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This study evaluates optimal carbon‐neutral power supply strategy in China up to 2060 with a multi‐region high spatial and temporal dynamic optimal power expansion planning model. Furthermore, this study explores installable potential of hydrogen and fuel cell system and analyzes the influences of its capital cost reduction at different levels. The results show that the national installed capacity would rise to be over 9000 GW in 2060, in which wind and solar PV will take up around 61%; the intermittency of renewable power generation is mainly managed with hydrogen production, power output curtailment and charge and discharge of energy storage; hydrogen and fuel cell system would improve the capacity factor and reduce the curtailment rate of renewable power generation. © 2023 The Authors. IEEJ Transactions on Electrical and Electronic Engineering published by Institute of Electrical Engineer of Japan and Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

Although the BBIN (Bangladesh-Bhutan-India-Nepal) sub-region shares identical socio-economic characteristics and secures considerable benefits from energy co-operation and power grid connectivity, it is still far behind to grasp its full potential. This paper reviews existing publications and papers from a viewpoint of resource distribution, energy supply, prospects, and policies related to power sector development and cross-border power trading with a detailed consideration of the spatial variation of the largest country, India. The member countries face similar energy problems and the challenge remains in overcoming growing energy demand by attaining emission reduction targets. Limited production but increasing use of imported fuel have also raised serious environmental and energy security concerns. The wide variation in the energy resource endowments among the countries, particularly with hydropower, coal, and natural gas presents both opportunity and challenge in sub-regional energy collaboration. [ABSTRACT FROM AUTHOR]

This research undertakes an investigation of global fuel cell vehicle (FCV) deployment, cognizant of optimal economic deployment and stakeholder preferences in a case study of Japan out to the year 2050. The model is mathematically formulated as a large‐scale linear optimization problem, aiming to minimize system costs, including generation type, fuel, conversion, and carbon reduction, subject to the constraint of carbon dioxide reduction targets. Results show that between ∼0.8 and 2% of global energy consumption needs can be met by hydrogen by 2050, with city gas and transport emerging as significant use cases. Passenger FCVs and hydrogen buses account for most of the hydrogen‐based transportation sector, leading to a global deployment of ∼120 million FCVs by 2050. Hydrogen production is reliant on fossil fuels, and OECD nations are net importers – especially Japan. To underpin hydrogen production from fossil fuels, carbon capture and storage is required in significant quantities when anticipating a large fleet of FCVs. Stakeholder engagement suggests optimism toward FCV deployment while policy issues identified include the necessity for large‐scale future energy system investment and rapid technical and economic feasibility progress for renewables and electrolysers to achieve a hydrogen economy which is not reliant on fossil fuels. [ABSTRACT FROM AUTHOR]

This study evaluates the optimal expansion of the electricity sector of the BBIN (Bangladesh, Bhutan, India, and Nepal) sub‐region with a detailed analysis of unevenly distributed resources and electricity demand, by developing a multi‐regional dynamic power sector optimization model, characterized by 27 nodes, 45 fuel transport lines, and 63 transmission lines in hourly temporal resolution. Scenarios developed in this paper assess the impact of 2 °C Paris agreement on production, transportation, and consumption of indigenous resources like coal and gas, the share of renewables and nuclear in the power generation mix, the utilization of huge untapped hydro resources through an expansion of cross‐border transmission lines. The simulation results show that hydro, wind, nuclear, and PV will be the dominant power sources, thus reducing the current share of coal, under carbon regulation scenario. The requirements of PV exceed its estimated commercially exploitable potential in most of the nodes in the nuclear‐restricted scenario. Expanding cross‐border transmission capacity will be an effective way to exploit untapped hydro resources so that Bangladesh and India can import power from Bhutan and Nepal. Although there is a slight increase in coal demand in the future, capacity expansion of fuel networks is not economical under adopted emission levels. © 2020 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

Byline: Yasumasa Fujii, Ryo Fukushima, Kenji Yamaji It has become important to address the question of which energy related infrastructure, such as transcontinental natural gas pipelines, should be constructed in Asia. In addition, one needs to ask how energy demand should be satisfied securely and economically, as well as environmentally benignly, over the next decades. This study investigates the possible future configuration of energy and CO2-related infrastructure in Asia and Eurasia, using a large-scale energy system model, which minimises inter-temporally the sum of the discounted total energy system costs until the year 2050. The model explicitly involves intra-regional transportation networks of fuels and recovered CO2 among approximately 100 nodes in Asia and Eurasia. The preliminary results indicate that long distance natural gas pipelines will be developed extensively in Asia and Eurasia, and that issuing carbon taxes of a few hundred dollars per ton of carbon enhance substantially the consumption of natural gas in electricity generation sectors, as a substitute fuel for coal. Such carbon taxes will make CO2 sequestration economically viable while increasing the cumulative amount of CO2 sequestration up to 15 gigatons (Gt) of CO2.

