A study of a micro co‐generation system's conformation for residential use considering observed fluctuating characteristics of hot‐water demand

This paper discusses a conformation of a micro co‐generation system (µCGS) for residential use. The evaluation is based on the hot‐water demand observed in three families who live in the same apartment house. Assuming DSS operation of µCGS, we evaluated the required capacity of PEFC, hot‐water tank, and backup boiler to meet a series of daily hot‐water demand observed in three houses. The results are: (1) µCGS with 2‐kW PEFC and 350‐L hot‐water tank are required in family B when µCGS is not equipped with the backup boiler, (2) the additional 5 kW of the backup boiler reduces the required capacity of the hot‐water tank by 50 L, (3) the evaluation based on hourly averaged hot‐water demand patterns would underestimate the required capacity of the hot‐water tank, (4) the required capacity of the hot‐water tank could be reduced by the leveling effect of the hot‐water demand pattern along three families. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 143(2): 30–37, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10080     

Proposal and evaluation of a gas engine and gas turbine hybrid cogeneration system in which cascaded heat is highly utilized

A high‐efficiency cogeneration system (CGS) is proposed for utilizing high‐temperature exhaust gas (HTEG) from a gas engine (GE). In the proposed system, for making use of heat energy of HTEG, H₂O turbine (HTb) is incorporated and steam produced by utilizing HTEG is used as working fluid of HTb. HTb exhaust gas is also utilized for increasing power output and for satisfying heat demand in the proposed system. Both of the thermodynamic characteristics of the proposed system and a gas engine CGS (GE‐CGS) constructed by using the original GE are estimated. Energy saving characteristics and CO₂ reduction effects of the proposed CGS and the GE‐CGS are also investigated. It was estimated that the net generated power of the proposed CGS has been increased 25.5% and net power generation efficiency 6.7%, compared with the original GE‐CGS. It was also shown that the proposed CGS could save 27.0% of energy consumption and reduce 1137 t‐CO₂/y, 1.41 times larger than those of GE‐CGS, when a case study was set and investigated. Improvements of performance by increasing turbine inlet temperature were also investigated. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 166(3): 37– 45, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20708     

Feasibility evaluation of on‐site generator network by cooperative game theory

An on‐site generator, such as CGS (cogeneration system), is considered to be an effective end‐use energy system in order to accomplish primary energy conservation, CO₂ emissions mitigation, and system cost reduction; these characteristics will eventually improve the complete performance of an existing energy system in the future. Considering the drawback of installing an end‐use CGS for a customer possessing small or middle‐scale floor space, however, it is difficult to achieve those distinctive features because the thermal‐electricity ratio of CGS is not always in agreement with that of customer energy demand. In order to overcome that matching deficiency, it is better to organize an on‐site generator network based on mutual electricity and heating transmission. But focusing on some cogenerators underlying their behaviors regarding maximizing their own profits, this on‐site network, whose situation corresponds to a grand coalition, is not necessarily established because of each cogenerator's motivation to form a partial coalition and acquire its own profit as much as possible. In this paper, we attempt to analyze the optimal operation of an on‐site generator network and identify by applying the nucleolus of cooperative game theory the optimal benefit allocation strategy in order for the cogenerators to construct the network. Regarding the installation site of this network, the center of Tokyo city is assumed; the locational information includes floor space and so forth through a GIS (geographic information system) database. The results from the nucleolus suggest that all districts should impartially obtain benefit from organizing the network for the purpose of jointly attaining system total cost reduction. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 150(4): 23–35, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20052     

Evaluation of the reduction in CO2 emissions by applying Micro‐Grid to home energy supply system

Dispersed generators such as wind power systems, photovoltaic systems, and cogeneration systems are expected to mitigate the environmental burden of energy consumption, and their installation has been promoted recently. Micro‐Grid is focused on as a method to solve some problems in a commercial electric power line when installing a large number of dispersed generators, and some demonstrative research on Micro‐Grid for large‐scale systems is being carried out now. Also, small cogeneration systems for houses, such as gas engines and fuel cells, are expected to improve CO₂ emissions. However, if the power and heat demand of a family are relatively small or are unbalanced, the cogeneration system does not operate effectively. The authors have studied the application of Micro‐Grid for home energy supply, and have developed a control system to solve this problem. The system achieves a reduction of CO₂ emissions and energy costs by sharing electric power and heat among some houses with cogeneration systems. This paper presents an outline of the newly developed system, and in particular describes the effect of the reduction in CO₂ emissions compared with a conventional energy supply method, and the case in which dispersed generators are installed in some houses and operate independently. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 170(3): 19–27, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20879     

