Development gaps and needs
Science
Version published:
June 2, 2026 - 3:07am
The gaps identified in this section impact delivered feedstock cost ($/dry ton) and the maximum scale at which seaweed biomass can be reliably produced offshore, the two variables that most directly govern whether seaweed-derived fuels can reach cost parity with fossil alternatives and achieve the production volumes needed to displace meaningful quantities of fossil fuel in aviation and shipping.
Species Selection and Cultivation
Biomass productivity is too variable to make biofuels cost-competitive with conventional products
Yield is one of the biggest cost drivers for macroalgae farms. Reported commercial yields for cultivated seaweed span an order of magnitude — from under 5 to over 40 dry tonnes per hectare per year — and the drivers of this variation (site oceanography, strain genetics, management intensity, measurement methodology) are poorly understood. At the high end of reported yields, seaweed farming approaches cost-competitiveness with terrestrial biofuel feedstocks; at the low end, it remains uneconomic. Identifying and reliably replicating high-yield conditions is therefore a research priority (State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017, Roesijadi et al., 2010)
Seaweeds contain compounds that inhibit conversion processes
Brown seaweeds have phenolic compounds that can inhibit the AD process. (Milledge & Harvey, 2018) High ash content (along with the salt in seaweeds) can reduce the biodegradability of seaweed and reduce methane yields in the AD process. (State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017) and the heating value of seaweed-based biofuels Heavy metals (e.g. cadmium, lead) pose risks for agricultural applications. Research is needed to optimize species selection, pretreatment, and conversion strategies to alleviate the inhibitory mechanisms in order to increase energy yield per biomass input (Milledge & Harvey, 2018).
Offshore farms may face nutrient limitations that restrict productivity
As cultivation goes offshore, it could hit up against nutrient limitations including the supply of dissolved iron, nitrogen and phosphorus. For example, oceanic iron concentrations are often 1000-fold lower than what Macrocystis pyrifera requires to sustain healthy growth (Paine et al., 2023). Artificial upwelling might alleviate nutrient limitation so we need targeted research and demonstrations in a range of conditions to understand these limits and potential interventions.
Some environmental risks of large-scale seaweed farming are poorly understood
Key knowledge gaps exist regarding the environmental risks of large-scale seaweed farming development. See “Environmental Benefits/Risks” section in the Cultivation chapter.
Open ocean cultivation systems remain unproven at scale
Offshore cultivation infrastructure needs to be developed to withstand challenging conditions. For example, in the case of deepwater mooring without fixed seafloor anchors; current designs lack validation at commercial scale in high-energy offshore environments. Similarly, combined weight of saturated biomass and infrastructure affects buoyancy, mooring design, and harvest vessel requirements in ways not yet systematically characterized.
Efficient nutrient delivery systems are underdeveloped
Dissolved nutrient concentrations increase in the deep ocean so artificial upwelling and depth cycling might be able to alleviate nutrient limitations at the surface. These methods need to developed and optimized so that they can be scaled up to address some of the nutrient challenges discussed above (ARPA-E, 2025).
Automated Harvesting technologies are still nascent
New methods are needed for mechanical harvesting and dewatering of seaweed biomass, especially offshore (ARPA-E, 2025).
The seasonal nature of macroalgae growth is a particular challenge for year-round biofuel production
Macroalgae growth and the proliferation of sargassum blooms are inherently seasonal, creating a mismatch with biofuel market structures that require feedstock availability year-round. Storage and preservation methods that maintain biomass quality and chemical composition through the off-season are not yet proven at scale, and the effect of different storage approaches (ensilage, drying, wet storage, fermentation) on downstream conversion performance is incompletely characterized. Exploration of HTL to address this is useful since HTL performance differences across species are minimal compared to experimental variation enabling the use of different species and still resulting in a consistent output.
The gaps identified in this section impact delivered feedstock cost ($/dry ton) and the maximum scale at which seaweed biomass can be reliably produced offshore, the two variables that most directly govern whether seaweed-derived fuels can reach cost parity with fossil alternatives and achieve the production volumes needed to displace meaningful quantities of fossil fuel in aviation and shipping.
Species Selection and Cultivation
Biomass productivity is too variable to make biofuels cost-competitive with conventional products Yield is one of the biggest cost drivers for macroalgae farms. Reported commercial yields for cultivated seaweed span an order of magnitude — from under 5 to over 40 dry tonnes per hectare per year — and the drivers of this variation (site oceanography, strain genetics, management intensity, measurement methodology) are poorly understood. At the high end of reported yields, seaweed farming approaches cost-competitiveness with terrestrial biofuel feedstocks; at the low end, it remains uneconomic. Identifying and reliably replicating high-yield conditions is therefore a research priority (State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017, Roesijadi et al., 2010) Seaweeds contain compounds that inhibit conversion processes Brown seaweeds have phenolic compounds that can inhibit the AD process. (Milledge & Harvey, 2018) High ash content (along with the salt in seaweeds) can reduce the biodegradability of seaweed and reduce methane yields in the AD process. (State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017) and the heating value of seaweed-based biofuels Heavy metals (e.g. cadmium, lead) pose risks for agricultural applications. Research is needed to optimize species selection, pretreatment, and conversion strategies to alleviate the inhibitory mechanisms in order to increase energy yield per biomass input (Milledge & Harvey, 2018). Offshore farms may face nutrient limitations that restrict productivity As cultivation goes offshore, it could hit up against nutrient limitations including the supply of dissolved iron, nitrogen and phosphorus. For example, oceanic iron concentrations are often 1000-fold lower than what Macrocystis pyrifera requires to sustain healthy growth (Paine et al., 2023). Artificial upwelling might alleviate nutrient limitation so we need targeted research and demonstrations in a range of conditions to understand these limits and potential interventions. Some environmental risks of large-scale seaweed farming are poorly understood Key knowledge gaps exist regarding the environmental risks of large-scale seaweed farming development. See “Environmental Benefits/Risks” section in the Cultivation chapter. Open ocean cultivation systems remain unproven at scale Offshore cultivation infrastructure needs to be developed to withstand challenging conditions. For example, in the case of deepwater mooring without fixed seafloor anchors; current designs lack validation at commercial scale in high-energy offshore environments. Similarly, combined weight of saturated biomass and infrastructure affects buoyancy, mooring design, and harvest vessel requirements in ways not yet systematically characterized. Efficient nutrient delivery systems are underdeveloped Dissolved nutrient concentrations increase in the deep ocean so artificial upwelling and depth cycling might be able to alleviate nutrient limitations at the surface. These methods need to developed and optimized so that they can be scaled up to address some of the nutrient challenges discussed above (ARPA-E, 2025). Automated Harvesting technologies are still nascent New methods are needed for mechanical harvesting and dewatering of seaweed biomass, especially offshore (ARPA-E, 2025). The seasonal nature of macroalgae growth is a particular challenge for year-round biofuel production Macroalgae growth and the proliferation of sargassum blooms are inherently seasonal, creating a mismatch with biofuel market structures that require feedstock availability year-round. Storage and preservation methods that maintain biomass quality and chemical composition through the off-season are not yet proven at scale, and the effect of different storage approaches (ensilage, drying, wet storage, fermentation) on downstream conversion performance is incompletely characterized. Exploration of HTL to address this is useful since HTL performance differences across species are minimal compared to experimental variation enabling the use of different species and still resulting in a consistent output.
The gaps identified in this section impact delivered feedstock cost ($/dry ton) and the maximum scale at which seaweed biomass can be reliably produced offshore, the two variables that most directly govern whether seaweed-derived fuels can reach cost parity with fossil alternatives and achieve the production volumes needed to displace meaningful quantities of fossil fuel in aviation and shipping.