Byline: Kenji Yamaji, Katsura Sato, Yasumasa Fujii, Keigo Akimoto The theoretical potential of tradable CO2 emission permits has attracted much interest as a means of achieving the efficiency and equity of CO2 control. This paper presents a simulation of the global market of CO2 emission permits with the New Earth 21 Model. The analysis focuses on the initial allocation of CO2 emission permits, the effects of transaction costs and the impact of those regions out of the market. Major findings are as follows: 1) A significant amount of income transfer is realised from developed regions to developing regions with the initial allocation in proportion to each regional population; 2) As transaction costs increase, the efficiency of the market decreases; and 3) North America and China play a key role in the success of the tradable permits market. The results suggest the use of joint implementation as a realistic means of realising tradable CO2 emission permits.

Byline: Keigo Akimoto, Yasumasa Fujii, Takashi Sekiguchi, Kenji Yamaji Global warming caused by the increase of atmospheric CO2 concentration is regarded as a serious environmental issue. Due to uncertainty relating to the mechanisms of the terrestrial carbon cycle and climate system, solution of the problem is considered to be extremely complicated. In such a context, to conduct a decision analysis under uncertain CO2 concentration control policies, we have developed a global energy model which minimises the expected value of discounted total energy system costs up to the year 2055. In this work, we analyse an optimal future global energy system, particularly focusing on the Japanese electric power sector and present insight into an optimal strategy for energy system development under uncertain CO2 regulation policies.

SUMMARY In order to address climate change and energy security issues, intermittent renewable energy sources such as solar photovoltaic (PV) and wind power are gaining considerable attention. However, due to their variability and surplus electricity, the expansion of these renewables is an important challenge for power grid management. Various countermeasures such as rechargeable batteries, suppression, and back-up generators, are considered necessary for the physical integration of intermittent renewables to create an efficient and reliable power generation mix. In this context, we developed a high time-resolution optimal power generation mix model to quantitatively assess the amount of surplus electricity available under the large-scale introduction of PV and wind power in the Hokkaido region of Japan and the potential roles for the countermeasures mentioned above. The main feature of the model is the detailed time resolution at 10 min through a year. This allows us to investigate the impact of variation in various short-cycle renewables on surplus electricity and the deployment of rechargeable batteries. The simulation results suggest that if a proportion of PV and wind power expands more than around 10% and 20% of total demand respectively or if the sum of the proportion of PV and wind power exceeds 20%, the need for suppression grows rapidly. The results also suggest that rechargeable batteries are more economically compatible with PV than wind power is. [ABSTRACT FROM AUTHOR]

SUMMARY After the Fukushima nuclear accident, Japanese power generation planning needs to be reassessed to reflect technical developments on both the power supply and demand sides. The Fukushima nuclear accident has complicated the position of nuclear energy in Japan's long-term power generation mix due to public acceptance and other associated issues such as nuclear waste management. There is a need for more studies concerning the peak grid integration of variable renewables such as PV and wind power, which are expected to potentially replace nuclear energy. On the power demand side, the anticipated future introduction of electric vehicles (EVs) and plug-in hybrid vehicle (PHEV) will have an impact on grid management in the electric power system. In this context, it is important to develop a computational tool to comprehensively analyze the optimal power generation mix and organize it in a consistent way. This paper develops a dynamic high time-resolution optimal power generation mix model as large-scale linear programming model with 18 million constraints and 8 million endogenous variables. It then analyzes the optimal deployment of variable renewables (VR) and EVs with the future possible nuclear scenario and CO2 regulation policy in Japan taken into consideration. In the calculated optimal solutions, EVs play an important role in integrating variable renewables and treating the imbalance in VR surplus output. [ABSTRACT FROM AUTHOR]

