U.S. Electric Power Infrastructure
PHEVs require electric power to charge their onboard batteries. Unlike fuel cell vehicles, which would require a brand new supply infrastructure, PHEVs have a ready and well-established energy source—the U.S. electric power system. This vast system includes a variety of fuel sources and generation technologies, a nationwide transmission network, and distribution operations that reach almost all Americans.
This chapter begins with a brief overview of the current system. It then describes two projections of how the system might evolve by 2050, one based on current policy and the other representing a concerted effort to reduce U.S. CO2 emissions. This section also discusses the charging of PHEVs and its potential impact on the electric system. Finally, it introduces several issues that are relevant but beyond the scope of this study.
U.S. ELECTRIC POWER SYSTEM
The nation’s 1 million megawatts (MW) of electric generating capacity produced over 4 billion megawatt-hours (MWh) in 2007 (EIA, 2009b). In comparison, 1 million PHEVs charging an average of 3 kWh every day for a year would consume only about 1 million MWh.1 The U.S. electric system can clearly handle a great many PHEVs, but there is one caveat. Electricity demand varies throughout the day and over the year. Demand usually peaks on hot afternoons when summer air conditioning loads are highest. On such days, some systems are seriously stressed—sometimes to the point where they have to shed loads (reduce demand) to avoid collapse.
In recent years, the North American Electric Reliability Corporation (NERC) has raised concerns about the reliability and development of the electric power system. In its 2007 report, NERC noted that “projected increases in peak demands continue to exceed projected committed resources beyond the first few years of the 10-year planning horizon” (NERC, 2007). In its 2008 report, NERC said that “while some progress has been made, action is still needed on all of the issues identified in last year’s report to ensure a reliable bulk electric system for the future” (NERC, 2008).
Charging a large number of PHEVs during peak hours could aggravate a potentially serious problem, possibly increasing the risk of brownouts and other power system disruptions that could adversely impact the public’s interest in PHEVs. Currently, electric system capacity is generally adequate, but as the economy recovers, demand will increase, stressing the system unless new generating and transmission capacity is built.
At the outset, the key to integrating PHEVs will be to encourage off-peak charging. Generation and transmission capacity must be adequate to handle peak loads, but most of the time, demand is much lower. Utilities would greatly prefer that PHEVs be charged at night, when they can employ their otherwise underutilized capacity or purchase power at lower rates. Many utilities offer time-of-use (TOU) rate structures to at least some of their residential customers, with lower rates at night than during peak hours.
Many plug-in hybrids can be charged with available power generation and grid capacity during off-peak hours. An analysis by the Pacific Northwest National Laboratory estimated that a PHEV fleet equal in size to 84 percent of all cars and light trucks on the road in 2001 could be charged during off-peak times without building new electric generation capacity (PNNL, 2007).
The picture is different if PHEVs are charged during peak hours. For example, a study by Southern California Edison concluded that PHEVs could account for as much as 11 percent of its system load by 2020, which could increase peak loads by several thousand megawatts if PHEV charging is not properly managed.2
The committee assumed that most PHEV charging will be accomplished at night, when electric power demand is lower and rates are likely to be lower than during the day. Encouraging PHEV owners to charge their vehicles during off-peak hours will require both rate schedules that reward time-appropriate charging and equipment that can monitor—or even control—time of use. Under the Energy Policy Act of 2005, utilities are “required to move towards smart meters that allow time-of-day pricing,” and smart meters are already being installed in certain areas to improve electric service, encourage efficiency, and shift energy use to off-peak hours. Many utilities are planning to deploy smart meters within the next few years.
Modernizing the transmission grid to achieve a smart grid as well as distribution systems would also benefit PHEVs by improving reliability, accommodating daytime charging, helping reduce carbon emissions, and controlling costs (NAS-NAE-NRC, 2009). DOE recently released a solicitation offering $3.9 billion in grants to “modernize the electric grid, allowing for greater integration of renewable energy sources while increasing the reliability, efficiency and security of the nation’s transmission and distribution system” (DOE, 2009a).
