Synthetic Fuels

There are several pathways for producing hydrocarbon fuels from non-petroleum sources, such as electricity. However, we find that electrofuels, or synthetic fuels from electricity, are cost prohibitive at this time.

Environmental Impacts

The following compares greenhouse gas emissions from several methods of producing complex hydrocarbons.

Sources: Lattanzio ¹, Steele et al. ², Tu et al. ³, EPA ⁴. Electrofuels, also known as power-to-fuel, are hydrocarbons that are produced from electrolyzed hydrogen. For these, the emissions intensity of electricity is taken from Schlömer et al. ⁵ and a conversion efficiency of 40-50% is applied, as estimated by Malins ⁶. No emissions other than those from electricity are assumed, though additional emissions should be attributed if the CO₂ source is from a flue gas and would otherwise be sequestered ⁶. Carbon capture and sequestration might also reduce emissions from coal- and gas-to-liquids ⁷.

Despite the low efficiency of electrofuel production, corn ethanol requires far more land per unit energy.

The land use estimate of algal biodiesel is estimated from Atabani et al. ⁸. Yeh et al. ⁹ report land use from oil production. Data from Building Energy Codes Program ¹⁰ is used to estimate the primary energy behind electricity, Malins ⁶ gives the conversion efficiency, and Ong et al. ¹¹ give the land use of solar power. Efficiency on gas-to-liquids is from Steynberg and Dry ¹², and for coal-to-liquids from Höök and Aleklett ¹³. Additional land use estimates are taken from General Electric ¹⁴, Stevens et al. ¹⁵, World Energy Council ¹⁶.

Energy Requirements

As an energy carrier, liquid fuels require more primary energy input to produce than energy they contain. The conversion efficiency of primary energy into usable fuel varies by production method.

Sources: Höök and Aleklett ¹³ for coal-to-liquids and Steynberg and Dry ¹² for gas-to-liquids. The low efficiency of electrofuels stem from two conversion processes: from a primary energy source into electricity, with efficiency about 32% (Building Energy Codes Program ¹⁰); and then from electricity into hydrocarbons, with efficiency 40-50% (Malins ⁶).

In cars, electrofuels are a much less efficient use of electricity than direct use in an electric vehicle, and also less efficient than hydrogen.

Source: Malins ⁶. The low efficiency of electrofuels stems from additional losses from the internal combustion engine, which has an efficiency of about 30% in modern cars (fueleconomy.gov ¹⁷).

Economics of Synthetic Fuels

With the exception of sugarcane ethanol, most alternatives to petroleum-based gasoline are more expensive and not widely used without policy support.

Sources: Biofuels and Emerging Technologies Team ¹⁸ for gas-to-liquids, Brynolf et al. ¹⁹ for electrofuels, Mantripragada and Rubin ²⁰ for coal-to-liquids, Moyo et al. ²¹ for biofuels, and the EIA ²² for wholesale gasoline as of June 2019. Electrofuels are especially expensive due to energy losses in the production processes. Prices are highly dependent on the price of feedstock.

The conversion of coal and natural gas into liquid fuels carry heavy greenhouse gas and other environmental costs, and they are not likely to ever be economically attractive options ²³, ²⁴. Aside from sugarcane, biofuels are also unlikely to be economically sound, and they carry major land use impacts. Electrofuels can be an acceptable option only with a low-cost and low-impact electricity source, and even then their use is likely to be confined to sectors that are difficult to electrify directly, such as aviation and long-distance trucking ⁶.

Carbon abatement costs of electrofuels are as follows.

Cost of synthetic fuels, with a carbon cost of $50/ton, and estimated carbon abatement cost. A plant size of 50,000 barrels per day is assumed, as per ²⁵.

With such high carbon abatement costs, it does not make sense for a private developer to build a synfuel plant.