SUMMARY This paper evaluates the impact of an extensive introduction of electric vehicles (EVs) and plug-in hybrid vehicles (PHEVs) on the energy supply mix in Japan. Energy consumption in Japan's transport sector has been dominated by petroleum, and CO2 emissions in this sector account for 20% of Japan's CO2 emissions. Therefore, the deployment of clean energy vehicles, such as EV and PHEV, is expected to play a significant role in tackling energy security and environmental concerns. In order to assess the energy and environmental benefits of EV and PHEV, we develop an energy system model integrating an optimal power generation mix model and a vehicle penetration model, with consideration of the optimal electricity charging profile of those advanced vehicles. The calculated results suggest that massive EV penetration serves as an energy saving measure in Japan's whole energy system due to significant petroleum reductions exceeding the growth of fuel input into the power generation sector derived from significant EV and PHEV penetration. Massive EV deployment is estimated to contribute to CO2 mitigation in the energy system as well. Evaluating CO2 emissions by mileage by automobile, however, carbon emissions by mileage for EVs is almost equivalent to that of gasoline hybrid vehicles (HEVs) in the case of decommissioning of nuclear power plants, which eventually causes a higher carbon intensity of the electricity supply. [ABSTRACT FROM AUTHOR]

SUMMARY This paper investigates Japan's long-term energy outlook to 2050 taking into consideration the massive deployment of solar photovoltaic (PV) systems and wind power generation under a nuclear energy scenario. The extensive introduction of PV systems and wind power systems is expected to play an important role in enhancing electricity supply security after the Fukushima nuclear power accident, which has increased the uncertainty of the future additional construction of nuclear power plants in Japan. Against this background, we develop an integrated energy assessment model composed of both an econometric energy demand and supply model and an optimal power generation mix model. The latter model is able to explicitly analyze the impact of output fluctuations for various renewable energy sources at a detailed time resolution of 10 min on 365 consecutive days, incorporating the role of stationary battery technology. The simulation results reveal that intermittent fluctuations derived from a high penetration level of those renewables are controlled by quick load following operation by natural gas combined cycle power plants, pumped-storage hydro power, stationary battery technology, and output suppression of PV and wind power generation. The results show as well that massive penetration of renewables does not necessarily require a comparable scale of stationary battery capacity. Additionally, in the scenario, which assumes the decommissioning of nuclear power plants with a lifetime of over 40 years, the required PV capacity in 2050 amounts to more than double the PV installation potential in both buildings and abandoned farmland areas. [ABSTRACT FROM AUTHOR]

SUMMARY This paper evaluates the optimal power generation mix considering massive deployment of variable renewable energy and regional power interchange. Japan has initiated the feed-in-tariff (FIT) and expected the significant introduction of PV and wind power for energy self-sufficiency and climate change. However, wind power resources in Japan are concentrated mainly in Hokkaido and the Tohoku region, which are remote from electricity-consuming areas such as Tokyo, and facilitating the considerable deployment of wind power requires the establishment of inter-regional power transmission lines. Against these backgrounds, we develop an optimal power generation mix model including regional electricity exchange as a large-scale linear programming model with 10 million variables and 30 million constraints. The calculation results show that regional grid expansion encourages wind power installation in the Hokkaido and Tohoku regions for power supply to the Tokyo area, where PV power and stationary batteries are alternatively replaced. Grid expansion too promotes the shift of PV installation to the Kyushu and Shikoku regions, which have longer sunshine duration, and interchangeably mitigates PV deployment in other regions through the transport of PV power from those two regions. [ABSTRACT FROM AUTHOR]

This paper presents an evaluation of the impact of extensive introduction of photovoltaic (PV) systems and stationary battery technology into the optimal power gen-eration mix in the Kanto and Kinki regions. The introduc-tion of solar PV systems is expected to be extensively deployed in the Japanese household sector and utility com-panies in order to address the concerns of energy security and climate change. Considering this expected large-scale deployment of PV systems in electric power systems, it is necessary to investigate the optimal power generation mix which is technologically capable of controlling and accom-modating the intermittent output-power fluctuations inher-ent in PV systems. Against this background, we develop both a solar photovoltaic power generation model and an optimal power generation mix model, including stationary battery technology, which can be used to explicitly analyze the impact of PV output fluctuations at a detailed time interval resolution such as 10 minutes for 365 consecutive days. Simulation results reveal that PV introduction does not necessarily increase battery technology due to the cost competitiveness of thermal power plants in the load-follow-ing requirement caused by PV systems. Additionally, on the basis of sensitivity analysis on PV system cost, dramatic cost reduction proves to be indispensable for PV to supply bulk electricity similarly to thermal and nuclear power plants. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 182(2): 9-19, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). [ABSTRACT FROM AUTHOR]

