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Abstract Japan has faced the rapid penetration of solar PV, and specific power service areas actually experience technical difficulty in integrating massive PV into the power grids. By developing an optimal power grid model with 352 buses and 441 power transmission lines in an hourly temporal resolution through 8,760 h, this manuscript aims to analyze the optimal integration of solar PV into a bulk power transmission network in Japan and to identify the best location of PV to be installed in the grid so as to minimize total power system cost. For optimizing PV installation in Japan, computational results recommend the deployment of PV system in the area with sufficient grid capacity and higher solar radiation, because enough grid adequacy is necessary to efficiently control PV output and higher solar insolation leads to reduce required PV capacity and the associated investment cost. In order to realize optimal PV integration in Japan, policy recommendation is to institutionalize the scheme informing preferable locations of PV integration in a power grid, such as developing a PV installable map or implementing a zoning regulation of the grid connection. Highlights • A power grid model with 352 buses and 441 lines is developed to optimize PV install in Japan. • PV is optimally integrated in the area with enough grid capacity and higher solar radiation. • Optimal PV integration reduces the regional gap of wholesale electricity prices. • Policy proposal is to arrange the scheme informing preferable locations of PV integration. [ABSTRACT FROM AUTHOR]

We present the results of photo-polarimetric observations for asteroids 9 Metis (S-type, main belt asteroid (MBA)), 52 Europa (C-type, MBA), and 1036 Ganymed (S-type, near-Earth asteroid), obtained at six wavelength bands. It is found, combining our new data with previous observations, that (1) larger maximum value of negative polarization [P.sub.min] =-1.37% and higher polarization slope h = 0.27% [deg.sup.-1] occur in 52 Europa, while smaller [P.sub.min] and lower h appear, i.e., -0.84%, 0.11% [deg.sup.-1] for 9 Metis and -0.57%, 0.095% [deg.sup.-1] for 1036 Ganymed. These results confirm the general trend of polarization-phase angle curves found previously between C- and S-type asteroids (see B. Goidet-Devel et al. 1995, Planet Space Sci. 43, 779-786). (2) An increase of polarization with wavelength from 0.42 to 0.76 [micro]m is found from the data with their root-mean-square errors in 9 Metis and 1036 Ganymed, in contrast with vice versa dependence in 52 Europa. (3) A relation of [P.sub.min] and geometric albedo A, presented in D. F. Lupishko and R. A. Mohamed (1996, Planet Space Sci. 46, 47-74), leads to the resulting values of A for 0.15, 0.082, and 0.24 for 9 Metis, 52 Europa, and 1036 Ganymed, respectively. (4) The polarization observed for 9 Metis shows a significant time variation modified with the rotation of asteroid, but no clear relation between lightcurve and polarization curve appears. For 52 Europa and 1036 Ganymed, the observed time variation of polarization is weak. (5) A comparison of model simulation to the observations of lightcurve and geometric albedo A variation for 9 Metis suggests the existence of inhomogeneous albedo features on its surface, where the albedo was derived from the relation of [P.sub.min] and A. Key Words: asteroids; polarimetry; photometry; time variation.

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]

• Modeled grid-connected hydrogen storage and carbon capture and storage (CCS) technology. • Hydrogen storage becomes economically feasible in carbon-regulated cases only when the system cost reduces by 20%. • The production and storage profiles of hydrogen are influenced by the seasonal, weather, and diurnal variations. • To reduce 80% emission by 2050, about 179 GW, 106 GW, and 35 GW of CCS-based coal power plants should be constructed in the eastern, western, southern parts of India. • Northern and southern part benefits the most from the CCS based power generation in the eastern part of India. This study integrates grid-connected hydrogen storage and carbon capture and storage (CCS) technology in a spatially disaggregated capacity expansion model, that can explicitly characterize the operational behavior of other conventional technologies. The model is then used to assess the decarbonizing pathways of the integrated power grid of four countries: Bangladesh, Bhutan, India, and Nepal of South Asia under multiple policy scenarios. The impact of the cost associated with hydrogen system components, and with capturing, transporting, and injecting CO 2 in storage sites on the technology choices and their capacities are further evaluated through sensitivity analysis. The hydrogen storage system is effective in tapping surplus energy produced from intermittent renewables mostly in coal deficit regions for both short as well as long-term duration, but its large-scale deployment depends on electrolyzer and fuel cell cost reductions by more than 20% to compete against battery technology. In a very optimistic situation of 90% cost reduction, northern, western, southern parts of India and Bangladesh can completely decarbonize its power sector by 2050 through the installation of about 593 GW, 395 GW, 138 GW, and 120 GW of hydrogen storage tank. The storage and production profiles of hydrogen are influenced by seasonal, weather, and diurnal variations. Under limited solar PV and nuclear scenario, India should start operating CCS-based coal power plants from 2030 to meet the 80% emission reduction target and techno-economically feasible capacity requirements reach about 179 GW, 106 GW, and 35 GW by 2050 in the eastern, western, and southern parts of India respectively. [ABSTRACT FROM AUTHOR]

