Plug-in hybrid electric vehicles (PHEVs) and all-electric vehicles (EVs) store electricity in batteries to power one or more electric motors. The batteries are charged primarily by plugging in to off-board sources of electricity, produced from oil, coal, nuclear energy, hydropower, natural gas, wind energy, solar energy, and stored hydrogen.
EVs and PHEVs, while operating in all-electric mode, do not produce tailpipe emissions. However, there are emissions associated with the majority of electricity production in the United States. See the emissions section for more information.
According to the U.S. Energy Information Administration, most of the nation’s electricity is generated by coal, natural gas, and nuclear energy.
Electricity is also produced from renewable sources such as hydropower, biomass, wind, geothermal, and solar power. Together, renewable energy sources generated about 17% of the country’s electricity in 2017.
With the exception of photovoltaic (PV) generation, most of the primary sources of energy are used directly or indirectly to move the blades of a turbine connected to an electric generator. The turbine generator set converts mechanical energy to electrical energy. In the cases of coal, oil, natural gas, nuclear fission, biomass, geothermal and solar thermal, the heat that is produced is used to create steam, which moves the blades of the turbine. In the cases of hydropower and wind power, turbine blades are moved directly by flowing water and wind, respectively. PV panels convert sunlight directly to electricity using semiconductors.
The sources of energy used to produce electricity vary from one geographic region to the next. To find out about the mix of fuels and other energy sources used in your area, see the emissions section. Learn more about electricity production from the U.S. Department of Energy’s Energy Information Administration.
Electricity Transmission and Distribution
Electricity in the United States travels long distances from generating facilities to local distribution substations through a transmission grid of nearly 160,000 miles of high-voltage transmission lines. Generating facilities provide power to the grid at low voltage, from 480 volts (V) in small generating facilities to 22 kilovolts (kV) in larger power plants. Once electricity leaves a generating facility, the voltage is increased, or “stepped up,” by a transformer to minimize the power losses over long distances. As electricity is transmitted through the grid and arrives in the load areas, voltage is stepped down by transformers at distribution substations (ranges of 69 kV to 4.16 kV), and finally lowered further for use by customers (residential customers use 120V and 240V; commercial and industrial customers typically use 120V, 208V, and 480V).
Plug-In Vehicles and Electricity Infrastructure Capacity
All-electric vehicles and plug-in hybrid electric vehicles represent a new demand for electricity, but they are not likely to strain much of our existing generation resources in the near term. Large increases in the number of these vehicles in the United States will not necessarily require the addition of new electricity-generation capacity depending on when, where, and at what power level the vehicles are charged.
Hourly demand for electricity rises and falls, depending on time of day and time of year. Electricity production, transmission, and distribution capacity must be able to meet demand during times of peak use; but most of the time, the electricity infrastructure is not operating at its full capacity. In the United States, roughly 50% of the generation capacity is used 100% of the time, while only 5% of the time (about 400 hours per year) generation greater than 90% of the capacity is used. As a result, EVs and PHEVs have the potential to create little or no need for additional capacity, as long as they charge predominantly during off-peak times, such as late at night, when the electric load on the system is at a minimum.
According to a study by Northwest National Laboratory (PDF), existing U.S. electricity infrastructure has sufficient capacity to meet about 73% of the energy needs of the country’s light-duty vehicles. According to deployment models (PDF) developed by researchers at the National Renewable Energy Laboratory (NREL), the diversity of household electricity loads and EV loads should allow introduction and growth of the plug-in electric vehicle (PEV) market while “smart grid” networks expand. These networks may provide the capability to monitor and protect residential distribution infrastructure from future vehicle impacts, ensure that charging occurs during off-peak periods, and reduce costs to utilities, grid operators, and consumers. The NREL analysis also demonstrated the potential for synergies between PEVs and distributed sources of renewable energy. For example, small-scale renewables, like solar panels on a rooftop, can both provide clean energy for vehicles and reduce demand on distribution infrastructure by generating electricity near the point of use. Similarly, high adoption rates of distributed solar generation may create a scenario requiring management via smart grid to avoid further imbalance between load and generation regardless of consumption by vehicles at the point of generation.
Utilities, vehicle manufacturers, charging equipment manufacturers, and researchers are working to ensure that PEVs are smoothly integrated into the U.S. electricity infrastructure. Some utilities offer lower rates at off-peak times to encourage residential vehicle charging when electricity demand is lowest. Vehicles and many types of charging equipment (also known as electric vehicle supply equipment or EVSE) can be programmed to restrict charging to off-peak times. “Smart” models are even capable of communicating with the grid, load aggregators, or facility/home owners, enabling them to charge automatically when electricity demand and prices are best; for example when prices are lowest, aligned with local distribution needs (such as temperature constraints), or aligned with renewable generation.