A multi‐objective optimization model for determining urban energy systems under integrated energy service in a specific area

The integrated energy service system for a specific area is supposed to deliver electric and thermal energy in an integrated manner for the purpose of reducing cost, primary energy consumption, and CO₂ emission. Under an assumption of the service system, this paper develops a multi‐objective optimization model for determining urban energy systems. Considering the various energy system alternatives, such as photovoltaic generations for residential houses and fuel‐cell cogenerations for business and commercial customers, the model determines the share of the energy system alternatives in order to minimize the above three indices. As numerical examples, this paper illustrates trade‐off analyses in the case when the proposed model is applied to a 2 km × 2 km square area in Osaka. Finally, this paper illustrates the role of various energy system alternatives from CO₂ reduction and fossil energy reduction points of view. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 147(3): 20–31, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10275     

An operational algorithm for residential cogeneration systems based on the monitored daily‐basis energy demand

Residential cogeneration systems with PEFC are promising as distributed power system resources with the ability to improve energy system efficiency. However, it is important to develop an efficient algorithm for operation because the energy demand at each house differs greatly from day to day. In this paper, we propose an operational algorithm and evaluate it from the viewpoint of energy conservation and economic effectiveness based on the energy demand characteristics. In the algorithm, the hot water and electricity demand on the next day are estimated based on the average of past data. The results of simulations using actually monitored energy demand data indicate that (1) the greater the electrical demand of a household, the more effective this algorithm becomes with respect to energy conservation; (2) the greater the hot water demand of a household, the more effective this algorithm becomes with respect to economic effectiveness. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 170(2): 37–45, 2010; Published online in Wiley InterScience ( www.interscience.wiley. com ). DOI 10.1002/eej.20892     

CO2 reduction effect of the utilization of waste heat and solar heat in a city gas system

We evaluated total energy consumption and CO₂ emissions in the phases of a city gas utilization system from obtaining raw materials to consuming the product. Assuming monthly and hourly demand figures for electricity, heat for space heating, and hot water in a typical hospital, we explore the optimal size and operation of a city gas system that minimizes the life cycle CO₂ emissions or total cost. The cost‐effectiveness of conventional cogeneration, a solar heating system, and hybrid cogeneration utilizing solar heat is compared. We formulate a problem of mixed integer programming that includes integral parameters that express the state of system devices such as the on/off condition of switches. As a result of optimization, the hybrid cogeneration can reduce annual CO₂ emissions by 43% compared with the system without cogeneration. The sensitivity of CO₂ reduction and cost to the scale of the CGS is also analyzed. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 149(1): 22–32, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10369     

Potential evaluation of energy supply system in grid power system,commercial, and residential sectors by minimizing energy cost

If the economic activity in the commercial and residential sector continues to grow, improvements in energy conversion efficiencies of energy supply systems is necessary for CO₂ mitigation. In recent years, the electricity driven hot water heat pump (EDHP) and the solar photovoltaic (PV) have been commercialized. The fuel cell (FC) of co‐generation system (CGS) for the commercial and residential sector will be commercialized in the future. Copyright © 2004 Wiley Periodicals, Inc. The aim is to indicate the ideal energy supply system of the users sector, which manages both the economical cost and CO₂ mitigation, considering the grid power system. In this paper, cooperative Japanese energy supply systems are modeled by linear programming. It includes the grid power system and energy system of five commercial sectors and a residential sector. The demands of sectors are given by the objective term for 2005 to 2025. Twenty‐four‐hour load for each three annual seasons are considered. The energy systems are simulated to minimize the total cost of energy supply, and to mitigate the CO₂ discharge. As a result, the ideal energy system at 2025 is shown. The CGS capacity grows to 30% (62 GW) of the total power system, and the EDHP capacity is 26 GW, in commercial and residential sectors. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(2): 9–19, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/ eej.20361     

Environmentally‐friendly Aspects and Innovative Lightweight Traction System Technologies of the Shinkansen High‐speed EMUs