The involvement of green hydrogen in energy transformation is getting global attention. This assessment examines the hydrogen production and its utilization potential in one of the hydropower-rich regions, Nepal under various demand growth and technology intervention scenarios by developing a power grid model of 52 nodes and 68 transmission lines operating at an hourly time-step. The model incorporates a grid-connected hydrogen storage system as well as charging stations for electric and hydrogen vehicles. The least-costly pathways for power grid expansion at the nodal and provincial levels are identified through optimization. The results show that 32 GW of installed capacity is required to meet domestic electricity demand and 14 GW more hydropower should be exploited to completely decarbonize the transport sector by 2050. For maintaining 50% shares of hydrogen vehicle in the transport sector and meet government electricity export targets, Nepal requires 5.7 GW, 12 GW and 23 GW of the additional electrolyzer, hydrogen storage tanks and storage-based hydropower capacities respectively. For a given electricity demand, introducing hydrogen systems can reduce the capacity requirements of hydro storage by storing surplus power generated from pondage run-of-the-river and run-of-the-river hydropower during the rainy season and using it in the dry season. • Integrated hydrogen energy storage system and charging stations within a power grid model. • 14 GW of additional hydropower plant is required to completely decarbonize the transport sector. • Huge storage-based hydropower is exploited only in export-oriented scenario. • Share of storage-based hydropower decreases with a reduction in hydrogen system cost. • Hydrogen system reduces power curtailment from pondage run-of-the-river and run-of-the-river hydropower. [ABSTRACT FROM AUTHOR]

The cost effective R&D strategy is required especially for large-scale technologies because their development demands a large amount of investment in general. A mixed integer programming model was developed for the optimum technology development strategy in the field of energy systems. The module of the technology development process in the model is based on GERT (Graphical Evaluation and Review Technique). In the module, a target technology is broken down into many elemental technologies. Usually several target technologies are involved for the evaluation of technology development strategy of one field and some of the elemental technologies are used common to a number of target technologies. Since elemental technologies are explicitly modeled, their spillover effects are necessarily evaluated in this model analysis. The proposed method was applied to the evaluation of the development strategy of four types of IGCC (Integrated coal Gasification Combined Cycle) technologies which have different levels of thermal efficiencies. The total investment on both their R&D and practical use is optimized under the constraint of meeting a certain exogenous scenario of electricity demand. The evaluation results include the optimum additional investment allocation among the developments of various elemental technologies; developments of integration technology for IGCC-43%, IGCC-55% and IGCC-48%, coal gasification technology, oxide dispersion strengthened superalloy technology for the gas turbine blade and vane, ceramic matrix composite technology for the gas turbine blade, dry sulfur-removal technology, etc. are cost-effective. [Copyright &y& Elsevier]

This paper presents a new modeling approach to incorporate operational characteristics of different types of hydropower in long-term power sector models. The existing literature and methods were reviewed, and the mathematical formulation of the developed model is presented. The model is then used to analyze the future power generation mix of Nepal, a country with huge untapped hydro resources, as a case study. The possible power sector development pathway has been assessed through three different electricity demand growth rate scenarios. The optimal deployment of indigenous hydro and renewables is further evaluated by developing zero-emission scenarios as a conceivable policy to strengthen national energy security. The sensitivity analysis of governing parameters and evaluation of simulation results was performed to validate the model. Simulation results for capacity and generation mix along with emission level and total power system costs have been discussed for each scenario. Power dispatch and operation schedule determined as a result of optimization take account of the seasonal variations of river inflow and operational benefits of hydropower. Sensitivity analysis is carried out to examine the impact of construction cost, availability factor and water storage capacity on total cost, capacity requirements and optimal operation of hydropower. • Represented different types of hydropower in dynamic power sector model. • Detailed analysis of the future power generation mix of Nepal. • Optimized the operation schedule and water storage strategy of hydro Pondage run-of-the-river and hydro storage. [ABSTRACT FROM AUTHOR]