Abstract: There is growing attention to the regulation of greenhouse gas (GHG) emissions to mitigate the global warming, and the target of 50% reduction of GHG emissions by the year 2050 has been discussed in concrete as a long-term goal. The authors have been revising the regionally disaggregated world energy model which is formulated as a large scale linear optimization model from the aspect of nuclear and photovoltaic power generation technologies and calculate the optimal energy system development path over the time horizon with the CO2 emissions constraints. The obtained results indicate that the world electricity in 2050 is to be mainly provided by natural gas-fired power plants and LWR (light-water reactors), and that in 2100 is to be done by FBR (fast breeder reactors) and IGCC with CCS. The results also indicate that the relative importance of major technologies, such as FBR and CCS, may differ significantly due to the regional availabilities of energy resources and CO2 storage capacities. [Copyright &y& Elsevier]

In deregulated electricity markets, the role of a distribution company is to purchase electricity from the wholesale electricity market at randomly fluctuating prices and to provide it to its customers at a given fixed price. Therefore, the company has to take risk stemming from the uncertainties of electricity prices and/or demand fluctuation instead of the customers. The way to avoid the risk is to make a bilateral contract with generating companies or install its own power generation facility. This entails the necessity to develop a certain method to make an optimal strategy for electric power procurement. In such a circumstance, this research proposes a mathematical method based on stochastic dynamic programming and considers the characteristics of the start-up cost of an electric power generation facility to evaluate strategies of combination of the bilateral contract and power auto-generation with its own facility for procuring electric power in a deregulated electricity market. In the beginning we proposed two approaches to solve the stochastic dynamic programming, and they are a Monte Carlo simulation method and a finite difference method to derive the solution of a partial differential equation of the total procurement cost of electric power. Finally we discussed the influences of the prime uncertainty on optimal strategies of power procurement. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(2): 20–29, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20296 [ABSTRACT FROM AUTHOR]

The player in deregulated electricity markets can be categorized into three groups of GENCO (Generator Companies), TRANSCO (Transmission Companies), and DISCO (Distribution Companies). This research focuses on the role of Distribution Companies, which purchase electricity from the market at randomly fluctuating prices, and provide it to their customers at given fixed prices. Therefore, Distribution Companies have to take the risk stemming from price fluctuation of electricity instead of the customers. This entails the necessity of developing a certain method to make an optimal strategy for electricity procurement. In such a circumstance, this research has the purpose of proposing a mathematical model based on stochastic dynamic programming to evaluate the value of a long-term bilateral contract for electricity trade, and also a project of combination of the bilateral contract and power generation with their own generators for procuring electric power in a deregulated market. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 156(2): 32–42, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20105 [ABSTRACT FROM AUTHOR]

In this paper, a regionally disaggregated global energy model treating energy and CO2 transportation in detail is used to examine a cost-effective pattern for their interregional transportation over the 21st century under the CO2 stabilization target of 550 ppm. Also, we assess future perspectives for the hydrogen economy in such a scenario. The results show that as major petroleum and gas supplies shift to unconventional resources along the second half of this century due to resource depletion, the Middle East loses its importance as a petroleum and gas exporter and the global patterns of their transportation change significantly. We then show that while hydrogen's competitiveness decreases due to the detailed treatment of energy and CO2 transportation, biomass- derived Fischer­Tropsch (FT) fuels become attractive because their production facilitates a wide diffusion of CO2-neutral energy carriers by considerably reducing the transportation cost. FT fuels are produced in regions rich in forest resources and then transported on a large scale by tanker. By contrast, hydrogen is produced mainly at the center of its consumption regions using domestic feedstock, and its interregional delivery, which is done only by pipeline, plays a marginal role due to its high transportation cost. It is confirmed that such a hydrogen supply structure offers energy security benefits. Finally, we show that the regional distribution of CO2 storage capacity is a major determinant of the pattern of hydrogen transportation around 2100, because all the CO2 generated from hydrogen production is required to be captured for sequestration in that period and because interregional CO2 transportation is hardly chosen for economic reasons. [ABSTRACT FROM AUTHOR]