Species Selection and Cultivation
Biomass productivity is too variable to make biofuels cost-competitive with conventional products Yield is one of the biggest cost drivers for macroalgae farms. Reported commercial yields for cultivated seaweed span an order of magnitude — from under 5 to over 40 dry tonnes per hectare per year — and the drivers of this variation (site oceanography, strain genetics, management intensity, measurement methodology) are poorly understood. At the high end of reported yields, seaweed farming approaches cost-competitiveness with terrestrial biofuel feedstocks; at the low end, it remains uneconomic. Identifying and reliably replicating high-yield conditions is therefore a research priority (State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017, Roesijadi et al., 2010) Offshore farms may face nutrient limitations that restrict productivity As cultivation goes offshore, it could hit up against nutrient limitations including the supply of dissolved iron, nitrogen and phosphorus. For example, oceanic iron concentrations are often 1000-fold lower than what Macrocystis pyrifera requires to sustain healthy growth (Paine et al., 2023). Artificial upwelling might alleviate nutrient limitation so we need targeted research and demonstrations in a range of conditions to understand these limits and potential interventions. Some environmental risks of large-scale seaweed farming are poorly understood Key knowledge gaps exist regarding the environmental risks of large-scale seaweed farming development. See “Environmental Benefits/Risks” section in the Cultivation chapter. Open ocean cultivation systems remain unproven at scale Offshore cultivation infrastructure needs to be developed to withstand challenging conditions. For example, in the case of deepwater mooring without fixed seafloor anchors; current designs lack validation at commercial scale in high-energy offshore environments. Similarly, combined weight of saturated biomass and infrastructure affects buoyancy, mooring design, and harvest vessel requirements in ways not yet systematically characterized. Efficient nutrient delivery systems are underdeveloped Dissolved nutrient concentrations increase in the deep ocean so artificial upwelling and depth cycling might be able to alleviate nutrient limitations at the surface. These methods need to developed and optimized so that they can be scaled up to address some of the nutrient challenges discussed above (ARPA-E, 2025). Automated Harvesting technologies are still nascent New methods are needed for mechanical harvesting and dewatering of seaweed biomass, especially offshore (ARPA-E, 2025). The seasonal nature of macroalgae growth is a particular challenge for year-round biofuel production Macroalgae growth and the proliferation of sargassum blooms are inherently seasonal, creating a mismatch with biofuel market structures that require feedstock availability year-round. Storage and preservation methods that maintain biomass quality and chemical composition through the off-season are not yet proven at scale, and the effect of different storage approaches (ensilage, drying, wet storage, fermentation) on downstream conversion performance is incompletely characterized. Exploration of HTL to address this is useful since HTL performance differences across species are minimal compared to experimental variation enabling the use of different species and still resulting in a consistent output.
The gaps identified in this section impact delivered feedstock cost ($/dry ton) and the maximum scale at which seaweed biomass can be reliably produced offshore, the two variables that most directly govern whether seaweed-derived fuels can reach cost parity with fossil alternatives and achieve the production volumes needed to displace meaningful quantities of fossil fuel in aviation and shipping.
Species Selection and Cultivation
Biomass productivity is too variable to make biofuels cost-competitive Yield is one of the biggest cost drivers for macroalgae farms. Reported commercial yields for cultivated seaweed span an order of magnitude — from under 5 to over 40 dry tonnes per hectare per year — and the drivers of this variation (site oceanography, strain genetics, management intensity, measurement methodology) are poorly understood. At the high end of reported yields, seaweed farming approaches cost-competitiveness with terrestrial biofuel feedstocks; at the low end, it remains uneconomic. Identifying and reliably replicating high-yield conditions is therefore a research priority (State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017, Roesijadi et al., 2010) Offshore farms may face nutrient limitations that restrict productivity As cultivation goes offshore, it could hit up against nutrient limitations including the supply of dissolved iron, nitrogen and phosphorus. For example, oceanic iron concentrations are often 1000-fold lower than what Macrocystis pyrifera requires to sustain healthy growth (Paine et al., 2023). Artificial upwelling might alleviate nutrient limitation so we need targeted research and demonstrations in a range of conditions to understand these limits and potential interventions. Some environmental risks of large-scale seaweed farming are poorly understood Key knowledge gaps exist regarding the environmental risks of large-scale seaweed farming development. See “Environmental Benefits/Risks” section in the Cultivation chapter. Open ocean cultivation systems remain unproven at scale Offshore cultivation infrastructure needs to be developed to withstand challenging conditions. For example, in the case of deepwater mooring without fixed seafloor anchors; current designs lack validation at commercial scale in high-energy offshore environments. Similarly, combined weight of saturated biomass and infrastructure affects buoyancy, mooring design, and harvest vessel requirements in ways not yet systematically characterized. Efficient nutrient delivery systems are underdeveloped Dissolved nutrient concentrations increase in the deep ocean so artificial upwelling and depth cycling might be able to alleviate nutrient limitations at the surface. These methods need to developed and optimized so that they can be scaled up to address some of the nutrient challenges discussed above (ARPA-E, 2025). Automated Harvesting technologies are still nascent New methods are needed for mechanical harvesting and dewatering of seaweed biomass, especially offshore (ARPA-E, 2025). The seasonal nature of macroalgae growth is a particular challenge for year-round biofuel production Macroalgae growth and the proliferation of sargassum blooms are inherently seasonal, creating a mismatch with biofuel market structures that require feedstock availability year-round. Storage and preservation methods that maintain biomass quality and chemical composition through the off-season are not yet proven at scale, and the effect of different storage approaches (ensilage, drying, wet storage, fermentation) on downstream conversion performance is incompletely characterized. Exploration of HTL to address this is useful since HTL performance differences across species are minimal compared to experimental variation enabling the use of different species and still resulting in a consistent output.Species Selection and Cultivation
Biomass productivity is too variable to make biofuels cost-competitive Yield is one of the biggest cost drivers for macroalgae farms. Reported commercial yields for cultivated seaweed span an order of magnitude — from under 5 to over 40 dry tonnes per hectare per year — and the drivers of this variation (site oceanography, strain genetics, management intensity, measurement methodology) are poorly understood. At the high end of reported yields, seaweed farming approaches cost-competitiveness with terrestrial biofuel feedstocks; at the low end, it remains uneconomic. Identifying and reliably replicating high-yield conditions is therefore a research priority (State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017, Roesijadi et al., 2010) Offshore farms may face nutrient limitations that restrict productivity As cultivation goes offshore, it could hit up against nutrient limitations including the supply of dissolved iron, nitrogen and phosphorus. For example, oceanic iron concentrations are often 1000-fold lower than what Macrocystis pyrifera requires to sustain healthy growth (Paine et al., 2023). Artificial upwelling might alleviate nutrient limitation so we need targeted research and demonstrations in a range of conditions to understand these limits and potential interventions. Some environmental risks of large-scale seaweed farming are poorly understood Key knowledge gaps exist regarding the environmental risks of large-scale seaweed farming development. See “Environmental Benefits/Risks” section in the Cultivation chapter. Open ocean cultivation systems remain unproven at scale Offshore cultivation infrastructure needs to be developed to withstand challenging conditions. For example, in the case of deepwater mooring without fixed seafloor anchors; current designs lack validation at commercial scale in high-energy offshore environments. Similarly, combined weight of saturated biomass and infrastructure affects buoyancy, mooring design, and harvest vessel requirements in ways not yet systematically characterized. Efficient nutrient delivery systems are underdeveloped Dissolved nutrient concentrations increase in the deep ocean so artificial upwelling and depth cycling might be able to alleviate nutrient limitations at the surface. These methods need to developed and optimized so that they can be scaled up to address some of the nutrient challenges discussed above (ARPA-E, 2025). Automated Harvesting technologies are still nascent New methods are needed for mechanical harvesting and dewatering of seaweed biomass, especially offshore (ARPA-E, 2025). The seasonal nature of macroalgae growth is a particular challenge for year-round biofuel production Macroalgae growth and the proliferation of sargassum blooms are inherently seasonal, creating a mismatch with biofuel market structures that require feedstock availability year-round. Storage and preservation methods that maintain biomass quality and chemical composition through the off-season are not yet proven at scale, and the effect of different storage approaches (ensilage, drying, wet storage, fermentation) on downstream conversion performance is incompletely characterized. Exploration of HTL to address this is useful since HTL performance differences across species are minimal compared to experimental variation enabling the use of different species and still resulting in a consistent output.Species Selection and Cultivation
