Second Generation Biofuels: High-Efficiency Microalgae for Biodiesel Production

The use of fossil fuels is now widely accepted as unsustainable due to depleting resources and the accumulation of greenhouse gases in the environment that have already exceeded the “dangerously high” threshold of 450 ppm CO₂-e. To achieve environmental and economic sustainability, fuel production processes are required that are not only renewable, but also capable of sequestering atmospheric CO₂. Currently, nearly all renewable energy sources (e.g. hydroelectric, solar, wind, tidal, geothermal) target the electricity market, while fuels make up a much larger share of the global energy demand (～66%). Biofuels are therefore rapidly being developed. Second generation microalgal systems have the advantage that they can produce a wide range of feedstocks for the production of biodiesel, bioethanol, biomethane and biohydrogen. Biodiesel is currently produced from oil synthesized by conventional fuel crops that harvest the sun’s energy and store it as chemical energy. This presents a route for renewable and carbon-neutral fuel production. However, current supplies from oil crops and animal fats account for only approximately 0.3% of the current demand for transport fuels. Increasing biofuel production on arable land could have severe consequences for global food supply. In contrast, producing biodiesel from algae is widely regarded as one of the most efficient ways of generating biofuels and also appears to represent the only current renewable source of oil that could meet the global demand for transport fuels. The main advantages of second generation microalgal systems are that they: (1) Have a higher photon conversion efficiency (as evidenced by increased biomass yields per hectare): (2) Can be harvested batch-wise nearly all-year-round, providing a reliable and continuous supply of oil: (3) Can utilize salt and waste water streams, thereby greatly reducing freshwater use: (4) Can couple CO₂-neutral fuel production with CO₂ sequestration: (5) Produce non-toxic and highly biodegradable biofuels. Current limitations exist mainly in the harvesting process and in the supply of CO₂ for high efficiency production. This review provides a brief overview of second generation biodiesel production systems using microalgae.     

Solar‐Light‐Driven CO2 Reduction by CH4 on Silica‐Cluster‐Modified Ni Nanocrystals with a High Solar‐to‐Fuel Efficiency and Excellent Durability

Catalytic CO₂ reforming of CH₄ (CRM) to produce syngas (H₂ and CO) provides a promising approach to reducing global CO₂ emissions and the extensive utilization of natural gas resources. However, the rapid deactivation of the reported catalysts due to severe carbon deposition at high reaction temperatures and the large energy consumption of the process hinder its industrial application. Here, a method for almost completely preventing carbon deposition is reported by modifying the surface of Ni nanocrystals with silica clusters. The obtained catalyst exhibits excellent durability for CRM with almost no carbon deposition and deactivation after reaction for 700 h. Very importantly, it is found that CRM on the catalyst can be driven by focused solar light, thus providing a promising new approach to the conversion of renewable solar energy to fuel due to the highly endothermic characteristics of CRM. The reaction yields high production rates of H₂ and CO (17.1 and 19.9 mmol min^?1 g^?1, respectively) with a very high solar‐to‐fuel efficiency (η, 12.5%). Even under focused IR irradiation with a wavelength above 830 nm, the η of the catalyst remains as high as 3.1%. The highly efficient catalytic activity arises from the efficient solar‐light‐driven thermocatalytic CRM enhanced by a novel photoactivation effect.     

CO2‐Mediated H2 Storage‐Release with Nanostructured Catalysts: Recent Progresses,Challenges, and Perspectives

It has increasingly become clear that economic growth worldwide based on fossil fuel energy supply cannot be sustained; thus, alternative, renewable energy sources and carriers must be urgently developed to maintain growth. Dihydrogen (H₂), which can produce energy without generating environmental pollutants, can play a major role in this endeavor. However, to use H₂ in renewable energy systems, systems and materials that can store and transport it, or convert it into easier‐to‐handle/transport synthetic fuels, need to be developed. In this article, first, many of the issues related to both homogeneous and heterogeneous catalysts that are being developed to help H₂'s use as energy carrier are discussed. More focus is then given to heterogeneous nanocatalysts that are developed for reversible CO₂‐mediated hydrogenation and dehydrogenation reactions involving chemical hydrogen carriers and delivery systems, mainly formic acid/CO₂ and formate/bicarbonate. The challenges associated with the development of nanocatalysts based on earth‐abundant elements for dehydrogenation and hydrogenation reactions of these compounds for H₂ storage and release are emphasized in the discussions. Finally, the pressing research questions and major issues that need to be addressed in the near future to help the realization of the “hydrogen economy” are outlined.     

