Natural gas is better used to generate electricity to power electric vehicles (EVs) than as a direct transportation fuel, according to a new study by Oak Ridge National Laboratory. The study, entitled Well-to-Wheel Analysis of Direct and Indirect Use of Natural Gas in Passenger Vehicles, rates EVs powered by electricity from natural gas as being more energy efficient, less polluting, and cheaper to fuel than natural gas vehicles.
A contributing factor in the analysis is that natural gas power plants, especially combined cycle power plants, are very efficient in creating electricity, and when that electricity is used for locomotion by an electric motor, the net efficiency is higher than that of a natural gas engine. The study assesses losses and energy used throughout the system, including leaks during transportation (from pipelines, etc.) and during compression and decompression of the gas in the case of compressed natural gas vehicles. In the case of EVs, the study assesses power losses throughout the distribution grid, EV charging, and the power transfer to and from the battery.
As seen in the figure below, the study concludes that even a low-efficiency natural gas power plant would provide a more energy efficient source of electricity than using gasoline in a car. The study used the Nissan LEAF and the natural gas Honda Civic GX as the baseline for the vehicle fuel efficiency.
Wheel-to-Wheel Energy Use
(Source: Oak Ridge National Laboratory)
Emissions of greenhouse gases, including CO2, are also lower in the case of EVs when either the current mix of generation sources or any type of natural gas power plant are used to create the electricity. And, as is well known, electricity is also cheaper as a transportation fuel. Oak Ridge estimated at time of the study that natural gas costs $1.65 per 25 miles for compressed natural gas vehicles, compared to $1.02 for electricity.
It may seem counterintuitive that an extra step in fuel conversion (i.e., gas to electricity) would still be more efficient, but the greater efficiency of stationary gas turbines relative to small engines (as referenced here by Forbes) explains the math.
However, turning natural gas into electricity for EVs requires sufficient pipeline capacity, and a surge of EVs could overwhelm the regional grid if charging occurs at peak times. Natural gas also has to compete with other forms of generation on price, and there’s no guarantee that the surplus of natural gas from shale would find its way into EVs, as it may simply replace coal.
The study makes the case for facilities that have combined heat and power to add EVs to the fleet instead of adding the significant cost of a natural gas refueling station. Conversely, a significant argument for natural gas vehicles is their longer driving range and lower upfront cost. If an EV’s driving range of 80 to 100 miles doesn’t match with the driving requirements, then the economics or efficiencies won’t matter.
Tags: Clean Transportation, Distributed energy, Electric Vehicles, EV Charging, Natural Gas, Smart Transportation Program
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