Fuelling a Clean Future: A Systematic Review of Techno-Economic and Life Cycle Assessments in E-Fuel Development

Abstract

The transition to sustainable energy has ushered in the era of electrofuels (e-fuels), which are synthesised using electricity from renewable sources, water, and CO₂ as a sustainable alternative to fossil fuels. This paper presents a systematic review of the techno-economic (TEA) and life cycle assessments (LCAs) of e-fuel production. We critically evaluate advancements in production technologies, economic feasibility, environmental implications, and potential societal impacts. Our findings indicate that while e-fuels offer a promising solution to reduce carbon emissions, their economic viability depends on optimising production processes and reducing input material costs. The LCA highlights the necessity of using renewable energy for hydrogen production to ensure the genuine sustainability of e-fuels. This review also identifies knowledge gaps, suggesting areas for future research and policy intervention. As the world moves toward a greener future, understanding the holistic implications of e-fuels becomes paramount. This review aims to provide a comprehensive overview to guide stakeholders in their decision-making processes.

1. Introduction

Over the past several decades, global conversations and strategies have increasingly focused on sustainability and environmental conservation [1]. This heightened interest has been driven by mounting scientific evidence revealing the detrimental impacts of human activities on Earth’s ecosystems, climate, and biodiversity [2]. A significant portion of these adversities can be attributed to the relentless emission of greenhouse gases (GHGs) into the atmosphere [3]. At the core of the climate challenge is the combustion of fossil fuels, which is deeply embedded in modern economies across sectors such as transportation, energy generation, and industrial activities [4,5,6]. Fossil fuel combustion releases substantial amounts of carbon dioxide (CO₂), methane (CH₄), and other GHGs [7,8]. Achieving emissions reduction goals is inherently tied to reducing CO₂ emissions [9]. These gases trap heat in the Earth’s atmosphere, leading to global warming and driving the cascade of changes known as climate change [10].

Aviation accounts for almost 3% of global CO₂ emissions, and aviation’s emissions are rising as other industries’ emissions decline [11]. Figure 1 illustrates global carbon dioxide emissions from aviation. Highlighting the magnitude of this challenge, the International Energy Agency (IEA) has presented alarming data: the energy sector alone is responsible for nearly three-quarters of global GHG emissions [12,13]. This paints a concerning picture, considering the vast array of other sectors and their cumulative contribution to this global challenge [14,15]. A particularly pressing concern is the rapid expansion of the global transportation sector [16,17]. Forecasts suggest that by 2050, the number of vehicles on the planet will have doubled [18,19]. This escalation not only is indicative of an increased demand for mobility solutions but also represents an enormous surge in energy consumption and associated carbon emissions [20,21]. With current technologies and fuels, this growth will likely lead to an unsustainable increase in GHG emissions, exacerbating the already severe impacts of climate change [22,23]. Amidst this challenging backdrop, the emergence of e-fuels offers a glimmer of hope [24,25].

Sustainable aviation fuel (SAF) emerges as a more accessible intermediate-term solution for reducing the aviation industry’s carbon footprint compared to other renewable energy such as hydrogen and batteries [26]. This accessibility is primarily driven by SAF’s compatibility with existing aircraft engines and fuel infrastructure, allowing for a seamless transition without the need for extensive modifications. Unlike hydrogen, which requires significant advancements in storage and handling technology due to its low energy density and cryogenic requirements, SAF can be integrated into current fuelling systems with minimal changes. Batteries, on the other hand, face limitations in energy density and weight, making them less viable for long-haul flights where significant power and endurance are essential. Figure 2 compares the technological potential of renewable aviation fuels. MPP’s Aviation Transition Strategy outlines a shared vision for a low-carbon future in the industry, with milestones for both 2050 and the near term. For instance, it specifies that 10–15% of jet fuel demand must be met with SAFs by 2030 to initiate the transition to net-zero emissions in the 2030s and 2040s [27]. SAF, derived from renewable sources such as biomass, waste oils, and synthetic processes, offers a practical and scalable approach to decarbonising aviation. It leverages existing supply chains and technologies while providing a substantial reduction in greenhouse gas emissions, thus serving as a critical bridge towards more sustainable aviation in the near future.

E-fuels are all fuels in gas or liquid form that are produced from renewable (solar or wind power, for example) or decarbonised electricity. These fuels are sometimes referred to as electrofuels because they involve the use of electricity (“electro-”) to generate the necessary chemical transformations. E-fuels are synthetic fuels produced by using renewable energy to convert carbon dioxide (CO₂) and hydrogen (often derived from water electrolysis) into liquid or gaseous hydrocarbons, which is also called the power-to-liquids (PtL) pathway. The synthesised hydrocarbon e-fuels can be created by combining hydrogen (often produced using renewable energy sources) with carbon dioxide directly captured from the atmosphere [28] or biomass/biogas. The proposition of e-fuels is truly transformative: they have the potential to deliver the high-energy demands of modern societies while ensuring a significantly lower carbon footprint [29]. In addition, their capacity to serve as a direct substitute for conventional fuels in existing infrastructures, without the need for extensive modifications, makes them especially attractive [30,31].

E-fuels are not merely another alternative energy source. They represent a potential cornerstone in the next phase of our global energy transition, as illustrated in Figure 3. By harnessing the power of e-fuels, humanity could pave the way towards a more sustainable energy landscape for carbon-neutral or even carbon-negative solutions, which would drastically reduce our carbon emissions and mitigate the worst effects of climate change [32]. Historically, the concept of e-fuels is rooted in the Fischer–Tropsch process, a method developed in the 1920s to convert coal into liquid hydrocarbons [33]. While the principle of synthesising liquid fuels from non-petroleum sources is not new, the integration of modern renewable energy sources to power such processes is a relatively recent development [34]. Over the past two decades, a burgeoning body of research has investigated the potential of e-fuels [35]. Initial studies were primarily focused on the technical feasibility of producing e-fuels [36]. Advances in direct air capture (DAC) technologies, as investigated by Gupta et al. (2017), have opened up the possibility of sourcing carbon dioxide directly from the atmosphere, providing a truly sustainable carbon source [37]. The economic viability of e-fuels has also been a topic of significant interest [38]. Cost analyses associated with the technologies employed, such as those conducted by Becker et al. (2019), have aimed to benchmark the production costs of e-fuels against conventional fossil fuels and other renewable alternatives [39]. These studies highlight both the challenges and potential cost reduction pathways, emphasising the role of technological innovation and economies of scale [40].

Life cycle assessments (LCAs) have been paramount from an environmental perspective [41]. These comprehensive studies, exemplified by recent works like that of Yang et al. (2022), evaluate not only the carbon footprint but also a broad spectrum of environmental impacts, from resource extraction to end-of-life considerations [42]. Such LCAs have provided nuanced insights into the genuine sustainability credentials of e-fuels, considering varied production pathways in methodologies and regional contexts [43]. However, despite these numerous and valuable individual research endeavours, there remains an evident gap: a holistic and integrated analysis that bridges techno-economic evaluations (TEAs) with life cycle assessments (LCAs), providing a comprehensive overview of e-fuel production [44,45,46]. Our study seeks to address this lacuna. By amalgamating insights from both a TEA and LCAs, we aim to provide an integrated perspective on e-fuels, offering a multifaceted understanding of their feasibility, costs, and environmental implications.

Following this enriched introduction, Section 2 delves into our systematic review methodology. Section 3 unpacks the result of the TEA and LCAs, also exploring the charting data based on production methods, including the most economically viable and environmentally friendly methods. Section 4 is dedicated to the TEA, presenting the production technologies and their efficiencies, capital and operational expenditures, break-even points, and return-on-investment calculations across e-fuel production pathways and LCA, presenting associated multifarious environmental impacts. In addition, Section 4 also outlines economic feasibility and technological challenges, strategic actions and policy implications, and research gaps and directions, integrating the insights from the previous sections. Conclusions are drawn in Section 5, with reflections on the broader implications and prospective research trajectories.

2. Methodology

2.1. Search Strategy

This study undertook a methodical evaluation of a TEA and LCAs pertaining to the generation of e-fuels, via hydrogen, biomass flue, and atmospheric carbon dioxide through electrolysis and direct air capture (DAC). We meticulously adhered to the bibliometric method, a quantitative method used to analyse and evaluate the scholarly literature, including publicly accessible scientific publications, articles, journals, and other types of academic content. The goal of bibliometrics is to assess the impact, influence, and relationships within the academic literature. This method relies on statistical and mathematical analyses to derive meaningful insights from patterns and trends in published works, and it includes the formulation of a precise search string, establishment of selection criteria, and meticulous data extraction. To ensure robust and scientifically credible outcomes, an extensive search was conducted across four prominent databases, Google Scholar, Web of Science, Scopus, and PubMed, which were combined with Energy Citation Database (ECD) and the International Nuclear Information System (INIS). The former, i.e., ECD, is owned by the US Department of Energy (US-DOE), and the latter, i.e., the INIS database, is run by the International Atomic Energy Agency (IAEA) and contains a large number of nuclear research papers collected from the member countries including the US, Japan, Germany, and France, and it hosts one of the world’s largest collections of published information on the peaceful uses of nuclear science and technology.

This review article aimed to systematically collate data including keywords, abstracts, and titles from pertinent journal articles and global conference proceedings spanning a decade from 2013 to 2024. The database search was guided by a carefully curated set of keywords: (“techno-economic analysis” OR “techno-economic assessment”) AND (“life cycle analysis” OR “life cycle assessment”) AND (e-fuel OR liquid hydrocarbon) AND (synthetic fuel OR sustainable aviation fuel). These keywords were feature-engineered after reviewing multiple papers and journal articles that focused on the techno-economic and life cycle assessments of e-fuel production using hydrogen and atmospheric carbon dioxide. To uphold the integrity of our bibliometric method, only peer-reviewed journal articles, publicly accessible technical reports, and relevant conference papers published in academic journals were considered.

2.2. Inclusion and Exclusion Criteria

During the initial search phase, we identified 156 scientific articles from the database query and last checked 5 July 2024. After eliminating 40 duplicates and disqualifying 41 records using automated tools, along with an additional 13 for various reasons, we narrowed down the selection to 62 publications for closer examination. Further scrutiny led to the exclusion of 12 more, and efforts were made to retrieve the remaining 50 reports. Unfortunately, four of these reports could not be retrieved, leaving us with 46 for a detailed eligibility assessment. Screening of titles, abstracts, and keywords resulted in the inclusion of 23 scientific articles. Subsequent in-depth full-text eligibility screening concluded with the selection of 22 articles for comprehensive analysis, including the following:

• Articles that specifically explored e-fuel production utilising H₂ and atmospheric CO₂.
• Studies offering a TEA or an LCA of the e-fuel production process.
• In addition, studies that were published in English during the years 2013 to 2024.

Conversely, exclusions were made based on the following:

• Articles that mainly focused on alternative renewable fuels without specifically addressing e-fuels.
• Publications that were deficient in substantial data or lacked clarity in their methodology.

The process of the literature search and the presentation of findings were conducted in alignment with the directives laid out in the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) Statement summarised in Figure 4 [47,48,49,50].

2.3. Data Analysis

The extracted data for TEA and LCA studies were synthesised and compared to provide a holistic understanding of the e-fuels production process. This process encompassed charting data based on production methods, highlighting the most economically viable methods, and identifying the most environmentally friendly approaches. The selected papers underwent analysis to extract details regarding production technologies and their efficiencies, capital and operational expenditures, as well as break-even points and return-on-investment calculations. LCA data were extracted, with a focus on raw material acquisition, production, use-phase emissions, and end-of-life considerations. In both analyses, a meta-analysis was conducted to synthesise the data and provide an aggregated result. The synthesised data helped identify areas with limited research or conflicting results through a gap analysis. This step is essential for highlighting areas requiring more in-depth study and guiding future research directions. To ensure the reliability of our findings, a panel of experts in the field of e-fuels were consulted. Their feedback was solicited, and the review was refined based on their valuable input.