In 1964, the Tokaido Shinkansen marked the start of the world's first commercial service high‐speed railway that operates at over 200 km/h. Since then, the Tokaido Shinkansen has demonstrated successful business and technological advancement. With the speeding‐up of the Shinkansen, environmental matters such as noise and vibration have become critical issues. Measures taken to counter noise and vibration—such as weight reduction and aerodynamics—also effect global environmental measures to reduce energy consumption and CO₂ emission. With the introduction of the Series 300, there was a system change of applying an AC drive system, and the lightweight body realized performance improvement over the earlier Series 0. The high‐speed EMUs have readily taken advantage of technological innovation such as those achieved in electronics technology. In particular, an innovative AC drive system comprising a power converter with a GTO thyristor and asynchronous motors realized a high‐performance and lightweight traction system for high‐speed EMUs in the 1990s. Furthermore, recent innovations in electronics technology, such as low switching loss power devices and high‐power permanent magnets, have improved the AC drive systems of the high‐speed EMUs of the 21st century. This article starts out by introducing environmentally friendliness of the Shinkansen trains in terms of low energy consumption by means of traction system change, and then proceeds to describe the recent technological innovations that have given birth to lightweight traction systems, such as the Permanent Magnet Synchronous traction Motor (PMSM) and power converters with train‐draft‐cooling systems. The article concludes by summing up the environmentally friendly aspects of the Tokaido Shinkansen. Copyright © 2008 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Development of a city‐type compact wind power generation system

It is necessary to use renewable energy, such as photovoltaic, wind power, and biomass energy, from the viewpoint of CO₂ regulation and environmental protection of the Earth. In recent years, the tendency is toward larger wind power generation systems to achieve cheaper electricity. Generators having capacities of 1500 kW to 2000 kW tend to dominate the market. However, a large wind power generation system has limitations in terms of location and can be installed only in the suburbs. At the same time, a city‐type compact wind power generation system, designed for city needs, has more flexibility and can be installed in the residential areas of a city. In this paper, we introduce an original control operation system called a “pump‐up” operation system, designed to effectively use the city wind, and report the results of its field test. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 158(2): 56–63, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20440     

Evaluation of a plug‐in hybrid electric vehicle considering power generation best mix

In the transport section, it is necessary to reduce the amount of CO₂ emissions and oil dependence. Bio fuels and fuel cell vehicle (FCV), electric vehicle (EV) and plug‐in hybrid electric vehicle (PHEV) are expected to reduce CO₂ emissions and oil dependence. We focus on PHEV. PHEV can reduce total energy consumption because of its high efficiency and can run with both oil and electricity. Introduction of PHEV reduces oil consumption, but it also increases electricity demands. Therefore, we must evaluate PHEV's CO₂ reduction potential, not only in the transport section but also in the power grid section. To take into account the distribution of the daily travel distance is also very important. All energy charged in the PHEV's battery cannot always be used. That influences the evaluation. We formulate the total model that combines passenger car model and power utility grid model, and we also consider the distribution of the daily travel distance. With this model, we show the battery cost per kWh at which PHEV begins to be introduced and oil dependence in the passenger car section is to be reduced to 80%. We also show PHEV's CO₂ reduction potentials and effects on the power supply system. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 171(2): 12–22, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20920     

Evaluation of energy saving and CO2 emission reduction technologies in energy supply and end‐use sectors using a global energy model

Assessments of global warming mitigation technologies are important for achieving the Kyoto target and planning post‐Kyoto regimes. Regional differences in energy resources, growth in energy consumption, current technology diffusions, etc., should be considered in the assessments. A global energy systems model, DNE21+, with high regional resolution had treated the energy supply sectors in a bottom‐up fashion and the end‐use sectors in a top‐down fashion, which was expressed by using long‐term price elasticity. However, the assessments of technological options in the end‐use sectors are currently more important, particularly for the near and middle terms. In order to evaluate the technological options not only in the energy supply sectors but also in the end‐use sectors for energy savings and CO₂ emission reductions, DNE21+ has been modified for treating two energy‐intensive end‐use sectors, i.e. steel and cement sectors, in the bottom‐up fashion. The results reveal that the cost‐effective global CO₂ emission reductions in 2030 for stabilizing the atmospheric CO₂ concentration at 550 ppmv in comparison with that in the reference case would be approximately 68 MtC/yr and almost zero in the steel and cement sectors, respectively. The cost‐effective options include next‐generation coke ovens and coke dry quenching (CDQ) in the steel sector. Copyright © 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Optimal daily operation of electric power systems with an ACC‐CAES generating system

