Study: even with high LDV electrification, low-carbon biofuels will be necessary to meet 80% GHG reduction target; “daunting” policy implications
A study by researchers from the University of Wisconsin-Madison and a Michigan State University colleague has concluded that even with a relatively high rate of electrification of the US light-duty fleet (40% of vehicle miles traveled and 26% by fuel), an 80% reduction in greenhouse gases by 2050 relative to 1990 can only be achieved with significant quantities of low-carbon liquid fuel. The paper is published in the ACS journal Environmental Science & Technology.
For the study, the researchers benchmarked 27 scenarios against a 50% petroleum-reduction target and an 80% GHG-reduction target. They found that with high rates of electrification (40% of miles traveled) the petroleum-reduction benchmark could be satisfied, even with high travel demand growth. The same highly electrified scenarios, however, could not satisfy 80% GHG-reduction targets, even assuming 80% decarbonized electricity and no growth in travel demand.
An 80% reduction in US greenhouse gas (GHG) emissions by 2050 has been generally established as the de facto required domestic contribution to stabilizing global concentrations at low to medium levels, that is, 450 and 550 ppm carbon dioxide equivalent (CO2-equiv). … Within the transportation sector, the two basic options for reducing petroleum use and greenhouse gas (GHG) emissions are fuel-use reduction and fuel substitution. … Hydrogen is not envisioned to be a major contributor in the near term because of techno-economic limitations leaving natural gas, liquid biofuel, and electricity as candidates to meet the dual national goals of replacing oil and reducing GHG emissions.
… Given the current barriers to increasing ethanol-based biofuels (blend wall, slow growth in cellulosic biofuel production, regulatory uncertainty surrounding the RFS), transportation electrification seemingly offers a more immediate opportunity to displace gasoline. Electrified vehicles (meaning all of hybrid, plug-in hybrid, or battery electric technologies) could largely replace conventional gasoline vehicles, under favorable conditions (e.g., consumer attitudes, fuel prices, battery technology advancement, vehicle costs and subsidies). The likelihood of these conditions being met is speculative, however, and projections for consumer adoption of electrified vehicles have varied widely.
We are interested in the extent to which electrified vehicles could reduce petroleum consumption and greenhouse gas (GHG) emissions and the sensitivity of these impacts across a range of travel demand and technology scenarios. We find that petroleum consumption and GHG emissions are highly sensitive to these inputs, with resulting petroleum consumption and GHG emissions varying widely. The implication for biofuels is important, to the extent they are aimed at meeting climate and petroleum use reduction goals.—Meier et al.
The study estimated national fuel and emissions impacts from increasing reliance on electrified light-duty transportation, and the resulting implications for advanced biofuels. For the study, the team reconstructed the vehicle technology portfolios from two national vehicle studies (the 2007 Environmental Assessment of Plug-In Hybrid Electric Vehicles by the Electric Power Research Institute and Natural Resources Defense Council; and the 2009 Multi-Path Transportation Futures study by Argonne National Laboratory).
These two studies disagree greatly in regard to petroleum and GHG impacts, stemming from very different rates of vehicle electrification and travel demand growth that each study assumed. Neither offered significant sensitivity analysis, making it difficult to extend their conclusions to alternative scenarios.
The Wisconsin and Michigan team normalized the highly detailed vehicle assumptions and transport calculations from these studies around the rates of electrified vehicle penetration; travel demand growth; and electricity decarbonization. They also examined the impact of substituting low-carbon advanced cellulosic biofuels in place of petroleum.
The two studies—EPRI-NRDC and ANL—serve as “excellent bookends” for comparing minimal and maximal electrification of passenger transportation, the researchers concluded. They based their low electrification scenario (0.3% electric powered miles) on the ANL Study’s “PHEV and Ethanol” scenario, and the high electrification scenario (40% electric-powered miles) on the EPRI- NRDC Study’s High scenario with 95% electrified vehicles. The researchers also considered intermediate (20% electric-powered miles) electrification—halfway between the high and low.
