Natural Gas for Cars Using Natural Gas for Vehicles: Comparing Three Technologies In the United States, natural gas is can also serve as the energy source in centrally-fueled fleets that use used primarily for electricity genera- for plug-in electric or hydrogen large quantities of fuel), but will not tion and residential, commercial, fuel cell electric vehicles. This fact be covered in this fact sheet. and industrial applications, but it sheet compares some efficiency and is also used as a fuel for on-road environmental metrics for three This comparison of pathways in vehicles, especially in medium- or possible options for using natural light-duty vehicles is based on a heavy-duty vehicles in centrally- gas in light-duty cars. detailed analysis (Wang and fueled fleets. Elgowainy 2015), which uses the The analysis presented here com- GREET model (Greenhouse Gases, It has been proposed for greater pares these pathways. It is not Regulated Emissions, and Energy use as a fuel for on-road vehicles, intended to recommend for or use in Transportation). Scientists particularly in light-duty vehicles. against increased use of natural at Argonne National Laboratory This can mean burning natural gas gas in light-duty vehicles. Related developed GREET to estimate in an internal combustion engine ongoing analysis considers use energy use and emissions across the like those used in most natural gas, ofnatural gas with these three entire fuel life cycle from extraction gasoline, diesel-powered vehicles on technology pathways in medium- to end use in transportation. the road today. However, natural gas or heavy-duty vehicles (for example, Natural Gas On-Road Vehicle Fuel: Three Technology Options Internal combustion Fuel cell electric Plug-in electric engine vehicle vehicle vehicle 1 2 3 BURNING REFORMING GENERATION COMPRESSED NATURAL GAS TO ELECTRICITY FROM NATURAL GAS HYDROGEN NATURAL GAS Figure 1. Compressed natural gas, natural gas to hydrogen, and electricity from natural gas 2 POLICY AND ANALYSIS Considering Life Cycle Efficiency Each of the three pathways for using natural gas has strengths and weaknesses that determine where efficiency losses and emissions occur across the entire life cycle. Vehicle efficiency determines only part of the story. Figure 2, which is based on GREET results, gives a look at the fuel life cycle for the three types of natural gas cars, showing how energy conversion efficiency at each major step leads to the ultimate system efficiency for each pathway. The percentages (light blue circles) show natural gas conversion efficiencies along steps of the life cycle. Below each pathway, the changes in the height of the light blue bar show how much of the energy92%* in one mmBtu of 99% 98% 16%** natural gas is used during each step. Natural gas internal combustion engine vehicles running on compressed natural gas (CNGV) have the greatest losses during combustion at the vehicle propulsion stage. Fuel cell 92%electric* vehicles (FCEVs) have the greatest99% losses 98% 16%** during hydrogen production via methane reforming andDrilling, during Processing, electricity generation and Transportation from hydrogen in the vehicle. NG Distribution NG Compression CNGV 175 92%* 99% 98% 16%** In addition, plug-in electric vehicles (PEVs) have the greatest losses during electricity generation. miles per 1 mmBtu mmBtu Drilling, Processing, and Transportation NG Distribution NG Compression CNGV 175 natural gas 92%* 99% 98% 16%** miles per Drilling,CNGV Processing, and Transportation1 mmBtu NG Distribution NG Compression CNGV 175 93% mmBtu ** 72% 97% miles per 92% 35% 1 mmBtu natural gas mmBtu Drilling, Processing, and Transportation NG Distribution NG Compression CNGV 175 natural gas City Gate City miles per ** 1 mmBtu 93% 72% mmBtu97% 92% 35% Drilling, Processing, and Transportation naturalNG gasSMR** Plant H **Compression H T&D H Fueling FCEV 93% 72% 97% 92% 35%2 | 2 | 2 255 FCEV 93% 72% 97% Gate City 92% 35%** miles per 1 mmBtu mmBtu Drilling, Processing, Gate City and Transportation NG SMR** Plant H2 Compression H2 T&D H2 Fueling FCEV City Gate City | | 255 natural gas Drilling,Drilling, Processing, Processing, and and Transportation Transportation NG SMR** Plant NGH CompressionSMR** Plant H T&DH CompressionH Fueling FCEV H T&D H Fueling FCEV miles per 1 mmBtu 2 | 2 2| 2 | 2 | 2 255 255 mmBtu miles per 1 mmBtu miles per ** 1 mmBtu 93% mmBtu 50% 94% 85% natural gas 67% (including natural gas mmBtu charging losses) natural gas PEV ** 93% 50% 93%94% 85% 67%50%** (including 94% 85% 67% (including charging losses) charging losses) 93% 50% 94% 85% 67%** (including Drilling, Processing, and Transportation NG Power Plants*** Electricitycharging T&Dlosses) Charging PEV 325 Drilling, Processing, and Transportation NG Power