The following guest blog was authored by Dr. Bruce E. Dale, University Distinguished Professor in the Department of Chemical Engineering and Material Science at Michigan State University and a leader in the DOE Great Lakes Bioenergy Research Center at MSU.
U. S. renewable fuel policy has two primary objectives: 1) to reduce petroleum imports and thereby increase energy security and 2) to reduce greenhouse gas (GHG) generation in the transportation sector. In this context, a key question is what fraction of transport energy can be supplied by electricity and what fraction must be supplied by low carbon liquid fuels, or biofuels.
Ocean shipping, air transport, off road equipment and heavy trucks represent approximately 30 percent of total transportation fuel consumption, and will require liquid fuels for the foreseeable future. The light duty vehicle fleet might be fueled by either electricity or biofuels.
Two recent papers, one focused on the U.S. situation, and another with a global perspective, show that the ability of electricity to serve the light duty fleet is probably much less than previously thought if both energy security and greenhouse gas policy objectives are to be achieved. Importantly, both studies conclude that by 2050 approximately 80 percent of total transportation fuel globally and in the U. S. will still be energy dense liquid fuels, even with aggressive efforts to electrify the light duty fleet.
The U. S.-focused paper tested a variety of scenarios. Regardless of the precise consumer preferences between hybrid, plug-in hybrid or battery electric vehicles, high-electrification scenarios (40 percent of miles traveled) corresponded to 26percent of light duty transport energy being supplied by electricity. At this level, both decarbonized electricity and substantial volumes of low-carbon liquid fuels (e.g. cellulosic biofuels compliant with the Renewable Fuel Standard, or RFS) would be required to meet an 80-percent GHG reduction target. To meet this GHG reduction target, approximately 80 percent (30 percent plus 74 percent of the remaining 70 percent) of total energy for mobility must still be met by high energy density, low carbon liquid fuels such as cellulosic biofuels.
The global-level analysis came to similar conclusions. The question of whether the world needs biofuels was approached by examining the feasibility of doing without them. Even with aggressive reductions in travel growth, shifts to mass transport modes, strong efficiency improvements, and deep market penetration by vehicles running on electricity and hydrogen, there remains a large demand for dense liquid fuels in 2050 (80 percent of transportation fuel) and even in 2075 (50 percent). This demand is due largely to aviation, ocean shipping and long haul trucking. Acknowledging the significant uncertainties involved in such projections and the challenges faced by all candidate technologies and fuels, it will likely be difficult to achieve a low-carbon transport sector without widespread use of biofuels. Therefore aggressive efforts to develop sustainable, low-carbon biofuels alongside other options are warranted.
The implications of these papers are daunting with regard to U. S. climate and energy 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 in light duty vehicle travel can be maintained and achieve an 80-percent GHG reduction only if nearly all petroleum is replaced with alternative low-carbon fuels.
Secondly, 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-percent GHG reduction, without additional low-carbon gasoline replacement such as that provided by cellulosic biofuels.
There is a U.S. policy conundrum. Current policies with respect to low carbon, renewable fuels are highly conflicted. The “blend wall” limiting ethanol to about 10 percent of the total gasoline pool is a policy barrier, not a true technical barrier. The blend wall effectively pits first generation ethanol from starch against potentially much more abundant and low-carbon ethanol from cellulosic biomass. The available “space” in the gasoline blending pool is essentially already taken by ethanol from corn. Very little investment in large cellulosic biofuels plants can be expected in this situation ‑ there is effectively no market for this low carbon fuel.
Thus the fate of second generation biofuels is currently dominated by whether or not a market will be available for these fuels. The Renewable Fuel Standard was intended to require that such a market be made available, but has not been enforced. At this point, it seems clear that if we are to move forward toward both energy security and low-carbon fuels, the RFS or something very like it must be enforced.
Thus low carbon biofuels are not optional. We must have them if we are to simultaneously achieve energy security and climate security. Electrified vehicles simply can’t do the job on their own.