characteristic of PEM-FC and woody biomass engine was investigated by the experiment and the numerical analysis. Furthermore, the response characteristic of the PWHC independent micro grid including auxiliary machinery was investigated by the numerical simulation. Moreover, an improvement of dynamic characteristics is proposed using the method of adding proportional-plus-integral control to PWHC. If woody biomass engine is introduced into a house, 10.2s will be required to stabilize power quality at the maximum. On the other hand, when woody biomass engine corresponds to a base load and PEM-FC corresponds to the load exceeding the base load, settling time is less than 1.6 s. In this study, relation between the system configuration of the PWHC micro grid and the dynamic characteristics of the power was clarified.

Small kerosene diesel-engine power generators are introduced into an independent micro-grid (IMG) that connects 20 houses, and power and heat are supplied to them. A 3 kW engine generator is installed in six houses, and a boiler and a heat storage tank are also installed, and exhaust heat to make up for insufficiency is supplied. The boiler is installed in the house that does not install the engine generator, and heat is supplied to the demand side. Partial load operation of the engine generator has a large influence on power generation efficiency. Therefore, this paper discusses the system that controls the power of the engine generator by the power distribution control system using the genetic algorithm (GA), and the control system that changes the number of operations of the engine generators according to the magnitude of the power load. As a case study, the energy-demand model of the 20 houses in Sapporo was analyzed. As a result, the annual energy cost of the number of operations system and the power distribution control system is reducible with 16% and 8% compared with the conventional method, respectively. However, it depends for this cutback effect on the heat demand characteristic greatly, and when the proposed system is introduced into a community with little heat demand, effectiveness will decrease greatly.

Reduction in fuel cell capacity linked to a fuel cell network system is considered. When the power demand of the whole network is small, some of the electric power generated by the fuel cell is supplied to a water electrolysis device, and hydrogen and oxygen gases are generated. Both gases are compressed with each compressor and they are stored in cylinders. When the electric demand of the whole network is large, both gases are supplied to the network, and fuel cells are operated by these hydrogen and oxygen gases. Furthermore, an optimization plan is made to minimize the quantity of heat release of the hot water piping that connects each building. Such an energy network is analyzed assuming connection of individual houses, a hospital, a hotel, a convenience store, an office building, and a factory. Consequently, compared with the conventional system, a reduction of 46% of fuel cell capacity is expected.

The fuel cell micro-grid is expected as a distributed power supply with little environmental impact. However, if a micro-grid is installed in an urban area, a generation efficiency of less than 21% on an all-year basis is expected. Generally, in planning an electric power network using a micro-grid, all the target buildings are connected and electric power is supplied. In this paper, a micro-grid is divided into multiple and each is optimized for the purpose of maximization of power generation efficiency. In the cooperation management of a micro-grid, large fluctuations in load, or increases and decreases in a building, can be followed with a grid using a system-interconnection device. The system proposed in this paper obtained results with high generation efficiency (from 21.1% to 27.6%) compared with the central system (generation efficiency is 20.6% to 24.8%) of a fuel cell micro-grid.

In this study, compactification (improvement of the light receiving density) and reduction of the directivity (dependence property for the sun position) are tried to improve the efficiency of the photovoltaics using Light Received Analysis Algorithm of a Plant Shoot (LAPS). The LAPS is a method of analysis to check the form of a plant shoot that has high light receiving density by numerical analysis using GA. A big scale plant needs big energy for maintenance and growth. A characteristic of the big scale plant is to have a branch structure. Thus, it means that a branch structure is necessary to get big energy by the solar cell module simulating a plant shoot. However, conventional LAPS was not able to express the branch structure so far. Therefore L-system is applied to LAPS. The purpose of this paper is to elucidate the influence that the branch structure gives to light receiving density. The analysis is carried out under sunshine condition of the summer solstice and the winter solstice in Sapporo, Hokkaido, and used a ginkgo for the shape of the leaf. As results, solar cell modules with the branch structure of a plant shoot optimized for sunshine condition of the summer solstice and the winter solstice were obtained. As the number of leaves increased, the solar cell module with the branch structure of a plant shoot came to have higher light receiving density than that of the solar cell module without the branch structure of a plant shoot. From this, it is confirmed that the branch structure increases the light receiving density of a plant with many leaves.

A small-scale energy network present at the Antarctic Syowa Base (Syowa Base microgrid, SBMG) has issues related to the amount of fuel transported from Japan and the environmental impact from emissions. Therefore, the Syowa Base is considering the introduction of photovoltaics (PV) and wind power generations to drastically increase the local supply and consumption of energy. After the introduction of a type of heat supply system, heat pump system, using engine exhaust heat and an electric storage heater hybrid system into SBMG, the reduced introductory rate of renewable energy and fuel consumption at the Syowa Base was investigated. Results confirmed a reduction in fuel consumption of the base by heat storage using renewable energy, following the introduction of a heat pump and electric storage heater hybrid system. However, for the electric storage heater to function year round, extensive wind power generation was required. The heat pump and electric storage heater hybrid system reduced fuel consumption of the Syowa Base by 15 % in January. On the other hand, hybrid systems reduced fuel consumption to about half of the present system. Fuel reduction was not observed in July and October because these months had a much greater heat demand. Reduction in fuel consumption of the whole base required an increase in the amount of wind power generation, which was influenced very little by the seasonal changes, and an optimization of the electric storage heater operation.