Japan Could Slash CO2 Emissions by 87% with PV and EV Systems

By Muhammad OsamaReviewed by Laura ThomsonMay 28 2025

In an article published in Applied Energy, researchers comprehensively explored the decarbonization potential of integrating rooftop photovoltaic (PV) systems with electric vehicles (EVs) as battery storage across all 1,741 municipalities in Japan. This innovative approach aims to reduce carbon emissions, enhance energy self-sufficiency, and support Japan's carbon neutrality goals, highlighting its potential to solve urban energy and climate challenges.

Rooftop PV Technology for Urban Sustainability

Rooftop solar panels are crucial in the global move toward carbon neutrality, particularly in Japan, where space for large solar farms is limited. These systems are easy to install, scalable, and reduce transmission losses. Technological advancements have made them more efficient and affordable for homes and businesses. However, wider adoption is still limited due to grid constraints and the need for effective energy storage systems.

EVs are evolving beyond their traditional transportation roles to serve as mobile batteries, storing excess solar energy and supplying it during peak demand, which helps stabilize the grid. Systems like Vehicle-to-Home (V2H) and Vehicle-to-Grid (V2G) allow EVs to send electricity back to homes or the grid, enhancing overall energy system flexibility.

Rooftop PV and EVs offer a practical solution for reducing carbon emissions, particularly in densely populated areas. This integrated approach enables communities to utilize more of their own clean energy and move closer to national climate targets.

Analyzing the Combination of Rooftop PV and EV System

The authors conducted a techno-economic analysis to assess the decarbonization potential of integrating rooftop PV systems with EVs across Japan. They estimated rooftop areas using publicly available building footprint data, assuming that 70% could be utilized for PV installation at an efficiency rate of 20%. Hourly electricity generation was simulated using weather data from MERRA-2 reanalysis, allowing for regional variability in solar output.

To model energy generation and consumption, the researchers employed MATLAB and Python-based simulations to evaluate hourly energy balances under various scenarios, including "PV only" and "PV + EV," with and without feed-in tariffs (FITs). Battery electric vehicles (BEVs) with a 40 kWh capacity were included, with 50% of the battery assumed available for grid support, enabling modeling of V2H and V2G applications.

Economic viability was assessed using metrics such as Net Present Value (NPV), which considered installation costs, electricity tariffs, and potential savings. The analysis accounted for factors like urbanization, climate, and rooftop area availability, providing a robust evaluation of the feasibility and benefits of combining rooftop PV and EV systems.

The Decarbonization Viability of PV + EV Systems

The outcomes demonstrated substantial decarbonization potential from integrating rooftop PV systems with EVs across Japan. The estimated total rooftop PV capacity reached approximately 1155 GW, generating around 1017 TWh of electricity annually, exceeding Japan's total electricity generation in fiscal year 2022 (834.8 TWh) by 1.2 times. Assuming 70% of rooftop areas are utilized at 20% efficiency, this generation capacity highlights the significant renewable energy potential in the built environment.

The "PV only" systems were projected to meet about 45% of municipalities' hourly electricity demands, while the integration of EVs as mobile energy storage increased this coverage to approximately 85%. This integration-enhanced system flexibility through V2H and V2G operations, contributing to grid stability and efficient energy use. Notably, carbon dioxide (CO2) emissions could be reduced by up to 87%, supporting Japan's neutrality goals.

Notable regional disparities were identified, with urban areas such as Tokyo and Osaka exhibiting lower energy self-sufficiency due to limited rooftop space and higher electricity demands.

In contrast, rural municipalities demonstrated greater decarbonization potential, with some capable of generating their local electricity needs multiple times. Southern regions generally indicated higher PV capacity factors than northern ones, reflecting climatic influences on solar productivity. These results highlight the importance of location-specific strategies that consider different factors to maximize the benefits of PV + EV systems.

Applications: Enabling a Sustainable Energy Future

Integrating rooftop PV systems and EVs offers significant energy resilience and policy planning potential. The research highlights the need for government-led initiatives to expand infrastructure, fund research, and launch pilot programs, particularly in energy-insecure northern municipalities. Addressing regional disparities in PV deployment and enhancing grid integration is essential to maximizing system benefits.

Encouraging EV adoption through incentives and developing robust infrastructure for V2H and V2G systems will optimize battery use and improve grid stability. Reducing the costs of PV/ EV technologies is improving the economic feasibility of integrated systems, offering cost savings. Policymakers can use these insights to design targeted strategies that accelerate adoption, mainly in areas with high solar potential and energy demand.

Conclusion and Future Direction Toward Decarbonization

Integrating rooftop PV systems with EVs presents a transformative path for urban decarbonization in Japan. This approach enhances energy self-sufficiency, reduces carbon emissions, and improves economic viability. To maximize the benefits of these systems, policymakers must address regional disparities and invest in infrastructure.

Future work should optimize energy generation and consumption models, advance energy storage and grid integration technologies, and explore innovative financing mechanisms.

Investigating the socio-economic impacts of widespread PV + EV adoption will help tailor effective strategies for different regions. Overall, leveraging the combination of rooftop PV and EV systems can guide Japan toward a sustainable, resilient energy future while providing a replicable model for other nations.

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