3. Results and Findings from the Existing Literature

This review encapsulates findings from 34 case studies featured in 23 articles, extensively examining the TEAs and LCAs of e-fuel production involving H₂ and atmospheric CO₂. The distribution of these studies is visually represented in Figure 5, showcasing a pie chart based on continents. Notably, a substantial majority of the investigations concentrate on European countries, constituting a significant 59% of the total cases, which amounts to 20 out of the 34 studies. Following this, North America emerges with an 11% share, while both Asian and South American studies each contribute 9%. Africa and Australia round out the distribution with equal shares of 6%. This continental breakdown underscores the regional focus of current research efforts, emphasising Europe’s prominent role in advancing the understanding of e-fuel production dynamics.

Figure 6 provides a detailed breakdown of selected countries contributing to the research landscape. The distribution is as follows: Germany (6/34), Italy (5/34), Sweden (2/34), and 1 each from Denmark, Netherlands, the UK, Turkey, Norway, Iceland, and others within the EU. For the North American continent (7/34), contributions come from the USA (3/7), Chile (2/7), and 1 each from Canada and Argentina. In Asia, with 3/34, the country-wise distribution of studies is equally distributed from China, Saudi Arabia, and the UAE. Examining economic comparisons of e-fuels in Africa (2/34), one each was found from Namibia and Egypt. Australia with two such studies is comparatively modest.

The primary energy sources in Europe are dominated by local renewables, with photovoltaic accounting for 25% (5/20) and wind contributing 15% (3/20). Furthermore, a significant portion, 40% (8/20), is derived from a combination of solar, PV, and hydro. Geothermal and nuclear sources collectively contribute 10% (2/20), while fossil and biomass sources make up 5% (1/20), along with 5% (1/20) from unspecified sources. In Asia, primary energy sources encompass a blend of local renewables and fossil fuels, with photovoltaic accounting for two out of three cases. Additionally, a single case involves a mix of natural gas, crude oil, and coal. Africa, while making a modest contribution, relies on solar and PV sources (2/2). Refer to Figure 6 for a visual representation of these distributions, and for a concise overview of previous research findings on the techno-economic analysis of e-fuel production, please consult Table 1. In North America (7/34), which includes North America (4/7) and South America (3/7), primary energy sources are diversified, combining fossil, nuclear, solar, and wind electricity [49].

Australia holds a prominent position as one of the world’s major exporters of renewable energy. The country’s primary energy sources draw from a combination of factors, notably high wind speeds and abundant solar radiation, constituting two out of two cases. Australia’s role as a significant energy exporter plays a pivotal role in the global energy landscape. Notably, hydrogen production solely from solar panels covering 3% of Australia’s land area has the potential to offset 10 times Germany’s non-electricity energy consumption. As hydrogen technologies continue to advance and achieve higher technological readiness levels, costs are consistently decreasing across all levels. However, the cost of storage and transportation distances remains a crucial consideration for Australia’s renewable energy export. Given that the global move towards defossilisation is a collective challenge, further studies are imperative, emphasising the need for global cooperation [50].

3.1. Techno-Economic Analysis (TEA)

The techno-economic analysis (TEA) is a vital component in evaluating the viability of e-fuels, providing insights into their economic feasibility, cost-effectiveness, and environmental impacts. This section systematically reviews various TEA assessments for e-fuels, exploring innovative production pathways, cost reduction strategies, and sustainability metrics. By examining methods such as catalytic deoxygenation, hydrothermal gasification, direct air capture, and power-to-liquid processes, this review highlights the economic and environmental potentials of e-fuels. The findings aim to inform policy decisions, guide industry practices, and identify areas for further research in the development of sustainable fuel alternatives.

In the quest to develop e-fuels, the techno-economic analysis (TEA) serves as a crucial tool in assessing the feasibility, cost-effectiveness, and environmental impact of various production pathways. This section reviews relevant TEA assessments regarding the development of e-fuels. It includes various methods such as the integration of catalytic deoxygenation and hydrothermal gasification methods for producing hydrogen gas from esters and fatty acids, emphasising tall oil fatty acid (TOFA) [51]; direct air capture (DAC) combined with hydrogenation of CO₂ to produce synthetic methane, as investigated by Tregambi et al. [52]; and the integration of DAC, offshore wind farms, and electrolysis for producing power-to-liquid (PtL) SAF by Rojas-Michaga and Michailos [51] in the UK.

In a recent comprehensive study conducted in 2023, Umenweke et al. [51] developed a detailed TEA concentrating on integrated catalytic deoxygenation and hydrothermal gasification methods. The primary aim was to produce H₂ gas from esters and fatty acids, with a specific emphasis on tall oil fatty acid (TOFA). Notably, the study revealed that the minimum fuel selling price (MFSP) for scenario 2 was USD 0.39/L, a figure lower than the USD 0.62/L observed in scenario 1. A pivotal recommendation stemming from the study was the imperative need for concentrating efforts on process optimisation and model improvement [51]. This optimisation would be particularly advantageous, especially if guided by the inclusion of both experimental data and kinetics data. The overarching theme of the analysis cantered on the TEA and LCA impacts associated with sustainable aviation fuel (SAF) production, utilising integrated catalytic deoxygenation and hydrothermal gasification methods. The findings indicate that optimising these processes could significantly reduce the minimum fuel selling price (MFSP), underscoring the importance of incorporating experimental and kinetics data for further improvements.

Direct air capture (DAC) is widely investigated to capture CO₂ emissions from decentralised sources [52]. As an alternative to geological storage, CO₂ from DAC can be reacted with H₂ from water electrolysis driven by renewable energy to produce synthetic CH₄, increasing the penetration of renewable energies and leading to a circular carbon economy [52]. In DAC methanation, Tregambi et al. [52] estimated the total project cost (TPC), levelised cost of CO₂ removal (LCCR), and levelised cost of methane (LCOM). The process involved the hydrogenation of CO₂ sourced from DAC, H₂ generated from water electrolysis, and renewable PV sources, culminating in the production of synthetic methane (CH₄). The results indicated that cities with varying solar energy distribution might have to invest heavily in H₂ storage tanks. The major cost contributors were found to be the electrolyser, followed by the PV field, H₂ storage, and reactors [52]. The LCOM was estimated at 4.9–8.2 USD·kg_CH4⁻¹ using integration with the DAC plant investigated, while it was 3.1–3.9 USD·kg_CH4⁻¹ when utilising integration with point-source carbon capture. The LCOM analysis found that the DAC process costs more than the prevailing market price of methane, suggesting the need for technical improvements or economic incentives to increase the competitiveness of this power-to-gas technology [52]. The study presents a promising yet currently expensive option, highlighting the need for technical advancements and economic incentives.

A recent TEA and LCA study for carbon conversion, hydrogen conversion, and power-to-liquids (PtL) efficiency conducted by Rojas-Michaga, Michailos [51] in the UK estimated a minimum jet fuel selling price (MJSP) of 5.16 GBP/kg, which is approximately 6.53 USD/kg (GBP 1 = USD 1.26992, 5 July 2024). In the study, the system integrated a DAC unit, an offshore wind farm, an alkaline electrolyser, and a refinery plant. These were used to produce PtL SAF. It was found that the SAF price is highly sensitive to electricity and DAC costs. The carbon hydrogen conversions were recorded at 88% and 39.16%, respectively, and the PtL efficiency stood at 25.6% [53]. Although this obtained MJSP is prohibitively expensive, given that the weekly averaged commercial jet fuel price ending the week of 5 July 2024 was 805.82 USD/t, which converts at 0.81 USD/kg, the LCA of the system showed that the global warming potential (GWP) of the SAF produced through this PtL pathway is lower than that of fossil jet fuel, and it can meet existing aviation emissions reduction targets, such as the UK SAF mandate [53]. The GWP is, however, sensitive to the carbon footprint of the electricity, indicating its dependence on the energy source. This again suggests the need for technical improvements or economic incentives.

Another TEA study by Ravi and Mazumder [52] employed the methanol-to-olefin/methanol-to-gasoline and diesel (MTO-MOGD) process, electrolysis, and DAC. Synthetic hydrocarbon was produced using CO₂ and green hydrogen. The economic implications of the study were primarily focused on the potential for decarbonising road transport. The MFSP for e-gasoline was determined to be 3.24 USD/litre, and for e-diesel, it was 2.89 USD/litre when powered by solar energy. The levelised cost of electricity (LCOe) ranged from 379 to 564 USD/MWh, indicating that e-fuels can emerge as a carbon-neutral option, especially with the implementation of fossil CO₂ taxation. In the study aimed at the technical and economic feasibility of turning bio-oil to naphtha, kerosene, glycerol, and diesel, Pipitone, Zoppi [53] used different methods including hydrogenation, electrolysis, and aqueous-phase reforming (APR) in the assessment using feedstocks such as palm oil and H₂. APR led to an increase of 6.6% in the fixed capital investment. However, it resulted in a 22% decrease in direct manufacturing costs. The calculated MFSP based on this study was 1.84 USD/kg per Pipitone, Zoppi [53]. It should be noted that the use of waste oils as feedstock can be challenging as they might contain higher fatty acids and lower triglycerides.

The economic feasibility and environmental impact study conducted by Habermeyer and Papantoni [54] focused on technical process evaluation, mass and energy balances, production cost estimation, and sensitivity analysis related to European SAF production potential. Utilising methods like Fischer–Tropsch and electrolysis with the Aspen plus^® (V10) computer software, the study found that only Norway and Sweden were suitable as PtL production sites in 2020 based on their grid mix. In the study, MFSP was found equal to 1.84 USD/kg, which is 17% lower than the one derived from conventional configurations of 2.20 USD/kg by Habermeyer and Papantoni [54]. In a distinct TEA study on e-fuels production from CO₂ and low-carbon H₂ conducted by Delgado and Cappello [55], the process involved high-temperature electrolysis, reactants compression, RWGS reaction, Fischer–Tropsch process, utilities, carbon conversion and energy efficiency, hydrocracking, and other processes. The study revealed promising results, particularly with the modelled Fischer–Tropsch process achieving a 99% carbon conversion rate through the recycling of CO₂ and oxycombustion, with a process energy efficiency of 70%. MFSP values were calculated at 0.95 USD/L, 0.74 USD/L, and 0.70 USD/L of FT fuel mix for nuclear power plant capacities of 100, 400, and 1000 MWe, respectively. The study revealed a high sensitivity of SAF costs to electricity and DAC expenses.

A TEA was conducted by Tozlu et al. [56], who utilised thermodynamic and economic analysis methods. The focus was on biogas-to-methanol conversion, where biogas was purified using water washing. Hydrogen was produced from a PEM electrolyser powered by solar PV. A hybrid system was then employed to produce methanol. The study concluded that the power required for methanol production was 2923 kW, predominantly sourced from the PEM system. Daily methanol production was found to be 1674 kg, with the associated costs for electricity, hydrogen, and methanol being 0.043 USD kWh⁻¹, 3.156 USD kg⁻¹, and 0.693 USD kg⁻¹, respectively. The process was found to have feasible methanol production costs with reasonable investment prospects.

An analysis of the future context of e-fuels in Europe was conducted by Romo and Martínez [28] with respect to their safety, environmental implications, societal acceptance, and regulatory barriers. The institutional economics theory was used to analyse the environmental governance system framework around the implementation of carbon capture and utilisation (CCU) and e-fuels. The economic assessment highlighted the potential economic benefits and challenges associated with H₂-based e-fuel production methodologies.

A comprehensive techno-economic assessment was carried out by Sollai, Porcu [57] for a power-to-fuel plant designed to produce e-methanol from green hydrogen and captured CO₂. The study served as a pre-feasibility analysis for a facility aiming to produce 500 kg/h of renewable methanol. The resultant levelised cost of methanol (LCoM) was found to be 960 USD/t (about 175 USD/MWh). Although currently not economically competitive, prospects indicate potential economic viability due to shifting European policies.