Toward a Carbon Dioxide Neutral Industrial Park

The industrial park of Herdersbrug (Brugge, Flanders, Belgium) comprises 92 small and medium‐sized enterprises, a waste‐to‐energy incinerator, and a power plant (not included in the study) on its site. To study the carbon dioxide (CO₂) neutrality of the park, we made a park‐wide inventory for 2007 of the CO₂ emissions due to energy consumption (electricity and fossil fuel) and waste incineration, as well as an inventory of the existing renewable electricity and heat generation. The definition of CO₂ neutrality in Flanders only considers CO₂ released as a consequence of consumption or generation of electricity, not the CO₂ emitted when fossil fuel is consumed for heat generation. To further decrease or avoid CO₂ emissions, we project and evaluate measures to increase renewable energy generation. The 21 kilotons (kt) of CO₂ emitted due to electricity consumption are more than compensated by the 25 kt of CO₂ avoided by generation of renewable electricity. Herdersbrug Industrial Park is thus CO₂ neutral, according to the definition of the Flemish government. Only a small fraction (6.6%) of the CO₂ emitted as a consequence of fossil fuel consumption (heat generation) and waste incineration is compensated by existing and projected measures for renewable heat generation. Of the total CO₂ emission (149 kt) due to energy consumption (electricity + heat generation) and waste incineration on the Herdersbrug Industrial Park in 2007, 70.5% is compensated by existing and projected renewable energy generated in the park. Forty‐seven percent of the yearly avoided CO₂ corresponds to renewable energy generated from waste incineration and biomass fermentation.     

Carbon Recycling for Renewable Materials and Energy Supply

The current flow of carbon for the production, use, and waste management of polymer‐based products is still mostly linear from the lithosphere to the atmosphere with rather low rates of material recycling. In view of a limited future supply of biomass, this article outlines the options to further develop carbon recycling (C‐REC). The focus is on carbon dioxide (CO₂) capture and use for synthesis of platform chemicals to produce polymers. CO₂ may be captured from exhaust gases after combustion or fermentation of waste in order to establish a C‐REC system within the technosphere. As a long‐term option, an external C‐REC system can be developed by capturing atmospheric CO₂. A central role may be expected from renewable methane (or synthetic natural gas), which is increasingly being used for storage and transport of energy, but may also be used for renewable carbon supply for chemistry. The energy input for the C‐REC processes can come from wind and solar systems, in particular, power for the production of hydrogen, which is combined with CO₂ to produce various hydrocarbons. Most of the technological components for the system already exist, and, first modules for renewable fuel and polymer production systems are underway in Germany. This article outlines how the system may further develop over the medium to long term, from a piggy‐back add‐on flow system toward a self‐carrying recycling system, which has the potential to provide the material and energy backbone of future societies. A critical bottleneck seems to be the capacity and costs of renewable energy supply, rather than the costs of carbon capture.     

Trading Off Global Fuel Supply,CO2 Emissions and Sustainable Development

The United Nations Conference on Climate Change (Paris 2015) reached an international agreement to keep the rise in global average temperature ‘well below 2°C’ and to ‘aim to limit the increase to 1.5°C’. These reductions will have to be made in the face of rising global energy demand. Here a thoroughly validated dynamic econometric model (Eq 1) is used to forecast global energy demand growth (International Energy Agency and BP), which is driven by an increase of the global population (UN), energy use per person and real GDP (World Bank and Maddison). Even relatively conservative assumptions put a severe upward pressure on forecast global energy demand and highlight three areas of concern. First, is the potential for an exponential increase of fossil fuel consumption, if renewable energy systems are not rapidly scaled up. Second, implementation of internationally mandated CO₂ emission controls are forecast to place serious constraints on fossil fuel use from ~2030 onward, raising energy security implications. Third is the challenge of maintaining the international ‘pro-growth’ strategy being used to meet poverty alleviation targets, while reducing CO₂ emissions. Our findings place global economists and environmentalists on the same side as they indicate that the scale up of CO₂ neutral renewable energy systems is not only important to protect against climate change, but to enhance global energy security by reducing our dependence of fossil fuels and to provide a sustainable basis for economic development and poverty alleviation. Very hard choices will have to be made to achieve ‘sustainable development’ goals.     

