Riding on The Wind


Plug-in hybrids usher a new era for wind power.

Fortnightly Magazine - December 2008

The days of windpower being considered an “alternative” energy are over. Second only to natural gas-fired generation in the category of new installed capacity during each of the last few years, windpower more than ever has become accepted as mainstream generation. Last year, wind power accounted for 35 percent of all new electric generating capacity, and it’s on pace to more than maintain that piece of the resource pie this year.

The transportation sector, meanwhile, is facing major new challenges, with growing oil demand occurring simultaneously with the increasing recognition of the economic, environmental, and national security consequences of U.S. oil dependence. Plug-in hybrid electric vehicles (PHEVs) have been considered an answer to many of these challenges, yet detractors often argue that deployment of such vehicles would simply shift emissions from the transportation sector to the energy sector, given that electric vehicles will need to be connected to the power grid and charged.

But a new intersection between the electricity sector and transportation sector nevertheless is opening up, thanks to the advent of PHEVs. By using the existing infrastructure in the electric industry—which significantly is under-utilized for many periods throughout the year, including at night, when electric loads greatly are reduced compared to daytime loads—the electric industry has a unique and enormous opportunity to power part of the transportation sector as never before.

And as a clean energy source, wind power stands to benefit the most. A major portion of our nation’s energy needs for transportation can be powered with clean, inexhaustible, renewable energy from wind turbines—energy inherently superior to petroleum imports and other forms of electricity production alike in terms of its ability to meet energy-security and environmental challenges.

If they weren’t convinced already, industry observers were reminded in July of wind power’s ability to contribute to the generation mix, when the U.S. Department of Energy released a long-awaited report entitled 20 percent Wind Energy by 2030.1 The report analyzes one possible future scenario under which wind power can provide a full 20 percent of the nation’s electricity by 2030. The bottom line of the report: 20 percent wind energy penetration technically is feasible, but will require changes to how we operate our electric grid in the United States, as well as overcoming a number of other challenges and barriers.

The benefits of such a scenario include an 11-percent reduction in natural gas use across all sectors and a 25-percent reduction in carbon-dioxide emissions from fossil-fueled generation. The 20-percent wind scenario is garnering significant attention as the country seeks to reduce emissions associated with burning fossil fuels.

Given increasing examination of dependence on foreign sources of transportation fuel, the arrival of PHEVs in the next few years will allow wind power the opportunity also to supply the energy vehicles need on a daily basis for commuting, household, and business purposes.

Driving Down Emissions

PHEVs—descendants of the first electric vehicles originally developed in the 1970s, and related to the currently-popular hybrid electric vehicles—use sophisticated battery technology to power most short-distance trips and are recharged from the electric grid. This recharging generally occurs at night, when vehicles typically sit idle (most likely by plugging the vehicles into a standard electrical outlet). PHEVs still carry on-board fuel—i.e., gasoline or diesel—for occasions when a trip exceeds the range of the battery. That option, however, might not be needed very often for most drivers during a typical week: Data from the U.S. Department of Transportation show that 78 percent of commuters travel 40 miles or less each day—a distance that corresponds well with the expected battery-only range of PHEVs.

Obviously, the use of wind energy to charge PHEVs can result in emissions reductions. But before examining those benefits, it’s worthwhile to take a look at the impact of PHEVs on emissions even without wind-power growth. The good news is that PHEVs are capable of putting a dent in emissions even without the extra help of wind power.

A report from the Pacific Northwest National Laboratory found that replacing 73 percent of the U.S. light-duty vehicle fleet with PHEVs would reduce oil consumption by 6.2 million barrels a day, cutting the need for imported oil by about 50 percent.2 Other studies confirm this, including one conducted jointly by the Electric Power Research Institute (EPRI) and the Natural Resources Defense Council (NRDC). That report found that replacing 60 percent of light vehicles in the U.S. with plug-in vehicles by 2050 would result in electricity consumption rising only about 8 percent. The emissions impact: Net carbon dioxide reductions of 450 million metric tons annually, equivalent to taking 82 million cars off the road.3 The EPRI-NRDC report analyzed nine scenarios based on three sets of electricity-sector emissions profiles and three levels of PHEV adoption rates for the nation’s light-duty vehicles:

Annual GHG emissions are reduced in all nine scenarios, when factoring in all life-cycle emissions (“well to wheels”)—dispelling the misperception that charging of PHEV batteries would increase emissions from an overall standpoint;

Cumulative GHG emissions reductions range from 3.4 to 10.3 billion metric tons over the 2010 to 2050 time period; and

Emissions reductions would occur in all regions of the country.

