Charging thousands of electric vehicles simultaneously will be a big challenge for cities, writes Concordia researcher
Market demand for electric vehicles (EVs) has been steadily rising in recent years and will likely continue to do so in rich and developing countries alike. However, as the consulting firm Deloitte projects in a recent report, that demand will slow considerably after 2030 if charging station infrastructure challenges are not addressed in a sustained manner.
In a new paper published in World Electric Vehicle Journal, Claude El-Bayeh, a postdoctoral fellow in the Department of Electrical and Computer Engineering at the Gina Cody School of Engineering and Computer Science, looks at current and future EV charging and discharging strategies. Considering variables including economics, the effects on power grids and complexity, El-Bayeh and his colleagues compare existing and planned strategies and rate them accordingly. Khaled Alzaareer of UQÀM, Al-Motasem Aldaoudeyeh of Tafila Technical University in Jordan, Brahim Brahmi of McGill University and Mohamed Zellagui of the University of Batna in Algeria co-authored the paper.
Network give and take
The researchers identify 14 different strategies that can be separated into two overarching categories: unidirectional, in which an EV draws electricity directly from the power grid to charge its batteries, and bidirectional, where the vehicle discharges power from its battery back into the grid. El-Bayeh estimates that widespread EV bidirectional charging technology is still roughly 20 years away.
Charging and discharging can be either coordinated or uncoordinated. An uncoordinated strategy, the kind we see most commonly today, involves individual EV owners charging their vehicles directly from the grid without scheduling, optimization techniques or regard to overall strain on the power grid or pricing mechanisms. A coordinated strategy takes all of these variables into account and uses complex algorithms to calculate the best way to charge large numbers of EVs simultaneously without overloading the grid.
“If you have a million electric cars and they all start charging at the same time, it will create a lot of problems for the network and perhaps cause a blackout,” El-Bayeh explains. “Instead of improving the stability of the network and reducing pollution by using EVs, you’ll have the reverse effect. That is why we need to develop algorithms to balance the network constraints and the needs of the EV owner.”
After looking at all 14 separate strategies, El-Bayeh and his colleagues conclude that there are two that stand out as most desirable. The first is Continuous Coordinated Direct Charging and Discharging. This uses optimization techniques to charge and discharge power to and from EVs that take best advantage of high electricity prices seen during peak hours.
The other is Discrete Coordinated Direct Charging and Discharging. This is similar to the previous strategy but breaks up charging time into smaller units, reducing peak demand and flattening it over a prolonged period. The researchers note that both approaches appear to be the most promising, but there is a lot to do before implementing them.
Still looking ahead, El-Bayeh says vehicle designers, utilities and city planners can and should do more to facilitate the transition from internal combustion engine vehicles to EVs.
“This includes developing solar-powered cars and buses, which would reduce dependency on the network and therefore reduce peak energy demand and losses,” he says. “We also have to work on introducing renewable energy system technologies such as photovoltaics and wind turbines and encourage more people to install them on their rooftops.”
Read the cited paper: “Charging and Discharging Strategies of Electric Vehicles: A Survey.”