Biomass productivity is too variable to make biofuels cost-competitive Yield is one of the biggest cost drivers for macroalgae farms. Reported commercial yields for cultivated seaweed span an order of magnitude — from under 5 to over 40 dry tonnes per hectare per year — and the drivers of this variation (site oceanography, strain genetics, management intensity, measurement methodology) are poorly understood. At the high end of reported yields, seaweed farming approaches cost-competitiveness with terrestrial biofuel feedstocks; at the low end, it remains uneconomic. Identifying and reliably replicating high-yield conditions is therefore a research priority (State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017, Roesijadi et al., 2010) Offshore farms may face nutrient limitations that restrict productivity As cultivation goes offshore, it could hit up against nutrient limitations including the supply of dissolved iron, nitrogen and phosphorus. For example, oceanic iron concentrations are often 1000-fold lower than what Macrocystis pyrifera requires to sustain healthy growth (Paine et al., 2023). Artificial upwelling might alleviate nutrient limitation so we need targeted research and demonstrations in a range of conditions to understand these limits and potential interventions. Some environmental risks of large-scale seaweed farming are poorly understood Key knowledge gaps exist regarding the environmental risks of large-scale seaweed farming development. See “Environmental Benefits/Risks” section in the Cultivation chapter. Open ocean cultivation systems remain unproven at scale Offshore cultivation infrastructure needs to be developed to withstand challenging conditions. For example, in the case of deepwater mooring without fixed seafloor anchors; current designs lack validation at commercial scale in high-energy offshore environments. Similarly, combined weight of saturated biomass and infrastructure affects buoyancy, mooring design, and harvest vessel requirements in ways not yet systematically characterized. Efficient nutrient delivery systems are underdeveloped Dissolved nutrient concentrations increase in the deep ocean so artificial upwelling and depth cycling might be able to alleviate nutrient limitations at the surface. These methods need to developed and optimized so that they can be scaled up to address some of the nutrient challenges discussed above (ARPA-E, 2025). Automated Harvesting technologies are still nascent New methods are needed for mechanical harvesting and dewatering of seaweed biomass, especially offshore (ARPA-E, 2025). The seasonal nature of macroalgae growth is a particular challenge for year-round biofuel production Developments are needed in storage/preservation methods to enable continuous supply. The effect of different storage methods , on chemical composition is not fully known. Exploration of HTL to address this is useful since HTL performance differences across species are minimal compared to experimental variation enabling the use of different species and still resulting in a consistent output.Species Selection and Cultivation (Cross-Cutting)
Biomass productivity is too variable to make biofuels cost-competitive. Yield is one of the biggest cost drivers for macroalgae farms. Reported commercial yields for cultivated seaweed span an order of magnitude — from under 5 to over 40 dry tonnes per hectare per year — and the drivers of this variation (site oceanography, strain genetics, management intensity, measurement methodology) are poorly understood. At the high end of reported yields, seaweed farming approaches cost-competitiveness with terrestrial biofuel feedstocks; at the low end, it remains uneconomic. Identifying and reliably replicating high-yield conditions is therefore a research priority (State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017, Roesijadi et al., 2010) Offshore farms may face nutrient limitations that restrict productivity. As cultivation goes offshore, it could hit up against nutrient limitations including the supply of dissolved iron, nitrogen and phosphorus. For example, oceanic iron concentrations are often 1000-fold lower than what Macrocystis pyrifera requires to sustain healthy growth (Paine et al., 2023). Artificial upwelling might alleviate nutrient limitation so we need targeted research and demonstrations in a range of conditions to understand these limits and potential interventions. Some environmental risks of large-scale seaweed farming are poorly understood. Key knowledge gaps exist regarding the environmental risks of large-scale seaweed farming development. See “Environmental Benefits/Risks” section in the Cultivation chapter. Open ocean cultivation systems remain unproven at scale. Offshore cultivation infrastructure needs to be developed to withstand challenging conditions. For example, in the case of deepwater mooring without fixed seafloor anchors; current designs lack validation at commercial scale in high-energy offshore environments. Similarly, combined weight of saturated biomass and infrastructure affects buoyancy, mooring design, and harvest vessel requirements in ways not yet systematically characterized. Efficient nutrient delivery systems are underdeveloped. Dissolved nutrient concentrations increase in the deep ocean so artificial upwelling and depth cycling might be able to alleviate nutrient limitations at the surface. These methods need to developed and optimized so that they can be scaled up to address some of the nutrient challenges discussed above (ARPA-E, 2025). Automated Harvesting technologies are still nascent. New methods are needed for mechanical harvesting and dewatering of seaweed biomass, especially offshore (ARPA-E, 2025). The seasonal nature of macroalgae growth is a particular challenge for year-round biofuel production. Developments are needed in storage/preservation methods to enable continuous supply. The effect of different storage methods , on chemical composition is not fully known. Exploration of HTL to address this is useful since HTL performance differences across species are minimal compared to experimental variation enabling the use of different species and still resulting in a consistent output.Species Selection and Cultivation (Cross-Cutting)
Biomass productivity is too variable to make biofuels cost-competitive. Yield is one of the biggest cost drivers for macroalgae farms. Reported commercial yields for cultivated seaweed span an order of magnitude — from under 5 to over 40 dry tonnes per hectare per year — and the drivers of this variation (site oceanography, strain genetics, management intensity, measurement methodology) are poorly understood. At the high end of reported yields, seaweed farming approaches cost-competitiveness with terrestrial biofuel feedstocks; at the low end, it remains uneconomic. Identifying and reliably replicating high-yield conditions is therefore a research priority (State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017, Roesijadi et al., 2010) Offshore farms may face nutrient limitations that restrict productivity. As cultivation goes offshore, it could hit up against nutrient limitations including the supply of dissolved iron, nitrogen and phosphorus. For example, oceanic iron concentrations are often 1000-fold lower than what Macrocystis pyrifera requires to sustain healthy growth.(Paine et al., 2023) Artificial upwelling might alleviate nutrient limitation so we need targeted research and demonstrations in a range of conditions to understand these limits and potential interventions. Some environmental risks of large-scale seaweed farming are poorly understood. Key knowledge gaps exist regarding the environmental risks of large-scale seaweed farming development. See “Environmental Benefits/Risks” section in the Cultivation chapter. Open ocean cultivation systems remain unproven at scale. Offshore cultivation infrastructure needs to be developed to withstand challenging conditions. For example, in the case of deepwater mooring without fixed seafloor anchors; current designs lack validation at commercial scale in high-energy offshore environments. Similarly, combined weight of saturated biomass and infrastructure affects buoyancy, mooring design, and harvest vessel requirements in ways not yet systematically characterized. Efficient nutrient delivery systems are underdeveloped. Dissolved nutrient concentrations increase in the deep ocean so artificial upwelling and depth cycling might be able to alleviate nutrient limitations at the surface. These methods need to developed and optimized so that they can be scaled up to address some of the nutrient challenges discussed above. (ARPA-E, 2025) Automated Harvesting technologies are still nascent. New methods are needed for mechanical harvesting and dewatering of seaweed biomass, especially offshore. (ARPA-E, 2025) The seasonal nature of macroalgae growth is a particular challenge for year-round biofuel production. Developments are needed in storage/preservation methods to enable continuous supply. The effect of different storage methods , on chemical composition is not fully known. Exploration of HTL to address this is useful since HTL performance differences across species are minimal compared to experimental variation enabling the use of different species and still resulting in a consistent output.