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 [ABSTRACT FROM AUTHOR]

Recently, many researches aiming at the realization of high-performance and high-precision control of induction motors have been reported, and instantaneous torque control of an induction motor can be regarded as one of the most important topics in this field. In previous works, the authors developed a new method to realize instantaneous torque control of an induction motor with a voltage-source inverter, and demonstrated both its numerical simulations and experimental results. Unfortunately, the mathematically complicated derivation of the control method made it difficult to understand intuitively, and hindered us from analyzing the detailed characteristics of motor speed changes. In this paper, the authors propose a new method to realize instantaneous torque control of an induction motor, which differs from the concept of vector control. The proposed method is a two-degree-of-freedom control which considers the instantaneous torque command and secondary flux command as parameters. The analytical solution reported here is a particular solution of the differential state equation of an induction motor, and can be expressed as a simple explicit function of the instantaneous torque command, secondary flux command, and motor speed. The authors show the validity of the proposed method through numerical simulations and experimental results. This paper aims the realization of high-performance control of an induction motor. The authors propose a new method to realize instantaneous torque control without transient torque with a voltage-source inverter. © 2001 Scripta Technica, Electr Eng Jpn, 137(1): 48–56, 2001 [ABSTRACT FROM AUTHOR]

Carbon emissions which would cause global warming were agreed to be constrained at COP3 in Kyoto. In addition, carbon emission permits trading was also approved to be introduced. The emission permits trading is expected to achieve efficient carbon emission reduction, equalizing the marginal costs of the emission reduction for the participating countries. In other words, the permits trading allows participants to reduce emissions where it is least expensive to do so. However, the inadequate introduction of the trading systems may impose an unfairly greater burden on some countries, and therefore careful evaluation of the system would be indispensable for its implementation. In this paper, we attempt to analyze emission permits trading, using the theory of cooperative games with a global energy model of optimization type. We assume that seven world regions as players participate in the permits trading system under the condition of the emission reduction target presented at COP3 and so on, and show the nucleolus of the grand coalition games, and the computational results of primary energy supplies and CO2 shadow prices. The insights of this research indicate that in order to stabilize the grand coalition, a noticeable amount of additional transfer of money would be needed besides the payments associated with the emission permits transactions. © 2000 Scripta Technica, Electr Eng Jpn, 131(2): 40–50, 2000 [ABSTRACT FROM AUTHOR]

Many efforts towards a settlement of the CO2 problem have already been made through internationally organized meetings. It is not unlikely that some targets will be set for the reduction of CO2 emissions. If a stringent reduction target should be imposed on CO2 emitted from a national energy system, this cw possibly have as severe an impact upon electric power sectors as the oil price crises experienced in the seventies. It is, however, quite uncertain whether or not political muscles will be used specifically for tackling the CO2 problem in the near future. In such a context, this paper presents a new method for optimal power system planning under uncertain CO2 emissions control policies. The derived optimal expansion plan gives us the minimum expected value of the sum of the total system cost and the total amount of carbon taxes levied on net CO2 emissions from fossil fuel-fired power plants. The stochastic dynamic optimization problem discussed here is formulated as a linear programming problem decomposable into several small subproblems. The proposed method can take into account a specific future scenario of the magnitude of control policy uncertainties, which can be presumably resolved in the first half of the next century due to the increase in scientific wisdom. Ln order to evaluate the usefulness of the method proposed here, the authors also present a simple cue study with the Japanese national power system up to the year 2050. [ABSTRACT FROM AUTHOR]

This paper presents a new method for power system planning which considers uncertainties of various system parameters as a part of the criterion function. The criterion function involves both the expected values of total system costs and the cost variances of different power plants. Previously, the authors proposed that these cost variances be evaluated from the existing power system plans in the form of the solutions to the inverse optimization problem, and then applied this procedure to the planning of power systems in Japan. However, because of the correlation between fuel and facility costs, the cost variances could not be determined as specific values. Here, to overcome this difficulty, the authors now introduce hydropower plants into the model as the so-called nonrisky elements and focus on the expenditure shares rather than the plant capacity shares. As a result, more reasonable results are obtained. This improved methodology is applied and the derived cost variances are shown. Further, using the resultant cost variances, the authors make Pareto-optimal power generation plans and demonstrate also the robustness of the method to price fluctuations. [ABSTRACT FROM AUTHOR]