Thermophilic Hydrogen Production from Renewable Resources: Current Status and Future Perspectives

Hydrogen (H₂) is considered an alternative fuel of the future due to its high energy density and non-polluting nature. H₂ energy provides many advantages over fossil fuels in that it is renewable, eco-friendly, and efficient. The global demand for H₂ is increasing significantly; however, matching the supply of cost-competitive H₂ to meet the current demand is a major technological barrier. H₂ can be produced from lignocellulosic biomass and serve as a raw material for the synthesis of many industrially important chemicals. The use of thermophilic bacteria for biological production of H₂ appears to be a promising alternative route to the current H₂ production technologies. However, the carbon and H₂ production metabolisms in most thermophilic bacteria have not yet been completely understood. This paper summarizes the recent research progress made toward understanding the carbon utilization for H₂ production and developing gene manipulation techniques to enhance the H₂ production capabilities in thermophilic bacteria. It reviews the current status, future directions and opportunities that thermophiles can offer to enable a cost-competitive and environmentally benign H₂ production bioprocess.     

The role of bioenergy for global deep decarbonization: CO2 removal or low‐carbon energy?

Bioenergy is expected to have a prominent role in limiting global greenhouse emissions to meet the climate change target of the Paris Agreement. Many studies identify negative emissions from bioenergy generation with carbon capture and storage (BECCS) as its key contribution, but assume that no other CO₂ removal technologies are available. We use a global integrated assessment model, TIAM‐UCL, to investigate the role of bioenergy within the global energy system when direct air capture and afforestation are available as cost‐competitive alternatives to BECCS. We find that the presence of other CO₂ removal technologies does not reduce the pressure on biomass resources but changes the use of bioenergy for climate mitigation. While we confirm that when available BECCS offers cheaper decarbonization pathways, we also find that its use delays the phase‐out of unabated fossil fuels in industry and transport. Furthermore, it displaces renewable electricity generation, potentially increasing the likelihood of missing the Paris Agreement target. We found that the most cost‐effective solution is to invest in a basket of CO₂ removal technologies. However, if these technologies rely on CCS, then urgent action is required to ramp up the necessary infrastructure. We conclude that a sustainable biomass supply is critical for decarbonizing the global energy system. Since only a few world regions carry the burden of producing the biomass resource and store CO₂ in geological storage, adequate international collaboration, policies and standards will be needed to realize this resource while avoiding undesired land‐use change.     

Active extracellular substances of Bacillus thuringiensis ITRI‐G1 induce microalgae self‐disruption for microalgal biofuel

Microalgal cultures are a clean and sustainable means to use solar energy for CO₂ fixation and fuel production. Microalgae grow efficiently and are rich in oil, but recovering that oil is typically expensive and consumes much energy. Therefore, effective and low‐cost techniques for microalgal disruption and oil or lipid extraction are required by the algal biofuel industry. This study introduces a novel technique that uses active extracellular substances to induce microalgal cell disruption. A bacterium indigenous to Taiwan, Bacillus thuringiensis, was used to produce the active extracellular substances, which were volatile compounds with high thermal stability. Approximately 74% of fresh microalgal cells were disrupted after a 12‐h treatment with the active extracellular substances. Algal lipid extraction efficiency was improved and the oil extraction time was decreased by approximately 37.5% compared with the control treatment. The substances effectively disrupted fresh microalgal cells but not dehydrated microalgal cells. An analysis of microalgal DNA from fresh cells after disruption treatment demonstrated typical DNA laddering, indicating that disruption may have resulted from programmed cell death. This study revealed that biological treatments are environmentally friendly methods for increasing microalgal lipid extraction efficiency, and introduced a microalgal cell self‐disruption mechanism.     

Highly Efficient Solar‐Driven Carbon Dioxide Reduction on Molybdenum Disulfide Catalyst Using Choline Chloride‐Based Electrolyte

Conversion of CO₂ to energy‐rich chemicals using renewable energy is of much interest to close the anthropogenic carbon cycle. However, the current photoelectrochemical systems are still far from being practically feasible. Here the successful demonstration of a continuous, energy efficient, and scalable solar‐driven CO₂ reduction process based on earth‐abundant molybdenum disulfide (MoS₂) catalyst, which works in synergy with an inexpensive hybrid electrolyte of choline chloride (a common food additive for livestock) and potassium hydroxide (KOH) is reported. The CO₂ saturated hybrid electrolyte utilized in this study also acts as a buffer solution (pH ≈ 7.6) to adjust pH during the reactions. This study reveals that this system can efficiently convert CO₂ to CO with solar‐to‐fuel and catalytic conversion efficiencies of 23% and 83%, respectively. Using density functional theory calculations, a new reaction mechanism in which the water molecules near the MoS₂ cathode act as proton donors to facilitate the CO₂ reduction process by MoS₂ catalyst is proposed. This demonstration of a continuous, cost‐effective, and energy efficient solar driven CO₂ conversion process is a key step toward the industrialization of this technology.     