The PESTEL analysis, which concentrated on diverse economic, technological, and environmental factors, emphasised the potential of blue hydrogen as an economically viable short-term solution. Insights revealed the influential variables on synthetic fuel pricing and their intertwined relationships [58].

A technical and economic analysis focused on the potential of waste-to-methanol and power-to-methanol processes, conducted by Salladini, Borgognga [59]. The feasibility study highlighted the innovation of combining the power-to-methanol process with MSW (municipal solid waste) gasification as aligning with energy transition and circular economy principles. The anticipation of an increase in renewable power soon could render the hybrid method more economically appealing.

In 2020, Drünert, Neuling [60] presented key techno-economic indicators for the production of power-to-liquid (PtL) kerosene. They employed DAC and electrolysis methodologies using CO₂ and water as feedstock. The study emphasised the significant impact of local CO₂ sources on PtL. There is a projection of a need for an additional 48–745 TWh of renewable electricity for scenarios spanning 2030–2050. Notably, the average fuel production costs are expected to range from 2.3 to 3.3 USD/kg in 2030, decreasing to 1.8–3.1 USD/kg by 2050. The research highlighted the importance of sustainable CO₂ sources and the achievement of renewable electricity development targets.

Furthermore, in 2023, Italy underwent a comprehensive technical and economic analysis of producing synthetic kerosene from green H₂ and DAC CO₂ by Colelli, Segneri [61]. Their methodology combined hydrogen derived from water electrolysis, CO₂ capture, RWGS, and FT synthesis. They performed sensitivity analyses and process evaluations. Results from both indirect and direct processes indicated production rates of 66.18 bbl/d and 38.46 bbl/d, respectively. Additionally, the product cost varied significantly, ranging from 460–1435 USD/bbl for the indirect process to 752–2364 USD/bbl for the direct process. The study pinpointed a strong dependency on power energy and hydrogen prices.

In 2021, Sweden also delved into a techno-economic assessment projected for the 2020–2050 timeline. Using the Fischer–Tropsch (FT), HTL, and PTL (with a Python 3.9 MILP model) methods, they focused on producing RJF from lignocellulosic biomass and captured CO₂ [62]. The study projected an increase in total RJF production, attributed to the blending ratio. By 2030–2050, they anticipate RJF production to be in the range of 3.85–16.87 TJ. Moreover, the HTL and PTL jet fuel production costs vary, with prices anticipated between 24.2–25.4 SEK/litre or 5–5.5 USD/litre and 16.7–22.0 SEK/litre or 3.5–4.5 USD/litre, respectively. Significantly, revenue generated from by-products could potentially make HTL and PTL methodologies price-competitive.

A techno-economic assessment (TEA) by Zimmermann, Gençer [63] revealed critical challenges related to the cost and market potential of e-fuels. Notably, OME3-5 e-fuels exhibit significantly higher cost of goods manufactured per gigajoule (GJ) compared to conventional diesel fuel available at gas stations in Germany. Additionally, the study indicated that less than 38.4% of electricity can be efficiently stored in e-fuel, based on lower heating value. The most substantial economic barriers identified in the analysis are associated with electricity consumption and the cost of electrolyser stacks rather than the OME conversion cost. Even with a significant reduction in electricity or electrolyser prices, the OME3-5 anhydrous pathway would not be economically competitive under current conditions. This emphasises the need for significant advancements in reaction processes and system improvements to enhance the economic viability of OME3-5 e-fuels in the future.

In 2019, Campion, Shapiro-Bengtsen [64] provided valuable insights into the costs and life cycle of greenhouse gas (GHG) emissions associated with the production of electrolytic hydrogen and subsequent conversion to ammonia (e-ammonia). The study highlights the critical role of electricity sources in determining the environmental footprint of e-ammonia production. Notably, the research underscores the influence of the grid’s electricity sources, with North Chile using a substantial 58% of grid electricity and emitting 183 gCO_2e/MJNH₃, whereas Denmark, with a higher share of green electricity, emits only 109 gCO_2e/MJNH₃ using 100% grid electricity to optimise the sustainability of e-ammonia production.

Cames, Chaudry [65] highlight a critical concern regarding the storage of CO₂ resulting from IPCC scenarios. The study emphasises that the significant volume of CO₂ requiring storage could potentially create a shortage of suitable, cost-effective, and readily available CO₂ storage sites. In this context, the analysis draws attention to the cost difference between e-fuels and direct air capture and carbon storage (DACCS) options, indicating that this difference ranges between 1.0% and 2.5% of the ticket price by 2050. Importantly, the study suggests that this cost variation is a reasonable burden for passengers to bear. Therefore, it encourages the consideration of the e-fuels option as a more consistent choice with the precautionary principle, which is a fundamental principle in environmental policy. The precautionary principle underscores the need to prioritise actions that prevent potential harm to the environment and human well-being. In essence, the study prompts a critical evaluation of the total costs, emissions, and environmental risks associated with e-fuels and DACCS to make informed decisions regarding sustainable and environmentally responsible aviation practices.

Hombach and Doré [66] focused on assessing the production costs and life cycle emissions of e-fuels produced through different electrolysis technologies and Fischer–Tropsch synthesis. The study investigated both current alkaline and future solid oxide electrolysis methods. The research aimed to provide insights into the economic feasibility and environmental impact of e-fuels as an alternative to traditional vehicle fuels. The findings suggested that e-fuel production costs, under optimistic assumptions for various parameters, were estimated to be approximately 1.17 V/leq diesel or 3.12 V ct/MJ in 2015.

The studies collectively stress the necessity for process optimisation, regulatory support, and innovative technological solutions to make SAF a viable, sustainable, and economically competitive alternative to conventional aviation fuels. Table 1 summarises and compares the processes and their associated costs of production of SAF.

3.2. Life Cycle Analysis (LCA)

Life cycle analysis (LCA) plays a pivotal role in understanding the environmental implications of e-fuels by evaluating their entire life cycle, from raw material extraction to end-of-life disposal. This section systematically reviews the LCA studies focused on e-fuels, providing insights into their greenhouse gas emissions, energy consumption, and overall sustainability. By examining various production pathways, including electrolysis, direct air capture (DAC), and Fischer–Tropsch synthesis, this review highlights the potential environmental benefits and challenges associated with e-fuels, thereby informing future research and policy decisions aimed at reducing the carbon footprint of the energy sector.

The study by Wang and Guo [67] revolved around a life cycle assessment (LCA) with a primary focus on energy consumption and GHG emissions, along with a sensitivity and uncertainty analysis. Utilising methods like direct fermentation and gasification plus fermentation, as modelled in Aspen Plus V11, ethanol-to-jet fuel (ETJ) was produced from feedstocks such as corn, cassava, and corn cob. A salient feature of this study was the revelation that there are only a few life cycle assessments of ETJs available in the context of China. The research, thus, plays a pivotal role in assisting policymakers in deciding the direction of China’s sustainable aviation fuel (SAF) evolution. A noteworthy result from the LCA showed the process had the least energy and GHG emission, registering at 370.05 KJ/MJ for jet fuel and 31.66 gCO₂eq/MJ for jet fuel. Additionally, the study revealed the potential to reduce GHG emissions by up to 21.55% when cleaner sources of electricity and heat are employed. The study encapsulated the process design and provided a holistic life cycle analysis on energy consumption and GHG emissions pertinent to jet fuel production from bioethanol.

A comprehensive life cycle assessment (LCA) was carried out alongside a techno-economic study by [51]. The LCA revealed a global warming potential (GWP) of 21.43 gCO₂eq/MJ synthetic aviation fuel (SAF) when dependent on offshore wind electricity. This GWP is significantly below the UK’s mandate, which demands a 50% emission reduction in comparison to fossil jet fuel. Additionally, the water-to-water adjusted (WtWa) water footprint was computed to be 0.480 l/MJSAF, showcasing the environmental impact of the process from a broader perspective.

The environmental feasibility of the process was evaluated, particularly focusing on the carbon footprint, by Pipitone, Zoppi [53]. The advanced scenario showed a carbon footprint of 12 g CO₂/MJSAF, which is 54% lower than conventional methods, indicating a significant improvement in environmental impact.

A life cycle analysis (LCA) study was carried out by Habermeyer, Papantoni [54] to assess the environmental impact of the methods. Based on the results, 25 Mt a⁻¹ fuel output is achievable using direct renewable electricity sources while consuming 33% forest residue. This has the potential to help the EU achieve its goal of 32% of total aviation fuel demand by SAF in 2040.

An LCA study focused on the WTW GHG emissions of FT fuels originating from electrolytic H₂ pathways and CO₂ sources, conducted by Zang, Sun [68]. By considering various process designs and system boundaries, the results showed that FT fuels have 57–65% lower WTW GHG emissions when integrated with corn ethanol production. Moreover, 45% of carbon in CO₂ was fixed in FT fuel, with an energy efficiency of 58%. Utilising sources like nuclear/solar/wind electricity, the WTW GHG emissions were reduced by a staggering 90–108% as compared to petroleum fuels.

Delgado, Cappello [55] presented a study incorporating an LCA using the GREET model. The study examined the environmental impact of electrofuels produced from CO₂ and low-carbon H₂. GHG emissions were quantified, resulting in values of 7 and −25 gCO₂e/MJ, showing a potential WTW GHG emissions reduction of at least 92%. This highlights the potential of such methods to significantly reduce GHG emissions and enhance energy security.

It was reported that by enhancing biogas content through purification, the cogeneration plant efficiency increased [56]. Additionally, the enrichment of biogas led to reduced emissions, thus ensuring a more sustainable energy production route. The life cycle implications of the methanol production process revealed significant influences from electricity prices, electrolyser capital costs, and plant capacity factors [57]. Furthermore, the study suggested that the methanol production process’s competitiveness is expected to increase in the mid-term future, driven primarily by new European policy directions.

van de Graaff [58] highlighted the environmental superiority of green hydrogen over blue hydrogen, as the former is carbon-free and does not require CO₂ storage. Further, the life cycle analysis pinpointed the need for advancements in essential processes for synthetic fuel production and stressed the potential synergy of local production combined with imported hydrogen or fuels.

From a life cycle viewpoint, the innovative process of combining the power-to-methanol process with MSW gasification presents a forward-thinking solution, valorising carbon within the MSW and decreasing dependency on fossil fuels [59]. The life cycle analysis also highlighted the potential of the hybrid scheme, which, considering future renewable energy trends and decreasing power costs, could emerge as an attractive solution in the near future.

Papantoni, Linke [69] undertook a comprehensive life cycle assessment focusing on fleet emissions and the overall climate impact. The methodology utilised involved producing hydrogen via water electrolysis followed by Fischer–Tropsch synthesis, aiming at power-to-liquid production. The study considered the environmental impacts and potential of PtL, particularly for the aviation sector. One striking result showed that PtL derived from wind energy could reduce environmental impact by up to 42%. Another noteworthy finding was the potential reduction in warming impact due to the phenomenon of contrail-induced cloudiness.

In 2018, Zimmermann, Gençer [63] focused on a life cycle analysis (LCA) of OME3-5 e-fuels produced through the anhydrous trioxane and OME1 pathways, considering inputs such as flue gas, water, electricity, and steam. OME3-5 e-fuels have been identified as a promising option for decarbonising heavy-duty transportation in the future.

Campion, Shapiro-Bengtsen [64] reported that where a substantial portion of electricity generation relies on fossil fuels, e-fuel production using renewable power demonstrates significant advantages in terms of GHG intensity. However, even with 47% renewable power in the mix, the life cycle emissions remain only 25% lower than those of traditional grey methanol. The findings indicate that the GHG footprint of e-fuels remains higher than that of grey fuels, particularly in regions with a larger share of fossil-based grid electricity. This review highlights the significance of transitioning to cleaner energy sources to optimise the sustainability of e-ammonia production.