Further, when wind power provides an even larger share of the generation mix that’s recharging the fleet of PHEV batteries, environmental benefits increase accordingly. In the 20-percent wind scenario, as more wind generation comes online each year, more energy to charge PHEVs overnight would come from wind power. Indeed, the growth of PHEVs would allow wind power to go well beyond the 20-percent penetration mark, and possibly before the year 2030 outlined in the DOE report. The result is more electricity from clean energy sources such as wind power, and less pollution released into the atmosphere.

A key factor related to PHEVs that significantly decreases net emissions is that electric motors are several times more efficient than gasoline internal combustion engines. According to studies from EPRI, the batteries in a typical PHEV will draw about as much energy as a dishwasher (1.4 kW to 2 kW).4 So in a future that includes a significant number of PHEVs, it will be highly advantageous to design electric rates ensuring that vehicle charging occurs almost exclusively at night, guaranteeing that PHEVs will use low-cost electricity. Doing so both takes maximum advantage of available grid infrastructure and minimizes the additional strain that increased electricity demand from PHEVs puts on the electric grid during daytime hours of peak electricity usage. Overall, the electric industry’s valuable assets, from generation to transmission, are put to better use.

Toward this end, the smart-grid concept will play a key role, allowing consumers and utilities to have greater control over when and how they use and generate electricity. Smart-grid and smart-charging technologies will allow utilities to ensure that PHEVs are charged during the optimum night-time hours. Consumers will be empowered with options that allow them to respond to price signals, as they choose when, and when not, to charge their PHEVs. In addition, some vehicle-to-grid (V2G) concepts even allow PHEV owners to receive price signals to recharge their vehicles when wind energy output in a given region is strongest—maximizing the emissions benefits for the utility and ensuring that consumers’ vehicles are “green.”

Electric Industry Impacts

The impact of PHEVs on the electric industry will be huge once their introduction and growth starts to occur. The potential for more electricity load growth than generally has been projected—exceeding, for instance, the amount assumed in DOE’s 20 percent Wind Energy by 2030 report—could result if widespread adoption of PHEVs occurs over the next couple of decades.

This issue already has begun to be examined. One study, completed in January 2008 by the Department of Energy’s Oak Ridge National Laboratory,5 considered a scenario of PHEVs capturing 25 percent of the new vehicle market starting in 2020—putting about 50 million such vehicles on the road by 2030. The study’s conclusion was not surprising: Most utilities will need to build some additional capacity or use demand-response initiatives to meet added electricity load as a result of the proliferation of PHEVs.

Who, then, holds the keys to unlocking this nexus between the transportation sector and the electricity sector, and who can benefit from the associated new business opportunities? The answer, of course, is electric utilities.

In July 2008, 34 U.S. and Canadian utilities announced a collaborative partnership with EPRI and General Motors to prepare for the large-scale integration of PHEVs into the electric grid.6 By charging a large fleet of PHEVs at night and during off-peak hours, electric utilities would end up significantly increasing the utilization factors for all aspects of their infrastructure. U.S. electric utilities hold a unique role in providing the new gas pump for PHEVs—i.e., the driver’s 110-volt outlet. “Considering that the primary infrastructure needed for consumers to begin using PHEVs—an ordinary wall socket—already exists in nearly every garage in America, we can help reduce our oil addiction as quickly as these new cars can roll off show room floors,” says Paul Bonavia, president of Xcel Energy’s utilities group.

Wind-PHEV Synergy

So how much windpower would it take to power our nation’s fleet of vehicles? The short answer is that meeting 100 percent of the energy needs of the light-duty vehicle fleet would require just over 150,000 MW of wind turbines (see Figure 1). The 21,000 MW of wind turbines already deployed in the United States produce enough electricity to power almost 14 percent of the nation’s light-duty vehicle fleet.

Of course, PHEVs connected to the electric grid will not be charged exclusively by wind energy, although increased electricity use caused by PHEV charging can be offset directly by more use of wind power.

PHEVs and wind power work well together for a number of reasons. Most important, wind-energy output typically is highest at night in most parts of the United States, just as PHEVs are likely to be charged almost exclusively at night. As a result, PHEVs will serve as an important source of demand for wind energy, keeping nighttime wholesale electricity prices from falling too steeply as increasing quantities of wind power are added to the grid. Conversely, adding increasing amounts of wind power will help ensure large amounts of low-cost, emissions-free electricity is available to power the nation’s vehicle fleet.