In its scenario analysis, the committee examined two cases that bracket the national average residential rate of 10.4 cents per kWh (EIA, 2009a) and that represent likely PHEV charging rates: 8 cents per kWh and 15 cents per kWh. The former would apply in areas with residential TOU rate structures; the latter would be in areas where rates are high or if they rise, perhaps because electric power generation is decarbonized.
CO2 will be emitted from power plants that generate the electricity that replaces gasoline that PHEVs do not require relative to conventional vehicles. As shown in Figure 3.1, the primary sources of electric power in 2007 were coal, natural gas, and nuclear energy. From 1997 through 2007, these three sources provided between 84.6 and 89.5 percent of total net generation. Nuclear power generation releases no CO2, but coal and (to a lesser extent) natural gas do.3
CO2 emissions by U.S. electric generators and combined heat and power facilities in 2007 were 2,517 million metric tons (EIA, 2009b), or an average of about 1.3 pounds of CO2 per kWh. One kWh will take a small electrically driven car about 5 miles. Over the same distance, an equivalent gasoline-powered car that gets 30 miles per gallon (mpg) would emit 3 pounds of CO2, more than twice as much. An HEV at 50 mpg would release about 2 pounds.
THE SYSTEM OUT TO 2030 AND BEYOND
Energy Information Administration Projection (Business as Usual)
From 2000 to 2007, average electricity demand increased by 1.1 percent per year. The 2009 EIA Reference Case projects electricity demand increasing by 26 percent from 2007 to 2030—about 1.0 percent per year on average. The largest increase is in the commercial sector (38 percent), where service industries continue to lead demand growth, followed by the residential sector (20 percent) and the industrial sector (7 percent) (EIA, 2009a). EIA also provides low and high growth cases for 2030. Figure 3.2 compares the generation mix for the three cases in 2030 with the 2007 case.
EIA’s Reference Case projects that the average retail price for electricity in 2030 will be very close that of 2008, 10.4 cents per kwh, with the high growth case at 10.8 cents and the low growth at 9.7 cents per kwh. These modest price differences are unlikely to have a material influence on PHEV economics and acceptance.
It should be noted that EIA forecasts are required to assume the continuation of existing policy, so no substantial efforts to reduce CO2 emissions from electric generation were included. The committee used the EIA projections for its business-as-usual scenario.
An Alternative View: EPRI/NRDC (Policy Driven)
For PHEVs to deliver their full potential to reduce CO2 emissions, the electricity used for charging them must be generated from technologies such as nuclear, renewable energy (e.g., solar, wind), and fossil fuels with carbon capture and sequestration. Because government policies will be required to drive these changes, the rate at which the country
moves toward this greener power generation mix remains uncertain.
An alternative set of scenarios for U.S. power generation was developed jointly by the Electric Power Research Institute (EPRI) and the Natural Resources Defense Council (NRDC) to explore the relationship between the grid and PHEVs if it becomes necessary to lower CO2 emissions from U.S. electric power generation (EPRI/NRDC, 2007). Nine modeling scenarios were developed spanning high, medium, and low emissions of CO2 and low, medium, and high penetrations of the fleet by PHEVs. Chapter 4 compares greenhouse gas (GHG) emission intensities of the EIA Reference Case with the EPRI/NRDC medium case.
Among other things, EPRI and NRDC concluded that all nine cases showed significant GHG reductions attributable to PHEV fleet penetration. Cumulative GHG savings from 2010 to 2050 could be significant, ranging from 3.4 to 10.3 billion MT of CO2.4
Recognizing that reductions of this magnitude are not likely to occur without public policy intervention, the committee used the EPRI/NRDC results to illustrate the potential benefits that PHEVs might provide under a policy-driven low-emission grid scenario.
CHARGING THE BATTERIES
If a dedicated circuit is not required, many PHEVs can be charged with little or no change to an owner’s electrical service. Although significant upgrades in the electrical distribution system might be required for a large PHEV population, utility planners should have sufficient time to prepare for these changes.
Charging a PHEV may be a simple matter of finding a suitable electrical outlet (most likely in a home garage) and plugging in. In other cases, however, it will be more complicated. The time required to charge a PHEV at regular household voltage may be quite long, so a voltage upgrade may be necessary. Zoning codes or standards may require upgraded or dedicated service for PHEVs, and PHEV-friendly, off-peak charging may require the installation of dedicated charging circuits and/or meters.
