Cryogenic Direct-air CO₂ Capture (Cryogenic DAC), the technology of capturing atmospheric CO₂ by desublimiting it as dry ice, can effectively utilize the abundant wind energy in Antarctica and it is estimated that the energy requirement will be competitive towards conventional aqueous solution DAC if substantial efficiency improvements and system enhancements occur. However, it hasn’t been implemented yet and the energy requirement and capital cost are uncertain. In this study, the feasibility of cryogenic DAC is analyzed by conducting a sensitivity analysis on the energy requirement/capital cost of cryogenic DAC and the capital cost of wind/solar energy in Antarctica under the 1.5℃/2.0℃ goals in Paris Agreement. As a result, if the capital cost of wind/solar power in Antarctica is the same as in Alaska the energy requirement/capital cost of cryogenic DAC require to be lower than that of aqueous solution DAC for cryogenic DAC introduction in both goals. In addition, when the energy requirement/capital cost of cryogenic DAC are fixed, it is found that the capital cost of wind/solar power generation in Antarctica requires to be limited to about 1.2 times the global standard cost for cryogenic DAC introduction in the 1.5℃ goal.

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Power retail companies have the risk of paying the penalty due to the imbalance between planned and actual power generation values. And the risk is supposed to increase in the future. Batteries and electrolyzers are a possible solution to reduce the imbalance. To mitigate the high installation cost of electrolyzers, it is important to increase the capacity factor of electrolyzers. In this study, a mathematical model was developed to simulate the operation of a power retail company using a battery and an electrolyzer. Then we proposed a new strategy to produce hydrogen using electricity from JEPX, when the wholesale electricity price is lower than a certain value. The model was formulated as a mixed integer linear programming problem, and the effect of the strategy was evaluated by solving this problem. As a result, this strategy achieved high capacity factor of the electrolyzer, around 60%. In order to reduce the risk of JEPX price fluctuation, we also proposed an electrolyzer’s operation strategy using the prediction error distribution of JEPX price. The effect was quantified through Monte-Carlo simulation. Although the deviation of the yearly revenue was not much reduced by this strategy, the high deviation was notably reduced in the daily revenue.

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After deregulation of electricity market in 2016, the amount of electricity trade is rapidly increasing in Japan, and the importance of accurate analysis on price in JEPX(electricity market in Japan) is increasing. When a large electricity companies bid on the electricity market in Japan, it is common to specify a power source that increases output by selling or a power source that decreases output by buying, and determine the selling/buying price by calculating the break-even price. This price is called as the marginal cost. We introduce a method to accurately calculate the marginal cost for each time frame when pumped storage power generation and thermal power generation, etc. are used for bidding. In addition, we introduce a method that simulates price spikes based on market principles, such as when the volume of buy bid is larger than that of sell bid. We calculated electricity market prices of January 2021, when unusual price spikes occurred, and found that this model reproduce the market price trends to the extent.

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The introduction of solar and storage battery systems is required as a countermeasure against global warming, which is becoming more serious every year, and as a way to improve resilience against power outages caused by natural disasters. However, the introduction of solar and storage battery systems has not progressed because the required capacity and the effect of the introduction are unclear for each facility. In this study, we have conducted a case study focusing on the economic evaluation of Solar photovoltaic battery systems and power outage response capability and calculated the effectiveness of installation. The target facilities are junior high schools that are actually used as emergency evacuation sites. The period of the analysis is assumed to 20 years with a power outage occurring once in the period. The profits include the selling electricity by the Solar photovoltaic during normal times, the savings in electricity charges, and the value of avoiding power outages. The value of avoiding power outages means the amount of time that power outages can be avoided with Solar photovoltaic battery systems, and defined as a monetary value using the power outage cost index called VOLL (Value of lost load). The costs include the system costs and O&M expenses.

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To maintain the power supply reliability, retail electricity suppliers notify transmission and distribution companies of the amount of power supply in advance and procure the power required for actual electricity trades. If the retail electricity suppliers are unable to procure the notified amount of power supply, the resulting power shortage or excess must be compensated by paying a heavy imbalance penalty. Focusing on the framework of energy resource aggregation business, the authors propose a calculation method of incentive payments in demand response programs for economic electricity trading by the retail electricity suppliers. Based on the concept of maximizing social welfare, the demand response-induced changes in each utility function of the retail electricity suppliers and their consumers are translated into a guide for rebate level settings. Moreover, the optimal rebate levels are defined in terms of minimizing the burden on the demand response programs. Through numerical simulations and discussion on their results, the validity of the proposal verified.

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Ongoing global warming poses a range of imminent threats. In an effort to mitigate global warming, floating offshore photovoltaic plants (FOPVs) are planned to be established in ocean areas within 30°north and south of the equator, where solar radiation levels are high, to produce sufficient electricity to meet the primary energy needs of Japan and the world. By converting generated electricity into fuel ammonia (NH₃) and storing it for 4–6 months, carbon-free energies can be stably and inexpensively supplied to numerous facilities, including power grids. The introduction of FOPV and NH₃ into the energy sector, which has thus far been dependent on fossil fuels, will bring about a major change in the world through carbon-free energy.

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