Several knowledge gaps exist in the scientific understanding, technological readiness, and engineering aspects of macroalgae-based biofuels:
Species Selection and Cultivation (Cross-Cutting)
Biomass productivity is too variable to make biofuels cost-competitive. Yield is one of the biggest cost drivers for macroalgae farms. Reported commercial yields for cultivated seaweed span an order of magnitude — from under 5 to over 40 dry tonnes per hectare per year — and the drivers of this variation (site oceanography, strain genetics, management intensity, measurement methodology) are poorly understood. At the high end of reported yields, seaweed farming approaches cost-competitiveness with terrestrial biofuel feedstocks; at the low end, it remains uneconomic. Identifying and reliably replicating high-yield conditions is therefore a research priority (State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017, Roesijadi et al., 2010) Offshore farms may face nutrient limitations that restrict productivity. As cultivation goes offshore, it could hit up against nutrient limitations including the supply of dissolved iron, nitrogen and phosphorus. For example, oceanic iron concentrations are often 1000-fold lower than what Macrocystis pyrifera requires to sustain healthy growth.(Paine et al., 2023) Artificial upwelling might alleviate nutrient limitation so we need targeted research and demonstrations in a range of conditions to understand these limits and potential interventions. Some environmental risks of large-scale seaweed farming are poorly understood. Key knowledge gaps exist regarding the environmental risks of large-scale seaweed farming development. See “Environmental Benefits/Risks” section in the Cultivation chapter. Open ocean cultivation systems remain unproven at scale. Offshore cultivation infrastructure needs to be developed to withstand challenging conditions. For example, in the case of deepwater mooring without fixed seafloor anchors; current designs lack validation at commercial scale in high-energy offshore environments. Similarly, combined weight of saturated biomass and infrastructure affects buoyancy, mooring design, and harvest vessel requirements in ways not yet systematically characterized. Efficient nutrient delivery systems are underdeveloped. Dissolved nutrient concentrations increase in the deep ocean so artificial upwelling and depth cycling might be able to alleviate nutrient limitations at the surface. These methods need to developed and optimized so that they can be scaled up to address some of the nutrient challenges discussed above. (ARPA-E, 2025) Automated Harvesting technologies are still nascent. New methods are needed for mechanical harvesting and dewatering of seaweed biomass, especially offshore. (ARPA-E, 2025) The seasonal nature of macroalgae growth is a particular challenge for year-round biofuel production. Developments are needed in storage/preservation methods to enable continuous supply. The effect of different storage methods , on chemical composition is not fully known. Exploration of HTL to address this is useful since HTL performance differences across species are minimal compared to experimental variation enabling the use of different species and still resulting in a consistent output.Processing and Conversion Technologies:
In general, conversion technologies which have been used for other feedstocks are at laboratory and pilot scale when it comes to incorporating seaweed as feedstock. Real-world methane yields from the AD process are low. as compared to theoretical values (Milledge & Harvey, 2018) Further research on the factors reducing practical methane yields is vital. Factors include the structural complexity of seaweed, presence of inhibiting compounds such as polyphenols, operational parameters as well as issues such as accumulation of salinity and sand in the reactors (McKennedy and Sherlock, 2015; Stefania Rocca et al., 2015; State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017). Yields for the bioethanol fermentation process are not optimized yet. Maximizing the yields for the lowest possible use of electricity will impact the environmental viability of the overall systems. (Stefania Rocca et al., 2015) HTL Process Mechanisms are not fully understood. A significant knowledge gap exists in accurately predicting HTL outcomes (like bio-crude yield and composition) solely based on the macroalgae's biochemical composition (lipids, proteins, carbohydrates, ash).(Raikova et al., 2017) Multi-product extractions important for economic viability remain at a nascent stage. The EU funded Macro Cascade project demonstrated lab/pilot extraction of alginate, fucoidan, etc., but integrating all steps and including biofuels as product industrial scale is the next frontier. Seaweeds contain compounds that inhibit conversion processes. Brown seaweeds have phenolic compounds that can inhibit the AD process. (Milledge & Harvey, 2018) High ash content (along with the salt in seaweeds) can reduce the biodegradability of seaweed and reduce methane yields in the AD process. (State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017) and the heating value of seaweed-based biofuels Heavy metals (e.g. cadmium, lead) pose risks for agricultural applications. Research is needed to optimize species selection, pretreatment, and conversion strategies. More work is also needed on the exact inhibitory mechanisms in order to alleviate them. (Milledge & Harvey, 2018)Data Availability and Harmonization
There is a lack of standardized, comparable LCA and TEA data. There is a general lack of good quality, comparable data from LCA and TEA studies against which to assess and validate results and make predictions about scale. This makes it difficult for macroalgae biofuels to meet renewable energy standards. (State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017)
Several knowledge gaps exist in the scientific understanding, technological readiness, and engineering aspects of macroalgae-based biofuels:
Species Selection and Cultivation (Cross-Cutting)
Biomass productivity is too variable to make biofuels cost-competitive. Yield is one of the biggest cost drivers for macroalgae farms. Reported commercial yields for cultivated seaweed span an order of magnitude — from under 5 to over 40 dry tonnes per hectare per year — and the drivers of this variation (site oceanography, strain genetics, management intensity, measurement methodology) are poorly understood. At the high end of reported yields, seaweed farming approaches cost-competitiveness with terrestrial biofuel feedstocks; at the low end, it remains uneconomic. Identifying and reliably replicating high-yield conditions is therefore a research priority (State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017, Roesijadi et al., 2010) Offshore farms may face nutrient limitations that restrict productivity. As cultivation goes offshore, it could hit up against nutrient limitations including the supply of dissolved iron, nitrogen and phosphorus. For example, oceanic iron concentrations are often 1000-fold lower than what Macrocystis pyrifera requires to sustain healthy growth.(Paine et al., 2023) Artificial upwelling might alleviate nutrient limitation so we need targeted research and demonstrations in a range of conditions to understand these limits and potential interventions. Some environmental risks of large-scale seaweed farming are poorly understood. Key knowledge gaps exist regarding the environmental risks of large-scale seaweed farming development. See “Environmental Benefits/Risks” section in the Cultivation chapter. Open ocean cultivation systems remain unproven at scale. Offshore cultivation infrastructure needs to be developed to withstand challenging conditions. For example, in the case of deepwater mooring without fixed seafloor anchors; current designs lack validation at commercial scale in high-energy offshore environments. Similarly, combined weight of saturated biomass and infrastructure affects buoyancy, mooring design, and harvest vessel requirements in ways not yet systematically characterized. Efficient nutrient delivery systems are underdeveloped. Dissolved nutrient concentrations increase in the deep ocean so artificial upwelling and depth cycling might be able to alleviate nutrient limitations at the surface. These methods need to developed and optimized so that they can be scaled up to address some of the nutrient challenges discussed above. (ARPA-E, 2025) Automated Harvesting technologies are still nascent. New methods are needed for mechanical harvesting and dewatering of seaweed biomass, especially offshore. (ARPA-E, 2025) The seasonal nature of macroalgae growth is a particular challenge for year-round biofuel production. Developments are needed in storage/preservation methods to enable continuous supply. The effect of different storage methods , on chemical composition is not fully known. Exploration of HTL to address this is useful since HTL performance differences across species are minimal compared to experimental variation enabling the use of different species and still resulting in a consistent output.Processing and Conversion Technologies:
In general, conversion technologies which have been used for other feedstocks are at laboratory and pilot scale when it comes to incorporating seaweed as feedstock Real-world methane yields from the AD process are low. as compared to theoretical values (Milledge & Harvey, 2018) Further research on the factors reducing practical methane yields is vital. Factors include the structural complexity of seaweed, presence of inhibiting compounds such as polyphenols, operational parameters as well as issues such as accumulation of salinity and sand in the reactors (McKennedy and Sherlock, 2015; Stefania Rocca et al., 2015; State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017). Yields for the bioethanol fermentation process are not optimized yet. Maximizing the yields for the lowest possible use of electricity will impact the environmental viability of the overall systems. (Stefania Rocca et al., 2015) HTL Process Mechanisms are not fully understood. A significant knowledge gap exists in accurately predicting HTL outcomes (like bio-crude yield and composition) solely based on the macroalgae's biochemical composition (lipids, proteins, carbohydrates, ash).(Raikova et al., 2017) Multi-product extractions important for economic viability remain at a nascent stage. The EU funded Macro Cascade project demonstrated lab/pilot extraction of alginate, fucoidan, etc., but integrating all steps and including biofuels as product industrial scale is the next frontier. Seaweeds contain compounds that inhibit conversion processes. Brown seaweeds have phenolic compounds that can inhibit the AD process. (Milledge & Harvey, 2018) High ash content (along with the salt in seaweeds) can reduce the biodegradability of seaweed and reduce methane yields in the AD process. (State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017) and the heating value of seaweed-based biofuels Heavy metals (e.g. cadmium, lead) pose risks for agricultural applications. Research is needed to optimize species selection, pretreatment, and conversion strategies. More work is also needed on the exact inhibitory mechanisms in order to alleviate them. (Milledge & Harvey, 2018)Data Availability and Harmonization
There is a lack of standardized, comparable LCA and TEA data. There is a general lack of good quality, comparable data from LCA and TEA studies against which to assess and validate results and make predictions about scale. This makes it difficult for macroalgae biofuels to meet renewable energy standards. (State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017)Processing and Engineering
Version published:
June 2, 2026 - 3:06am
The gaps in this section determine how efficiently biomass energy is converted into usable fuel, directly setting both the carbon intensity (gCO₂eq/Joule) of the final product and the cost per unit energy ($/Joule), both critical to the viability of seaweed-based biofuels.