Hydrogen production by microalgae

The production of H₂ gas from water and sunlightusing microalgae, `biophotolysis', has been a subjectof applied research since the early 1970s. A numberof approaches have been investigated, but most provedto have fundamental limitations or requireunpredictable research breakthroughs. Examples areprocesses based on nitrogen-fixing microalgae andthose producing H<sub>2</sub> and O<sub>2</sub> simultaneously fromwater (`direct biophotolysis'). The most plausibleprocesses for future applied R & D are those whichcouple separate stages of microalgal photosynthesisand fermentations (`indirect biophotolysis'). Theseinvolve fixation of CO₂ into storagecarbohydrates followed by their conversion to H₂by the reversible hydrogenase, both in dark andpossibly light-driven anaerobic metabolic processes. Based on a preliminary engineering and economicanalysis, biophotolysis processes must achieve closeto an overall 10% solar energy conversion efficiencyto be competitive with alternatives sources ofrenewable H₂, such as photovoltaic-electrolysisprocesses. Such high solar conversion efficiencies inphotosynthetic CO₂ fixation could be reached bygenetically reducing the number of light harvesting(antenna) chlorophylls and other pigments inmicroalgae. Similarly, greatly increased yields ofH₂ from dark fermentation by microalgae could beobtained through application of the techniques ofmetabolic engineering. Another challenge is toscale-up biohydrogen processes with economicallyviable bioreactors.Solar energy driven microalgae processes forbiohydrogen production are potentially large-scale,but also involve long-term and economically high-riskR&D. In the nearer-term, it may be possible tocombine microalgal H₂ production with wastewatertreatment.     

China's bioenergy potential

Despite great enthusiasm about developing renewable energy in China, the country's bioenergy potential remains unclear. Traditional utilization of bioenergy through primarily household combustion of crop residue and fuelwood is still a predominant energy source for rural China. More efficient utilization of ～300 million tons of crop residues for bioelectricity generation could add a couple of percent of renewable energy to China's total energy production. With <9% of the world's arable land supporting ～20% of the world's population, China is already a net grain importer and has little extra farmland for producing a significantly additional amount of biofuels from first‐generation energy crops, such as maize, sugarcane, and soybean. Second‐generation energy crops hold the greatest potential for bioenergy development worldwide. Miscanthus, a native perennial C4 grass that produces high biomass across almost the entire climatic zone of China, is the most promising second‐generation energy crop to domesticate and cultivate. A reasonable near‐term goal is to produce 1 billion tons of Miscanthus biomass annually from ～100 million hectares of marginal and degraded land concentrated in northern and northwestern China. This can generate ～1458 TW h electricity and mitigate ～1.7 billion tons of CO₂ emission from power coal, which account for ～45% of China's electricity output and ～28% of CO₂ emission in 2007. Furthermore, growing perennial grasses on marginal and degraded land will contribute to the ongoing efforts in China to restore vast areas of land under serious threat of desertification. With this potential taken into account, bioenergy can play a major role in meeting China's rapidly growing energy demand while substantially reducing greenhouse gas emission.     

The Potential Role of Reactive Metals for a Clean Energy Transition

Reactive metal‐based storage systems are a new alternative to support the clean energy transition. Herein, the cases of Al and Na are presented, both preliminarily fulfilling the constraints regarding sustainability, but employing two rather different processes. Both, the steam combustion of molten Al for H₂ and heat production, and a new rechargeable battery, which makes use of seawater and sodium as electrodes, show promising round‐trip efficiencies. The latter technology also allows CO₂‐trapping, desalination, Na metal, and chlorine production. It is argued that further research efforts are needed to verify the sustainability and ability of reactive metal‐based technologies to compete with other storage technologies.     

