This paper aims to study how secondary energy and supply-demand of entire energy system should be towards 2050 and beyond where renewable energy plays a major role as energy sources. In various future scenarios, using mathematical models for supply-demand analysis of electric power and hydrogen, we assume generation of surplus electricity, operation of power storage, hydrogen production and storage equipment. We also conduct an assumption, economic analysis and optimization of capital and operation costs. The result indicates that “hydrogen system comprised of hydrogen production, storage” and “renewable energy for power generation” have mutually supportive relationship with each other and it is possible that their massive, integrated and coordinated introduction is one of desirable forms of energy system to realize decarbonization in an economically feasible manner.

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Residential solar photovoltaic (PV) system has been in widespread use since the FIT program which began in 2012 and has phased out after 2019. The problem of decreasing collection of wheeling charge and the associated disparity in cost burden is a problem caused by the massive introduction of residential PV. The current wheeling charge system is mainly based on a pay-as-you-go system. Therefore, when residential PV is installed in large numbers, the demand for grid electricity decreases. As a result, there will be a shortfall in the collection of wheeling charge by transmission and distribution (T&D) sectors. This results in an increase in the price of the wheeling charge. This leads to an increase in the cost burden for households without residential PV installations. On the other hand, households with residential PV installations will be able to reduce the cost burden of the transmission tariff. This is the problem of cost-sharing disparity. This study develops a bottom-up energy model based on a cost-effective technology selection. By assuming various wheeling charge systems, the authors analyzed the optimal wheeling charge system not causing the cost burden gap problem. A result reveals that the current wheeling charge system requires an increase in the unit price of the wheeling charge and causes cost burden disparity problems. The solution to this problem is to increase the basic rate ratio and to introduce a partial generation charge.

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In this study, we quantitatively elucidated the diffusion mechanism of China's new energy vehicle (NEV) and conducted a simulation analysis on diffusion measures. We found that the relative total cost, development of charging infrastructure, and NEV sales ratio regulation were factors affecting the spread of NEV. Moreover, as a result of estimating lithium ion battery price using learning curve theory, it was confirmed that the rate of decrease of the price was 18.1% every time the cumulative production volume doubled. As a result of simulation analysis, in the reference scenario, even if all subsidies are abolished from 2023, sales volume will expand steadily due to the introduction of The passenger Cars Corporate Average Fuel Consumption and New Energy Vehicle Credit Regulation(dual-credit policy), but the target for 2030 cannot be achieved. In order to achieve the target, it is effective to reduce the number of points per NEV and increase the NEV credit ratio. The sales share of passenger NEV in total passenger vehicles is expected to reach 39.5% by 2030, achieving the target.

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In recent years, a car-sharing service in which a plurality of member users share a specific PLDVs (Passenger Light Duty Vehicles) has been popularized mainly in urban areas. For a long-term period from 2020 to 2050, we calculated the number of global PLDVs stock in the future based on 2 different scenarios for the dissemination of car-sharing services (Normal and High scenarios) and simulated the impact on greenhouse gas emissions. Car share is projected to reduce global PLDVs stock in 2050 would be reduced by 19% to 28% in the normal scenario and by 57% to 83% in the high scenario. The reduction in greenhouse gas emissions associated with a decline in the number of global PLDVs stock is projected to be 16 ~ 25% in the normal scenario and 48 ~ 75% in the high scenario. And the normal scenario is calculated to reduce the estimated demand for Li and Co by 52%(no recycling) and 72%(recycling).

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Best–Worst Scaling (BWS) is applied to assess Japanese consumer preferences for combination of power generation sources and a power producer and supplier (PPS). Although the concept of renewable energies has been disseminated, the PPS is still unfamiliar to most of the Japanese consumers. BWS has advantages in obtaining information on preferences by identifying “best” and “worst” options. An online questionnaire survey was conducted in 2020 and its sample size was 2,496. BWS object case and BWS multi-profile case are both applied in this study. Results of BWS object case reveal that solar PV is the most important factor. Conversely, other renewables and thermal power generation are less important. Nuclear power is a fairly low rating. Random parameters logit analysis reveals the difference by generations, gender and residential solar PV installation. BWS multi-profile case reveals that different results are obtained if a plan with 100% renewables is added to the generic three alternatives. Random parameters logit estimates of multi-profile case demonstrate the preference heterogeneity of renewables though its mean parameter is not statistically significant. The evaluation of coal-fired and nuclear power generation is low.