PHEVs also have the potential to use their batteries as a form of energy storage, which helps accommodate variability on the electric grid by working to ensure that electricity supply and demand stay in balance. This service has tremendous potential value to utilities and grid operators, who today rely on expensive spinning and non-spinning generation reserves to alter the supply of electricity in response to changes in supply and demand on the grid. Increasing use of wind energy likely will result in modest increases in the need for these reserves, as the variability of wind energy output adds incrementally to the overall variability on the electric grid. PHEVs offer a potentially lower-cost way for grid operators to accommodate the overall variability on the grid, including that introduced by wind energy. “As smart-grid technologies evolve, the nation’s utilities could eventually tap into a wind power-charged, mobile fleet and draw energy out, thereby adding to the value of the wind power,” Bonavia says.

The simplest way PHEVs can serve as a form of energy storage is by altering their rate of charging in response to signals from the grid operator. Under this uni-directional response, the PHEV charges when there’s excess electricity on the grid and stops charging when electricity demand exceeds supply. As smart-grid technologies become more advanced, this response can become bi-directional, with the PHEV using its battery to add power to the grid when demand exceeds supply, as well as charging when supply exceeds demand. Of course, putting this concept to work will require innovative thinking about how the PHEV owner will be compensated for providing this service to the grid. Regardless, the tremendous potential for a symbiotic relationship between PHEVs and the electric grid will help ensure these obstacles are overcome.

An April 2006 study by the National Renewable Energy Laboratory assessed the benefits PHEVs could provide for wind energy, concluding that “PHEVs could be a significant enabling factor for increased penetration of wind energy.”7 This study examined three scenarios for PHEV penetration by the year 2050: An aggressive scenario in which 50 percent of the nation’s light-duty vehicles are replaced by PHEVs with an effective battery-powered driving range of 60 miles; a more conservative scenario with a lower penetration; and a scenario with no PHEV use. In the high-PHEV scenario, the benefits of PHEVs allow windpower to double its market penetration compared to the scenario without PHEVs. While overall electricity use increases by 7.3 percent in this scenario because of the additional demand from PHEVs, the use of natural gas and coal actually decreases because wind energy provides a significant share of the electricity for the PHEVs.

The scenario with a lower penetration of PHEVs also found significant benefits for wind power, with wind generation increasing by 13 percent over the no-PHEVs scenario. Aggregate emissions were reduced in both the aggressive and conservative PHEV scenarios, as more transportation energy comes from clean, inexhaustible, and domestically-produced wind energy.

Beyond 20 Percent

Wind-powered cars aren’t the only solution to the transportation sector’s environmental and energy-independence challenges. Meeting those challenges inevitably will mean dramatic changes to entire sectors of the economy—a reality that makes consideration of multiple models an appropriate and necessary response.

Yet wind power, enjoying its newfound position as a mainstream energy source, seems to be at the center of most plans for America’s energy future. This year, for example, T. Boone Pickens unveiled an energy plan under which much of the nation’s vehicle fleet would be powered not by electricity but by natural gas. In unveiling the plan, Pickens captured the public’s attention with a multi-million dollar media campaign rife with spinning wind turbines.

Under the Pickens plan, wind power would replace large amounts of natural-gas fired generation in the electric industry, freeing the natural gas saved to be used in the transportation sector. So regardless of the model, wind energy will be a key part of the equation for cutting dependence on foreign oil. And under that new paradigm, 20-percent wind energy penetration becomes only a starting point.



1. 20 percent Wind Energy by 2030, U.S. Department of Energy Office of Efficiency and Renewable Energy, July 2008.

2. Impacts Assessment of Plug-In Hybrid Vehicles on Electric Utilities and Regional U.S. Power Grids – Part 1: Technical Analysis”, Pacific Northwest National Laboratory, November 2007.

3. Environmental Assessment of Plug-In Hybrid Electric Vehicles, EPRI and NRDC Report, 2007.

4. Plug In Hybrids on the Horizon,” EPRI Journal, Spring 2008.

5. Potential Impacts of Plug-in Hybrid Electric Vehicles on Regional Power Generation, Stanton W. Hadley and Alexandra Tsvetkova, Oak Ridge National Laboratory, January 2008.

6. EPRI Press Release, “EPRI, GM, 34 Utilities Collaborate to Advance Plug-In Hybrid Electric Vehicles,” July 22, 2008.

7. A Preliminary Assessment of Plug-In Hybrid Electric Vehicles on Wind Energy Markets, W. Short and P. Denholm, National Renewable Energy Laboratory, Technical Report NREL/TP-620-39729, April 2006.