In order to maximize the environmental benefits of plug-in vehicles, says a new study, charging needs to be controlled to keep costs down and maximize renewable energy sources.
A research team from Carnegie Mellon University (CMU) addressed the complicated relationship between the production costs and emissions for power companies to recharge an electrified car, publishing results in American Chemical Society’s Environmental Science & Technology Letters.
“Although plug-in electric vehicles currently make up a small percentage of the vehicle fleet, federal and state subsidies are promoting electric vehicle sales, and they may become a significant portion of the fleet in the future,” said Allison Weis, a CMU graduate student and member of the research team.
“If owners regularly plug in these electric vehicles when they get home from work, this would add to greater demand, when the most expensive power plants are running.”
The cheapest solution, for both vehicle owners as well as other utility customers, is to program the charging for off-peak hours.
“Controlled charging can shift loads later in the night when cheaper power plants are again available,” explained researcher and assistant professor Paulina Jaramillo.
Operating systems built into many electrified vehicles already allow owners to customize a number of charging settings. But the researchers took the concept of controlled charging a step farther. By giving grid operators the ability to control how fast the vehicle is recharged, costs could go down even further.
The problem is that shifting to source the cheaper after-hours energy often means coal-based power plants are being used. In other words, fossil fuels are burned to energize plug-in vehicles, a paradox often cited by EV critics.
“Although electric vehicles have lower tailpipe emissions than gasoline powered vehicles, the changes in emissions associated with vehicle electrification on a life cycle basis will depend on the emissions associated with the operations of the power plants used to charge the battery,” said the research team.
“Power generation also accounts for over 40 percent of [greenhouse gas] emissions. Electric vehicle charging may affect these trends.”
But here again, the team said that judicious management of charging could ensure that when electrified vehicles are plugged in, they are tapping into more eco-friendly sources.
“Controlled charging could help to manage fluctuations from renewable energy sources like wind and solar power, which change their output as the wind changes and as clouds pass by,” Jaramillo explained.
Adding to the complexity of this issue, the CMU researchers said it’s difficult to set a charging standard that could be applied across the country.
They analyzed the PJM Interconnection, a large, independent system that coordinates wholesale power for a large region that includes New Jersey, Illinois, Michigan and Ohio. But not all power providers are set up in the same way, which affects the controlled charging formula.
“In general, controlled charging has potential for reducing generation costs, but its net implications depend on the characteristics of the power plant fleet,” the team said.
“In other regions with tighter environmental regulations, more renewable generation, less coal power, and/or inexpensive natural gas plants, controlled charging could lead to lower environmental and health damages.”