Energize Weekly, January 31, 2018
The growth in plug-in electric vehicles (PEVs) will not have a big impact on overall residential power demand, but even one vehicle charging at home could stress a local transformer, according to a study by the National Renewable Energy Laboratory (NREL).
The modeling study using data for 200 Midwest homes found that the while not affecting overall demand, increasing penetration of PEVs had a potential impact on local areas and peak demand.
“Clustering effects in vehicle adoption at the local level might lead to high PEV concentrations even if overall adoption remains low, significantly increasing peak demand and requiring upgrades to the electricity distribution infrastructure,” NREL researcher Matteo Muratori wrote in a paper appearing in Nature Energy.
“This effect is exacerbated when adopting higher in-home power charging,” Muratori said.
The prospects for PEVs to be concentrated in certain neighborhoods is high. “The adoption of alternative-fuel vehicles is characterized by significant clustering effects, driven by socio-economic and behavioral factors influencing the decision of individual customers,” the study said.
Previous studies have assumed that PEV owners would always charge their vehicles at the most advantageous times, such as overnight. Muratori modeled “uncoordinated” in-home charging.
“While the increase in aggregate demand might be minimal even for high levels of PEV adoption, uncoordinated PEV charging could significantly change the shape of the aggregate residential demand, with impacts for electricity infrastructure,” Muratori said.
These changes will add complexity to managing power generation, transmission and distribution, according to Muratori. At the same time, the growth in PEVs offers utilities a new market and the possibility of PEV batteries as a source of utility storage, a so-called virtual power plant.
The modeling results found the overall impact of uncoordinated in-home charging to be small with a 10 percent PEV market share leading to about a 5 percent increase in demand.
“In these results, a 3 percent PEV market share, which translates to about 7.5 million vehicles on the road—a number far above the current 0.6 million PEVs deployed—does not significantly affect the aggregate residential power demand under either charging level,” the study said.
The shape of the demand and its peak are more affected by the introduction of electric vehicles, especially if faster Level 2 chargers are used. Level 1 charges use 120 volts, while Level 2 charges at 240 volts.
On the local level, the study said the use of the Level 2 chargers “can negatively affect the electric power generation and transmission infrastructure,” as well as creating higher peak demand and more variability.
For example, at a 10 percent PEV market share with Level 1 charging, the average transformer demand is 8,735 kilowatts (kW) and the peak demand is 30,955 kW. A switch to Level 2 charging does not change average demand and raises the peak demand by 15 percent. For Level 1 charging, transformers are not forced to operate above their nominal capacity. Level 2 charging lead to seven hours of continuous operation above capacity.
When PEVs rise to a 50 percent market penetration with Level 1 charging, the average demand rises to 10,840 kW with a peak of 37,535 kW.
Switching to Level 2 with this many PEVs does not change the average demand, but the peak demand jumps 26 percent. In addition, while Level 1 charging leads transformers to operate nine continuous hours above nominal capacity, that rises to 63 hours with Level 2 charging.
Level 2 charging “significantly exacerbates the impact of PEVs on the residential distribution infrastructure, since charging events are shorter but steeper,” Muratori said.
“Even when only one PEV is connected to the distribution transformer, abrupt peaks in the local electricity demand are introduced when Level 2 charging is used . . . This effect is exacerbated for higher PEV market shares,” the study said.
