For the alternative fuel sometimes referred to as "electrofuel", see Metal fuel.
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Electrofuels, also known as e-fuels, are a class of synthetic fuels which function as drop-in replacement fuels for internal combustion engines. They are manufactured using captured carbon dioxide or carbon monoxide, together with hydrogen obtained from water split.[1] Electrolysis is possible with both traditional fossil fuel energy sources, as well as low-carbon electricity sources such as wind, solar and nuclear power.[2]:7[3]
The process uses carbon dioxide in manufacturing and releases around the same amount of carbon dioxide into the air when the fuel is burned, for an overall low carbon footprint. Electrofuels are thus an option for reducing greenhouse gas emissions from transport, particularly for long-distance freight, marine, and air transport.[2]:9–13
The primary targets are methanol, and diesel, but include other alcohols and carbon-containing gases such as methane and butane.
Characterization
Electrofuels are hydrocarbons that are artificially synthesized from hydrogen and carbon dioxide. Carbon dioxide can be extracted from three different sources: from ambient air (direct air capture), from point sources such as power plants (carbon capture and utility) or from biomass. To maximize climate-friendly production, atmospheric capture by biomass or direct capture from the air by direct air capture are preferred.[4] When using biomass, there are different ways of getting the CO2 needed. This can be achieved by the biome production of biogas or bioethanol. In all these processes, CO2 is produced as a by-product and must then be separated and purified. In the direct air capture process, ambient air is sucked in and transferred to a sorbent, in which the carbon dioxide forms a chemical bond with an absorbent or adsorbent, separating it from the air. Subsequently, during regeneration of the sorbent, or desorption, the carbon dioxide is separated by the addition of thermal energy and prepared for further use or storage.[4]
Hydrogen can be produced in different ways. For CO2-neutral e-fuels, it is essential to produce green hydrogen.[4] With the help of renewable electricity, water can be separated into its components, hydrogen and oxygen, as part of water electrolysis.
To produce e-fuels, a synthesis gas consisting of hydrogen and carbon dioxide is provided, which is then converted into hydrocarbons in a subsequent synthesis process, which can then be used as a fuel. In the past, such synthesis processes have been carried out with other sources of carbon and hydrogen and there are therefore a number of different types of processes which could be used, e.g.:[5]
Thus, e-fuels are not primary energy sources, but secondary energy sources. They make it possible to use electric energy to produce fuels with high energy density, storage, transport and combustion properties which, due to their properties and versatility, can theoretically replace them in all possible applications. The fuels are chemically identical to the fossil counterpart and have identical properties. This similarity with fossil fuels make it possible to use them not only in the existing fleet, it is also possible to use them in use existing infrastructure in the form of sea transport, pipelines, tankers and filling station networks.[4] At the same time, the difficulties of handling hydrogen are avoided.
Electrofuels are largely seen as a supplement and eventual replacement for fuels used in transport, such as jet fuel, diesel fuel, and fuel oil.[2]
Price
According to the study “The Future Costs of Electricity-Based Synthetic Fuels” published in 2018 by Agora Verkehrswende, synthetic fuels such as e-fuels need two prerequisites in order to be able to offer a competitive price. First, high full-load hours are essential, as the plant complexes for producing e-fuels require significantly high investment costs and consequently have high fixed costs. Each additional operating hour reduces costs. According to the study, at least 3,000-4,000 full-load hours are required per year.[6]
The second important aspect is cheap electricity costs. The synthesis of e-fuels requires very large amounts of electricity and is characterized by conversion losses. In order to keep the price as low as possible, cheap renewable electricity is essential.