Hombach, Doré [66] highlighted that abatement costs for e-fuels were considerably higher, ranging from 544 to 6424 V/tCO₂-eq, when compared to competing vehicle fuel technology options. Furthermore, the analysis revealed a significant improvement in e-fuel production costs and life cycle emissions by 2030, with estimates indicating 3.24 V/leq diesel and 6.63 gCO₂-eq/MJ, underscoring the potential for cost reduction and emissions mitigation in 2030.

The global quest for sustainable energy sources represents a critical challenge, and the United Nations Sustainable Development Goals (UNSDGs) offer a comprehensive framework to address this challenge. This review reveals that the application of the life cycle assessment (LCA) and techno-economic analysis (TEA) framework directly contributes to the achievement of various SDGs. For example, the LCA aligns with objectives such as promoting good health and well-being (SDG-3), ensuring clean water and sanitation (SDG-6), facilitating affordable and clean energy (SDG-7), fostering sustainable cities and communities (SDG-11), encouraging responsible consumption and production (SDG-12), supporting climate action (SDG-13), preserving life below water (SDG-14), and protecting life on land (SDG-15). Conversely, the TEA is intertwined with the realisation of other SDGs, as illustrated in Figure 7.

3.3. Charting Data: Exploring Optimal Methods Both Economically and Environmentally

A variety of e-fuel production methods have been explored globally. Some examples follow. Direct fermentation and gasification plus fermentation: used in China, this method utilises corn, cassava, and corn cob feedstocks to produce ethanol-to-jet fuel (ETJ) [67]; integrated catalytic deoxygenation and hydrothermal gasification: employed in the US, the process used esters and fatty acids as feedstocks, aiming for hydrogen gas production [70]; hydrogenation processes: various methods of hydrogenation have been utilised across multiple countries including Abu Dhabi, Italy, and Turkey, using different sources of CO₂ and H₂ to produce synthetic methane, methanol, and other e-fuels [71]; power-to-liquid (PtL) processes: both the UK and Germany have used methods involving direct air capture (DAC) units, water electrolysis, and refinery plants, targeting power-to-liquid production for jet fuel hydrocarbons [51]; and Fischer–Tropsch (FT) synthesis: utilised in several studies, spanning the US and Europe, this process has been used with various feedstocks like H₂, waste CO₂, e-hydrogen, and biomass to produce diverse e-fuels [54].

The economic viability of e-fuel production processes varies. For example, the hydrogenation of CO₂ from DAC in Abu Dhabi and Benevento indicated the electrolyser as the most expensive component, with the least cost of methane production being between 3.1 and 3.9 USD kgCH₄⁻¹ when using point-source capture [71]; the integrated catalytic deoxygenation and hydrothermal gasification in the US showcased that scenario 2 (0.39 USD/L) was more cost-effective than scenario 1 (0.62 USD/L) [68]; a study in Italy using hydrogenation, electrolysis, and aqueous-phase reforming showed that the advanced scenario could produce fuels at a minimum selling price of 1.84 USD/kg [53]. However, it is essential to consider that while some methods might currently seem less economically viable, such as the e-methanol production in Italy at 960 USD/t, they have the potential to become competitive in the future due to evolving market conditions and policy frameworks [57].

Life cycle assessment (LCA) results provide insights into the environmental sustainability of the different methods. The ETJ production in China using direct fermentation and gasification indicated the lowest GHG emission at 31.66 gCO₂eq/MJ jet fuel [67]; PtL production in the UK revealed a greenhouse gas potential of 21.43 gCO_2eq/MJSAF, which is below the UK mandate of a 50% emission reduction compared to fossil jet fuel [51]; a unique method in the US integrating Fischer–Tropsch fuel production with corn ethanol by-product CO₂ showcased an impressive WTW GHG emissions reduction by 90–108% against petroleum fuels [68]; and another study in the US involving nuclear energy demonstrated the potential to achieve a WTW GHG emissions reduction of at least 92% [55].

Conclusively, while economic viability is a crucial factor in the widespread adoption of e-fuel production methods, the combined techno-economic and life cycle assessments highlight the importance of balancing costs with environmental sustainability. As the global community continues to prioritise low-carbon solutions, these integrated assessments become pivotal in charting the path forward for sustainable aviation fuels and other e-fuels [64].

These studies employed an integrated approach that combines life cycle assessment (LCA) and techno-economic analysis (TEA) to assess the baseline climate change impact and cost of a standard system. In this analysis, both the LCA model and TEA model (Figure 8) share common scenarios, system boundaries, and input parameters.

Table 1. Summary of the findings of the previous research on the techno-economic and life cycle analyses of e-fuel production.