They examined each of these three vehicle mixtures under low-, medium-, and high-growth assumptions for travel demand. These 9 combinations became the reference scenarios with defined fuel requirements and GHG emissions. These same vehicle combinations and growth rates are used to examine nine petroleum-targeted scenarios and nine GHG-targeted scenarios.
Fuel and emission impacts were determined by four primary considerations: (1) the total travel demand; (2) the vehicle mix that satisfies this demand; (3) the vehicle efficiency assumptions that determine fuel requirements; and (4) the GHG intensity of the vehicles’ fuels.
They estimated GHG emissions from direct vehicle-fuel combustion; power plant emissions (from electrified vehicle charging demands); and “upstream” life-cycle contributions from the petroleum fuel-cycle and electricity fuel-cycle.
They considered three levels of GHG-intensity for US electricity supply. The reference case scenarios assume no change to GHG intensity from current levels. The petroleum-targeted scenarios assume that electricity supply is decarbonized by 40%. while the climate-targeted scenarios assume that electricity supply is decarbonized by 80%. In the climate-targeted scenarios, they assumed that electrified vehicles receive their electricity from an 80% decarbonized electricity grid.
They considered state-specific contributions from nine generating technologies: coal, oil, natural gas, hydro, biogas, geothermal, nuclear, wind, and solar.
Their findings included:
None of the 9 reference scenarios met the 80% GHG reduction target, although 4 were below the 50% petroleum target and one was only slightly above.
In the petroleum-targeted scenarios, they substituted a hypothetical RFS-compliant advanced biofuel (i.e., advanced cellulosic biofuel) for gasoline on an energy basis, if needed, until the petroleum reduction target is exactly met—(i.e., to the point where gasoline and diesel consumption is reduced to 50% of 2011 levels).
Thus, petroleum requirements for all scenarios exactly meet, or are otherwise below, the 50% reduction target. None of the 40%-electrified cases required any contributions from cellulosic biofuel, as the electrification alone provided sufficient petroleum displace- ment.
No cellulosic biofuel was required under low growth and 20%-electrified conditions. The remaining five scenarios required widely varying contributions of cellulosic biofuel, from 316 to 8638 PJ. For comparison, they team estimated the RFS goal for cellulosic fuels to be equivalent to 1289 PJ.
The climate-targeted scenarios included cellulosic biofuel substitution to reduce GHG from light duty transportation to 20% of the reference GHG. The team also assumed that electricity is largely “decarbonized”, reducing GHG intensity by 80%.
No scenarios achieved the 80% GHG reduction without contributions from RFS-compliant advanced cellulosic biofuel. Only three scenarios actually met the GHG target of 294 MT. The remaining six scenarios exceeded the target even while replacing all petroleum with low GHG cellulosic biofuel (at 60% lower GHG intensity).
The researchers then took the results of the climate-targeted scenarios and performed additional sensitivity analysis to extend the assessment to more than 135 cases, with the output the amount of cellulosic biofuel volumes required to meet GHG targets.
These cases span 5 levels of electrification, 3 levels of demand growth, 3 rates of technology advancement, and 3 levels of economy-wide carbon intensity. Electrification scenarios corresponded to the ANL study (PHEV & ethanol scenario), the EPRI/NRDC study (low, medium, high scenarios), and one additional 20% electrification scenario.For each of these scenarios, three results were shown assuming high, moderate, and low rates of technology advancement—high tech advancement corresponds to the lowest biofuel volume and vice versa.
The low carbon economy assumes electricity is decarbonized by 80% and petroleum has 15% lower GHG intensity than current levels.
The moderate carbon economy assumes electricity is decarbonized by 40% and petroleum has the same GHG intensity as current levels.
The high carbon economy assumes electricity has the same GHG intensity as current levels and petroleum has 15% higher GHG intensity than current levels.
Near misses (within 5%) are included as meeting the GHG target.
