Influence of system operation method on CO2 emissions of PV/solar heat/cogeneration system

A PV/solar heat/cogeneration system is assumed to be installed in a hotel. The system is operated with various operation methods: CO₂ minimum operation, fees minimum operation, seasonal operation, daytime operation, and heat demand following operation. Of these five operations, the former two are virtual operations that are operated with the dynamic programming method, and the latter three are actual operations. Computer simulation is implemented using hourly data of solar radiation intensity, atmospheric temperature, electric, cooling, heating, and hot water supply demands for one year, and the life‐cycle CO₂ emission and the total cost are calculated for every operation. The calculation results show that the two virtual and the three actual operations reduce the life‐cycle CO₂ emission by 21% and 13% compared with the conventional system, respectively. In regard to both the CO₂ emission and the cost, there is no significant difference between the two virtual operation methods or among the three actual operation methods. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 164(2): 54–63, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20414     

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 hydrogen production method using latent heat of liquefied natural gas

In recent years, fuel cell electrical vehicles have offered promise of improving the urban environment. In particular, hydrogen‐fueled FCEVs have been considered for urban use because of their excellent characteristics such as short start‐up time, high responsiveness, and zero emissions. On the other hand, as far as hydrogen production is concerned, large amounts of CO₂ are exhausted into the atmosphere by the process of LNG reforming. In our research, we studied the utilization of LNG latent heat for hydrogen gas production as well as the liquefied hydrogen process. CO₂ capture in the liquid or solid state from hydrogen gas production by LNG was also studied. The results of our research show that the latent heat of LNG is very effective in cooling hydrogen gas for the conventional hydrogen liquefaction process. However, the latent heat LNG is not available for the LNG reforming process. If we want to use LNG latent heat for this process, we must develop a new hydrogen gas production process. In this new method, both hydrogen and CO₂ are cooled directly by LNG, and CO₂ is removed from the reforming gas. In order to make this method practical, we must develop a new type of heat exchanger to prevent solid CO₂ from interfering with performance. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 147(4): 32–42, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10299     

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     

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.     

Stochastic PSO-based heat and power dispatch under environmental constraints incorporating CHP and wind power units

In this paper an extended stochastic multi-objective model for economic dispatch (ED) is proposed, that incorporates in the optimization process heat and power from CHP units and expected wind power. Stochastic restrictions for the CO₂, SO₂ and NO_x emissions are used as inequality constraints. The ED problem is solved using a multi-objective particle swarm optimization technique. The available wind power is estimated from a transformation of the wind speed considered as a random variable to wind power. Simulations are performed on the modified IEEE 30 bus network with 2 cogeneration units and actual wind data. Results concerning minimum cost and emissions reduction options are finally drawn.     

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     

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     

Life cycle CO2 emissions of a photovoltaic/wind/diesel generating system

A photovoltaic/wind/diesel generating system with a battery (PWD system) is discussed from the viewpoint of total CO₂ gas emissions during system lifetime. The total emissions are the sum of the emissions occurring at manufacturing and operating. First, the manufacturing CO₂ emissions of the photovoltaic generator and the wind turbine generator are calculated by “the process analysis method.” This method considers the material used in each generator, its weight and its CO₂ emission rate. On the other hand, the manufacturing CO₂ emissions of the diesel generator and the battery are calculated using “the interindustry (input‐output) table.” Second, the PWD system is operated on a computer so that the fuel consumption of the diesel generator is a minimum assuming that hourly series data of electric load, insolation intensity, wind speed, and air temperature are known during the year. And CO₂ emissions occurring at system operation are obtained from the annual fuel consumption of the diesel generator. The results show that CO₂ total emissions of the PWD system are lower than those of the conventional diesel generator system. The CO₂ total emissions reach a minimum when the photovoltaic/wind generating ratio is 50/50. The CO₂ emissions of manufacturing decrease with increasing of the wind generating ratio from 100/0 to 0/100. The CO₂ total emissions decrease as the natural energy ratio increases. It is, however, saturated to about 60% when the ratio is more than 60%. And the CO₂ total emissions increase with increasing of the battery capacity. It is concluded that the PWD system plays an important role in decreasing considerably the CO₂ total emissions while the total system cost is high under the present price circumstances. © 2001 Scripta Technica, Electr Eng Jpn, 138(2): 14–23, 2002     