Country	Year	Study Parameter	Method and Simulation	Primary Energy Sources	Feedstock	Obtained Process	Highlight	Result	Others	Refs.
China	2023	Life cycle assessment (LCA): energy consumption, GHG, sensitivity and uncertainty analysis.	Direct fermentation, gasification, fermentation (Aspen Plus V11).	Crude coal, crude oil, and natural gas	Corn, cassava, corn cob	Ethanol-to-jet fuel (ETJ).	Few LCAs of ETJs in China; study assists policymakers for China’s SAF evolution.	Least energy and GHG emission: 370.05 KJ/MJ jet fuel and 31.66 gCO2eq/MJ jet fuel.	GHG emissions reduced up to 21.55% with cleaner electricity and heat.	[69]
USA	2023	Techno-economic and life cycle analyses: exergy, economic evaluation.	Integrated catalytic deoxygenation and hydrothermal gasification.	Fossil fuel, renewable energy sources	Esters, fatty acids (TOFA)	Hydrogen (H2) gas.	Both scenarios are economically feasible for SAF: DCFA, GWP, acidification, eutrophication, smog, ozone depletion.	Scenario 2’s MFSP (0.39 USD/L) < scenario 1 (0.62 USD/L).	Focus on process optimisation and model improvement; include experimental and kinetics data.	[51]
Abu Dhabi and Benevento (Italy)	2023	Techno-economic: DAC, methanation, TPC, LCCR, LCOM.	Hydrogenation of CO2 from DAC, H2 from water electrolysis, and renewable PV source.	Solar PV	CO2, H2	Synthetic methane (CH4).	Cities with uneven solar energy distribution might need high H2 storage tank investments.	Electrolyser is most expensive, followed by PV field, H2 storage, reactors. LCOM: 4.9–8.2 EUR kgCH4−1 with DAC, 3.1–3.9 EUR kgCH4−1 with point-source capture.	LCOM > current methane price; need improvements/economic incentives.	[52]
UK	2023	Techno-economic and life cycle assessments focusing on carbon conversion, hydrogen conversion.	DAC unit, offshore wind farm, alkaline electrolyser, and a refinery plant.	An offshore wind farm	DAC unit, water electrolysis, and refinery plant for jet fuel hydrocarbons	Power-to-liquid (PtL).	LCA shows GWP of 21.43 gCO2eq/MJSAF. Dependent on offshore wind electricity.	Carbon conversion of 88%, hydrogen conversion of 39.16%, power-to-liquids efficiency of 25.6%. MJSP of 5.16 GBP/kg.	GWP below UK mandate of 50% emission reduction vs. fossil jet fuel. WtWa water footprint is 0.480 l/MJSAF.	[53]
KSA	2023	Techno-economic assessment focusing on fuel consumption, solar energy potential, etc.	MTO-MOGD process, electrolysis, and DAC.	Solar PV	CO2 and green hydrogen	Production of synthetic hydrocarbon.	Economic implications for decarbonising road transport.	MFSP of 3.24 USD/litre for e-gasoline and 2.89 USD/litre for e-diesel with solar power. LCOe from 379 to 564 USD/MWh.	E-fuels can become a carbon-neutral option with fossil CO2 taxation.	[54]
Italy	2023	Technical, economic, and environmental feasibility.	Hydrogenation, electrolysis, aqueous-phase reforming (APR).	Renewable energy	Palm oil, H2	Bio-oil to naphtha, kerosene, glycerol, and diesel.	Carbon footprint of advanced scenario is 12 g CO2/MJSAF, 54% lower than conventional.	APR led to a 6.6% increase in fixed capital investment, but 22% decrease in direct manufacturing costs. Minimum fuel selling price is 1.84 USD/kg.	Limitation: waste oils may contain higher fatty acids and lower triglycerides.	[55]
EU	2023	Technical process evaluation, mass and energy balances, production cost estimation, LCA, sensitivity analysis, European SAF production potential.	Fischer–Tropsch, electrolysis by Aspen Plus® (V10).	PV and onshore wind, nuclear and electricity from national grid	Forest residue	Power- and biomass-to-liquid (PBtL).	Only Norway and Sweden suitable as PBtL production sites in 2020 based on grid mix. Economic feasibility and environmental impact.	25 Mt a−1 fuel output achievable with direct renewable electricity sources, using 33% forest residue.	EU goal: 32% of total aviation fuel demand by SAF in 2040 can be met.	[56]
USA	2021	LCA: WTW GHG emissions of FT fuels from electrolytic H2 pathways and CO2 sources.	H2 and waste CO2 using Aspen Plus. Different process designs and system boundaries considered.	Nuclear/solar/wind electricity	H2 and waste CO2	Electrofuels from renewable H2 and waste CO2.	FT fuels have 57–65% lower WTW GHG emissions when integrated with corn ethanol production.	A total of 45% carbon in CO2 fixed in FT fuel with 58% energy efficiency.	Using nuclear/solar/wind electricity, WTW GHG emissions reduced by 90–108% vs. petroleum fuels.	[70]
USA	2023	Techno-economic and LCA: utilities, carbon conversion and energy efficiency, hydrocracking, plant construction and operation, capital and operating expenses, GHG LCA using GREET model.	Reverse water–gas shift and Fischer–Tropsch (FT) synthesis process with nuclear energy. High-temperature electrolysis, reactants compression.	Nuclear	CO2 and low-carbon H2	Electrofuels from CO2 and low-carbon H2.	Modelled FT process: 99% carbon conversion by recycling CO2 and oxycombustion. A total of 70% process energy efficiency.	MFSP: 0.95 USD/L, 0.74 USD/L, and 0.70 USD/L of FT fuel mix for 100, 400, and 1000 MWe nuclear power plant capacities, respectively. GHG emissions: 7 and −25 gCO2e/MJ.	WTW GHG emissions reduction of at least 92%. Potential to significantly reduce GHG emissions and ensure energy security.	[57]
Turkey	2022	Techno-economic assessment: thermodynamic and economic analysis.	Hydrogenation, PEM electrolyser, biogas purification, CO2 and hydrogen compressor. Analyses in Engineering Equation Solver program.	PV	CO2 from biogas in a wastewater treatment plant	Biogas-to-methanol: Biogas purification by water washing. Hydrogen from PEM electrolyser and solar PV. Methanol from hybrid system.	Required power for methanol production is 2923 kW, mainly from the PEM system.	Daily methanol production: 1674 kg. Electricity, hydrogen, and methanol costs: 0.043 USD kWh−1, 3.156 USD kg−1, and 0.693 USD kg−1, respectively.	Feasible methanol production costs with reasonable investments. Increased cogeneration plant efficiency and reduced emissions by enriching biogas.	[58]
Italy	2023	Techno-economic assessment, including detailed economic analysis, cost estimation, financial assumptions.	Water electrolysis, amine-based CO2 absorption, Aspen Plus.	Wind or solar electricity	Hydrogen and captured CO2	e-methanol from green hydrogen and captured CO2.	Pre-feasibility study for a power-to-fuel plant for producing 500 kg/h renewable methanol.	Levelised cost of methanol (LCoM) calculated to be 960 EUR/t (about 175 EUR/MWh). Technology not currently economically competitive.	Process expected to become competitive in the mid-term future due to new European policies. LCoM affected by electricity price and electrolyser capital cost.	[59]
Netherlands	2021	PESTEL analysis focusing on critical uncertainties, economic factors, technological innovation, environmental concerns, legal factors, etc.	Electrolysis, DAC.	Renewable energy sources (wind or solar)	CO2 and H2	e-Fuel.	The relevance of blue hydrogen versus green hydrogen in terms of costs and environmental benefits.	The impact of certain factors on synthetic fuel pricing and their interdependencies.	Technological advancements for essential processes will be important in the future. Local production combined with imported fuels/hydrogen may be the best combination.	[60]
Italy	2020	Technical and economic assessment focusing on waste and power-to-methanol, CO2 emission, sensitivity analysis, etc.	Syngas from waste gasification, enriched with hydrogen via water electrolysis.	Natural gas, fossil power	Waste and water	Waste-to-methanol, hybrid waste-to-methanol with hydrogen integration; power-to-methanol.	Feasibility of power-to-methanol combined with MSW gasification, aligning with energy transition and circular economy concepts.	Renewable power increase in coming years could make the hybrid case more attractive.	The hybrid scheme may become a more attractive solution in the near future considering renewable energy increases and power cost reductions.	[61]
Germany	2020	Techno-economic indicators: CO2 demand, electricity demand, avg. fuel production costs.	DAC, electrolysis.	Renewable: solar/wind electricity and nuclear energy	CO2, Water	Power-to-liquid (PtL) kerosene.	Impact of local CO2 sources on PtL.	Need for 48–745 TWh additional renewable electricity for 2030–2050 cases. Fuel production costs: 2.3–3.3 EUR/kg in 2030 drops to 1.8–3.1 EUR/kg in 2050.	Importance of sustainable CO2 sources and renewable electricity development targets.	[62]
Italy	2023	Technical and economic analysis.	Hydrogen from water electrolysis, CO2 capture, RWGS, FT synthesis.	Renewable energy (solar/wind electricity)	H2 and CO2	Synthetic kerosene from green H2 and DAC CO2.	Sensitivity analysis and process evaluations.	Indirect and direct processes produce 66.18 bbl/d and 38.46 bbl/d respectively. Product cost varies: 460–1435 EUR/bbl and 752–2364 EUR/bbl.	Dependency on power energy and hydrogen prices.	[63]
Germany	2021	Life cycle assessment: fleet emissions and climate impact.	Hydrogen via water electrolysis followed by Fischer–Tropsch synthesis.	Wind	Water	Power-to-liquid.	Potential of PtL for aviation considering environmental impacts.	PtL from wind energy reduces impact by up to 42%.	Reduction in warming impact due to contrail-induced cloudiness.	[71]
Sweden	2021	Techno-economic assessment for 2020–2050.	Fischer–Tropsch (FT), HTL, PTL (Python 3.9 MILP model).	Fossil and biomass and renewable	Biomass, CO2	RJF from lignocellulosic biomass and captured CO2.	Total RJF production increase due to the blending ratio.	RJF production: 3.85–16.87 TJ for 2030–2050. HTL and PTL jet fuel production cost varies: 24.2–25.4 SEK/litre and 16.7–22.0 SEK/litre.	Revenue from by-products could make HTL and PTL price-competitive.	[64]
Germany	2018	TEA and LCA: carbon capture and utilisation option for the industry.	Carbon capture and utilisation (CCU) on e-fuels generated through the anhydrous trioxane and OME1 pathway.	Renewable electricity: PV and wind	Flue gas, water, electricity, and steam	e-fuels.	OME3-5 is considered a potential solution for decarbonising heavy-duty transportation in the future. However, there is uncertainty surrounding both its cost and the resulting market potential.	OME3-5 e-fuels exhibit a notably elevated cost of production per gigajoule (GJ) compared to conventional diesel fuel available at German gas stations, and they can store less than 38.4% of electricity based on their lower heating value.	The most significant economic obstacles are associated with electricity consumption and the cost of electrolyser stacks rather than the conversion cost of OME. Nevertheless, even a substantial decrease in electricity or electrolyser prices alone would not render the OME3-5 anhydrous pathway economically competitive given the existing circumstances. Significant advancements in reaction and process efficiency are imperative to achieve competitiveness.	[65]
Chile, Denmark, Australia	2019	Costs and life cycle GHGs emissions.	Electrolytic.	Renewable: solar/wind	Hydrogen and nitrogen or carbon	e-ammonia.	In South Australia, the current energy mix relies heavily on fossil electricity, with 55% of it being produced or imported, primarily sourced from natural gas. Despite having 47% renewable power, the production of fuel under these conditions results in the lowest greenhouse gas (GHG) intensity for e-fuels when utilising the grid. Nevertheless, the life cycle emissions are only marginally lower, approximately 25%, than those of grey methanol.	When focusing on e-ammonia production, our analysis revealed that in North Chile, with its abundant solar potential and 2019 hourly grid emissions and prices, the most cost-effective solution involves using 58% of grid electricity and results in emissions of 183 gCO2e/MJNH3. In contrast, in Denmark, the least expensive option necessitates utilising 100% grid electricity, yielding emissions of 109 gCO2e/MJNH3.	It is important to note that the GHG footprint of e-fuels is often higher compared to the same fuels produced from natural gas (grey fuels). This disparity is especially pronounced in Chile, where 60% of the grid electricity originates from fossil sources such as gas, coal, and oil. In Denmark, only 20% of the electricity in 2019 came from coal, gas, or oil, which explains the relatively lower GHG footprint, even when exclusively relying on grid electricity.	[66]
Germany	2021	TEA: total costs of electrofuels and direct air capture and carbon storage.	DSACCS.	Renewable energy sources	CO2	e-fuel.	Meeting the CO2 storage requirements outlined in the IPCC scenarios could potentially strain the availability of cost-effective and readily accessible CO2 storage sites.	Considering that the variation in costs between e-fuels and direct air capture and carbon storage (DACCS) options by 2050 falls within the range of 1.0% to 2.5% of ticket prices, a manageable expense for passengers, it prompts an evaluation of whether pursuing the e-fuels option aligns better with the precautionary principle, a fundamental tenet of environmental policy.	Given the potential limitations in CO2 storage sites and the relatively modest cost differences between e-fuels and DACCS, the choice to invest in e-fuels may be more in line with the precautionary principle, underscoring the importance of cautious and proactive environmental decision making.	[67]
Germany	2015	EEA, LCA: economic and environmental assessment of current (2015) and future (2030).	Different electrolysis technologies and Fischer–Tropsch synthesis.	Renewable energy sources: unspecified	Current alkaline and future solid oxide	e-fuel.	Using a set of optimistic estimates for these parameters resulted in a production cost of 1.17 V/leq diesel (equivalent to 3.12 V ct/MJ). Notably, abatement costs within the range of 544 to 6424 V/tCO2-eq were projected for e-fuels, signifying a substantially higher cost compared to alternative vehicle fuel technologies.	In terms of e-fuel production costs and life cycle emissions, the estimates indicated values of 4.97 V/leq diesel and 64.07 gCO2-eq/MJ in 2015. Looking ahead to 2030, the projections anticipate a reduction in costs, with figures of 3.24 V/leq diesel and 6.63 gCO2-eq/MJ.	It is essential to highlight that these estimates provide insights into the economic and environmental aspects of e-fuel production and its associated costs and emissions, underlining the challenges and potential improvements that lie ahead in this field.	[68]
Argentina, Namibia, Egypt, Australia, Canada, Iceland, Chile	2020	Economic comparison.	Fischer–Tropsch, electrolytic water splitting.	Patagonia in Argentina: wind energy Karas in Namibia: solar Egypt scenario on the Gulf of Suez: combines high wind speeds and good solar radiation Labrador in Canada: very good wind conditions and hydropower Iceland: wind, hydropower, geothermal Atacama Desert, Chile: geothermal West Australia: wind and solar	CO2, H2O	Four e-fuels: Fischer–Tropsch diesel (FTD), methanol (MeOH), dibenzyltoluene/perhydrodibenzyltoluene (H0-DBT/H18-DBT), and liquid hydrogen (LH2) −253 °C.	Particularly in the case of diesel, the levelised cost of electricity, as determined by the full load hours of the renewable energy source in use, exerts a substantial influence.	An LOHC-based system demonstrates reduced dependence on the electricity source in comparison to other technologies, primarily due to its lower electricity consumption. However, it is worth noting that factors such as the length of the transportation route and the cost of filling station infrastructure can elevate the mobility cost associated with LOHC and LH2.	Based on the established boundary conditions and assumptions, it becomes evident that methanol, cryogenic hydrogen, and liquid organic hydrogen carriers emerge as the most advantageous choices across all seven examined locations.	[72]
Norway	2021	Institutional economics theory for examining the framework of the environmental governance system concerning the adoption of CCU and e-fuels.	Carbon capture and utilisation (CCU), electrolysis, and Norwegian renewable energy.	Norwegian renewable energy: hydropower is the primary source of renewable energy, with thermal and wind power	From CO2 and water	Hydrogen-based e-fuel.	The discussions revealed a dynamic, ongoing effort within both national and international governance structures to establish more defined policy tools for the adoption or rejection of CCU and e-fuels.	Findings indicate that Norway boasts a resilient environmental governance framework that wields significant influence in conjunction with international guidelines, particularly in shaping the implementation of e-fuels and the CCU value chain.	Nevertheless, the research has pinpointed a range of challenges and uncertainties surrounding the development and integration of these technologies. These obstacles have been subject to active deliberations among key stakeholders involved in the process.	[28]
China	2024	Techno-economic analysis, and environmental impact assessment.	Gasification–Fischer–Tropsch conversion pathway.	Bioenergy	Six conventional crop straws (rice, wheat, corn, peanut, cotton, beans)	Biomass-to-liquid FT fuel.	Showing the huge decarbonisation potential of sustainable aviation fuel.	When the blending ratio of sustainable aviation fuel reaches 50%, about 60 Mt CO2e emission can be reduced, which accounts for 43% of the emission for China’s aviation sector in 2023.	Corn straw can support future large-scale sustainable aviation fuel application.	[73]
USA	2024	Techno-economic and life cycle analysis.	Electrolysis, DAC, condensation, and triethylene glycol (TEG) absorption.	Wind, solar, nuclear, hydro	Low-carbon H2 and point-source or atmospheric CO2	Synthetic natural gas (SNG).	SNG cost can be reduced with a tax credit in the US for low-carbon H2 production.	SNG can reduce life cycle GHG emissions by 52–88% compared to fossil NG.	With a lower electricity price of 0.03 USD/kWh for water electrolysis and accounting for a 45 V tax credit, the SNG cost reaches parity with the cost of fossil NG.	[74]

Table 1. Summary of the findings of the previous research on the techno-economic and life cycle analyses of e-fuel production.