Decarbonization of the energy system is a key goal of the Paris Agreements, in order to limit temperature rises to under 2° Celsius. Hydrogen has the potential to play a key role through its versatile production methods, end uses and as a storage medium for renewable energy, engendering the future low-carbon energy system. This research uses a global model cognizant of energy policy, technology learning curves and international carbon reduction targets to optimize the future energy system in terms of cost and carbon emissions to the year 2050. Exploring combinations of four exploratory scenarios incorporating hydrogen city gas blend levels, nuclear restrictions, regional emission reduction obligations and carbon capture and storage deployment timelines, it was identified that hydrogen has the potential to supply approximately two percent of global energy needs by 2050. Irrespective of the quantity of hydrogen produced, the transport sector and passenger fuel cell vehicles are consistently a preferential end use for future hydrogen across regions and modeled scenarios. In addition to the potential contribution of hydrogen, a shift toward renewable energy and a significant role for carbon capture and storage is identified to underpin carbon target achievement by 2050. • Global linear optimization model of hydrogens role in the future energy system. • Cognizant of policy, technology learning curves and carbon targets. • Hydrogen is estimated to account for approximately 2% of energy needs by 2050. • Hydrogen to play a prominent role in the transportation sector. • Perverse incentives of different carbon reduction goals investigated. [ABSTRACT FROM AUTHOR]

Abstract Hydrogen as an energy carrier allows the decarbonization of transport, industry, and space heating as well as storage for intermittent renewable energy. The objective of this paper is to assess the future engineering potential for hydrogen and provide insight to areas of research to help lower economic barriers for hydrogen adoption. This assessment was accomplished by creating top-level system models based on energy requirements for end-use services. Those models were used to investigate four case studies that provide a global view augmented with specific national examples. The first case study assesses the potential penetration of hydrogen using a global energy system model. The second applies the dynamic integrated climate–ecosystem–economics model to derive an estimate of the impact of the diffusion of hydrogen as an energy carrier. The third determines the required growth in renewable power and water usage to power transportation in the United States (US) with hydrogen. The fourth assesses the use of hydrogen for heating in the United Kingdom (UK). In all cases, there appeared to be significant potential for hydrogen adoption and net energetic benefit. Globally, hydrogen has the potential to account for approximately 3% of energy consumption by 2050. In the US, using hydrogen for on-road transportation could enable a reduction in rejected energy of nearly 10%. Also, hydrogen might provide the least cost alternative to decarbonizing space heating in the UK. The research highlights a challenge raised by widespread abandonment of nuclear power. It is currently unclear what the removal of nuclear would do to the cost of energy as nations attempt to limit global greenhouse gas emissions. Nuclear power has also been proposed as a source for large scale production of hydrogen. Finally, this analysis shows that with today's technological maturity making the transition to a hydrogen economy would incur significant costs. Highlights • Explores four case studies of the societal penetration of hydrogen. • Identifies the decarbonizing benefits of hydrogen in transport and heating. • Global model identifies nation specific opportunities for hydrogen penetration. • Cost remains a significant challenge to the ushering in of the hydrogen economy. • Cost reductions in hydrogen production, storage and transmission are necessary. [ABSTRACT FROM AUTHOR]

Abstract Japan is the sixth largest greenhouse gas emitter in 2016 and plays an important role to attain the long-term climate goals of the Paris Agreement. One of the key policy issues in Japan's energy and environmental policy arena is the energy system transition to achieve 80% emissions reduction in 2050, a current policy goal set in 2016. To contribute to the ongoing policy debate, this paper focuses on energy-related CO 2 emissions and analyzes such decarbonization scenarios that are consistent with the government goals. We employ six energy-economic and integrated assessment models to reveal decarbonization challenges in the energy system. The modeling results show that Japan's mitigation scenarios are characterized by high marginal costs of abatement. They also suggest that the industrial sector is likely to have a large final energy share and significant residual emissions under the 80% reduction scenario, though it is generally thought that the transport sector would have large decarbonization challenges. The present findings imply that not only energy policy but also industrial policy may be relevant to the long-term environmental target. Given the high marginal costs exceeding those of negative emissions technologies that could place a cost ceiling, further model development would be crucial. Highlights • We analyze the energy system scenarios to achieve 80% reduction in carbon dioxide emissions by 2050. • We employ six integrated assessment models to reveal decarbonization challenges in the energy system. • The model results show that the industrial sector has a large final energy share and significant residual carbon dioxide emissions under the 80% reduction scenario. • We also show that Japan's mitigation scenarios are accompanied with high marginal costs of abatement. [ABSTRACT FROM AUTHOR]

