Made in the shade: How electric vehicles could be the perfect partner to rooftop solar in tropical cities

As rooftop solar uptake spreads to all corners of the globe, the problem of how to manage distributed generation in cities with tropical climates – where rolling thunderstorms regularly eclipse the sun – is becoming increasingly acute. But what if cars could come to the rescue?

New research published this week has demonstrated how electric vehicles (EVs) could better enable the large-scale adoption of solar PV in tropical cities by storing solar and acting as temporary grid capacity when clouds roll in.

In a paper published in the prestigious Nature journal, researchers from Columbia University in the United States and the Singapore-ETH Centre highlighted the potential role that electric vehicles could play in mitigating the downsides of building solar PV systems in tropical cities.

One of the authors of the paper, civil engineer Markus Schläpfer, moved to Singapore a decade ago and began noticing the emerging engineering challenge of afternoon thunderstorms, which can plunge entire neighbourhoods into temporary moments of darkness.

Standalone storage is obviously one solution – as is being played out across Australia, with large-scale batteries and smaller-scale community and home batteries – but Schläpfer and his colleagues considered a second option, one that would avoid expensive infrastructure buildouts.

“If you have a thunderstorm moving over an area with solar energy, you can have your electric cars that are parked serve as the energy source and balance out this lack of energy generation,” said Schläpfer, assistant professor of civil engineering and engineering mechanics at Columbia Engineering.

“When the thunderstorm moves away, the cars are charged again by the photovoltaics.”

Tropical thunderstorms do not necessarily last for long, and can often affect some neighbourhoods and not others, despite their proximity. As such, electricity can be transported from neighbouring regions that are generating power, but even if the journey is only a mile or two, the amount of electricity flowing through powerlines can often overwhelm the grid’s capacity.

Tropical thunderstorms lead to additional stress on electricity grids

Traditionally, in order to fix the problem, new infrastructure is required that will be capable of carrying increased levels of electricity, but this can be expensive – especially in dense cities like Singapore, where underground transmission lines, for example, cost around 60 million Singapore dollars per kilometre (around $A66.7 million).

“Building new infrastructure is extremely challenging and expensive in dense cities,” Schläpfer said.

“This is a way to use the existing network in a more efficient way and integrate more solar photovoltaics, which would otherwise need more transmission line capacity.”

That’s where electric car batteries could potentially come into play, according to Schläpfer and his colleagues. When a thunderstorm rolls over a particular neighbourhood or region, nearby parked EVs discharge their stored energy into the local grid, absorbing the shortfall without the need for transporting electricity from elsewhere. And when the storm passes, the solar panels are able to quickly recharge the cars.

“Car batteries can feed in the electricity stored in their batteries to the grid,” Schläpfer explained.

“We do not need to import the electricity from nearby neighborhoods. Therefore, we do not need to install a new cable.”

The research, Decentralized electric vehicle charging enables large-scale photovoltaic integration in tropical cities, uses Singapore as a case study to “develop a decentralised, district-level vehicle charging strategy that aligns with urban mobility patterns inferred from mobile phone data.”

Importantly, unlike conventional centralised charging strategies, the approach demonstrated by Schläpfer and co significantly reduces grid flows and enables greater solar PV integration into existing grid infrastructure.

The research also demonstrates that EV ownership does not have to be particularly high in a particular neighbourhood for the method to work. “This solution is really working in very car-light environments,” Schläpfer said. “We need only a small number of cars, and it works.”

The paper is free to read in its entirety here.

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