Country	Year	Study Parameter	Method and Simulation	Primary Energy Sources	Feedstock	Obtained Process	Highlight	Result	Others	Refs.
China	2023	Life cycle assessment (LCA): energy consumption, GHG, sensitivity and uncertainty analysis.	Direct fermentation, gasification, fermentation (Aspen Plus V11).	Crude coal, crude oil, and natural gas	Corn, cassava, corn cob	Ethanol-to-jet fuel (ETJ).	Few LCAs of ETJs in China; study assists policymakers for China’s SAF evolution.	Least energy and GHG emission: 370.05 KJ/MJ jet fuel and 31.66 gCO2eq/MJ jet fuel.	GHG emissions reduced up to 21.55% with cleaner electricity and heat.	[69]
USA	2023	Techno-economic and life cycle analyses: exergy, economic evaluation.	Integrated catalytic deoxygenation and hydrothermal gasification.	Fossil fuel, renewable energy sources	Esters, fatty acids (TOFA)	Hydrogen (H2) gas.	Both scenarios are economically feasible for SAF: DCFA, GWP, acidification, eutrophication, smog, ozone depletion.	Scenario 2’s MFSP (0.39 USD/L) < scenario 1 (0.62 USD/L).	Focus on process optimisation and model improvement; include experimental and kinetics data.	[51]
Abu Dhabi and Benevento (Italy)	2023	Techno-economic: DAC, methanation, TPC, LCCR, LCOM.	Hydrogenation of CO2 from DAC, H2 from water electrolysis, and renewable PV source.	Solar PV	CO2, H2	Synthetic methane (CH4).	Cities with uneven solar energy distribution might need high H2 storage tank investments.	Electrolyser is most expensive, followed by PV field, H2 storage, reactors. LCOM: 4.9–8.2 EUR kgCH4−1 with DAC, 3.1–3.9 EUR kgCH4−1 with point-source capture.	LCOM > current methane price; need improvements/economic incentives.	[52]
UK	2023	Techno-economic and life cycle assessments focusing on carbon conversion, hydrogen conversion.	DAC unit, offshore wind farm, alkaline electrolyser, and a refinery plant.	An offshore wind farm	DAC unit, water electrolysis, and refinery plant for jet fuel hydrocarbons	Power-to-liquid (PtL).	LCA shows GWP of 21.43 gCO2eq/MJSAF. Dependent on offshore wind electricity.	Carbon conversion of 88%, hydrogen conversion of 39.16%, power-to-liquids efficiency of 25.6%. MJSP of 5.16 GBP/kg.	GWP below UK mandate of 50% emission reduction vs. fossil jet fuel. WtWa water footprint is 0.480 l/MJSAF.	[53]
KSA	2023	Techno-economic assessment focusing on fuel consumption, solar energy potential, etc.	MTO-MOGD process, electrolysis, and DAC.	Solar PV	CO2 and green hydrogen	Production of synthetic hydrocarbon.	Economic implications for decarbonising road transport.	MFSP of 3.24 USD/litre for e-gasoline and 2.89 USD/litre for e-diesel with solar power. LCOe from 379 to 564 USD/MWh.	E-fuels can become a carbon-neutral option with fossil CO2 taxation.	[54]
Italy	2023	Technical, economic, and environmental feasibility.	Hydrogenation, electrolysis, aqueous-phase reforming (APR).	Renewable energy	Palm oil, H2	Bio-oil to naphtha, kerosene, glycerol, and diesel.	Carbon footprint of advanced scenario is 12 g CO2/MJSAF, 54% lower than conventional.	APR led to a 6.6% increase in fixed capital investment, but 22% decrease in direct manufacturing costs. Minimum fuel selling price is 1.84 USD/kg.	Limitation: waste oils may contain higher fatty acids and lower triglycerides.	[55]
EU	2023	Technical process evaluation, mass and energy balances, production cost estimation, LCA, sensitivity analysis, European SAF production potential.	Fischer–Tropsch, electrolysis by Aspen Plus® (V10).	PV and onshore wind, nuclear and electricity from national grid	Forest residue	Power- and biomass-to-liquid (PBtL).	Only Norway and Sweden suitable as PBtL production sites in 2020 based on grid mix. Economic feasibility and environmental impact.	25 Mt a−1 fuel output achievable with direct renewable electricity sources, using 33% forest residue.	EU goal: 32% of total aviation fuel demand by SAF in 2040 can be met.	[56]
USA	2021	LCA: WTW GHG emissions of FT fuels from electrolytic H2 pathways and CO2 sources.	H2 and waste CO2 using Aspen Plus. Different process designs and system boundaries considered.	Nuclear/solar/wind electricity	H2 and waste CO2	Electrofuels from renewable H2 and waste CO2.	FT fuels have 57–65% lower WTW GHG emissions when integrated with corn ethanol production.	A total of 45% carbon in CO2 fixed in FT fuel with 58% energy efficiency.	Using nuclear/solar/wind electricity, WTW GHG emissions reduced by 90–108% vs. petroleum fuels.	[70]
USA	2023	Techno-economic and LCA: utilities, carbon conversion and energy efficiency, hydrocracking, plant construction and operation, capital and operating expenses, GHG LCA using GREET model.	Reverse water–gas shift and Fischer–Tropsch (FT) synthesis process with nuclear energy. High-temperature electrolysis, reactants compression.	Nuclear	CO2 and low-carbon H2	Electrofuels from CO2 and low-carbon H2.	Modelled FT process: 99% carbon conversion by recycling CO2 and oxycombustion. A total of 70% process energy efficiency.	MFSP: 0.95 USD/L, 0.74 USD/L, and 0.70 USD/L of FT fuel mix for 100, 400, and 1000 MWe nuclear power plant capacities, respectively. GHG emissions: 7 and −25 gCO2e/MJ.	WTW GHG emissions reduction of at least 92%. Potential to significantly reduce GHG emissions and ensure energy security.	[57]
Turkey	2022	Techno-economic assessment: thermodynamic and economic analysis.	Hydrogenation, PEM electrolyser, biogas purification, CO2 and hydrogen compressor. Analyses in Engineering Equation Solver program.	PV	CO2 from biogas in a wastewater treatment plant	Biogas-to-methanol: Biogas purification by water washing. Hydrogen from PEM electrolyser and solar PV. Methanol from hybrid system.	Required power for methanol production is 2923 kW, mainly from the PEM system.	Daily methanol production: 1674 kg. Electricity, hydrogen, and methanol costs: 0.043 USD kWh−1, 3.156 USD kg−1, and 0.693 USD kg−1, respectively.	Feasible methanol production costs with reasonable investments. Increased cogeneration plant efficiency and reduced emissions by enriching biogas.	[58]
Italy	2023	Techno-economic assessment, including detailed economic analysis, cost estimation, financial assumptions.	Water electrolysis, amine-based CO2 absorption, Aspen Plus.	Wind or solar electricity	Hydrogen and captured CO2	e-methanol from green hydrogen and captured CO2.	Pre-feasibility study for a power-to-fuel plant for producing 500 kg/h renewable methanol.	Levelised cost of methanol (LCoM) calculated to be 960 EUR/t (about 175 EUR/MWh). Technology not currently economically competitive.	Process expected to become competitive in the mid-term future due to new European policies. LCoM affected by electricity price and electrolyser capital cost.	[59]
Netherlands	2021	PESTEL analysis focusing on critical uncertainties, economic factors, technological innovation, environmental concerns, legal factors, etc.	Electrolysis, DAC.	Renewable energy sources (wind or solar)	CO2 and H2	e-Fuel.	The relevance of blue hydrogen versus green hydrogen in terms of costs and environmental benefits.	The impact of certain factors on synthetic fuel pricing and their interdependencies.	Technological advancements for essential processes will be important in the future. Local production combined with imported fuels/hydrogen may be the best combination.	[60]
Italy	2020	Technical and economic assessment focusing on waste and power-to-methanol, CO2 emission, sensitivity analysis, etc.	Syngas from waste gasification, enriched with hydrogen via water electrolysis.	Natural gas, fossil power	Waste and water	Waste-to-methanol, hybrid waste-to-methanol with hydrogen integration; power-to-methanol.	Feasibility of power-to-methanol combined with MSW gasification, aligning with energy transition and circular economy concepts.	Renewable power increase in coming years could make the hybrid case more attractive.	The hybrid scheme may become a more attractive solution in the near future considering renewable energy increases and power cost reductions.	[61]
Germany	2020	Techno-economic indicators: CO2 demand, electricity demand, avg. fuel production costs.	DAC, electrolysis.	Renewable: solar/wind electricity and nuclear energy	CO2, Water	Power-to-liquid (PtL) kerosene.	Impact of local CO2 sources on PtL.	Need for 48–745 TWh additional renewable electricity for 2030–2050 cases. Fuel production costs: 2.3–3.3 EUR/kg in 2030 drops to 1.8–3.1 EUR/kg in 2050.	Importance of sustainable CO2 sources and renewable electricity development targets.	[62]
Italy	2023	Technical and economic analysis.	Hydrogen from water electrolysis, CO2 capture, RWGS, FT synthesis.	Renewable energy (solar/wind electricity)	H2 and CO2	Synthetic kerosene from green H2 and DAC CO2.	Sensitivity analysis and process evaluations.	Indirect and direct processes produce 66.18 bbl/d and 38.46 bbl/d respectively. Product cost varies: 460–1435 EUR/bbl and 752–2364 EUR/bbl.	Dependency on power energy and hydrogen prices.	[63]
Germany	2021	Life cycle assessment: fleet emissions and climate impact.	Hydrogen via water electrolysis followed by Fischer–Tropsch synthesis.	Wind	Water	Power-to-liquid.	Potential of PtL for aviation considering environmental impacts.	PtL from wind energy reduces impact by up to 42%.	Reduction in warming impact due to contrail-induced cloudiness.	[71]
Sweden	2021	Techno-economic assessment for 2020–2050.	Fischer–Tropsch (FT), HTL, PTL (Python 3.9 MILP model).	Fossil and biomass and renewable	Biomass, CO2	RJF from lignocellulosic biomass and captured CO2.	Total RJF production increase due to the blending ratio.	RJF production: 3.85–16.87 TJ for 2030–2050. HTL and PTL jet fuel production cost varies: 24.2–25.4 SEK/litre and 16.7–22.0 SEK/litre.	Revenue from by-products could make HTL and PTL price-competitive.	[64]
Germany	2018	TEA and LCA: carbon capture and utilisation option for the industry.	Carbon capture and utilisation (CCU) on e-fuels generated through the anhydrous trioxane and OME1 pathway.	Renewable electricity: PV and wind	Flue gas, water, electricity, and steam	e-fuels.	OME3-5 is considered a potential solution for decarbonising heavy-duty transportation in the future. However, there is uncertainty surrounding both its cost and the resulting market potential.	OME3-5 e-fuels exhibit a notably elevated cost of production per gigajoule (GJ) compared to conventional diesel fuel available at German gas stations, and they can store less than 38.4% of electricity based on their lower heating value.	The most significant economic obstacles are associated with electricity consumption and the cost of electrolyser stacks rather than the conversion cost of OME. Nevertheless, even a substantial decrease in electricity or electrolyser prices alone would not render the OME3-5 anhydrous pathway economically competitive given the existing circumstances. Significant advancements in reaction and process efficiency are imperative to achieve competitiveness.	[65]
Chile, Denmark, Australia	2019	Costs and life cycle GHGs emissions.	Electrolytic.	Renewable: solar/wind	Hydrogen and nitrogen or carbon	e-ammonia.	In South Australia, the current energy mix relies heavily on fossil electricity, with 55% of it being produced or imported, primarily sourced from natural gas. Despite having 47% renewable power, the production of fuel under these conditions results in the lowest greenhouse gas (GHG) intensity for e-fuels when utilising the grid. Nevertheless, the life cycle emissions are only marginally lower, approximately 25%, than those of grey methanol.	When focusing on e-ammonia production, our analysis revealed that in North Chile, with its abundant solar potential and 2019 hourly grid emissions and prices, the most cost-effective solution involves using 58% of grid electricity and results in emissions of 183 gCO2e/MJNH3. In contrast, in Denmark, the least expensive option necessitates utilising 100% grid electricity, yielding emissions of 109 gCO2e/MJNH3.	It is important to note that the GHG footprint of e-fuels is often higher compared to the same fuels produced from natural gas (grey fuels). This disparity is especially pronounced in Chile, where 60% of the grid electricity originates from fossil sources such as gas, coal, and oil. In Denmark, only 20% of the electricity in 2019 came from coal, gas, or oil, which explains the relatively lower GHG footprint, even when exclusively relying on grid electricity.	[66]
Germany	2021	TEA: total costs of electrofuels and direct air capture and carbon storage.	DSACCS.	Renewable energy sources	CO2	e-fuel.	Meeting the CO2 storage requirements outlined in the IPCC scenarios could potentially strain the availability of cost-effective and readily accessible CO2 storage sites.	Considering that the variation in costs between e-fuels and direct air capture and carbon storage (DACCS) options by 2050 falls within the range of 1.0% to 2.5% of ticket prices, a manageable expense for passengers, it prompts an evaluation of whether pursuing the e-fuels option aligns better with the precautionary principle, a fundamental tenet of environmental policy.	Given the potential limitations in CO2 storage sites and the relatively modest cost differences between e-fuels and DACCS, the choice to invest in e-fuels may be more in line with the precautionary principle, underscoring the importance of cautious and proactive environmental decision making.	[67]
Germany	2015	EEA, LCA: economic and environmental assessment of current (2015) and future (2030).	Different electrolysis technologies and Fischer–Tropsch synthesis.	Renewable energy sources: unspecified	Current alkaline and future solid oxide	e-fuel.	Using a set of optimistic estimates for these parameters resulted in a production cost of 1.17 V/leq diesel (equivalent to 3.12 V ct/MJ). Notably, abatement costs within the range of 544 to 6424 V/tCO2-eq were projected for e-fuels, signifying a substantially higher cost compared to alternative vehicle fuel technologies.	In terms of e-fuel production costs and life cycle emissions, the estimates indicated values of 4.97 V/leq diesel and 64.07 gCO2-eq/MJ in 2015. Looking ahead to 2030, the projections anticipate a reduction in costs, with figures of 3.24 V/leq diesel and 6.63 gCO2-eq/MJ.	It is essential to highlight that these estimates provide insights into the economic and environmental aspects of e-fuel production and its associated costs and emissions, underlining the challenges and potential improvements that lie ahead in this field.	[68]
Argentina, Namibia, Egypt, Australia, Canada, Iceland, Chile	2020	Economic comparison.	Fischer–Tropsch, electrolytic water splitting.	Patagonia in Argentina: wind energy Karas in Namibia: solar Egypt scenario on the Gulf of Suez: combines high wind speeds and good solar radiation Labrador in Canada: very good wind conditions and hydropower Iceland: wind, hydropower, geothermal Atacama Desert, Chile: geothermal West Australia: wind and solar	CO2, H2O	Four e-fuels: Fischer–Tropsch diesel (FTD), methanol (MeOH), dibenzyltoluene/perhydrodibenzyltoluene (H0-DBT/H18-DBT), and liquid hydrogen (LH2) −253 °C.	Particularly in the case of diesel, the levelised cost of electricity, as determined by the full load hours of the renewable energy source in use, exerts a substantial influence.	An LOHC-based system demonstrates reduced dependence on the electricity source in comparison to other technologies, primarily due to its lower electricity consumption. However, it is worth noting that factors such as the length of the transportation route and the cost of filling station infrastructure can elevate the mobility cost associated with LOHC and LH2.	Based on the established boundary conditions and assumptions, it becomes evident that methanol, cryogenic hydrogen, and liquid organic hydrogen carriers emerge as the most advantageous choices across all seven examined locations.	[72]
Norway	2021	Institutional economics theory for examining the framework of the environmental governance system concerning the adoption of CCU and e-fuels.	Carbon capture and utilisation (CCU), electrolysis, and Norwegian renewable energy.	Norwegian renewable energy: hydropower is the primary source of renewable energy, with thermal and wind power	From CO2 and water	Hydrogen-based e-fuel.	The discussions revealed a dynamic, ongoing effort within both national and international governance structures to establish more defined policy tools for the adoption or rejection of CCU and e-fuels.	Findings indicate that Norway boasts a resilient environmental governance framework that wields significant influence in conjunction with international guidelines, particularly in shaping the implementation of e-fuels and the CCU value chain.	Nevertheless, the research has pinpointed a range of challenges and uncertainties surrounding the development and integration of these technologies. These obstacles have been subject to active deliberations among key stakeholders involved in the process.	[28]
China	2024	Techno-economic analysis, and environmental impact assessment.	Gasification–Fischer–Tropsch conversion pathway.	Bioenergy	Six conventional crop straws (rice, wheat, corn, peanut, cotton, beans)	Biomass-to-liquid FT fuel.	Showing the huge decarbonisation potential of sustainable aviation fuel.	When the blending ratio of sustainable aviation fuel reaches 50%, about 60 Mt CO2e emission can be reduced, which accounts for 43% of the emission for China’s aviation sector in 2023.	Corn straw can support future large-scale sustainable aviation fuel application.	[73]
USA	2024	Techno-economic and life cycle analysis.	Electrolysis, DAC, condensation, and triethylene glycol (TEG) absorption.	Wind, solar, nuclear, hydro	Low-carbon H2 and point-source or atmospheric CO2	Synthetic natural gas (SNG).	SNG cost can be reduced with a tax credit in the US for low-carbon H2 production.	SNG can reduce life cycle GHG emissions by 52–88% compared to fossil NG.	With a lower electricity price of 0.03 USD/kWh for water electrolysis and accounting for a 45 V tax credit, the SNG cost reaches parity with the cost of fossil NG.	[74]