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Renewable Power-to-Gas has spread in European countries since the early 2000s as penetrating variable renewable energies. As an aid to implement the basic hydrogen strategy of Japan, the authors developed a photovoltaic generation (PV)-powered hydrogen production system at a hydrogen refueling station in 2017, and have studied the operation planning and control for improving its capacity factor since then. In this paper, the authors set the operating policy to maximize hydrogen production keeping two cases of environmental criteria (case 2020 and 2030), and propose the operation control to levelize the input power for the PEM-electrolyzer by the grid and the operation planning using weather forecast data on the PV-powered hydrogen production system. Through four one-year operating simulations in each case, the results show that more than one and a half times hydrogen production is available compared to the PV-followed operation control without planning in the case 2020, but only a little increase of hydrogen production is attained under the harder environmental criteria in the case 2030. This results from the higher carbon dioxide emission factor of the power grid in Japan based on the energy mix plan in 2030 as compared to the definition of green hydrogen in the European Union.

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The number of municipalities declaring "2050 Zero Carbon City" is increasing, but many of these don’t plan concretely. In this study, the greenhouse gas emissions of municipalities are estimated by subtracting the amount of CO₂ reduction by renewable energy and the amount of CO₂ absorption by forests from the amount of CO₂ emissions from these municipalities. As a result, it is estimated that 1/5 of the municipalities in the Tohoku 7 prefectures are already zero carbon cities. These Zero Carbon Cities are more affected by the amount of CO₂ absorption by forests than the amount of CO₂ reduction by renewable energy. This study also reveals that as for the prefectural capitals, it is difficult to become Zero Carbon Cities by themselves, but for Morioka City, Iwate Prefecture and so on, it is possible to become Zero Carbon Cities by regional partnership with neighboring municipalities. According to the estimation of 2050, if at least 30% of the renewable energy potential is installed, about half of the municipalities in the Tohoku will become Zero Carbon Cities.

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As the Japan’s feed-in tariff scheme, a renewable energy surcharge is charged in proportion to the grid power consumption. Authors proposed to replace this with a “CO₂ reduction surcharge” which is charged in proportion to CO₂ emissions. This paper evaluates nationwide effects of introducing this surcharge and storage battery when renewable energy is largely introduced. By optimizing hourly thermal power generation output of each type, PV/wind energy curtailment, charge/discharge amount and tie line power flow, the annual thermal power cost in Japan is minimized with linear programming methods. Then the CO₂ emissions and costs are evaluated. Results show the introduction of storage battery decreases PV/wind energy curtailment, but CO₂ emissions are not decreased because the energy share of coal-fired power generation is increased. When the surcharge unit price is increased, the availability and capacity of lower efficiency coal-fired power generation are decreased. Results also show that CO₂ emission intensity can be decreased to 0.2kg-CO₂/kWh when most of coal-fired plants are abolished, but then more capacity of LNG combined cycle power generation and more fuel costs are required.

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This study analyzed the factors causing the difference in the amount of utility bill payments by housing construction period, using micro data of about 9,000 households. The analysis consisted of (1) building a model of gradient boosting decision tree, which is one of the machine learning techniques, (2) identifying contribution of each household and each feature using SHAP value, which is a novel method to improve the interpretability of machine learning, and (3) revealing the breakdown of differences on a macro level by aggregating each contribution. The results showed that the factors that have reduced the amount of payments in recently constructed houses were partly caused by the spread of heat pump water heaters and IH cooking heaters, in addition to the improvement of housing insulation performance. It was also confirmed that the effects of higher efficiency refrigerators and lighting have been steadily increasing.

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