For this reason, the authors recommend producing in sunny and windy regions instead of using renewable electricity from off-shore wind turbines from Regions like North Sea or the Baltic Sea. Three of the regions examined provided excellent conditions and had the potential to significantly reduce the price. For instance, by utilizing PV systems in North Africa and the Middle East, the production costs of synthetic liquid fuels could reach as high as €11 cents per kilowatt-hour (€ct/kWh), equating to 0.96 euros per liter or 3.63 euros per gallon by 2030. (3,94 US-$ per Gallon based on calculations from 26 May 2024 without taxes). Another notable location, according to the authors, would be Iceland using existing geothermal energy.[6]
Similar findings were reported in the 2018 report by Prognos AG, the Fraunhofer Institute for Environmental, Safety, and Energy Technology, and the German Biomass Research Center (DBF). According to their data, by 2050, with production in the MENA region and utilizing the Fischer-Tropsch process, depending on various parameters such as interest rates, electrolysis efficiency, direct air capture costs, electricity costs, as well as investment and production costs among others, manufacturing costs could range from at least €0.70/L to €1.30/L ( 2,88 US-$ per Gallon and 5,34 US-$ per Gallon based on calculations from 26 May 2024), excluding taxes.[5]
Research
A primary source of funding for research on liquid electrofuels for transportation was the Electrofuels Program of the Advanced Research Projects Agency-Energy (ARPA-E), headed by Eric Toone.[7] ARPA-E, created in 2009 under President Obama’s Secretary of Energy Steven Chu, is the Department of Energy’s attempt to duplicate the effectiveness of the Defense Advanced Research Projects Agency, DARPA. Examples of projects funded under this program include OPX Biotechnologies’ biodiesel effort led by Michael Lynch[8] and Derek Lovley's work on microbial electrosynthesis at the University of Massachusetts Amherst,[9] which reportedly produced the first liquid electrofuel using CO2 as the feedstock.[10][11]
The first Electrofuels Conference, sponsored by the American Institute of Chemical Engineers was held in Providence, RI in November 2011.[12] At that conference, Director Eric Toone stated that "Eighteen months into the program, we know it works. We need to know if we can make it matter." Several groups are beyond proof-of-principle, and are working to scale up cost-effectively. Porsche is currently considered to be the leader on these projects with their estimated cost per gallon of efuel at forty-five dollars per gallon.[13]
Electrofuels have the potential to be disruptive if carbon-neutral electrofuels are cheaper than petroleum fuels, and if chemical feedstocks produced by electrosynthesis are cheaper than those refined from crude oil. Electrofuels also has significant potential in altering the renewable energy landscape, as electrofuels allows renewables from all sources to be stored conveniently as a liquid fuel and reducing curtailment.[3]
As of 2014[update], prompted by the fracking boom, ARPA-E's focus has moved from electrical feedstocks to natural-gas based feedstocks, and thus away from electrofuels.[14]
In 2021, Audi announced that it was working on e-diesel and e-gasoline projects.[15] British company Zero, which was founded in 2020 by former F1 engineer Paddy Lowe, has developed a process it terms 'petrosynthesis' to create sustainable fuel and has set up a development plant in Bicester Heritage business centre near Oxford.[16]
Stellantis (Important brands: are Alfa Romeo, Peugeot, Opel, Citroen and Chrysler) announced in September 2023 that it would approve the use of 28 million vehicles in Europe with Electofuels. This information came after a lengthy test process in collaboration with Saudi Aramco. 24 engine families installed in Europe since 2014 were tested for exhaust emissions, startability, engine performance, reliability, durability, oil dilution, fuel tank, fuel lines and filters, as well as fuel performance in extreme cold and high temperatures. Stellantis expects to save up to 400 million tonnes of CO2 by 2050.[17]
In 2023, a study published by the NATO Energy Security Centre of Excellence, concluded that e-fuels offer one of the most promising decarbonization pathways for military mobility across the land, sea and air domains.[18]
Efficiency
There are regions in the world with significantly higher potential for renewable energy than others. According to sources such as the eFuel Alliance, an advocacy group, the evaluation should consider not only the efficiency of the vehicle but also how much of the energy generated by the energy system can be converted into kinetic energy. However, this high potential for renewable energy often exists in regions where the demand is not as pronounced. By converting this electrical energy into liquid energy carriers, it can be more feasibly transported, as transporting liquids is easier than electricity.