Flue gas compounds and microalgae: (Bio-)chemical interactions leading to biotechnological opportunities

Flue gases are a resource yet to be fully utilised in microalgal biotechnology, not only to moderate the anthropogenic effects on our climate, but also to steer microalgal resource management towards innovative applications of microalgal biomass compounds. These gases, both untreated and treated into current discharge standards, contain CO₂, N₂, H₂O, O₂, NO_x, SO_x, C_xH_y, CO, particulate matter, halogen acids and heavy metals. To better steer and engineer flue gas-fed microalgal cultures, all these compounds need to be considered. Therefore, here, we review (i) the chemical composition and treatment technologies of flue gas, (ii) the uptake pathways and removal of the different compounds in microalgae reactors, and (iii) the tolerance and effects on microalgae of all flue gas compounds. By emphasising the interactions between microalgae and flue gas compounds, we envisage new pathways for microalgal biomass valorisation such as enzyme production for environmental technology, novel biogas production and biosequestration of minerals. Furthermore, we highlight fundamental and applied research niches that merit further investigation.     

Recent Advanced Materials for Electrochemical and Photoelectrochemical Synthesis of Ammonia from Dinitrogen: One Step Closer to a Sustainable Energy Future

Ammonia (NH₃), an important raw material for chemical industry and agriculture, is also considered to be an intriguing energy storage and transportation media for chemical conversion schemes. The world's primary NH₃ supply is based on the natural nitrogen fixation by diazotrophs through an enzymatic nitrogenase process and the industrial nitrogen fixation through a traditional Haber–Bosch process. The natural synthesis of NH₃ can hardly meet the rapidly growing global demand. Meanwhile, the industrial NH₃ production is still dominated by the high‐temperature and high‐pressure reaction between nitrogen and hydrogen (N₂ + 3H₂ → 2NH₃), requiring intensive energy input and generating massive CO₂. Therefore, seeking a breakthrough in the development of catalysts toward efficient ammonia synthesis has become the frontier of energy and chemical conversion schemes. This review summarizes and discusses the recent progress on developing new strategies to optimize the efficiency of NH₃ production coupled with renewable energy sources, with a specific focus on electrocatalytic and photoelectrocatalytic conversion of N₂ to NH₃. The most recent advances in the development of catalytic materials, the design of the reaction systems, and the computational insights for electrochemical and photoelectrochemical ammonia synthesis are covered.     

Cultivation, photobioreactor design and harvesting of microalgae for biodiesel production: A critical review

Microalgae have the ability to mitigate CO₂ emission and produce oil with a high productivity, thereby having the potential for applications in producing the third-generation of biofuels. The key technologies for producing microalgal biofuels include identification of preferable culture conditions for high oil productivity, development of effective and economical microalgae cultivation systems, as well as separation and harvesting of microalgal biomass and oil. This review presents recent advances in microalgal cultivation, photobioreactor design, and harvesting technologies with a focus on microalgal oil (mainly triglycerides) production. The effects of different microalgal metabolisms (i.e., phototrophic, heterotrophic, mixotrophic, and photoheterotrophic growth), cultivation systems (emphasizing the effect of light sources), and biomass harvesting methods (chemical/physical methods) on microalgal biomass and oil production are compared and critically discussed. This review aims to provide useful information to help future development of efficient and commercially viable technology for microalgae-based biodiesel production.     

Empirical Fuel Consumption and CO2 Emissions of Plug‐In Hybrid Electric Vehicles

Plug‐in hybrid electric vehicles (PHEVs) combine electric and conventional propulsion. Official fuel consumption values of PHEVs are based on standardized driving cycles, which show a growing discrepancy with real‐world fuel consumption. However, no comprehensive empirical results on PHEV fuel consumption are available, and the discrepancy between driving cycle and empirical fuel consumption has been conjectured to be large for PHEV. Here, we analyze real‐world fuel consumption data from 2,005 individual PHEVs of five PHEV models and observe large variations in individual fuel consumption with deviation from test‐cycle values in the range of 2% to 120% for PHEV model averages. Deviations are larger for short‐ranged PHEVs. Among others, range and vehicle power are influencing factors for PHEV model fuel consumption with average direct carbon dioxide (CO₂) emissions decreasing by 2% to 3% per additional kilometer (km) of electric range. Additional simulations show that PHEVs recharged from renewable electricity can noteworthily reduce well‐to‐wheel CO₂ emissions of passenger cars, but electric ranges should not exceed 200 to 300 km since battery production is CO₂‐intense. Our findings indicate that regulations should (1) be based on real‐world fuel consumption measurements for PHEV, (2) take into account charging behavior and annual mileages, and (3) incentivize long‐ranged PHEV.     

