The US Department of Energy’s Advanced Research Projects Agency-Energy (ARPA-E) announced up to $30 million in funding for a new program for technologies that use renewable energy to convert air and water into cost-competitive liquid fuels. (DE-FOA-0001562)
ARPA-E’s Renewable Energy to Fuels through Utilization of Energy-dense Liquids (REFUEL) program seeks to develop technologies that use renewable energy to convert air and water into Carbon Neutral Liquid Fuels (CNLF). The program is focused in two areas: (1) the synthesis of CNLFs using intermittent renewable energy sources and water and air (N2 and CO2) as the only chemical input streams; and (2) the conversion of CNLFs delivered to the end point to another form of energy (e.g. hydrogen or electricity).
|The production, transport and use of carbon-neutral liquid fuels for energy delivery. Areas of interest within Category 2 are shown in bold. Click to enlarge.|
REFUEL seeks to develop technologies that convert water and air into CNLFs using chemical or electrochemical processes powered by renewable electricity sources, such as wind and solar. By transforming renewable resources into liquid fuels, renewable power can be stored for longer periods and transported efficiently and inexpensively as liquids via existing infrastructure to consumers. REFUEL also targets technologies that convert CNLFs into electricity or into hydrogen to power zero-emission vehicles.
The program’s overall goal is a competitive total cost (including production, transportation, storage, and conversion costs) of delivered (source-to-use) energy (e.g. converted to motive power for transportation) as opposed to the primary energy stored in chemical form below $0.3/kWh—the price needed to be competitive with other carbon-free delivery methods
ARPA-E defines source-to-use energy cost as the sum of the fuel production cost (CF), the cost of transportation or transmission from production to the user (CT), and the cost of any storage (CS), divided by the conversion efficiency (η) to account for any losses during the conversion steps.
|Comparative costs of current different energy delivery options for transportation|
|Gasoline||H2 via SMR||NH3 via
|Specific energy density, kWh/kg||12.7||33.3||5.16|
|Energy density, kWh/L||8.76||0.8||4.25|
|Fuel cost $/kg||0.54||1.95||0.325|
|Fuel cost, $/kWh||0.047||0.058||0.063||0.065|
|Transmission cost, $/kWh||0.001||0.060||0.004||0.038|
|Storage cost, $/kWh||0.001||0.030||0.007||0.160|
|Conversion efficiency, %||30||55||55||92|
|Source-to-use energy cost, $/kWh||0.159||0.292||0.135||0.285|
|Source: ARPA-E. Assumptions listed in the DE-FOA-0001562 document.|
Chemicals, such as hydrocarbons, are effective energy carriers and return the largest fraction of their energy density when delivered via a pipeline. However, fossil fuels are major CO2 emitters and also drive energy imports. … Because of the inherent difficulties in achieving zero-carbon emissions with fossil fuels in the transportation sector, we must consider new options. The REFUEL program seeks to address these challenges by developing CNLFs that provide a new set of technology options for storing renewable energy in CNLFs, and delivering it economically and effectively when and where it is needed.—DE-FOA-0001562
ARPA-E provided some representative examples of the types of hydrogen-rich liquid fuels that would be responsive to the FOA (only as examples, not as an exhaustive list). These include:
Ammonia (NH3). Modern Haber-Bosch plants, using hydrogen generation by SMR, release about 1.6 – 1.8 ton CO2 per ton of NH3 of which only 0.95 ton comes from the SMR process and the rest from heating and pressurization needs. Energy consumption for NH3 production using SMR varies from 7.8 to 10.5 MWh per ton of NH3 (including feedstock, which accounts for 80% of energy).
A potentially greener technology option of using hydrogen from water electrolysis requires 9.5 MWh to make 1 metric ton NH3 (of which 8.9 MWh comes from hydrogen production, assuming 50.2 kWh/kg H2). Solid-state electrochemical ammonia synthesis, a possible alternative to the Haber-Bosch process, has potentially lower energy input and operational pressure and temperature thus simplifying the balance of plant, and could be cost competitive as long as the reaction rate is significantly increased.
Hydrazine hydrate (N2H4·H2O). This is currently produced by oxidation of ammonia at a large scale (80,000 ton/year globally) and is therefore more expensive than ammonia. However, it has a high energy density (3.56 kWh/L), is easy to handle (freezing point -51.7 °C, flash point 74 °C) and, if low-cost synthetic methods are developed, may fit the technical targets of the FOA.
To accomplish wide-scale implementation of CNLFs, technological advances in both the production and conversion of this fuel would need to be achieved. An example of a non-toxic substitute for hydrazine with low carbon footprint is carbohydrazide (CH6N4O). Carbohydrazide has been used as a fuel in a fuel cell with an OCV 1.65V.
Carbon-containing CNLFs. There are numerous examples of carbon-containing CNLFs that would fit APRA-E’s targets synthetic gasoline or diesel fuel, alcohols, and dimethyl ether. The requirements are that the carbon is directly taken from the atmosphere or another sustainable CO2 source and that the fuel is produced in a one-pot chemical or electrochemical process.
Current processes for production of synthetic fuels such as Fischer- Tropsch process are multi-step, very capital intensive and eventually not economical. Reducing the process complexity may allow increased efficiency and lower costs.
SBIR/STTR. Under REFUEL, ARPA-E will allocate up to $5 million to small businesses through its Small Business Innovation Research (SBIR) and Small Business Technology Transfer (STTR) program, with up to $25 million made available to all applicants.