A new study from Tohoku University has found that Japan could meet 85% of its electricity needs using just rooftop solar panels and electric vehicles (EVs) as home batteries.
This approach could also cut the country’s carbon dioxide emissions by 87%, making it a promising path toward a greener future.
Japan faces unique challenges in its push to reduce emissions.
The country’s mountainous terrain and limited land space make it difficult to build large solar or wind farms.
But there’s one thing Japan does have plenty of—rooftops. More than 8,000 square kilometers of them, in fact. Combined with the rapid rise in electric vehicle ownership, this offers a big opportunity.
The study, published in the journal Applied Energy, looked at how much electricity could be generated if 70% of Japan’s rooftops had solar panels, and how EV batteries could store and manage that power.
Researchers assumed that the average EV battery could share about half of its 40 kWh capacity with the power grid, helping balance electricity use throughout the day and night.
The results were impressive. Solar panels alone could provide about 45% of Japan’s total electricity demand.
But when combined with EVs, that figure jumped to 85%. The solar panels could generate more electricity than the country produced in all of 2022.
Not only would this reduce emissions from both electricity and driving, it could also cut energy costs by a third by 2030.
The study also found that many rural areas could generate far more electricity than they use, just from rooftops.
Urban areas like Tokyo, which have fewer rooftops and vehicles per person, wouldn’t be able to meet all their needs with this system—but they’d still benefit from lower costs and more flexible energy use thanks to EV batteries.
Lead researcher Takuro Kobayashi explained that the goal of the study was to give policymakers detailed, science-based guidance.
While Japan already offers some subsidies for solar panels and EVs, he said much stronger support is needed—especially for charging infrastructure that allows power to flow between homes and the grid, known as vehicle-to-home (V2H) and vehicle-to-grid (V2G) technology.
Policymakers will also need to ensure that northern regions with less sunlight aren’t left behind, and that everyone can afford to make the switch.
The study was conducted by researchers from Tohoku University, the University of Tokyo, the National Institute for Environmental Studies, Radboud University in the Netherlands, and Japan’s Meteorological Research Institute.
Their findings offer a powerful reminder that major climate progress can start with something as simple as our rooftops and cars.
Source: Tohoku University.
Credit: Unsplash+.