Abstract In this study, the authors developed an Optimal Power Generation Mix model, which takes into account the supply chain of imported and domestically produced hydrogen, also modeling the intermittency of renewable energy at a 10-min resolution, and applied it to the case of Japan, to investigate quantitatively the possibility of achieving zero emission in 2050. Even if the costs of wind and solar PV decline drastically towards 2050 and the huge potentials that have been assumed in the literature are realized, the total system costs escalate significantly with very high shares of intermittent renewables. Since the use of hydrogen produced by excess electricity from renewable power generation sources can only make a slight contribution to reducing this escalation, it would be invaluable to introduce at least a significant amount of electricity generated by "zero-emission thermal power" technologies, including CO 2 -free imported hydrogen or conventional thermal power generation with carbon capture and sequestration (CCS). Nuclear power is also estimated as being effective in reducing the cost hike associated with achieving zero emissions. The results of this study could contribute to giving insights regarding global deployment of hydrogen-related technologies, as well as to presenting a frame of reference for Japan's future energy policies. Highlights • Variable renewables can contribute greatly to zero emission power in 2050 in Japan. • A very high share of them, however, could escalate the total cost to 20–30 JPY/kWh. • "Zero emission thermal" power generation is a necessity to meet the 2050 target. • Use of imported hydrogen is one possibility for zero emission thermal power. • Use of nuclear power is also an effective way to reduce the cost escalation. [ABSTRACT FROM AUTHOR]

Climate change significantly impacts hydrological systems resulting in hydropower generation uncertainties. In this study, a high-resolution glacio-hydrological model is coupled with an hourly-resolution power grid model to evaluate the climate change influences on hydropower generation across Nepal. Four climate future scenarios namely Cold-Dry, Warm-Dry, Cold-Wet, and Warm-Wet are developed to compare the changes in water availability and optimal power system with historical climate. The total flow increases for the wet scenarios (+11.4% under Cold-Wet for the Koshi basin), compared to the dry scenarios (−24.6% under Warm-Dry for the Karnali basin) for all the major river basins in Nepal. The results illustrate the distribution and magnitude of changes in total water availability and power generation are not proportional for dry and wet scenarios as a ∼20% reduction of water availability in the dry scenarios only results in a ∼2–3% decrease in electricity generation. The capacity requirements of hydro storage decrease by 7.2 GW for Cold-Wet and 6.8 GW for Warm-Wet scenarios compared to historical climate indicating higher capacity requirements in dry scenarios. Larger impacts observed at higher altitudes suggest more attentive adaptation strategies in developing climate-resilient hydropower systems. Results suggest that Nepal should not be entirely focused on exploiting its hydropower potential but rather diversifying the generation mix including solar PV and hydrogen technology. For the least-cost power system expansion, the Warm-Wet climate appears to be the most desirable and a cost savings of about 3.76 billion USD in hydropower development can be realized if better adaptation strategies are employed. [Display omitted] • Climate change impacts on hydro-dominated power systems in a high-mountain country. • Coupling of glacio-hydrological model and a high spatial-temporal power grid model. • Adaptation strategies for surplus electricity management are more critical in wet scenarios. • Storage hydro capacity needs drop by 7.2 in Cold-Wet & 6.8 GW in Warm-Wet scenarios. • Employing adaptation strategies results in cost savings of about 3.76 billion USD. [ABSTRACT FROM AUTHOR]

• Estimated the cost of a zero emission power sector with 28-yearly data. • Power storage requirement is decided by the duration of "windless & sunless" periods. • A "cumulative residual load" approach can correctly estimate the storage requirement. • Use of "power to gas" technologies can reduce the total system cost significantly. • Firm capacities are required even in a case with very high renewable penetrations. In recent years, several studies have been published focusing on the economics of the power sector under the high penetration of variable renewable energy (VRE) following the rapid expansion of VRE capacities worldwide. However, detailed analyses of the fluctuations in meteorological conditions have hitherto been scarce, despite the expectation that VRE output will be significantly affected by them. To fill this gap, we investigated the economic likelihood of achieving a zero-emission power system in Japan by 2050, using multi-annual meteorological data from 1990 to 2017. We used a detailed linear programming optimization model, as well as a method that uses cumulative residual loads (CRL), which proved to be useful for estimating required energy storage capacities and for understanding the complex substitution of power generation and storage technologies. The estimated unit cost for a 100% renewable electricity system depends heavily on meteorological conditions, standing at 20.9 JPY/kWh with a standard deviation of 1.2 JPY/kWh, which declines to 18.3 JPY/kWh with a standard deviation of 0.6 JPY/kWh for a system with hydrogen storage. The calculations indicate that the required storage capacity is determined mainly by the duration of "windless and sunless" periods, or "dark doldrums", and the greatest risk under high VRE penetrations is the possibility of supply disruption during such periods. The results also highlight the considerable value of "firm capacities", such as thermal and nuclear power generation, under a high share of VRE, although it should be noted that the profitability of these capacities may differ significantly from current situations, with large VRE outputs with negligible marginal costs. [ABSTRACT FROM AUTHOR]