Processing and Conversion Technologies
Challenges exist in all three conversion processes in optimizing yield. While cultivation costs are the major factor in determining how cost-competitive seaweed-based fuels are, improving conversion yields can further help to improve this metric.
Real-world methane yields from the AD process are low as compared to theoretical values
Anaerobic Digestion (AD) is the most near-term viable conversion pathway for wet seaweed biomass but reported practical methane yields are well below theoretical values predicted from biochemical composition. Factors include the structural complexity of seaweed, presence of inhibiting compounds such as polyphenols, operational parameters as well as issues such as accumulation of salinity and sand in the reactors (McKennedy and Sherlock, 2015; Stefania Rocca et al., 2015; State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017). Closing this gap requires controlled reactor trials that isolate the contribution of each loss factor and development of reactor configurations and operating regimes that manage salinity and demonstrate sustained methane yields above a minimum threshold (≥250 LCH₄/kg volatile solids) over a minimum continuous operation period.
Yields for the bioethanol fermentation process are not optimized yet
Fermentation yields remain below commercially relevant thresholds, and the electricity and thermal energy inputs required for saccharification and fermentation have not been minimized (Stefania Rocca et al., 2015). Closing this gap requires: process integration studies that optimize sugar yield for a given energy input for multiple key species.
HTL Process Mechanisms are not fully understood
A significant knowledge gap exists in accurately predicting HTL outcomes (like bio-crude yield and composition) solely based on the macroalgae’s biochemical composition (lipids, proteins, carbohydrates, ash)(Raikova et al., 2017). Closing this gap requires a systematic experimental matrix mapping HTL outputs (bio-crude yield, elemental composition, higher heating value, nitrogen and sulfur content) against controlled variation in biochemical composition supporting development and validation of a predictive compositional model and pilot-scale demonstration validating that model predictions hold under continuous operation.
Multi-product extractions important for economic viability remain at a nascent stage
Higher-value co-products such as alginate, fucoidan, and other bioactive compounds are important to biorefinery economics — their revenue can partially offset biofuel production costs and improve overall project returns. The EU funded Macro Cascade project demonstrated lab/pilot extraction of alginate, fucoidan, etc., but integrating all steps and including biofuels as product industrial scale is the next frontier. Key unknowns include whether pretreatment and extraction steps for high-value compounds alter the composition or convertibility of the residual biomass fraction.
The gaps in this section determine how efficiently biomass energy is converted into usable fuel, directly setting both the carbon intensity (gCO₂eq/Joule) of the final product and the cost per unit energy ($/Joule), both critical to the viability of seaweed-based biofuels.
Processing and Conversion Technologies
Challenges exist in all three conversion processes in optimizing yield. While cultivation costs are the major factor in determining how cost-competitive seaweed-based fuels are, improving conversion yields can further help to improve this metric. Real-world methane yields from the AD process are low as compared to theoretical values Anaerobic Digestion (AD) is the most near-term viable conversion pathway for wet seaweed biomass but reported practical methane yields are well below theoretical values predicted from biochemical composition. Factors include the structural complexity of seaweed, presence of inhibiting compounds such as polyphenols, operational parameters as well as issues such as accumulation of salinity and sand in the reactors (McKennedy and Sherlock, 2015; Stefania Rocca et al., 2015; State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017). Closing this gap requires controlled reactor trials that isolate the contribution of each loss factor and development of reactor configurations and operating regimes that manage salinity and demonstrate sustained methane yields above a minimum threshold (≥250 LCH₄/kg volatile solids) over a minimum continuous operation period. Yields for the bioethanol fermentation process are not optimized yet Fermentation yields remain below commercially relevant thresholds, and the electricity and thermal energy inputs required for saccharification and fermentation have not been minimized (Stefania Rocca et al., 2015). Closing this gap requires: process integration studies that optimize sugar yield for a given energy input for multiple key species. HTL Process Mechanisms are not fully understood A significant knowledge gap exists in accurately predicting HTL outcomes (like bio-crude yield and composition) solely based on the macroalgae's biochemical composition (lipids, proteins, carbohydrates, ash)(Raikova et al., 2017). Closing this gap requires a systematic experimental matrix mapping HTL outputs (bio-crude yield, elemental composition, higher heating value, nitrogen and sulfur content) against controlled variation in biochemical composition supporting development and validation of a predictive compositional model and pilot-scale demonstration validating that model predictions hold under continuous operation. Multi-product extractions important for economic viability remain at a nascent stage Higher-value co-products such as alginate, fucoidan, and other bioactive compounds are important to biorefinery economics — their revenue can partially offset biofuel production costs and improve overall project returns. The EU funded Macro Cascade project demonstrated lab/pilot extraction of alginate, fucoidan, etc., but integrating all steps and including biofuels as product industrial scale is the next frontier. Key unknowns include whether pretreatment and extraction steps for high-value compounds alter the composition or convertibility of the residual biomass fraction.
The gaps in this section determine how efficiently biomass energy is converted into usable fuel, directly setting both the carbon intensity (gCO₂eq/Joule) of the final product and the cost per unit energy ($/Joule), both critical to the viability of seaweed-based biofuels.
Processing and Conversion Technologies
Challenges exist in all three conversion processes in optimizing yield. While cultivation costs are the major factor in determining how cost-competitive seaweed-based fuels are, improving conversion yields can further help to improve this metric. Real-world methane yields from the AD process are low as compared to theoretical values Anaerobic Digestion (AD) is the most near-term viable conversion pathway for wet seaweed biomass but reported practical methane yields are well below theoretical values predicted from biochemical composition. Factors include the structural complexity of seaweed, presence of inhibiting compounds such as polyphenols, operational parameters as well as issues such as accumulation of salinity and sand in the reactors (McKennedy and Sherlock, 2015; Stefania Rocca et al., 2015; State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017). Closing this gap requires controlled reactor trials that isolate the contribution of each loss factor and development of reactor configurations and operating regimes that manage salinity and demonstrate sustained methane yields above a minimum threshold (≥250 LCH₄/kg volatile solids) over a minimum continuous operation period. Yields for the bioethanol fermentation process are not optimized yet Fermentation yields remain below commercially relevant thresholds, and the electricity and thermal energy inputs required for saccharification and fermentation have not been minimized (Stefania Rocca et al., 2015). Closing this gap requires: process integration studies that optimize sugar yield for a given energy input for multiple key species. HTL Process Mechanisms are not fully understood A significant knowledge gap exists in accurately predicting HTL outcomes (like bio-crude yield and composition) solely based on the macroalgae's biochemical composition (lipids, proteins, carbohydrates, ash)(Raikova et al., 2017). Closing this gap requires a systematic experimental matrix mapping HTL outputs (bio-crude yield, elemental composition, higher heating value, nitrogen and sulfur content) against controlled variation in biochemical composition supporting development and validation of a predictive compositional model and pilot-scale demonstration validating that model predictions hold under continuous operation. Multi-product extractions important for economic viability remain at a nascent stage Higher-value co-products such as alginate, fucoidan, and other bioactive compounds are important to biorefinery economics — their revenue can partially offset biofuel production costs and improve overall project returns. The EU funded Macro Cascade project demonstrated lab/pilot extraction of alginate, fucoidan, etc., but integrating all steps and including biofuels as product industrial scale is the next frontier. Key unknowns include whether pretreatment and extraction steps for high-value compounds alter the composition or convertibility of the residual biomass fraction. Seaweeds contain compounds that inhibit conversion processes Brown seaweeds have phenolic compounds that can inhibit the AD process. (Milledge & Harvey, 2018) High ash content (along with the salt in seaweeds) can reduce the biodegradability of seaweed and reduce methane yields in the AD process. (State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017) and the heating value of seaweed-based biofuels Heavy metals (e.g. cadmium, lead) pose risks for agricultural applications. Research is needed to optimize species selection, pretreatment, and conversion strategies to alleviate the inhibitory mechanisms in order to increase energy yield per biomass input (Milledge & Harvey, 2018).
