Cities are at the forefront of the battle against climate change, being responsible for over 70% of the world's CO2 emissions.
A recent study from Tohoku University, however, has laid out a roadmap for turning this narrative on its head. It revealed that pairing rooftop solar panels with electric vehicles (EVs) in suburban neighborhoods could cut carbon dioxide (CO2) emissions from electricity and transport by up to 90%. This innovative approach, called the "SolarEV City Concept," positions suburbs not as energy consumers, but as clean energy powerhouses that could one day supply surplus electricity to urban centers.
By strategically using rooftops and drivewaysーspaces already available in residential areasーsurban planners can implement highly effective climate solutions without needing large-scale land developments.
"Our research shows a clear path forward for cities to achieve deep decarbonization in a way that is both economically and socially beneficial," said lead author Takuro Kobashi, an associate professor at Tohoku University's Graduate School of Environmental Studies. "The EVs in your driveway is one of the most powerful tools we have in the fight against climate change. When parked, their batteries can serve as mobile power banks for homes through a Vehicle-to-Home" (V2H) system, allowing families to store surplus daytime solar power and use it at night, reducing reliance on fossil-fuel-based grid electricity."
Kobashi and his colleagues' findings demonstrate three key benefits for the public. First, families can save significantly on energy and fuel bills. By 2030, a suburban home with rooftop solar and an EV could lower annual energy costs by as much as 40%, with the initial investment paying for itself in about six years. Second, local power generation increases resilience, making suburbs less vulnerable to blackouts and extreme weather events. Third, the research envisions energy-sharing neighborhoods, where suburbs with excess solar capacity sell clean power to city centers, fostering a more equitable energy system.
Since city districts are not uniform, the research group also determined whether this combined "PV+EV" system would work equally well when factoring in the different building densities, rooftop sizes, and patterns of vehicle ownership across urban and suburban areas. Using a highly detailed digital model of Kyoto, the team simulated rooftop solar potential, hourly electricity demand, and vehicle availability across both dense downtown and suburban areas for the years 2020 and 2030.
The results revealed a striking contrast. In suburbs, the "PV+EV" system achieved up to a 90% reduction in CO2 emissions and an 87% rate of energy self-sufficiency, while cutting household energy costs significantly. Dense urban centers, however, faced physical limitations: with little rooftop space and heavy demand, they reached only about 42% self-sufficiency. The study found that adding EVs as storage nearly doubled solar panel adoption compared to solar alone, as the EV batteries enabled families to maximize every unit of clean energy produced.
This gives city planners food for thought when designing future smart cities. Suburbsーsonce criticized for sprawl and car dependenceーscould instead anchor sustainable urban ecosystems by serving as hubs of renewable power.
"This research shows that suburbs can play a surprising and vital role in powering the green transition," explained Kobashi. "By rethinking how energy is produced and shared, we can transform residential areas into active participants in a cleaner, more resilient energy future."
Looking ahead, the researchers stress that grid modernization is essential to realize this vision. As energy flows move not just from power plants to homes, but also from homes to city centers, investment in smart grid infrastructure will be critical. With targeted policies and technological integration, the SolarEV City Concept could help redefine how cities worldwide combat climate change.
- Publication Details:
Title: Enabling maximum decarbonization from districts in Kyoto through rooftop PVs by integrating with EVs as battery
Authors: Takuro Kobashi, Junbin Xiao, Tuo Zhang
Journal: Sustainable Cities and Society