FACE facts hold for multiple generations; Evidence from natural CO2 springs

Rising atmospheric CO₂ concentration is a key driver of enhanced global greening, thought to account for up to 70% of increased global vegetation in recent decades. CO₂ fertilization effects have further profound implications for ecosystems, food security and biosphere‐atmosphere feedbacks. However, it is also possible that current trends will not continue, due to ecosystem level constraints and as plants acclimate to future CO₂ concentrations. Future predictions of plant response to rising [CO₂] are often validated using single‐generation short‐term FACE (Free Air CO₂ Enrichment) experiments but whether this accurately represents vegetation response over decades is unclear. The role of transgenerational plasticity and adaptation in the multigenerational response has yet to be elucidated. Here, we propose that naturally occurring high CO₂ springs provide a proxy to quantify the multigenerational and long‐term impacts of rising [CO₂] in herbaceous and woody species respectively, such that plasticity, transgenerational effects and genetic adaptation can be quantified together in these systems. In this first meta‐analysis of responses to elevated [CO₂] at natural CO₂ springs, we show that the magnitude and direction of change in eight of nine functional plant traits are consistent between spring and FACE experiments. We found increased photosynthesis (49.8% in spring experiments, comparable to 32.1% in FACE experiments) and leaf starch (58.6% spring, 84.3% FACE), decreased stomatal conductance (g_s, 27.2% spring, 21.1% FACE), leaf nitrogen content (6.3% spring, 13.3% FACE) and Specific Leaf Area (SLA, 9.7% spring, 6.0% FACE). These findings not only validate the use of these sites for studying multigenerational plant response to elevated [CO₂], but additionally suggest that long‐term positive photosynthetic response to rising [CO₂] are likely to continue as predicted by single‐generation exposure FACE experiments.     

Heterogeneous Catalysts with Well‐Defined Active Metal Sites toward CO2 Electrocatalytic Reduction

The global atmospheric CO₂ concentration reached 147% of pre‐industrial levels in 2019, and is still increasing with an accelerated rate. A series of methods have been developed to convert CO₂ to other non‐greenhouse molecules. Elelctrocatalytic CO₂ reduction reaction (CO2RR) is one of the promising methods, since it could support renewable energy. Optimizing the CO2RR system requires finding highly efficient catalysts, as well as electrolysis systems. In this essay, the development of promising heterogeneous catalysts with well‐defined active metal sites is discussed. These catalysts could be prepared by immobilizing metal cations onto chemically well‐defined substrates, such as metal‐organic frameworks, covalent‐organic frameworks, polyoxometalates, or immobilizing well‐defined molecular catalysts on conducting substrates. A clear perspective on the catalyst's structures contributes to the understanding of structure‐reactivity correlations, which could, in turn, shed light on designing better catalysts. Some methods to assist the electrocatalysis process, such as coupling with solar or heat energy, are also briefly discussed.     

Energy crops: current status and future prospects

Energy crops currently contribute a relatively small proportion to the total energy produced from biomass each year, but the proportion is set to grow over the next few decades. This paper reviews the current status of energy crops and their conversion technologies, assesses their potential to contribute to global energy demand and climate mitigation over the next few decades, and examines the future prospects. Previous estimates have suggested a technical potential for energy crops of～400 EJ yr^?1 by 2050. In a new analysis based on energy crop areas for each of the IPCC SRES scenarios in 2025 (as projected by the IMAGE 2.2 integrated assessment model), more conservative dry matter and energy yield estimates and an assessment of the impact on non‐CO₂ greenhouse gases were used to estimate the realistically achievable potential for energy crops by 2025 to be between 2 and 22 EJ yr^?1, which will offset～100–2070 Mt CO₂‐eq. yr^?1. These results suggest that additional production of energy crops alone is not sufficient to reduce emissions to meet a 550 μmol mol^?1 atmospheric CO₂ stabilization trajectory, but is sufficient to form an important component in a portfolio of climate mitigation measures, as well as to provide a significant sustainable energy resource to displace fossil fuel resources. Realizing the potential of energy crops will necessitate optimizing the dry matter and energy yield of these crops per area of land through the latest biotechnological routes, with or without the need for genetic modification. In future, the co‐benefits of bioenergy production will need to be optimized and methods will need to be developed to extract and refine high‐value products from the feedstock before it is used for energy production.