Electric vehicles should fear the ‘dragon curve,’ researchers say

Source: David Ferris, E&E News reporte • Posted: Thursday, April 26, 2018

Swarms of electric vehicles could balloon energy demand in the evening, researchers say, calling the phenomenon a “dragon curve” that grid managers will have to tame.

The findings and the catchy name come from a studyby the California Energy Commission and National Renewable Energy Laboratory that projected what sort of charging infrastructure the state will need to meet Gov. Jerry Brown’s (D) goal of 1.5 million EVs by 2025.

If drivers do in fact embrace EVs, the Golden State will have to hustle.

Researchers saw a need for as many as 279,000 charging stations, a tally that doesn’t include chargers at single-family homes. Currently, the state has almost 14,000 public charging stations and about 350,000 EVs.

Almost every major carmaker plans to roll out fully electric or plug-in hybrid models in the U.S. in the next few years. Where to put the chargers and what type to build are puzzles because no one knows what customer tastes will be.

Will drivers prefer to charge at home or work? Will people actually need the fancier direct-current fast chargers that can fill an EV battery in about half an hour, and if so, where should they be built?

Based on recent travel data, the study estimates the California EV fleet will need 133,000 destination chargers — the public ones located away from home — and 25,000 fast chargers. Multifamily housing like apartments might need 121,000. The study didn’t include estimates for single-family homes.

At the end of 2017, the state had 1,500 DC fast chargers.

A spiky problem

The study’s authors came up with the term “dragon curve” to describe the effect that charging patterns might have on electricity use.

It’s too early to say whether the term will catch on like the “duck curve,” which also sprung from the heads of California energy researchers. That chart describes what happens when a grid starts using prodigious amounts of solar power. It causes a crater of cumulative energy demand in the middle of the day, which is the belly of the duck (Energywire, May 2, 2014).

In the EV case, the researchers highlighted two notable curves: one bump when commuters arrive and plug in at workplace chargers, and another, much more dramatic climb in the evening, when the use of residential and public chargers crest simultaneously.

The filigree of spikes atop the chart line are from fast chargers, which consume short but strong bursts of energy.

“It created this undulating and kind of spiky shape, which helps tell the story of the most surprising finding, which is that if millions of users are plugging in at home right when they arrive, that could bring some strain to the grid,” said Noel Crisostomo, an air pollution specialist at the energy commission and a report author.

The researchers first thought it looked like a dinosaur back, particularly like a stegosaurus, but “dragon” imparted the kind of urgency they think the situation demands.

By 2025, the morning wave would demand 200 megawatts of electricity, and the evening tsunami would reach almost a gigawatt. Both peaks are lower on weekends.

Slaying this dragon, Crisostomo said, will require installing chargers intelligent enough to change the price of electricity in real time, which would nudge EV drivers to charge when energy is more available and cheaper.

Another aid would be higher-power chargers at home, more powerful than the slow, Level 1 chargers that are common now. A more powerful charger would allow grid managers to fill the battery quickly in the middle of the night when demand is low.