A widespread rollout of rooftop solar panels connected to electric vehicle (EV) batteries in the region surrounding Paris, France could supply 60% of the area’s electricity demand and reduce energy costs by 23%, according to a new analysis.
The study is the latest in a series of investigations of how the so-called SolarEV City concept could play out in urban areas in different parts of the world. The basic idea is that linking EV batteries with rooftop solar panels or photovoltaics (PVs) would not only provide a cleaner transport option, but also store extra energy to power houses when the sun isn’t out.
“We need to prioritize the use of the rooftop PV + EV system to minimize the impacts of renewable energy development on nature,” says study team member Takuro Kobashi, an environmental scientist at Tohoku University in Sendai, Japan.
A previous study showed that the setup could reduce carbon emissions from cars by almost three-quarters and energy costs by almost 40% in Kyoto, Japan. The system’s potential has been evaluated in nine Japanese cities, as well as South Korea, China, and Indonesia.
Few studies have yet investigated the approach in cities farther North, where it takes a lot of electricity to heat buildings in winter, precisely when sunlight is scarce. The new analysis is the first to take into account how the SolarEV City concept would fare with hour-by-hour variations in both solar energy and electricity demand in a high-latitude city.
Kobashi and his colleagues gathered existing data on weather patterns, sunlight availability, electricity use, and electricity prices in Paris and the surrounding Ile-de-France region. They also assembled information about the price of solar panels and EV chargers, how much people drive, and the roof area available to host solar panels.
All of these data went into a computer model to determine the impact of solar panels or the solar panel-EV combination on energy availability, use, and costs.
Rooftop solar could only supply about 30% of electricity for Paris, the researchers report in the journal Applied Energy. This is because the city is so dense: there’s just not enough rooftop space per capita for solar panels, or space on the ground to charge EVs. And Paris has a great public transit system, so there are relatively few cars per capita.
“It is not entirely clear to me what is the realistic rooftop area in Paris where PV can be installed, given all other considerations such as social acceptance for a city like Paris with many historic buildings and monuments,” adds study team member Katsumasa Tanaka, a climate researcher at Paris-Saclay University in France.
“But,” Tanaka says, “I also think that it is important to start testing and implementing such an idea first on a small scale.”
The picture is different in the suburban Ile-de-France region outside of Paris. There, covering 70% of rooftop area with solar panels could supply 78% of electricity demand, the researchers calculated. With EV batteries incorporated into the system, it could supply 60% of electricity demand and reduce energy costs by 23%.
The findings are in line with studies of the SolarEV City concept elsewhere: the potential tends to be greatest in smaller, slightly more spread-out cities than in the biggest, densest metropolises.
But the benefits don’t have to remain entirely local, the researchers found. “If [the] PV + EV system develops through Ile-de-France, Paris can get [a] fair amount of electricity from suburban houses,” Kobashi says.
The decarbonization benefits of the rooftop solar-EV combination aren’t as great as they are in some other places, because France already has a high proportion of low-carbon energy in the form of nuclear power.
But the system could provide the electricity needed to support further electrification of homes and other buildings in the future, the researchers say.
The findings suggest the SolarEV City concept is worth exploring in other high-latitude cities. “I personally think that Berlin would also be an interesting city to test this concept,” says Tanaka. “Berlin is less densely populated than Paris and larger in area than Paris. Rooftop PV is already relatively common in Germany and EVs are gaining traction, so it could potentially have good public support there.”
Source: Deroubaix P. et al. “SolarEV City Concept for Paris.” Applied Energy 2023.
Image: Anthropocene Magazine, based on an image by ChrisGoldNY via Flickr.
