Most EV drivers charge their cars during the same peak evening period. We must plan for that to change

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Most electric vehicles are charged at home. You return after a day’s work and plug it in. That means most EV drivers are accessing the power grid during the same peak evening period. Right now, that’s not a problem. There aren’t many EVs on the road – but there will be soon, as well as the EV chargers required to power them. According to Natural Resources Canada data collected by Electric Autonomy, since the start of 2022, Canada’s public EV charging network has grown by almost one-third.

Down the road, this could present a challenge. In a few decades when most cars on the road are forecast to be EVs, how do we prevent the cars from becoming so electricity hungry that it’s necessary to build more power plants to meet peak loads? We can’t just scatter chargers around like pumpkin seeds and hope they sprout. We must develop strategies that guide and channel charger use, or we could see some unintended consequences.

A new study from the Massachusetts Institute of Technology published in the journal Cell Reports Physical Science examines the risks. It found it’s possible to avoid the pitfalls by encouraging the strategic placement of EV charging stations and incentivizing delayed times for “home-charging” (which includes street and apartment parking).

The MIT team collected data from drivers in New York and Dallas. It included records collected using onboard devices in vehicles and surveys that sampled population variables along with data that showed the “times of day cars are used and for how long, and how much time the vehicles spend at different kinds of locations.”

The authors found it’s bad news when everyone finishes work and plugs in at the same time. Depending on a transportation system’s charging patterns, “the electricity grid may reach generation and distribution limits at certain times, potentially leading to transformer blowouts. This might occur if, for example, peak charging coincides with peak residential electricity demand in the early evening during higher-demand summer months.”

On the hottest day of the year, for instance, charging demands for EVs would combine with the demands of increased electricity use caused by such factors as air conditioning (both at home and at work). In such a situation, the researchers believe “the evening peaks in EV charging demand could require installing upwards of 20 per cent more power-generation capacity.”

Along with taxing peak usage periods, home-charging also fails to tap into the peak solar power produced at midday. This power is wasted because it is too costly to build enough storage capacity to save it for use later in the day. This can lead to an oversupply of electricity during midday followed by a decline in the evening, resulting in the “Duck Effect” – curtailed solar energy followed by an inefficient “ramp-up of fossil-fuel-powered plants to meet the early evening peak.”

Peak home-charging usage could be mitigated using apps that estimate the time to begin the charging cycle just before it is needed the next day. So, you could plug your EV in after work, but it would not start charging until 2 a.m.

The researchers determined that increased use of workplace chargers would reduce peak use home-charging. The one-two punch of “last-minute overnight home charging and shifting charging demand from the home to the workplace” could alleviate many problems. Workplace charging has the dual effect of reducing peak use and midday solar overgeneration. Delayed home-charging could significantly also reduce peak electricity demand.

According to one of the paper’s authors, Prof. Jessika Trancik of MIT’s Institute for Data Systems and Society, a strategic approach means there won’t be a need for new physical infrastructure. “Your electric vehicles can displace some of the need for stationary energy storage, and you can also avoid the need to expand the capacity of power plants, by thinking about the location of chargers as a tool for managing demands – where they occur and when they occur.”

The MIT study is not the only one to find that workplace charging and delayed home-charging can mitigate the power demand caused by EVs. A 2022 study out of Stanford predicted that by 2035, rapid EV growth could increase peak electricity demand in the western United States and California by up to 25 per cent if drivers continue to favour nighttime home-charging. The study suggested that policy-makers use utility rates to get drivers to charge during the day and incentivize investment in charging infrastructure to shift drivers from home to work for charging.

According to the study’s lead author Siobhan Powell, “We were able to show that with less home charging and more daytime charging, the Western U.S. would need less generating capacity and storage, and it would not waste as much solar and wind power. And it’s not just California and Western states. All states may need to rethink electricity pricing structures as their EV charging needs increase and their grid changes.”

We’ve seen how the gas-powered automobile transformed our cities and the world (not always for the better). We can get strategic now about EV charger usage or we can get blindsided later. It’s time to take heed of the work researchers like those at MIT are doing. None of us want to be left in the dark.