New modelling highlights the untapped opportunities of pairing rooftop solar with EV batteries.
Recent research shows that combining home solar with vehicle-to-grid technology could reshape how electricity is generated, stored and shared.
The new study finds Japan could meet 85 per cent of its electricity demand using rooftop solar and EV batteries, using a model that is likely to be highly effective in Australia.
The research, led by Tohoku University and published in Applied Energy, modelled the energy and emissions potential of a nationwide “PV + EV” system across all 1,741 Japanese municipalities.
Using real municipal-level data, the team simulated 70 per cent rooftop solar coverage with 20 per cent efficient panels, combined with EVs contributing 20 kilowatt-hour (kWh) of household-scale battery storage via bidirectional charging.
Annual rooftop PV output under this scenario was estimated at 1,017 terawatt-hour (TWh) – surpassing Japan’s 2022 electricity demand.
While a PV-only system could deliver 45 per cent of needs on average, integrating EV storage increased supply potential to 85 per cent.
Rural areas with ample roof space and fewer grid constraints could generate several times their local demand, suggesting potential for net-positive energy regions.
“The combination of rooftop solar and EVs is not only technically feasible, but highly effective,” said lead author Takuro Kobayashi.
“To make this system a reality and move towards a greener society, we need policy support at the end of the day.”
Beyond emissions reductions of up to 87 per cent, the model also predicts 33 per cent lower electricity costs by 2030 due to reduced peak demand and avoided fossil fuel use.
However, researchers caution that urban centres like Tokyo – with dense populations and less rooftop space – would benefit less without complementary technologies or grid upgrades.
Importantly, the study’s granular municipal analysis exposes regional disparities in solar potential. Northern areas with lower irradiation may struggle to achieve energy self-sufficiency, raising energy equity concerns unless subsidised or supported with alternative storage.
The authors call for stronger government support for V2H/V2G infrastructure, public education, and incentives that reflect regional constraints.
While Japan already subsidises solar and EV uptake, the report says systemic integration remains underdeveloped.
By demonstrating a viable pathway to local energy autonomy using only existing infrastructure – rooftops and vehicles – the study’s ‘SolarEV City’ model offers a template not just for Japan, but for cities and towns globally grappling with land scarcity and decarbonisation goals.