4. Discussion

4.1. Techno-Economic Analysis Research on e-Fuel Production

The techno-economic analysis of e-fuel production and utilisation presents a rapidly evolving landscape of opportunities, challenges, and implications. Various production technologies have been assessed across multiple studies, revealing contrasting efficiencies and intricacies based on geographical, technological, and economic contexts.

• Production technologies and their efficiencies.

This is a recurrent theme observed across the studies and includes, for example, the integration of catalytic deoxygenation, hydrothermal gasification, direct air capture (DAC), and methanation [70,71]. These methods, combined with other processes such as Fischer–Tropsch and electrolysis, are central to producing synthetic fuels, including sustainable aviation fuel (SAF), methane, and e-diesel. The overall efficiency of these methods, however, varies. In the UK, for instance, the system efficiency for power-to-liquids stood at 25.6%, while in the US, a carbon conversion rate of 99% was achieved in a modelled FT process [51,55]. Such variations emphasise the need for continuous optimisation and the incorporation of experimental and kinetics data into model improvements.

2.

Capital and operational expenditures.

Major contributors to costs have been identified in different scenarios. The significant expenses were associated with the electrolyser, the PV field, and H₂ storage [71]. The research by [53] further underscored the capital implications of processes like aqueous-phase reforming (APR), which led to a 6.6% increase in fixed capital investment. Operational expenses are equally impactful. Direct manufacturing costs, for instance, saw a decrease of 22% when APR was employed in Italy.

3.

Break-even points and return-on-investment calculations.

Break-even points, often denoted by metrics such as the minimum fuel selling price (MFSP), provide crucial insights into the economic feasibility of e-fuel production across different contexts. In the US, MFSP values varied based on nuclear power plant capacities, highlighting the significance of the energy source in determining production costs [55]. Similarly, the levelised cost of methane (LCOM) in Abu Dhabi and Benevento and the levelised cost of electricity (LCOe) in Saudi Arabia provide crucial benchmarks for assessing the economic implications of e-fuel production [52,71].

While some studies suggest favourable return-on-investment scenarios—like the feasible methanol production costs observed in Turkey in 2022—others hint at the need for further economic incentives or technological improvements [56]. The LCOM values in Abu Dhabi and Benevento, for instance, exceeded prevailing market prices for methane [71]. This divergence accentuates the importance of contextualising techno-economic analyses and recognising the fluidity of market dynamics, technological advancements, and policy implications.

In China the techno-economic analysis considers the costs associated with gasifying six types of crop straws, the Fischer–Tropsch (FT) synthesis process, and the required infrastructure and operations, evaluating these costs in terms of capital expenditure (CapEx) and operational expenditure (OpEx). The study demonstrates the economic viability of producing sustainable aviation fuel (SAF) from crop straws through the gasification–FT pathway, especially given China’s abundant agricultural biomass resources in 2024. Corn straw, in particular, shows significant promise, supporting the potential for large-scale SAF applications in the future [73].

The analysis considers the costs associated with electrolysis for hydrogen production, direct air capture (DAC) for CO₂, and the processes of condensation and TEG absorption for producing synthetic natural gas (SNG). The study reveals that SNG costs can be significantly reduced with US tax credits for low-carbon hydrogen production. With an electricity price of 0.03 USD/kWh for water electrolysis and a 45 V tax credit, the cost of SNG reaches parity with fossil natural gas (NG). The 45 V tax credit enhances the economic feasibility of SNG, making it a competitive alternative to fossil NG [74].

4.

Quantitative economic analysis.

Studies have evaluated the techno-economic feasibility of e-fuel production across various countries, focusing on metrics such as minimum fuel selling price (MFSP), levelised cost of methanol (LCoM), and levelised cost of electricity (LCoE). For instance, the MFSP for e-gasoline and e-diesel in KSA is USD 3.24 and USD 2.89 per litre, respectively. Economic analysis in Italy indicates that the LCoM is 960 EUR/t, and another study in Germany projects the production costs of e-fuels to drop to 1.8–3.1 EUR/kg by 2050.

5.

Technical parameters.

Key technical parameters considered in these studies include efficiency, effectiveness, and specific energy consumption. For example, a study in the UK reports a power-to-liquids efficiency of 25.6% and a carbon conversion efficiency of 88%. In the USA, another study details a 70% process energy efficiency for FT synthesis processes.

4.2. Life Cycle Analysis Research on e-Fuel Production

Life cycle analysis (LCA) is an invaluable tool for understanding the environmental implications of various fuels, from raw material acquisition through end-of-life considerations. As the transition from conventional fuels to sustainable alternatives accelerates, a comprehensive understanding of LCA provides pivotal insights to stakeholders and policymakers.

• Raw material acquisition.

As elucidated by [67] in 2023, feedstocks such as corn, cassava, and corn cob are pivotal raw materials for ethanol-to-jet fuel (ETJ) production using methods like direct fermentation and gasification plus fermentation. Similarly, LCA underscored the significance of raw materials such as electrolytic H₂ pathways and CO₂ sources in the production of FT fuels [68]. Raw material acquisition can have varying environmental impacts. For instance, while crops like corn and cassava require agricultural inputs and can lead to land-use change implications, utilising CO₂ sources can contribute to carbon capture and sequestration. The sourcing, transportation, and processing of these raw materials significantly influence the overall environmental footprint of the resultant fuel.

2.

Production process.

Several studies have delved deep into the production processes and their inherent efficiencies and environmental repercussions. van de Graaff [58] emphasised the environmental superiority of green hydrogen production over blue hydrogen. Green hydrogen is derived from renewable energy sources, whereas blue hydrogen comes from natural gas with carbon capture and storage. The latter’s dependence on CO₂ storage and the former’s carbon-free nature distinctly portray the environmental ramifications associated with production methodologies.

In addition, the Italian studies from 2020 and 2023 brought to the fore the impacts of combining power-to-methanol with MSW gasification and the implications of electricity prices, electrolyser capital costs, and plant capacity factors on methanol production processes [57,59]. As methanol emerges as a prominent e-fuel, understanding these variables becomes crucial for optimising production from an environmental perspective.

3.

Use-phase emissions.

Different studies accentuated the potential for significant reductions in GHG emissions during the use phase of synthetic aviation fuels [53,54,55,67,68,70]. For instance, the global warming potential (GWP) of synthetic aviation fuel (SAF) in the UK was determined to be significantly below the nation’s emission reduction mandate [51]. Similarly, [53] elucidated a 54% reduction in carbon footprint from conventional methods. These findings reiterate the importance of e-fuels in achieving global carbon neutrality goals. However, it is pivotal to emphasise that these use-phase emission reductions are intricately linked to the fuel’s production processes and raw material sources.

4.

End-of-life considerations.

