|Sum for all 13 regions of projected 2030 generating capacity (top left), base generation (top right), and new generation dispatched (bottom) to meet demand for each PHEV recharging scenario. Click to enlarge.|
A recent Oak Ridge National Laboratory (ORNL) study examines how an expected increase in ownership of plug-in hybrid electric cars and trucks could affect regional power generation requirements depending on what time of day or night the vehicles are charged. The researchers concluded that supporting a 25% market share of light-duty (cars and SUVs) PHEVs in 2030 could require either major new power generation resources or no new resources at all, depending on when people recharge.
The ORNL study also factors in the impact of the different options for connecting vehicles to the grid. As Dr. Mark Duvall at EPRI has outlined, at 120 volts AC, a 15 amp circuit would be about a 1.4 kW load, while a 20 amp circuit would be about 2 kW. Using a 208/240 volt and 30 amp circuit instead, the load could be as much as 6 kW.
In the worst-case scenario—if all PHEV owners charged their vehicles at 5 p.m., at 6 kW of power—up to 160 large power plants would be needed nationwide to supply the extra electricity, and the demand would reduce the reserve power margins for a particular region’s system.
The best-case scenario occurs when vehicles are plugged in after 10 p.m., when the electric load on the system is at a minimum and the wholesale price for energy is least expensive. Depending on the power demand per household, charging vehicles after 10 p.m. would require, at lower demand levels, no additional power generation or, in higher-demand projections, just eight additional power plants nationwide.
In aggregate, the model predicts an increase in demand, generation, electricity prices, and emissions from the utilities created by the introduction of PHEVs. It also suggests that by 2030 almost all regions (10 out of 13) will need to add capacity to provide for charging PHEVs, mostly in the scenario where PHEVs are charged at 6 kW in the evenings. In all likelihood, to avoid these problems the utilities in the regions would expand their capacity, increase their imports, or establish demand response programs beyond the level that NEMS had calculated, but these factors were not modeled in the scenarios.—“Potential Impacts of Plug-in Hybrid Electric Vehicles on Regional Power Generation”
Some assessments of the impact of electric vehicles assume owners will charge them only at night, said Stan Hadley of ORNL’s Cooling, Heating and Power Technologies Program.
That assumption doesn’t necessarily take into account human nature. Consumers’ inclination will be to plug in when convenient, rather than when utilities would prefer. Utilities will need to create incentives to encourage people to wait. There are also technologies such as smart chargers that know the price of power, the demands on the system and the time when the car will be needed next to optimize charging for both the owner and the utility that can help too.—Stan Hadley
The paper also compares the fuel use, emissions, and cost of using a PHEV versus a hybrid electric vehicle (HEV) for each region, with both vehicles going 20 miles per day and the efficient HEV getting 40 miles per gallon, in the different scenarios.
In both of the 2020 scenarios and the night scenario in 2030, CO2 emissions are higher with PHEVs than with efficient HEVs. Coal and oil generation is sufficient to raise CO2 emissions higher than if the vehicles had used gasoline. However, in the 2030 2 kW evening scenario, CO2 emissions are lower, because higher-efficiency combined cycle plants and gas-fired turbines with relatively low emissions are used to meet the added demand.
Even though NOx emissions at first calculation are much higher for much of the country, these will be offset by reductions elsewhere. Even though new power plants are very clean, the plants that are on the margin and are run because of the extra demand may actually be older plants with higher emissions. SO2 emissions are likewise positive, but will be offset by reductions elsewhere in the electric system because of the legal caps on total emissions.
Costs are much lower with the PHEVs, from 22% to 42% of the gasoline cost, depending on the scenario. Electricity is likely to be much cheaper than gasoline, though this does not take into account the added initial cost of the plug-in capability for the vehicle.—“Potential Impacts of Plug-in Hybrid Electric Vehicles on Regional Power Generation”
The researchers analyzed the potential impacts of PHEVs on electricity demand, supply, generation structure, prices, and associated emission levels in 2020 and 2030 in the 13 regions specified by the North American Electric Reliability Corporation (NERC) and the US Department of Energy’s (DOE’s) Energy Information Administration (EIA), and on which the data and analysis in EIA’s Annual Energy Outlook 2007 are based.
The estimates of power plant supplies and regional hourly electricity demand come from publicly available sources from EIA and the Federal Energy Regulatory Commission. Electricity requirements for PHEVs are based on analysis from the Electric Power Research Institute, with an optimistic projection of 25% market penetration established by 2020 and continuing at this percentage level through 2030, involving a mixture of sedans and sport utility vehicles. Even though the market share remains the same, the increase in the fleet size results in larger annual sales of PHEVs post-2020.
The calculations were done using the Oak Ridge Competitive Electricity Dispatch (ORCED) model, a model developed over the past 12 years to evaluate a wide variety of critical electricity sector issues. Seven scenarios were run for each region for 2020 and 2030, for a total of 182 scenarios. In addition to a base scenario of no PHEVs, the authors modeled scenarios assuming that vehicles were either plugged in starting at 5:00 p.m. (evening) or at 10:00 p.m.(night) and left until fully charged. Three charging rates were examined: 120V/15A (1.4 kW), 120V/20A (2 kW), and 220V/30A (6 kW).
The analysis, the authors note, uses simplifications in modeling electric sector supply and demand. The model applies rigid recharging schedules to all vehicles in each scenario, it does not adjust electricity supply to meet increased demand, its inventory of supply is based on results from a different model (the National Energy Modeling System, or NEMS) that simulates supply and demand somewhat differently, it does not model the transmission system, and it does not reflect all the complexities of air emissions regulations.
However, it does offer insights into the issues involved with PHEVs and the electric grid. PHEV penetration of the vehicle market will potentially create a substantial change on the electric grid. By evaluating these issues early, DOE will be able to help utilities, manufacturers, and regulators understand the issues involved, suggest ideas that will better optimize the combined system, and help avoid negative consequences.
Stanton W. Hadley and Alexandra Tsvetkova. Potential Impacts of Plug-in Hybrid Electric Vehicles on Regional Power Generation (ORNL/TM-2007/150)