Total efficiency of Mobility
Under these circumstances, according to some studies, the efficiency of internal combustion engine vehicles can significantly increase when considering the electricity generation of an energy facility in a high-potential region and comparing the full-load hours of energy facilities for both internal combustion engine vehicles and battery electric vehicles. The poor efficiency of combustion engines can be offset by increased electricity generation, according to the Karlsruhe Institute of Technology. Some favorable locations can have up to three times as many full-load hours and thus generate up to three times as much electricity as the same facility with the same capacity in other locations.
Frontier Economics found in its 2020 study that by using favorable locations with very high potential for renewable energy, internal combustion engine vehicles can achieve similar efficiency to battery electric vehicles. This similar efficiency is ensured by increased electricity production in favorable locations, which is harnessed through power-to-fuel applications. According to these study results, the efficiency ratio is not 5-7 but rather a manageable 1.6 (e.g., the figure "total efficiency of mobility").[19]
The eFuel Alliance states that "the perspective of the lack of efficiency of electrofuels is misleading as what is critical for global energy transition is not the degree of efficiency of electricity’s end usage, but rather how efficiently electricity can be produced from renewable energies, and then made usable".[20]
Criticism
Some current processes that claim to produce electrofuels are powered by electricity generated by non-renewable fossil fuels; academics have acknowledged the necessity of these methods in the early stages of electrofuel production despite their counterintuitive nature.[21]
By 2021, the European Federation for Transport and Environment, an advocacy group, advised the aviation sector needs e-kerosene to be deployed as it could substantially reduce their climate impact,[22] and similarly for shipping.[23] It also stated that electrofuel usage in cars emits two significant greenhouse gases beyond the CO2 captured for the production: methane (CH4) and nitrous oxide (N2O); local air pollution was still a concern, and it was five times less efficient than direct electrification.[24]
Classification
Europe defines a class of electrofuels called "Renewable Liquid and Gaseous Transport Fuels of Non-Biological Origin" (RFNBO), chemically the same as e-fuels in general, but with stricter requirements. The power must be made by new renewable unsubsidized power plants located in the same bidding zone as the e-fuel facility, power production and e-fuel production must occur simultaneously, and carbon sources must be certain types.[3][25]
Towards the end of 2020, Porsche announced its investment in electrofuels, including the Haru Oni project in Chile, creating synthetic methanol from wind power.[28] In December 2022, Porsche and Chilean company Highly Innovative Fuels opened the Haru Oni pilot plant in Punta Arenas, Chile, based on wind power and producing ~130 m3 of eFuel per year in the pilot phase, scaling to 55,000 m3 per year by the mid-2020s, and 550,000 m3 after another two years, to be exported through its port.[29] As of 2023 this facility can successfully produce 34,340 gallons a year with commercial applications coming later down the line.[30]
Syngas, or synthesis gas, is a mixture of hydrogen and carbon monoxide, in various ratios. The gas often contains some carbon dioxide and methane. It is principally used for producing ammonia or methanol. Syngas is combustible and can be used as a fuel. Historically, it has been used as a replacement for gasoline, when gasoline supply has been limited; for example, wood gas was used to power cars in Europe during WWII.
Gasification is a process that converts biomass- or fossil fuel-based carbonaceous materials into gases, including as the largest fractions: nitrogen (N2), carbon monoxide (CO), hydrogen (H2), and carbon dioxide (CO2). This is achieved by reacting the feedstock material at high temperatures (typically >700 °C), without combustion, via controlling the amount of oxygen and/or steam present in the reaction. The resulting gas mixture is called syngas (from synthesis gas) or producer gas and is itself a fuel due to the flammability of the H2 and CO of which the gas is largely composed. Power can be derived from the subsequent combustion of the resultant gas, and is considered to be a source of renewable energy if the gasified compounds were obtained from biomass feedstock.