End-of-life considerations primarily concern the fate and impacts of products post-utilisation. In the context of e-fuels, this predominantly relates to emissions and environmental effects. It has been demonstrated that electrofuels derived from CO₂ and low-carbon H₂ have potential life cycle GHG emissions that are not only significantly reduced but can even reach negative values [55]. Such insights are indicative of the potential for carbon-negative solutions, which not only offset their own emissions but also contribute to capturing additional atmospheric CO₂. However, other end-of-life considerations might include factors like degradation by-products, recyclability, or repurposing potential. Though not directly addressed in the mentioned studies, these factors can be vital in a comprehensive LCA, especially when considering novel fuels and technologies.

Life cycle assessments (LCAs) focus on energy consumption, greenhouse gas (GHG) emissions, material requirements, recycling effectiveness, and utilisation energy. A study in China found that the least energy and GHG emissions for ethanol-to-jet fuel (ETJ) were 370.05 KJ/MJ jet fuel and 31.66 gCO2eq/MJ jet fuel, respectively. The USA research shows that electrofuels from renewable H₂ and waste CO₂ can reduce WTW GHG emissions by 57–65%. Another study in Norway highlights the significant influence of the environmental governance framework on the implementation of CCU and e-fuels.

4.3. Economic Feasibility and Technological Challenges

This review draws special attention to the economic practicality of converting esters and fatty acids into H₂ gas for SAF production, as evidenced by [55]. The notable discrepancy in the minimum fuel selling price (MFSP) between different scenarios in this study underscores the significant influence of process optimisation on cost-effectiveness. This finding emphasises the vital need for constant enhancement of production technologies to ensure economic viability.

The impact of regional factors like solar energy potential and market conditions is markedly underlined by studies [52,71]. These studies are indispensable, particularly when contemplating the amalgamation of renewable energy sources into e-fuel production processes and the consequential effects on elements like the levelised cost of methane (LCOM) and the overall project cost.

The life cycle assessment (LCA) evaluates the environmental impacts of the entire production chain, from biomass collection and gasification to FT synthesis and the final use of sustainable aviation fuel (SAF). The study demonstrates that a 50% blending ratio of SAF can reduce emissions by about 60 Mt CO2e, which accounts for approximately 43% of the emissions from China’s aviation sector in 2023. The analysis highlights the significant decarbonisation potential of SAF, especially from crop residues like corn straw, which can substantially reduce the carbon footprint of aviation fuel [73].

The life cycle assessment (LCA) examines the environmental impacts of producing low-carbon hydrogen via electrolysis, capturing CO₂ through direct air capture (DAC), and synthesising synthetic natural gas (SNG). The study reveals that SNG can reduce life cycle greenhouse gas (GHG) emissions by 52–88% compared to fossil natural gas, depending on the energy sources used for electrolysis and DAC. Utilising renewable energy sources such as wind, solar, nuclear, and hydro for producing low-carbon hydrogen and capturing CO₂ significantly reduces the overall carbon footprint of SNG, aligning with sustainable energy goals in USA [74].

The approach of incorporating life cycle assessments alongside techno-economic evaluations presents a comprehensive understanding of the sustainability of e-fuels [75]. This approach is crucial to guarantee that the long-term environmental outcomes are in harmony with the initial economic estimations [76]. Advancements in processes such as high-temperature electrolysis and the reverse water–gas shift (RWGS) reaction, as observed by [55], are crucial. These technologies exhibit high carbon conversion efficiency, but their economic viability remains heavily contingent on their scale of operation and future technological enhancements [77,78,79,80]. These studies highlight the potential of innovative pathways for producing sustainable aviation fuels, emphasising their economic viability and substantial environmental benefits [81,82]. The findings can inform policy decisions, guide industry practices, and promote further research in sustainable fuel production [83,84,85].

4.4. Gap Analysis

There seems to be a diversity of metrics used in different studies for evaluating both the techno-economic and environmental aspects of e-fuels production. Examples follow.

Studies range from using metrics like “minimum fuel selling price (MFSP)” to “levelised cost of methanol (LCoM)” to assess economic viability, making direct comparisons challenging. This variance suggests a need for standardised metrics to provide clearer benchmarks for comparisons [51,52,53,54,70,71].

The studies primarily revolve around common feedstocks like CO₂, H₂, and biomass. However, the source of these feedstocks (e.g., direct air capture vs. point-source capture for CO₂, or different types of biomass) can lead to significant differences in economic and environmental outcomes. Research that focuses on comparing feedstock sources more directly is relatively limited [55,57,59,68].

Some studies highlight the benefits of integrated systems, such as combining Fischer–Tropsch synthesis with corn ethanol production or integrating power-to-methanol with MSW gasification. However, the comparative advantages of these integrated systems versus standalone processes need more comprehensive research [51,55,68].

The studies hail from different geographical regions [62,63,64,65,66,72], each with unique energy infrastructures, policies, and natural resources. While some studies provide specific insights about their respective regions, a comprehensive comparative analysis on how geographical factors impact e-fuel production’s economic and environmental outcomes is missing.

Some studies [58,59,60,61,62,63,64] hint at the importance of technological advancements, but in-depth analyses of how emerging technologies (like advancements in catalysts, electrolysers, or carbon capture methods) might shift the paradigms are relatively sparse.

While many studies [59,60,61,62,63,64,65,66] employ life cycle assessments (LCAs) and primarily focus on greenhouse gas emissions, other environmental impacts, such as water usage, land use, or impacts on biodiversity, are less frequently addressed. This lack of comprehensive environmental assessments might miss some indirect negative impacts of certain e-fuel production methods.

The study by Romo Martínez [28] hints at the importance of CCU- and H₂-based e-fuel considering societal acceptance, regulatory factors, and safety. However, these socio-political factors are less frequently addressed in other studies, suggesting a potential research gap.

In terms of economic feasibility, some studies [51,71] highlight the high costs associated with uneven solar energy distribution, while others, such as the study in the UK, indicate relatively lower costs and positive outcomes. These conflicting outcomes indicate that variables like local conditions, technology choices, and feedstock sources can greatly influence results, emphasising the need for more standardised assumptions and scenarios.

4.5. Strategic Actions and Policy Implications

4.5.1. In the Context of Techno-Economic Analysis

Insights from the European Union (EU) and Sweden distinctly signal that policy frameworks and effective management of energy resources are integral to the success of e-fuel production [54,62]. Choosing production locations strategically, based on grid mix and the availability of renewable resources, becomes essential to curtail costs and optimise production efficiency. The necessity for economic incentives or policies like fossil CO₂ taxation to make some technologies more cost-competitive, like the production of e-diesel in Saudi Arabia and synthetic methane in Abu Dhabi and Benevento, is highlighted [52,71]. These mechanisms are fundamental in ensuring the feasibility of these e-fuels compared to their conventional counterparts.

4.5.2. In the Context of Life Cycle Analysis

Given the LCA findings, it is evident that the utilisation of cleaner sources of electricity and heat can significantly reduce GHG emissions (up to 21.55%). It underscores the strategic need for policies to promote the development and deployment of cleaner energy sources, like wind and solar, in the aviation fuel sector [67]. It is demonstrated that utilising offshore wind electricity could produce SAF with a GWP that is substantially lower than the current UK mandate [51]. Governments can raise the bar by setting more stringent emission standards, thus pushing industries to adopt cleaner production methods. The 54% reduction in carbon footprint from conventional methods suggests the effectiveness of advanced production scenarios [71]. Policymakers should consider providing incentives for research and adoption of these advanced scenarios. A study by Habermeyer, Papantoni [54] indicated the possibility of achieving significant SAF output using forest residue. This necessitates sustainable forest management policies to ensure long-term availability of feedstock and avoid deforestation. van de Graaff [58] emphasises the superiority of green hydrogen over blue hydrogen from a life cycle perspective. Policies should, therefore, not only focus on the immediate benefits but consider the entire life cycle impacts of technologies. Given the potential synergy of local production combined with imported hydrogen or fuels highlighted in [58], international collaborations and trade agreements can be fostered to optimise energy production and consumption.

4.6. Future Outlook and Research Directions

Future research should prioritise addressing the existing methodological deficiencies, with a particular emphasis on reducing costs, improving process efficiency, and effectively incorporating renewable energy sources in the context of TEAs and LCAs.

4.6.1. In the Context of Techno-Economic Analysis Research

There is a consistent recommendation across studies for more focused research on process optimisation and model improvements, particularly informed by experimental and kinetics data. The integration of renewable energy sources (e.g., solar PV, wind farms) is a recurring theme in the viability of e-fuel processes [66,72]. Future research should further explore the efficient coupling of e-fuel production with fluctuating renewable energy sources. The broader implications of these studies suggest a shift towards more sustainable fuel options. However, this shift requires not only technological advancements but also supportive policy frameworks and market mechanisms.

4.6.2. In the Context of Life Cycle Analysis Research

Wang, Guo [67] highlighted the use of corn, cassava, and corn cob as feedstocks. Future research should investigate the use of non-food biomass and waste materials to address food security concerns and broaden the array of usable feedstocks. The potential of FT fuels, especially when integrated with corn ethanol production, is showcased. Continued research in techno-economic evaluation of innovative pathways and integration strategies is necessary [68]. With a study showing potential WTW GHG emissions reduction of at least 92% using electrofuels, it is evident that the future of aviation fuel might lean heavily on these innovations [55]. More detailed studies into optimising e-fuel production are warranted. A study focusing on PtL production highlighted its potential, especially for the aviation sector [69]. Further research into the scale-up, optimisation, and commercial viability of PtL processes is a promising direction. The study [61] hinted at the increasing competitiveness of the methanol production process in the mid-term future. Future research could delve deeper into market trends, economic feasibility, and cost structures. While GHG emissions remain central, the phenomenon of contrail-induced cloudiness highlights the importance of addressing broader climate impacts. Further studies into the atmospheric and climate effects of different SAFs and their production processes are essential [65].

5. Conclusions

The breadth and depth of studies on the techno-economic analysis (TEA) of e-fuels highlight a promising yet challenging landscape. Production efficiencies, capital and operational expenditures, and break-even points vary based on regional considerations, available technologies, and evolving market conditions. As Europe and other regions adopt e-fuels as a key component in their energy transition strategies, the techno-economic narrative will likely become more complex and refined. While technology and economics are central to this evolution, the alignment with policy, societal acceptance, and environmental considerations will be crucial to realising the full potential of e-fuels. The rapid evolution of e-fuels underscores the importance of comprehensive life cycle assessments (LCAs) to understand their true environmental implications. From raw material acquisition, production, and use-phase emissions to end-of-life considerations, it is evident that while e-fuels offer a promising solution to decarbonising the transportation sector, their sustainability depends on multiple factors. Various studies from 2020 to 2023 show that advancing technology, policy, and stakeholder awareness can potentially steer e-fuels towards becoming the sustainable energy solution of the future.

In summary, while the manufacturing processes for e-fuels such as synthetic methane, sustainable aviation fuels (SAFs), and synthetic diesel are progressively maturing, their economic feasibility remains deeply influenced by regional variables, technological development stages, and the nature of the energy sources used. Continuous research and development efforts, combined with robust policy and economic strategies, are critical for advancing these technologies towards widespread commercial use and deployment. Future studies should aim to bridge current methodological gaps by focusing on several critical areas. Firstly, efforts should be directed towards significantly reducing costs in the production and deployment of sustainable aviation fuels. This includes exploring innovative technologies and optimising existing processes to make SAF production more economically viable. Secondly, enhancing process efficiency is crucial, which involves refining conversion processes, improving yield rates, and minimising energy consumption throughout the production cycle.

Lastly, the seamless integration of renewable energy resources into SAF production must be prioritised. This entails developing hybrid systems that combine various renewable energy sources, such as solar, wind, and biomass, to create a more sustainable and resilient fuel supply chain. Addressing these areas will advance the field of sustainable aviation fuels and contribute to broader goals of environmental sustainability and energy security. This study focuses on the techno-economic and life cycle analysis of sustainable aviation fuels, aiming to provide comprehensive understanding and strategic insights necessary for the successful deployment of SAFs, thereby paving the way for a sustainable future in aviation.