Recently, an ACC‐CAES generating system has been developed by applying ACC (Advanced Combined Cycle) technology to a conventional CAES (Compressed Air Energy Storage) system. The ACC‐CAES has a potential advantage of high efficiency and high capacity factor over other energy storage. However, its advantages from the viewpoints of power system operation are not fully revealed because of its peculiar operation characteristics compared with other energy storage. The characteristics include (1) it requires fossil fuel even in the case of operation using stored compressed air and (2) it has an ACC generating mode as one of its generating states to be used as a conventional ACC generating system while detaching the air storage system. Therefore, it is necessary to examine operation patterns of the ACC‐CAES and its contribution to economic operation of a power system. In order to achieve the objective, operation simulations of a power system with ACC‐CAES generating systems are needed because operation of energy storage systems such as the ACC‐CAES must be studied through an operation scheduling of a power system. This paper develops an optimal daily scheduling method of a power system with both ACC‐CAES generating systems and pumped hydro storage systems using two‐dimensional dynamic programming. Sensitivity analyses are undertaken with the developed method; the results show that ACC‐CAES generating systems tend to be operated as a peak or intermediate power source that bears some similarities to thermal plants or storage systems and, from an operation point of view, they have an economic advantage over pumped hydro storage systems. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 152(1): 15–23, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20087     

Multiple roles coordinated control of battery storage units in a large‐scale island microgrid application

In order to build a large‐scale island microgrid with 100% penetration intermittent photovoltaic power generation as the only power source, a structure with multiple role battery energy storage systems (BESSs) is proposed in this paper based on the analysis of energy storage demand in the island microgrid and performance comparison of two types of batteries. The storage system in the proposed structure is composed of three types of functional BESSs. In detail, the master control units (MCUs) with LiFePO4 batteries are responsible for the voltage and frequency stability and instantaneous power balance, slave storage units (SSUs) with lead‐acid batteries are responsible for daily energy storage, and multi‐function units (MFUs) with LiFePO4 batteries are used for short‐time energy regulation. A hierarchical control structure is adopted in the system. At the local level, the converters of the MCUs are controlled as the voltage sources in paralleled mode as grid‐forming units, and those of SSUs and MFUs are controlled in the current source mode as grid‐feeding units. At the system level, a real‐time power balance coordinated control strategy is proposed, which has the capability of efficient and orderly operation of different types of BESSs. Simulation and practical operation analysis of the Qumalai 7.023 MW microgrid demonstrate the practicality and effectiveness of the research methods of the island microgrid. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

A Two‐Stage Stochastic Mixed‐Integer Programming Approach to the Smart House Scheduling Problem

A “smart house” is a highly energy‐optimized house equipped with photovoltaic (PV) systems, electric battery systems, fuel cell (FC) cogeneration systems, electric vehicles (EVs), and so on. Smart houses are attracting much attention recently because of their enhanced ability to save energy by making full use of renewable energy and by achieving power grid stability despite an increased power draw for installed PV systems. Yet running a smart house's power system, with its multiple power sources and power storages, is no simple task. In this paper, we consider the problem of power scheduling for a smart house with a PV system, an FC cogeneration system, and an EV. We formulate the problem as a mixed‐integer programming problem, and then extend it to a stochastic programming problem involving recourse costs to cope with uncertain electricity demand, heat demand, and PV power generation. Using our method, we seek to achieve the optimal power schedule running at the minimum expected operation cost. We present some results of numerical experiments with data on real‐life demands and PV power generation to show the effectiveness of our method. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 186(4): 48–58, 2014; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.22336     

Coordinated control of OLTC and multi‐CEMSs for overvoltage prevention in power distribution system

The high degree of penetration of residential rooftop photovoltaic systems causes the overvoltage problem in power distribution systems. This paper aims to introduce demand‐side management for a distribution system for overvoltage prevention. A real‐time overvoltage prevention coordination scheme between an on‐load tap changer (OLTC ) and multi‐community energy management systems (multi‐CEMSs ) is proposed. The main objectives of this control are to relieve the stress in the OLTC tap operation using household schedulable loads and to maximize customer profit in each CEMS . The load scheduling performed by each CEMS is formulated as a combinatorial, nonlinear, time‐series scheduling optimization problem and is solved by a sequential search method named voltage‐ranking‐based load combination search algorithm. The effectiveness of the proposed method is validated in a model distribution system with1800 customers. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Proposal and Evaluation of a New‐Type Cogeneration System for Energy Saving and CO2 Emission Reduction