The gaps in this section determine how efficiently biomass energy is converted into usable fuel, directly setting both the carbon intensity (gCO₂eq/Joule) of the final product and the cost per unit energy ($/Joule), both critical to the viability of seaweed-based biofuels.
Processing and Conversion Technologies
Challenges exist in all three conversion processes in optimizing yield. While cultivation costs are the major factor in determining the cost-competitiveness of seaweed-based fuels, improving conversion yields can further help to improve cost-competitiveness. Real-world methane yields from the AD process are low as compared to theoretical values Anaerobic Digestion (AD) is the most near-term viable conversion pathway for wet seaweed biomass but reported practical methane yields are well below theoretical values predicted from biochemical composition. Factors include the structural complexity of seaweed, presence of inhibiting compounds such as polyphenols, operational parameters as well as issues such as accumulation of salinity and sand in the reactors (McKennedy and Sherlock, 2015; Stefania Rocca et al., 2015; State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017). Closing this gap requires controlled reactor trials that isolate the contribution of each loss factor and development of reactor configurations and operating regimes that manage salinity and demonstrate sustained methane yields above a minimum threshold (≥250 LCH₄/kg volatile solids) over a minimum continuous operation period. Yields for the bioethanol fermentation process are not optimized yet Fermentation yields remain below commercially relevant thresholds, and the electricity and thermal energy inputs required for saccharification and fermentation have not been minimized (Stefania Rocca et al., 2015). Closing this gap requires: process integration studies that optimize sugar yield for a given energy input for multiple key species. HTL Process Mechanisms are not fully understood A significant knowledge gap exists in accurately predicting HTL outcomes (like bio-crude yield and composition) solely based on the macroalgae's biochemical composition (lipids, proteins, carbohydrates, ash)(Raikova et al., 2017). Closing this gap requires a systematic experimental matrix mapping HTL outputs (bio-crude yield, elemental composition, higher heating value, nitrogen and sulfur content) against controlled variation in biochemical composition supporting development and validation of a predictive compositional model and pilot-scale demonstration validating that model predictions hold under continuous operation. Multi-product extractions important for economic viability remain at a nascent stage Higher-value co-products such as alginate, fucoidan, and other bioactive compounds are important to biorefinery economics — their revenue can partially offset biofuel production costs and improve overall project returns. The EU funded Macro Cascade project demonstrated lab/pilot extraction of alginate, fucoidan, etc., but integrating all steps and including biofuels as product industrial scale is the next frontier. Key unknowns include whether pretreatment and extraction steps for high-value compounds alter the composition or convertibility of the residual biomass fraction. Seaweeds contain compounds that inhibit conversion processes Brown seaweeds have phenolic compounds that can inhibit the AD process. (Milledge & Harvey, 2018) High ash content (along with the salt in seaweeds) can reduce the biodegradability of seaweed and reduce methane yields in the AD process. (State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017) and the heating value of seaweed-based biofuels Heavy metals (e.g. cadmium, lead) pose risks for agricultural applications. Research is needed to optimize species selection, pretreatment, and conversion strategies to alleviate the inhibitory mechanisms in order to increase energy yield per biomass input (Milledge & Harvey, 2018).Processing and Conversion Technologies
Challenges exist in all three conversion processes in optimizing yield. While cultivation costs are the major factor in determining the cost-competitiveness of seaweed-based fuels, improving conversion yields can further help to improve cost-competitiveness. Real-world methane yields from the AD process are low as compared to theoretical values Anaerobic Digestion (AD) is the most near-term viable conversion pathway for wet seaweed biomass but reported practical methane yields are well below theoretical values predicted from biochemical composition. Factors include the structural complexity of seaweed, presence of inhibiting compounds such as polyphenols, operational parameters as well as issues such as accumulation of salinity and sand in the reactors (McKennedy and Sherlock, 2015; Stefania Rocca et al., 2015; State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017). Closing this gap requires controlled reactor trials that isolate the contribution of each loss factor and development of reactor configurations and operating regimes that manage salinity and demonstrate sustained methane yields above a minimum threshold (≥250 LCH₄/kg volatile solids) over a minimum continuous operation period. Yields for the bioethanol fermentation process are not optimized yet Fermentation yields remain below commercially relevant thresholds, and the electricity and thermal energy inputs required for saccharification and fermentation have not been minimized (Stefania Rocca et al., 2015). Closing this gap requires: process integration studies that optimize sugar yield for a given energy input for multiple key species. HTL Process Mechanisms are not fully understood A significant knowledge gap exists in accurately predicting HTL outcomes (like bio-crude yield and composition) solely based on the macroalgae's biochemical composition (lipids, proteins, carbohydrates, ash)(Raikova et al., 2017). Closing this gap requires a systematic experimental matrix mapping HTL outputs (bio-crude yield, elemental composition, higher heating value, nitrogen and sulfur content) against controlled variation in biochemical composition supporting development and validation of a predictive compositional model and pilot-scale demonstration validating that model predictions hold under continuous operation. Multi-product extractions important for economic viability remain at a nascent stage Higher-value co-products such as alginate, fucoidan, and other bioactive compounds are important to biorefinery economics — their revenue can partially offset biofuel production costs and improve overall project returns. The EU funded Macro Cascade project demonstrated lab/pilot extraction of alginate, fucoidan, etc., but integrating all steps and including biofuels as product industrial scale is the next frontier. Key unknowns include whether pretreatment and extraction steps for high-value compounds alter the composition or convertibility of the residual biomass fraction. Seaweeds contain compounds that inhibit conversion processes Brown seaweeds have phenolic compounds that can inhibit the AD process. (Milledge & Harvey, 2018) High ash content (along with the salt in seaweeds) can reduce the biodegradability of seaweed and reduce methane yields in the AD process. (State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017) and the heating value of seaweed-based biofuels Heavy metals (e.g. cadmium, lead) pose risks for agricultural applications. Research is needed to optimize species selection, pretreatment, and conversion strategies to alleviate the inhibitory mechanisms in order to increase energy yield per biomass input (Milledge & Harvey, 2018).Processing and Conversion Technologies
Real-world methane yields from the AD process are low as compared to theoretical values Further research on the factors reducing practical methane yields is vital. Factors include the structural complexity of seaweed, presence of inhibiting compounds such as polyphenols, operational parameters as well as issues such as accumulation of salinity and sand in the reactors (McKennedy and Sherlock, 2015; Stefania Rocca et al., 2015; State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017). Yields for the bioethanol fermentation process are not optimized yet Maximizing the yields for the lowest possible use of electricity will impact the environmental viability of the overall systems (Stefania Rocca et al., 2015). HTL Process Mechanisms are not fully understood A significant knowledge gap exists in accurately predicting HTL outcomes (like bio-crude yield and composition) solely based on the macroalgae's biochemical composition (lipids, proteins, carbohydrates, ash)(Raikova et al., 2017). Multi-product extractions important for economic viability remain at a nascent stage The EU funded Macro Cascade project demonstrated lab/pilot extraction of alginate, fucoidan, etc., but integrating all steps and including biofuels as product industrial scale is the next frontier. Seaweeds contain compounds that inhibit conversion processes Brown seaweeds have phenolic compounds that can inhibit the AD process. (Milledge & Harvey, 2018) High ash content (along with the salt in seaweeds) can reduce the biodegradability of seaweed and reduce methane yields in the AD process. (State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017) and the heating value of seaweed-based biofuels Heavy metals (e.g. cadmium, lead) pose risks for agricultural applications. Research is needed to optimize species selection, pretreatment, and conversion strategies. More work is also needed on the exact inhibitory mechanisms in order to alleviate them (Milledge & Harvey, 2018).Processing and Conversion Technologies