Fuel efficiency is a form of thermal efficiency, meaning the ratio of effort to result of a process that converts chemical potential energy contained in a carrier (fuel) into kinetic energy or work. Overall fuel efficiency may vary per device, which in turn may vary per application, and this spectrum of variance is often illustrated as a continuous energy profile. Non-transportation applications, such as industry, benefit from increased fuel efficiency, especially fossil fuel power plants or industries dealing with combustion, such as ammonia production during the Haber process.
Alternative fuels, also known as non-conventional and advanced fuels, are fuels derived from sources other than petroleum. Alternative fuels include gaseous fossil fuels like propane, natural gas, methane, and ammonia; biofuels like biodiesel, bioalcohol, and refuse-derived fuel; and other renewable fuels like hydrogen and electricity.
Liquid fuels are combustible or energy-generating molecules that can be harnessed to create mechanical energy, usually producing kinetic energy; they also must take the shape of their container. It is the fumes of liquid fuels that are flammable instead of the fluid. Most liquid fuels in widespread use are derived from fossil fuels; however, there are several types, such as hydrogen fuel, ethanol, and biodiesel, which are also categorized as a liquid fuel. Many liquid fuels play a primary role in transportation and the economy.
The hydrogen economy is an umbrella term for the roles hydrogen can play alongside low-carbon electricity to reduce emissions of greenhouse gases. The aim is to reduce emissions where cheaper and more energy-efficient clean solutions are not available. In this context, hydrogen economy encompasses the production of hydrogen and the use of hydrogen in ways that contribute to phasing-out fossil fuels and limiting climate change.
Energy is sustainable if it "meets the needs of the present without compromising the ability of future generations to meet their own needs." Definitions of sustainable energy usually look at its effects on the environment, the economy, and society. These impacts range from greenhouse gas emissions and air pollution to energy poverty and toxic waste. Renewable energy sources such as wind, hydro, solar, and geothermal energy can cause environmental damage but are generally far more sustainable than fossil fuel sources.
A fossil fuel power station is a thermal power station which burns a fossil fuel, such as coal, oil, or natural gas, to produce electricity. Fossil fuel power stations have machinery to convert the heat energy of combustion into mechanical energy, which then operates an electrical generator. The prime mover may be a steam turbine, a gas turbine or, in small plants, a reciprocating gas engine. All plants use the energy extracted from the expansion of a hot gas, either steam or combustion gases. Although different energy conversion methods exist, all thermal power station conversion methods have their efficiency limited by the Carnot efficiency and therefore produce waste heat.
The methanol economy is a suggested future economy in which methanol and dimethyl ether replace fossil fuels as a means of energy storage, ground transportation fuel, and raw material for synthetic hydrocarbons and their products. It offers an alternative to the proposed hydrogen economy or ethanol economy, although these concepts are not exclusive. Methanol can be produced from a variety of sources including fossil fuels as well as agricultural products and municipal waste, wood and varied biomass. It can also be made from chemical recycling of carbon dioxide.
Synthetic fuel or synfuel is a liquid fuel, or sometimes gaseous fuel, obtained from syngas, a mixture of carbon monoxide and hydrogen, in which the syngas was derived from gasification of solid feedstocks such as coal or biomass or by reforming of natural gas.
Renewable natural gas (RNG), also known as biomethane, is a renewable fuel and biogas which has been upgraded to a quality similar to fossil natural gas and has a methane concentration of 90% or greater. By removing CO2 and other impurities from biogas, and increasing the concentration of methane to a level similar to fossil natural gas, it becomes possible to distribute RNG via existing gas pipeline infrastructure. RNG can be used in existing appliances, including vehicles with natural gas burning engines (natural gas vehicles).