The paper proposes a cogeneration system which generates four types of energy or material resources: electricity, steam, hot water, and freshwater. The proposed system can capture CO₂, and be constructed on the basis of a combined cycle power generation system which consists of a gas turbine and a back‐pressure extraction turbine. In the proposed system, power is produced by driving the gas turbine system. High‐pressure saturated steam with medium temperature is produced in the heat recovery steam generator by using gas turbine exhaust gas, and then superheated with a regenerative superheater in which the fuel is burned by using oxygen instead of air for driving the steam turbine generator. Water and CO₂ are recovered from the flue gas of the regenerative superheater. It has been estimated that the proposed system has a net power generation efficiency of 41.2%, a heat generation efficiency of 41.5%, and a total efficiency of 82.7%. Freshwater of 1.34 t/h and CO₂ of 1.76 t/h can be recovered. It has also been shown, when a case study was set and evaluated, that the proposed system can save 31.3% of energy compared with the conventional energy supply system, and reduce CO₂ emission by 28.2% compared with the conventional cogeneration system. Copyright © 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Characteristics and economic evaluation of a CO2‐capturing solar thermal hybrid power generation system with heat storage

For wide use of a power plant utilizing solar energy, improvement of its economics is important. Both the economics and characteristics of a CO₂‐capturing solar thermal hybrid power generation system are evaluated in this paper. Since a relatively low temperature steam of 220 °C is produced by using solar thermal energy and is utilized as the working fluid of a gas turbine, the solar collector can attain high heat collecting efficiency. The net fuel‐to‐electricity conversion efficiency of the hybrid system is estimated to be higher than 60% on the lower‐heating‐value‐ basis. It has been estimated that the gross income and the period of depreciation of the proposed system are 34.8 × 10⁵ yen/year and 8.89 years, respectively, and that the system is economically feasible, under the assumptions of a solar collector area of 10 ha, a maximum net power output of 4 MW, and a heat storage capacity of 2000 m³. The amount of fuel saving and reduction of CO₂ emission of our system, compared to a conventional natural gas firing plant, are also estimated in the paper. © 1999 Scripta Technica, Electr Eng Jpn, 126(4): 21–29, 1999     

Advanced analysis of grid‐connected PV system's performance and effect of batteries

An advanced method of analysis for grid‐connected PV systems is developed in this research. To investigate the issues which may arise in the clustered PV systems, a “Demonstration Project on Clustered PV Systems” was initiated in December 2002 in Oota, Japan, involving the installation of more than 500 residential PV systems in the demonstrative research area, and the development of battery‐integrated PV systems to avoid restrictions on output power due to the raising of the grid voltage. The annual performance of commercial PV systems without battery was analyzed and a performance ratio of 80% on average was found to have been achieved. Overvoltage of power distribution lines and snow are two major factors capable of causing very low performance ratio on a daily basis. The effects of batteries have also been analyzed, and the results indicate that there will be some reduction of energy losses due to the grid voltage, but the PCS efficiency will be at least 8% worse than that of commercial PV systems. It was also found that nonoptimized battery operation sometimes results in a fully charged situation at noontime and maximum reverse power flow may not be minimized in this situation. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 164(1): 21–33, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20660     

The Environmental Potential of IT for the Ubiquitous Society

As typically represented by the popularization of the Internet, the rapid development of information technology (IT) is largely affecting all areas of activity as the foundation of societies with higher efficiency, making it really a tool for social innovation. On the other hand, along with the globalization of the economic activities and the related change of lifestyle with mass‐energy and mass‐material consumptions, the social concern and sense of crisis against global warming and other environmental problems have been more and more highlighted. Under these situations, much discussion is on with regard to the possibility that the features of IT that are considered to improve the efficiency of traditional activities could contribute to the solution of environmental problems, particularly in prevention of global warming. This way, the services and systems utilizing IT not only improve the traditional work efficiency but also reduce the energy and resource consumption for the activities, resulting in reduction of the amount of CO₂ emission. In this article, the relation between IT and the environmental issues mentioned above are highlighted. Also, some ideas on how to evaluate the quantitative effects of CO₂ reduction as the result of applied services and systems incorporating relevant IT programs, and tools and actual evaluation cases are introduced to show the potential of IT in tackling environmental issues. Copyright © 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.