Real-world methane yields from the AD process are low. as compared to theoretical values Further research on the factors reducing practical methane yields is vital. Factors include the structural complexity of seaweed, presence of inhibiting compounds such as polyphenols, operational parameters as well as issues such as accumulation of salinity and sand in the reactors (McKennedy and Sherlock, 2015; Stefania Rocca et al., 2015; State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017). Yields for the bioethanol fermentation process are not optimized yet. Maximizing the yields for the lowest possible use of electricity will impact the environmental viability of the overall systems. (Stefania Rocca et al., 2015) HTL Process Mechanisms are not fully understood. A significant knowledge gap exists in accurately predicting HTL outcomes (like bio-crude yield and composition) solely based on the macroalgae's biochemical composition (lipids, proteins, carbohydrates, ash).(Raikova et al., 2017) Multi-product extractions important for economic viability remain at a nascent stage. The EU funded Macro Cascade project demonstrated lab/pilot extraction of alginate, fucoidan, etc., but integrating all steps and including biofuels as product industrial scale is the next frontier. Seaweeds contain compounds that inhibit conversion processes. Brown seaweeds have phenolic compounds that can inhibit the AD process. (Milledge & Harvey, 2018) High ash content (along with the salt in seaweeds) can reduce the biodegradability of seaweed and reduce methane yields in the AD process. (State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017) and the heating value of seaweed-based biofuels Heavy metals (e.g. cadmium, lead) pose risks for agricultural applications. Research is needed to optimize species selection, pretreatment, and conversion strategies. More work is also needed on the exact inhibitory mechanisms in order to alleviate them. (Milledge & Harvey, 2018)Processing and Conversion Technologies
Real-world methane yields from the AD process are low. as compared to theoretical values Further research on the factors reducing practical methane yields is vital. Factors include the structural complexity of seaweed, presence of inhibiting compounds such as polyphenols, operational parameters as well as issues such as accumulation of salinity and sand in the reactors (McKennedy and Sherlock, 2015; Stefania Rocca et al., 2015; State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017). Yields for the bioethanol fermentation process are not optimized yet. Maximizing the yields for the lowest possible use of electricity will impact the environmental viability of the overall systems. (Stefania Rocca et al., 2015) HTL Process Mechanisms are not fully understood. A significant knowledge gap exists in accurately predicting HTL outcomes (like bio-crude yield and composition) solely based on the macroalgae's biochemical composition (lipids, proteins, carbohydrates, ash).(Raikova et al., 2017) Multi-product extractions important for economic viability remain at a nascent stage. The EU funded Macro Cascade project demonstrated lab/pilot extraction of alginate, fucoidan, etc., but integrating all steps and including biofuels as product industrial scale is the next frontier. Seaweeds contain compounds that inhibit conversion processes. Brown seaweeds have phenolic compounds that can inhibit the AD process. (Milledge & Harvey, 2018) High ash content (along with the salt in seaweeds) can reduce the biodegradability of seaweed and reduce methane yields in the AD process. (State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017) and the heating value of seaweed-based biofuels Heavy metals (e.g. cadmium, lead) pose risks for agricultural applications. Research is needed to optimize species selection, pretreatment, and conversion strategies. More work is also needed on the exact inhibitory mechanisms in order to alleviate them. (Milledge & Harvey, 2018)Data Availability and Harmonization
There is a lack of standardized, comparable LCA and TEA data. There is a general lack of good quality, comparable data from LCA and TEA studies against which to assess and validate results and make predictions about scale. This makes it difficult for macroalgae biofuels to meet renewable energy standards. (State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017)Markets and Investments
Version published:
May 28, 2026 - 3:26pm
The gaps in this section determine whether the investment conditions exist for seaweed biofuels to reach commercial scale: without bankable project economics, stable policy signals, and certified carbon intensity data, seaweed-derived fuels cannot enter the offtake agreements, blending mandates, or compliance frameworks that would constitute meaningful fossil fuel displacement in hard-to-electrify sectors.
Biofuels from macroalgae are not yet economically viable
High cultivation and harvesting costs as well as non-optimized conversion processes mean seaweed-derived fuels are currently uncompetitive with fossil alternatives and with most first-generation biofuels. However, the gap is poorly quantified in decision-useful terms: existing cost estimates vary widely because they rely on incomparable assumptions about yield, farm scale, conversion pathway, and co-product revenue.
Incumbent macroalgae producers do not have an incentive to explore a highly uncertain market
The biomass from existing commercial macroalgae cultivation is primarily used for existing traditional and higher-value markets such as food, feed, and the extraction of specialty products. Given the lack of economic viability and the lack of focus on alternative biofuels even in hard to electrify sectors such as aviation, there is limited incentive for producers to invest in the biofuel market.
Data Availability and Harmonization
There is a lack of standardized, comparable LCA and TEA data
There is a general lack of good quality, comparable data from LCA and TEA studies against which to assess and validate results and make predictions about scale. This makes it difficult for macroalgae biofuels to meet renewable energy standards such as the EU Renewable Energy Directive orCORSIA (State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017).
The gaps in this section determine whether the investment conditions exist for seaweed biofuels to reach commercial scale: without bankable project economics, stable policy signals, and certified carbon intensity data, seaweed-derived fuels cannot enter the offtake agreements, blending mandates, or compliance frameworks that would constitute meaningful fossil fuel displacement in hard-to-electrify sectors.
Biofuels from macroalgae are not yet economically viable
High cultivation and harvesting costs as well as non-optimized conversion processes mean seaweed-derived fuels are currently uncompetitive with fossil alternatives and with most first-generation biofuels. However, the gap is poorly quantified in decision-useful terms: existing cost estimates vary widely because they rely on incomparable assumptions about yield, farm scale, conversion pathway, and co-product revenue.
Incumbent macroalgae producers do not have an incentive to explore a highly uncertain market
The biomass from existing commercial macroalgae cultivation is primarily used for existing traditional and higher-value markets such as food, feed, and the extraction of specialty products. Given the lack of economic viability and the lack of focus on alternative biofuels even in hard to electrify sectors such as aviation, there is limited incentive for producers to invest in the biofuel market.
Data Availability and Harmonization
There is a lack of standardized, comparable LCA and TEA data There is a general lack of good quality, comparable data from LCA and TEA studies against which to assess and validate results and make predictions about scale. This makes it difficult for macroalgae biofuels to meet renewable energy standards such as the EU Renewable Energy Directive orCORSIA (State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017).
Biofuels from macroalgae are not yet economically viable
High cultivation and harvesting costs as well as non-optimized conversion processes mean seaweed-derived fuels are currently uncompetitive with fossil alternatives and with most first-generation biofuels. However, the gap is poorly quantified in decision-useful terms: existing cost estimates vary widely because they rely on incomparable assumptions about yield, farm scale, conversion pathway, and co-product revenue.
Incumbent macroalgae producers do not have an incentive to explore a highly uncertain market
The biomass from existing commercial macroalgae cultivation is primarily used for existing traditional and higher-value markets such as food, feed, and the extraction of specialty products. Given the lack of economic viability and the lack of focus on alternative biofuels even in hard to electrify sectors such as aviation, there is limited incentive for producers to invest in the biofuel market.
Data Availability and Harmonization
There is a lack of standardized, comparable LCA and TEA data There is a general lack of good quality, comparable data from LCA and TEA studies against which to assess and validate results and make predictions about scale. This makes it difficult for macroalgae biofuels to meet renewable energy standards such as the EU Renewable Energy Directive orCORSIA (State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017).