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     

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     

离岸微型综合能源系统多目标随机规划

离岸微型综合能源系统与海洋工程的生产工艺环节结合紧密,并独立运行。因此,如何在克服生产工艺环节或外界环境不确定性影响的同时,尽可能减少CO_2的排放,并尽量节省成本是其规划的难点。文中从综合能源系统优化规划的角度,根据能源集线器的思想,建立离岸微型综合能源系统的电-热-CO_2耦合模型,构建以总成本最小、CO_2排放量最少为目标,以电、热网络平衡等条件为约束,并考虑生产工艺环节和外界环境不确定性影响的多目标随机规划模型,进而利用多目标进化算法求解该模型,实现兼顾成本与环保的离岸微型综合能源系统多目标优化规划。通过海上油气平台群及全电舰船的微型综合能源系统的优化规划,验证了所提方法的可行性与有效性。     

DC‐linked hybrid generation system with an energy storage device including photovoltaic generation and gas engine cogeneration for residential houses

For the past few years, hybrid generation systems including solar panel and gas cogeneration have been used for residential houses. Solar panels can generate electronic power at daytime but not at night. But the power consumption of residential houses usually peaks in the evening. The gas engine cogeneration system can generate electronic power without such a restriction, and it also can generate heat power to warm up a house or to produce hot water. In this paper we propose a solar panel and gas engine cogeneration hybrid system with an energy storage device, combined by a DC bus. If a blackout occurs, the system still can supply electronic power for special house loads. We propose a control scheme for the system related to the charging level of the energy storage device and the voltage of the utility grid, which can be applied to both grid‐connected and standalone operation. Finally, we report experiments designed to demonstrate system operation and calculations for loss estimation. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 182(4): 29–46, 2013; Published online in Wiley Online Library ( wileyonlinelibrary.com ).DOI 10.1002/eej.22321     

热电联产项目供热、供电成本分摊机制的研究

合理的电价和热价有利于推动热电联产事业的发展，热电联产项目的热价和电价主要与其成本有很大关系，文中对热、电成本分摊比进行分析研究得出：对于可变成本应按热量法求出燃料消耗比来分摊，对于供采暖热负荷的两用机组将其供热发电节煤量的1/3效益补贴在供热方面是合理的；对于固定成本与财务费用，小型热电广以燃料分摊比来分摊计算是可行的．而两用机组按纯供热投资所占两用机组总投资的百分比．或接平均供热抽汽量计算出减少的发电量与额定发电量的比值来分摊是合理的。     

Study of DC circuit breaker of H2‐N2 gas mixture for high voltage

Global warming caused by such gases as CO₂ is a subject of great concern. Automobile emissions are an especially great problem in this respect. Therefore, hybrid cars are being widely developed and used. Because hybrid cars use electric power and gasoline, their emissions of CO₂ are reduced. The electric motor of a hybrid car is driven by a battery, which has large capacity. Therefore, relays must interrupt a high DC current on switching between the electric motor and the gasoline engine, and hydrogen gas‐filled relays are used for the purpose. In interruption tests in which we investigated the basic characteristics of hydrogen gas, the DC current did not reach a current‐zero point. Thus, the current must be coerced to zero by using a high arc voltage. The loss coefficient and arc voltages of hydrogen are high, and we therefore performed interruption tests using a high arc voltage. Interruption tests and dielectric breakdowns test of air, pure hydrogen, and a hydrogen‐nitrogen mixture indicated that an 80%–20% H₂–N₂ mixture is the most effective. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 174(2): 9–17, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21042     

Regional integration of renewable energy systems in Ireland – The role of hybrid energy systems for small communities

Due to a lack of indigenous fossil energy resources, Ireland’s energy supply constantly teeters on the brink of political, geopolitical, and geographical unease. The potential risk to the security of the energy supply combined with the contribution of anthropogenic greenhouse gas emissions to climate change gives a clear indication of Ireland’s need to reduce dependency on imported fossil fuels as primary energy source. A feasibility analysis to investigate the available renewable energy options was conducted using HOMER software. The net present cost, the cost of energy, and the CO₂ emissions of each potential energy combination were considered in determining the most suitable renewable and non-renewable hybrid energy system. Wind energy was shown to have the greatest potential for renewable energy generation in Ireland: wind energy was a component of the majority of the optimal hybrid systems both in stand-alone and grid-connected systems. In 2010 the contribution of wind energy to gross electricity consumption in Ireland approximated 10%, and the results of this feasibility study indicate that there is great potential for wind-generated energy production in Ireland. Due to the inherent variability of wind energy the grid-connected system results are particularly relevant, which show that in more than half of the analyses investigating electrical energy demand the incorporation of wind energy offset the CO₂ emissions of the non-renewable elements to such a degree that the whole system had negative CO₂ emissions, which has serious implications for Kyoto Protocol emissions limits. Ireland also has significant potential for hydropower generation despite only accounting for 2% of the gross electricity consumption in 2010. Wind and hydro energy should therefore be thoroughly explored to secure an indigenous primary energy source in Ireland.     