From this analysis, they found that, assuming travel demand grows at historic rates, vehicle efficiency alone reduces petroleum consumption, but the reduction only exceeds 50% with a very high reliance on electrified vehicles. Holding VMT constant coupled with vehicle efficiency improvements, results in extensive fuel reductions: roughly halving petroleum use with almost no reliance on electricity.
However, significant contributions from both cellulosic biofuel and electricity were necessary to meet the 80% GHG target across the range of scenarios.
Scenarios relying almost exclusively on cellulosic biofuel exceeded the GHG target by 15% with constant VMT (no growth) and by 134% under high-growth conditions.
Scenarios with the highest rates of electrification (scenarios 25−27) were still not able to meet the GHG target, except with very large contributions from cellulosic biofuels.
Cellulosic biofuels contributions exceeded the 16 billion gallons (1289 PJ) RFS goal for 2022 in all cases. The lowest cellulosic biofuel contribution was 17% higher than the RFS goal in the case of 40% electrification and no VMT growth.
With 40% electrification, the low growth and moderate growth cases met the GHG target with cellulosic biofuel contributions of 1508 PJ (18.7 billion gallon) and 4540 PJ (56.4 billion gallon), respectively, well below the 7233 PJ (90 billion gallon) benchmark.
Importantly, we are considering only fuel demands for light duty transportation, that is, cars, vans, SUVs, and light trucks. A significant level of electrification is certainly viable for these vehicles, as BEVs and PHEVs are currently commercially available. Light duty vehicles are responsible for slightly more than half of the US petroleum used in the transportation sector. The remainder of transportation petroleum, however, is used for on-road and off-road heavy duty vehicles, trains, planes, and marine vessels. Electricity is not feasible for powering planes, marine vessels, heavy trucks, and most off-road mobile work platforms though some electrification of rail transport is possible. Therefore, achieving comparable GHG targets across these transportation modes would presumably require even higher reliance on cellulosic biofuel, in addition to the volumes required for light duty transportation.
… The implications of this research are daunting with regard to climate policy. Successfully decarbonizing light duty transportation requires simultaneous “successes” around several key challenges. First, growth in light duty vehicle travel would need to be moderate at most, but preferably low. Historic growth can be maintained and achieve an 80% GHG reduction only if nearly all petroleum is replaced with alternative low-carbon fuels. Second, an extremely high rate of electrified vehicle technology adoption would need to be achieved, such that nearly all light duty vehicles would need to be hybrid or electrified by 2050 and coupled to ongoing improvements in vehicle efficiency. Third, U.S. electricity supply cannot resemble the current fuel mix, but would have to be massively decarbonized; displacing the vast majority of fossil-fuel derived electricity with nuclear and renewable resources. Changes of this magnitude to transportation demand, vehicle fleet, and electricity are necessary, but still insufficient to meet an 80% GHG reduction, without additional low-carbon gasoline replacement such as that provided by cellulosic biofuels.
Over the course of 35 years, the fuel-mix powering light duty transportation could be radically different than today’s, requiring only a small fraction (0−13%) of current petroleum consumption. Simultaneously achieving the petroleum and GHG reduction targets would require a monumental effort to commercialize cellulosic biofuels, as well as impressive achievements spanning transportation planning, vehicle manufacturing, electric power supply, and public policy. Still, it is technically achievable. Our assumed vehicle efficiencies were based on average (not high) rates of technology improvement. Renewable and nuclear electricity supply technologies are available today. Though continued research and development is needed, the necessary biofuel contributions are within the range of recent estimates of achievable potential.—Meier et al.
Paul J. Meier, Keith R. Cronin, Ethan A. Frost, Troy M. Runge, Bruce E. Dale, Douglas J. Reinemann, and Jennifer Detlor (2015) “Potential for Electrified Vehicles to Contribute to US Petroleum and Climate Goals and Implications for Advanced Biofuels” Environmental Science & Technology doi: 10.1021/acs.est.5b01691