An integrated gasification combined cycle (IGCC) is a technology using a high pressure gasifier to turn coal and other carbon based fuels into pressurized gas—synthesis gas (syngas). It can then remove impurities from the syngas prior to the electricity generation cycle. Some of these pollutants, such as sulfur, can be turned into re-usable byproducts through the Claus process. This results in lower emissions of sulfur dioxide, particulates, mercury, and in some cases carbon dioxide. With additional process equipment, a water-gas shift reaction can increase gasification efficiency and reduce carbon monoxide emissions by converting it to carbon dioxide. The resulting carbon dioxide from the shift reaction can be separated, compressed, and stored through sequestration. Excess heat from the primary combustion and syngas fired generation is then passed to a steam cycle, similar to a combined cycle gas turbine. This process results in improved thermodynamic efficiency, compared to conventional pulverized coal combustion.
Waste-to-energy (WtE) or energy-from-waste (EfW) refers to a series of processes designed to convert waste materials into usable forms of energy, typically electricity or heat. As a form of energy recovery, WtE plays a crucial role in both waste management and sustainable energy production by reducing the volume of waste in landfills and providing an alternative energy source.
Renewable fuels are fuels produced from renewable resources. Examples include: biofuels, Hydrogen fuel, and fully synthetic fuel produced from ambient carbon dioxide and water. This is in contrast to non-renewable fuels such as natural gas, LPG (propane), petroleum and other fossil fuels and nuclear energy. Renewable fuels can include fuels that are synthesized from renewable energy sources, such as wind and solar. Renewable fuels have gained in popularity due to their sustainability, low contributions to the carbon cycle, and in some cases lower amounts of greenhouse gases. The geo-political ramifications of these fuels are also of interest, particularly to industrialized economies which desire independence from Middle Eastern oil.
The Glossary of fuel cell terms lists the definitions of many terms used within the fuel cell industry. The terms in this fuel cell glossary may be used by fuel cell industry associations, in education material and fuel cell codes and standards to name but a few.
Landfill gas utilization is a process of gathering, processing, and treating the methane or another gas emitted from decomposing garbage to produce electricity, heat, fuels, and various chemical compounds. After fossil fuel and agriculture, landfill gas is the third largest human generated source of methane. Compared to CO2, methane is 25 times more potent as a greenhouse gas. It is important not only to control its emission but, where conditions allow, use it to generate energy, thus offsetting the contribution of two major sources of greenhouse gases towards climate change.
Carbon Recycling International (CRI) is an Icelandic limited liability company which has developed a technology designed to produce renewable methanol, also known as e-methanol, from carbon dioxide and hydrogen, using water electrolysis or, alternatively, hydrogen captured from industrial waste gases. The technology is trademarked by CRI as Emissions-to-Liquids (ETL) and the renewable methanol produced by CRI is trademarked as Vulcanol. In 2011 CRI became the first company to produce and sell liquid renewable transport fuel produced using only carbon dioxide, water and electricity from renewable sources.
Carbon-neutral fuel is fuel which produces no net-greenhouse gas emissions or carbon footprint. In practice, this usually means fuels that are made using carbon dioxide (CO2) as a feedstock. Proposed carbon-neutral fuels can broadly be grouped into synthetic fuels, which are made by chemically hydrogenating carbon dioxide, and biofuels, which are produced using natural CO2-consuming processes like photosynthesis.
Power-to-gas is a technology that uses electric power to produce a gaseous fuel.
E-diesel is a synthetic diesel fuel for use in automobiles. Currently, e-diesel is created at two sites: by an Audi research facility Germany in partnership with a company named Sunfire, and in Texas. The fuel is created from carbon dioxide, water, and electricity with a process powered by renewable energy sources to create a liquid energy carrier called blue crude which is then refined to generate e-diesel. E-diesel is considered to be a carbon-neutral fuel as it does not extract new carbon and the energy sources to drive the process are from carbon-neutral sources.
↑ Biello, David (March 20, 2014). "Fracking Hammers Clean Energy Research". Scientific American. Retrieved April 14, 2014. The cheap natural gas freed from shale by horizontal drilling and hydraulic fracturing (or fracking) has helped kill off bleeding-edge programs like Electrofuels, a bid to use microbes to turn cheap electricity into liquid fuels, and ushered in programs like REMOTE, a bid to use microbes to turn cheap natural gas into liquid fuels.
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