Proposal and characteristics evaluation of a CO2-recovering hybrid power generation system utilizing solar thermal energy

A CO₂-recovering hybrid power generation system utilizing solar thermal energy is proposed. In the system, relatively low temperature saturated steam around 220°C is produced by using solar thermal energy and is utilized as the working fluid of a gas turbine in which generated CO₂ is recovered based on the oxygen combustion method. Hence, solar thermal utilization efficiency is considerably higher as compared with that of conventional solar thermal power plants in which superheated steam near 400°C must be produced for use as the working fluid of steam turbines; the requirement for solar radiation in the location in which the system is constructed can be significantly relaxed. The proposed system is a hybrid energy system using both the fossil fuel and solar thermal energy, thus the capacity factor of the system becomes very high. The fuel can be used exergetically in the system; i.e., it can be utilized for raising the temperature of the steam heated by utilizing the turbine exhaust gas more than 1000°C. The generated CO₂ can be recovered by using an oxygen combustion method, so that a high CO₂ capturing ratio of near 100 percent as well as no thermal NO_x emission characteristics can be attained. It has been shown through simulation study that the proposed system has a net power generation efficiency of 63.4 percent, which is higher than 45.7 percent as compared with that of the conventional power plant with 43.5 percent efficiency, when the amount of utilized solar energy is neglected and the temperature of the saturated steam is 220°C.     

U.S. sulfur dioxide emission reductions: Shifting factors and a carbon dioxide penalty

For more than 20 years, the large-scale application of flue gas desulfurization technology has been a dominant cause of SO₂ emission reductions. From 1994–2004, electricity generation from coal increased, but the shift to low-sulfur coal eclipsed this. From 2004–2014, electricity generation from coal decreased, but a shift to higher-sulfur subbituminous and lignite coal overshadowed this. The shift in coal quality has also created a CO₂ emissions penalty, representing 2% of the sector’s total emissions in 2014.     

Evaluation of the plug‐in hybrid electric vehicle considering learning curve on battery and power generation best mix

The plug‐in hybrid electric vehicle (PHEV) is a technology intended to reduce CO₂ emissions in the transport sector. This paper presents scenarios that show how widely used PHEVs will be in the future, how much CO₂ emissions will be reduced by the introduction of PHEVs, and whether there will be serious effects on the power supply system. PHEVs can run on both gasoline and electricity, and therefore we evaluate CO₂ emissions not only from gasoline consumption but also from electricity consumption. Consideration of the distribution of daily trip distances is important for evaluating the economical benefits and CO₂ emissions resulting from the introduction of PHEVs. Also, future battery costs are very important in constructing PHEV growth scenarios. The growth of the number of PHEVs will make battery costs lower. Thus, we formulate an overall model that combines the passenger car sector and power supply sector, taking account of the distribution of daily trip distances and incorporating a learning curve for battery costs. We use the iteration method to provide a learning curve that is nonlinear. Therefore, we set the battery cost only in the first year of the simulation: battery costs in the later years are calculated in the model. We focus on a 25‐year time period in Japan, starting from 2010, and divided into 5 parts (1st to 5th). The model selects the most economical combinations of car types and power sources. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 176(2): 31–40, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21098     

The Conceptual Process Arrangement of a Steam–Gas Power Plant with Fully Capturing Carbon Dioxide from Combustion Products

The article proposes a new concept for designing power plants operating on natural gas and involving means for fully removing carbon dioxide from the cycle in the liquid phase form in order to subsequently bind or bury it for reducing the emissions of greenhouse gases into the atmosphere. In contrast to means used in the conventional power plant process arrangements for capturing CO₂ from the combustion products, the proposed concept involves the need to develop fundamentally new power engineering technologies, in which the CO₂ utilization system is intrinsically built into the cycle structure already at the initial stage of power plant design and optimization of its parameters. As an example, the process flow diagram of a natural gas fired power plant generating electricity and heat is considered. The integral indicators characterizing the thermal efficiency of such a power plant are given and compared with the similar indicators of the operating or newly designed plants fitted with CO₂ capturing systems, the process arrangement of which implies direct emission of carbon dioxide into the atmosphere. The comparison is carried out for the average ratio between the generated electricity and heat that has historically been established in the climatic zone of central Russia. It is shown that the proposed cycle features high thermodynamic efficiency and competitiveness with respect to the same indicators of alternative systems for combined generation of electricity and heat. The article suggests versions of the CO₂ capturing system configuration that allows, with the modern technological level of equipment, the carbon dioxide emissions to be reduced down to 0.5–5.0% of the total amount produced in firing natural gas.