One recent study considered three levels for PHEV charging (Morrow et al., 2008):
Level 1 charging uses a standard 110 volt, 15 to 20 ampere circuit, standard in residential and commercial buildings. Level 1 provides relatively little power and may necessitate prolonged charge times.
Level 2 charging involves a 220 volt, single-phase, 40 ampere circuit. At the higher voltages and currents, charging would be more rapid, but Level 2 service is not common in residential garages and would generally entail a system upgrade.
Level 3 charging uses a 440 volt, three-phase circuit supplying 60-150 kW of power and can deliver a 50 percent charge in 10-15 minutes, depending on vehicle size and electrical range. Level 3 charging might be the choice for public garages, parking lots, and shopping centers.
The committee has considered charging only at Levels 1 and 2, believing that charging at Level 3 will not become important until much later. Table 3.1 provides estimated charging times for representative PHEVs and charging stations. Costs per charging station were estimated (numbers rounded by the committee) as follows (Morrow et al., 2008):
Residential garage charging
Level 1, $880
Level 2, $2,100
Apartment complex charging
Level 1, $830
Level 2, $1,500
Commercial facility charging
Level 2, $1,900
At the time this report was prepared, manufacturers had not announced whether they would equip PHEVs for charging at both 110 and 220 volts. The committee believes, however, that the additional cost for dual voltage vehicle charging is probably small and not likely to significantly affect the committee’s analysis.
In summary, some PHEV owners may be able to charge their vehicles using their existing home electrical service, but many others probably will not. The cost of upgrading
TABLE 3.1 Approximate Charging Time as a Function of Vehicle Size and Electric Driving Range (hours)
home service to allow PHEV charging, whether desired or required, is estimated to range from slightly less than $1,000 to slightly more than $2,000. PHEV-40s are more likely to need costly new circuitry for 220 volts.
PHEV subsidies may soften the financial concerns associated with this issue, and in some cases (especially for meter upgrades), utilities may pay for such upgrades and amortize the costs over a series of electric bills. However, an open question remains: To what extent will these additional costs, or just the inconvenience of making the modifications, dissuade potential PHEV buyers?
As PHEVs proliferate, there will be a growing demand for public charging, much of which could occur during day-time hours, when electric power costs are higher. It seems likely that some office complexes will install chargers for their employees and visitors, and shopping malls may install chargers to attract customers. In some cases, businesses may not even charge for the electric power, treating it instead as a promotional expense.
As an indication of interest in public charging, one company, Electric Transportation Engineering Corp., was recently awarded a stimulus grant of nearly $100 million from the Department of Energy to build 12,800 charging stations for electric vehicles and PHEVs in Arizona, Washington, Oregon, California, and Tennessee (DOE, 2009b).
The committee identified some related issues that are beyond the scope of this study and will require detailed assessment to understand the impact of PHEVs on the grid and vice versa:
Outlet access. An accurate estimate is needed of the number of existing homes and buildings where charging would be easy. About 35 percent of housing units do not have a garage or carport, which is probably essential for an outlet for home charging (Bureau of the Census, 2008). PHEV owners without ready access to an outlet would need a public charging infrastructure; it is uncertain how many consumers would be willing to rely on public charging.
Charging at 440 V. Some carmakers may be interested in 440-V charging to reduce charging times (Carney, 2009). The cost and potential extent of such service needs study.
Distribution system upgrades. In some areas, local utility electric distribution capacity may not be adequate for the simultaneous charging of many PHEVs on one circuit, particularly for fast charges. These areas should be identified and plans for upgrading developed.
Safety. Safety issues associated with charging PHEVs must be thoroughly studied and problems minimized.
Energy stored in PHEVs. It has been suggested that the electric grid might use the electric energy stored in PHEVs to help meet peak demand (when the costs of producing power are very high) and replace it later, when costs are lower. The willingness of PHEV owners to allow this, and the benefits to them of doing so, need to be assessed. Conditions and terms under which this might be feasible and beneficial need to be developed. Alternatively, a charged PHEV might be used to provide electric power to a home during a blackout. It would be useful to know the viability of these options.