Plants*** Electricity T&D Charging PEV | | 325 miles per miles per 1 mmBtu Drilling, Processing,1 andmmBtu Transportation NG Power Plants*** Electricity T&D Charging PEV mmBtu | 325 mmBtu natural gas miles per natural gas Drilling, Processing, and Transportation1 mmBtu NG Power Plants*** Electricity T&D Charging PEV | 325 mmBtu Eciency miles per 1 mmBtu natural gas Key Loss Steps Eciency mmBtu Figure 2. Fuel life cycle efficiency natural gas Remaining Energy Eciency Key Loss Steps Energy conversion efficiency Key loss steps Remaining energy Eciency Key Loss Steps Remaining Energy Key Loss Steps Remaining Energy * Efficiency of drilling, processing, and transportation varies slightly between pathways due to expected differences in pipeline distanceRemaining to use, as Energy shown in Wang and Elgowainy (2015). ** Actual end-use efficiency will depend on drive cycle and other factors. Efficiency values here are representative based on an estimate of 17% average efficiency of gasoline engines for typical drive cycles and the relative MPGGE of each vehicle. Drive cycle simulations adjusted for on-road performance were used to estimate miles/mmBtu. *** Primarily from natural gas combined cycle plants. Reference: Wang, Michael and Amgad Elgowainy (2015). “Well-to-Wheels GHG Emissions of Natural Gas Use in Transportation: CNGVs, LNGVs, EVs, and FCVs. Presented October 10, 2014. Argonne National Laboratory. https://greet.es.anl.gov/publication-EERE-LCA-NG. POLICY AND ANALYSIS 3 Understanding Life Cycle Greenhouse Gas Emissions An accounting of greenhouse gas emissions involves more than vehicle fuel economy and life cycle system efficiency. With natural gas, a variable and uncertain portion of greenhouse gas emission occurs due to leakage of methane throughout the life cycle. Using GREET, greenhouse gas emissions can be compared across pathways with very different distributions205 miles per mmBtu of emissions across the fuel life cycle. natural gas In Figure 3, the grey bars show how greenhouse gas emissions (in carbon dioxide equivalents) are distributed across Drilling, Processing,different steps and of Transportation the life cycle for each pathway.NG DistributionThe figure also shows howNG the Compressiondifferent fuel economies in the lightCNGV blue 200 miles per mmBtu circles contribute to the final grams of emissions per mile shown in figures 3 and 4. ang(W and Elgowainy 2015). natural gas390 g/mi WTW CO e miles per mmBtu 2 * Drilling, Processing, and Transportation NG Distribution NG Compression205 natural gas CNGV emissions 14 kg CO2/mmBtu of NG 16 kg of CO2/mmBtu 19 kg CO2/mmBtu 80 kg CO2/mmBtu of NG of CNG of CNG Drilling, Processing, and Transportation NG Distribution NG Compression CNGV * 14 kg CO2/mmBtu of NG 16 kg of CO2/mmBtu 19 kg CO2/mmBtu 39080 kg CO2/mmBtu WTW CO2e of NG of CNG g/mi of CNG emissions: 390 g/mi WTW CO e miles per 2460 * emissions mmBtu H2 14 kg CO2/mmBtu of NG 16 kg of CO2/mmBtu 19 kg CO2/mmBtu 80 kg CO2/mmBtu of NG of CNG of CNG 452 miles per mmBtu H2 Drilling, Processing, and Transportation NG SMR Plant Gate City H Compression H T&D H Fueling miles per FCEV 2 | 2 | 2 460 mmBtu H2 260 Drilling, Processing, and Transportation NG SMR Plant H Compression H T&D H Fueling FCEV g/mi 2 | 2 | 2 WTW CO2e Drilling, Processing, and Transportation NG SMR Plant H Compression H T&D H Fueling FCEV emissions 2 | 2 | 2 260 9 kg CO2/mmBtu of NG 97 kg CO2/mmBtu 103 kg CO2/mmBtu 120 kg CO2/mmBtu 120 kg CO2/mmBtu g/mi of H2 of H2 of H2 WTWof CO H2e 9 kg CO2/mmBtu of NG 97 kg CO2/mmBtu 103 kg CO2/mmBtu 120 kg CO2/mmBtu 1202 kg CO2/mmBtu WTW CO2e emissions emissions: 255 g/mi of H2 of H2 of H2 of H2 9 kg CO2/mmBtu of NG 97 kg CO2/mmBtu 103 kg CO2/mmBtu 120 kg CO2/mmBtu 120 kg CO2/mmBtu of H2 of H2 of H2 of H2 miles per mmBtu 880 electricitymiles (including per mmBtu miles per mmBtu 861 electricity (including 880 electricity (including chargingcharging losses) losses) charging losses) Drilling, Processing, and TransportationDrilling, Processing, and TransportationNG Power Plants** NG PowerElectricity Plants** T&D Electricity Charging T&D Charging PEV BEV Drilling, Processing, and Transportation NG Power Plants** Electricity T&D | Charging | PEV | 200 200 g/mi g/mi WTW CO2e emissions WTW CO2e 11 kg CO2/mmBtu of NG 140 kg CO /mmBtu 150 kg CO /mmBtu 175 kg CO /mmBtu 175 kg CO /mmBtu 11 kg CO2/mmBtu of NG 2 1402 kg CO /mmBtu 2 150 kg CO /mmBtu2 175 kg CO /mmBtu 175 kg CO /mmBtu WTWemissions CO2e of electricity of electricity 2 of electricity 2 of electricity 2 2 200 g/mi 11 kg CO2/mmBtu of NG 140 kg CO2/mmBtu 150of electricity kg CO2/mmBtu of electricity175 kg CO2/mmBtuof electricity 175 kg CO2/mmBtuof electricity emissions: Figure 3. Fuel life cycle greenhouse gas emissionsof electricity of electricity of electricity