The self-consumption rate of residential solar photovoltaic (PV) systems is an important indicator for understanding energy balances, estimating grid electricity demand, and assessing the economic impact on system owners. This study analyzed approximately 2,000 PV-equipped households using the Survey on Carbon Dioxide Emissions from the Residential Sector statistical dataset from 2017 to 2022, focusing on self-consumption rates and related variables. The use of multi-year data enabled the analysis of historical trends and statistical analysis. The results show that (1) PV system capacity factors and self-consumption rates vary across regions and seasons, (2) the declining price of electricity sold to the grid and increasing adoption of battery storage are driving higher self-consumption rates, and (3) self-consumption rates are influenced by supply-side factors, such as PV system capacity, and demand-side factors, including electricity consumption and daytime occupancy rates.

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A stable and sustainable supply of critical minerals becomes an important policy agenda from climate change and economic security perspectives. This study newly develops a global energy and mineral supply-demand model to assess the cost-effective energy technology choice considering resource constraints and material balances of critical minerals. We focus on lithium, cobalt, and nickel, which are the basic materials for lithium-ion batteries for mobility and stationary uses. The simulation results suggest the following two points. First, resource constraints of these three minerals affect the optimal penetration of BEV (battery electric vehicles) and stationary batteries. In particular, conventional NMC (nickel manganese cobalt oxide) batteries are constrained by the availability of nickel and cobalt resources. Nickel and cobalt-free batteries, such as LFP (lithium-iron phosphate) batteries, would be necessary to accelerate the deployment of BEV and stationary batteries. Second, from the viewpoints of lithium supply and demand, our results imply that lithium-ion batteries for vehicles would be the main demand, rather than stationary batteries. Lithium brine resources play a key role in meeting the demand in the long-term.

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The massive deployment of solar and wind power (VRE: variable renewable energy), which will enable decarbonized energy supply, will bring with it a variety of new challenges. Among them is the reduction in the operating capacity of synchronous generators in the power system, which causes a reduction in the inertia of the power system. With reduced system inertia, grid frequency deviations become faster and larger, and these deviations sometimes make power system operation unstable. In this paper, we analyze the situation of system inertia degradation by conducting an hourly-granularity annual power supply-demand analysis based on the power supply-demand scenario of conventional power sources, VRE, batteries in 2030-2040 under the mass introduction of renewable energy with the parameter of the required quantity setting for supply and demand of the flexibilities from primary to tertiary in the demand-supply adjustment market.

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Synthetic methane (e-methane) can contribute to supplying carbon-neutral heat and electricity while utilizing existing technologies and infrastructures. This study investigates the role of e-methane in Japan’s energy system by 2050. The author employs an energy system optimization model that encompasses the entire energy system with detailed modeling for e-methane supply (e.g., innovative e-methane productions and e-methane imports) and consumption (e.g., industry, transport, and power generation). Key findings include the following three points. First, imported e-methane would be a cost-effective option for industries and buildings. In the industry, fuel switching from coal and oil to natural gas in the medium term and then to e-methane in the longer term is estimated to be cost-effective for decarbonizing heat demand. Electrification is important for buildings, although e-methane can be a part of the optimal final energy mix. Second, our results imply the potential of e-methane as a fuel for large-scale power generation, whereas e-methane for road transport is projected to be modest. Finally, this study found that the innovative e-methane production process can reduce the CO₂ abatement cost by 7%-16% in 2050. E-methane is estimated to improve the economic feasibility of net-zero CO₂ energy systems.

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A thermal power plant employing amine-based post-combustion CO₂ capture (PCC) is a key technology for low-carbon, dispatchable power sources for the carbon-neutral electric power sector. Power-to-heat amine-based PCC is likely an economically promising system operation, which conducts CO₂ absorption along with the power generation and facilitates CO₂ desorption through a heat pump driven by exceptionally inexpensive electricity procured during peak power generation periods from electricity market via the grid. The combination of mathematical modelling and cost analysis evaluated the annual profits of the proposed system in future electricity markets (2030–2050) in Japan, which was predicted by an energy system optimization model. The results demonstrated that employing power to heat amine-based PCC instead of the conventional one increased the annual profits by approximately 2–27%. Notably, depending on economic factors (e.g., electricity market prices, capacity factor, or interest rate), annual profits were positive without further improvement in the amine-based PCC technologies. This result indicates that now is the time to move from laboratory investigations to real-world implementation and that techno economic analysis regarding investment decision is more important rather than calculation of carbon capture costs to showcase the feasibility of thermal power plants with PCC, propelling its swift implementation.

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