SUMMARY This paper investigates the impact of an extensive introduction of electric vehicles ( EV) and plug-in hybrid vehicles ( PHEV) into the global energy system by 2050. The significant growth of automobile ownership in emerging countries is likely to increase world oil demand and the associated carbon dioxide emissions. In order to address these energy, security, and environmental concerns, the deployment of clean energy vehicles, such as EV and PHEV, is expected to play a crucial role due to their high fuel efficiency. Consequently, we develop both a global energy system model and a world vehicle penetration model, which can explicitly analyze the impact of EV introduction into the seasonal daily electric load curve, with consideration of the specific electricity charging profile through 2050. The simulation results confirm that EV deployment contributes to energy conservation, because oil demand reduction outstrips the growth in electricity demand and the associated fuel input into the power generation mix. Concerning carbon dioxide abatement, the magnitude of the impact relies on the carbon intensity of the power generation mix. If the intensity is low enough to guarantee a carbon mitigation effect due to EV fuel saving, emissions reduction is well assured. It should be noted, however, that in regions with high carbon intensity in the power generation mix, carbon emissions per mileage of EVs is almost equivalent to that of efficient gasoline vehicles such as hybrid vehicles, and the figure for PHEV is slightly higher than for hybrid vehicles. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 186(4): 20-36, 2014; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22373 [ABSTRACT FROM AUTHOR]

This paper analyzes Japan's optimal power generation mix considering massive deployment of solar photovoltaic ( PV) systems and wind power generation. The extensive introduction of PV systems and wind power system is expected to play an important role in addressing energy security and climate change concerns in Japan. Considering this expected large-scale deployment of PV systems in the electric power system, it is necessary to investigate the optimal power generation mix which is technologically capable of controlling and accommodating the intermittent output-power fluctuations inherent in PV and wind energy systems. Against these backgrounds, we develop an optimal power generation mix model, explicitly analyzing the impact of output fluctuation in variable renewables in the detailed resolution of time intervals like 10 minutes for 365 consecutive days, with the role of stationary battery technology incorporated. Simulation results reveal that considerable deployment of those variable renewables does not necessarily require a scale of battery capacity similar to that of the variable renewable capacity, due to quick load-following treatment by thermal power plants, pumped-storage hydropower, and battery technology over renewable output fluctuation. [ABSTRACT FROM AUTHOR]

In germinal centers (GCs), B cells are selected through interaction with follicular dendritic cells bearing immune complexes and follicular helper T (Tfh) cells secreting Tfh cytokines, including IL-21. To analyze these cellular interactions, we have explored culture conditions that can simulate GC B cell selection in vitro using a mouse follicular dendritic cell line, FL-YB. FL-YB cells efficiently enhanced viability of cocultured mouse B cells in a BAFF-dependent fashion. Interestingly, we found that addition of IL-21, a major Tfh cytokine, readily induced death of B cells that were cocultured with FL-YB cells, whereas IL-21 alone sustained viability of B cells in the absence of FL-YB cells. The IL-21-induced death was dependent on a low m.w. soluble factor that was released from FL-YB cells, which was finally identified as PGE2. Treatment of B cells with IL-21 plus PGE2, but not either alone, resulted in enhanced expression of a proapoptotic protein Bim and the upstream transcription factor Foxo1. A PGE2 receptor isoform, EP4, was responsible for IL-21/PGE2-induced B cell death. Thus, PGE2 is an endogenous chemical mediator that can switch pleiotropic actions of IL-21 on B cells. IL-21/PGE2-induced B cell death was rescued if B cells were costimulated via CD40. In immunized mice, deficiency of IL-21R in B cells led to a significant decrease in the frequency of activated caspase-3-positive GC B cells concomitant with impaired affinity maturation of Abs. Taken together, results implicate a physiological role of IL-21/PGE2-induced B cell death in GC B cell selection. [ABSTRACT FROM AUTHOR]