Biofuels from macroalgae are not yet economically viable
The high cost of cultivation and harvesting is the single biggest barrier. Algae-based fuels are unlikely to be viable in the near to medium term.
Incumbent macroalgae producers do not have an incentive to explore a highly uncertain market
The biomass from existing commercial macroalgae cultivation is primarily used for existing traditional and higher-value markets such as food, feed, and the extraction of specialty products. Given the lack of economic viability and the lack of focus on alternative biofuels even in hard to electrify sectors such as aviation, there is limited incentive for producers to invest in the biofuel market.
Data Availability and Harmonization
There is a lack of standardized, comparable LCA and TEA data There is a general lack of good quality, comparable data from LCA and TEA studies against which to assess and validate results and make predictions about scale. This makes it difficult for macroalgae biofuels to meet renewable energy standards. (State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017)
Biofuels from macroalgae are not yet economically viable.
The high cost of cultivation and harvesting is the single biggest barrier. Algae-based fuels are unlikely to be viable in the near to medium term.
Incumbent macroalgae producers do not have an incentive to explore a highly uncertain market.
The biomass from existing commercial macroalgae cultivation is primarily used for existing traditional and higher-value markets such as food, feed, and the extraction of specialty products. Given the lack of economic viability and the lack of focus on alternative biofuels even in hard to electrify sectors such as aviation, there is limited incentive for producers to invest in the biofuel market.
Data Availability and Harmonization
There is a lack of standardized, comparable LCA and TEA data. There is a general lack of good quality, comparable data from LCA and TEA studies against which to assess and validate results and make predictions about scale. This makes it difficult for macroalgae biofuels to meet renewable energy standards. (State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017)
Biofuels from macroalgae are not yet economically viable.
The high cost of cultivation and harvesting is the single biggest barrier. Algae-based fuels are unlikely to be viable in the near to medium term.
Incumbent macroalgae producers do not have an incentive to explore a highly uncertain market.
The biomass from existing commercial macroalgae cultivation is primarily used for existing traditional and higher-value markets such as food, feed, and the extraction of specialty products. Given the lack of economic viability and the lack of focus on alternative biofuels even in hard to electrify sectors such as aviation, there is limited incentive for producers to invest in the biofuel market.
Policy and Governance
Version published:
May 29, 2026 - 3:52pm
The gaps in this section determine whether the regulatory environment can support the project timelines and investment horizons that commercial-scale seaweed biofuel development requires — fragmented permitting, volatile subsidy regimes, and the absence of carbon pricing all extend the time-to-market for projects and reduce their bankability, delaying any contribution to the sectoral decarbonization milestones that anchor current SAF mandate and IMO shipping targets.
Permitting seaweed farms is fragmented and slow
Without streamlined, growth-supportive policies, scaling efforts will remain constrained. This creates unpredictable timelines, duplicative requirements, and high transaction costs that disproportionately burden smaller developers and early-stage projects (Camarena Gómez and Lähteenmäki-Uutela, 2024).
Biofuels policy is inconsistent and sensitive to external conditions.
Funding and regulatory support for macroalgae-based biofuels has historically tracked fossil fuel prices and short-term political priorities rather than long-term decarbonization commitments. The absence of durable carbon pricing in most jurisdictions means that the economic case for seaweed biofuels depends on volatile subsidy regimes rather than a stable market signal. This makes it difficult for developers to plan multi-year investment programs or for lenders to underwrite project debt (State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017, p. 111).
Lack of early-stage public funding deters private investment
Commercial-scale seaweed biofuel projects carry technology, market, and policy risks that private investors are unwilling to absorb at the current stage of development. Public investment to de-risk early-stage innovation has not been sustained enough to overcome the risks or to rule out the viability of seaweed-based biofuels.
The gaps in this section determine whether the regulatory environment can support the project timelines and investment horizons that commercial-scale seaweed biofuel development requires — fragmented permitting, volatile subsidy regimes, and the absence of carbon pricing all extend the time-to-market for projects and reduce their bankability, delaying any contribution to the sectoral decarbonization milestones that anchor current SAF mandate and IMO shipping targets.
Permitting seaweed farms is fragmented and slow
Without streamlined, growth-supportive policies, scaling efforts will remain constrained. This creates unpredictable timelines, duplicative requirements, and high transaction costs that disproportionately burden smaller developers and early-stage projects (Camarena Gómez and Lähteenmäki-Uutela, 2024).
Biofuels policy is inconsistent and sensitive to external conditions.
Funding and regulatory support for macroalgae-based biofuels has historically tracked fossil fuel prices and short-term political priorities rather than long-term decarbonization commitments. The absence of durable carbon pricing in most jurisdictions means that the economic case for seaweed biofuels depends on volatile subsidy regimes rather than a stable market signal. This makes it difficult for developers to plan multi-year investment programs or for lenders to underwrite project debt (State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017, p. 111).
Lack of early-stage public funding deters private investment
Commercial-scale seaweed biofuel projects carry technology, market, and policy risks that private investors are unwilling to absorb at the current stage of development. Public investment to de-risk early-stage innovation has not been sustained enough to overcome the risks or to rule out the viability of seaweed-based biofuels.
The gaps in this section determine whether the regulatory environment can support the project timelines and investment horizons that commercial-scale seaweed biofuel development requires — fragmented permitting, volatile subsidy regimes, and the absence of carbon pricing all extend the time-to-market for projects and reduce their bankability, delaying any contribution to the sectoral decarbonization milestones that anchor current SAF mandate and IMO shipping targets.
Permitting seaweed farms is fragmented and slow
Without streamlined, growth-supportive policies, scaling efforts will remain constrained. This creates unpredictable timelines, duplicative requirements, and high transaction costs that disproportionately burden smaller developers and early-stage projects. (Camarena Gómez and Lähteenmäki-Uutela, 2024).
Biofuels policy is inconsistent and sensitive to external conditions.
Funding and regulatory support for macroalgae-based biofuels has historically tracked fossil fuel prices and short-term political priorities rather than long-term decarbonization commitments. The absence of durable carbon pricing in most jurisdictions means that the economic case for seaweed biofuels depends on volatile subsidy regimes rather than a stable market signal. This makes it difficult for developers to plan multi-year investment programs or for lenders to underwrite project debt (State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017, p. 111).
Lack of early-stage public funding deters private investment
Commercial-scale seaweed biofuel projects carry technology, market, and policy risks that private investors are unwilling to absorb at the current stage of development. Public investment to de-risk early-stage innovation has not been sustained enough to overcome the risks or to rule out the viability of seaweed based biofuels.
Permitting seaweed farms is fragmented and slow
Without streamlined, growth-supportive policies, scaling efforts will remain constrained. This creates unpredictable timelines, duplicative requirements, and high transaction costs that disproportionately burden smaller developers and early-stage projects. (Camarena Gómez and Lähteenmäki-Uutela, 2024).
Biofuels policy is inconsistent and sensitive to external conditions.
Funding and regulatory support for macroalgae-based biofuels has historically tracked fossil fuel prices and short-term political priorities rather than long-term decarbonization commitments. The absence of durable carbon pricing in most jurisdictions means that the economic case for seaweed biofuels depends on volatile subsidy regimes rather than a stable market signal. This makes it difficult for developers to plan multi-year investment programs or for lenders to underwrite project debt (State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017, p. 111).
Lack of early-stage public funding deters private investment
Commercial-scale seaweed biofuel projects carry technology, market, and policy risks that private investors are unwilling to absorb at the current stage of development. Public investment to de-risk early-stage innovation has not been sustained enough to overcome the risks or to rule out the viability of seaweed based biofuels.
Permitting seaweed farms is fragmented and slow
Without streamlined, growth-supportive policies, scaling efforts will remain constrained. For example, burdensome and lengthy permitting can create unnecessary farming requirements and discourage investment, particularly in Europe and North America (Camarena Gómez and Lähteenmäki-Uutela, 2024).
Biofuels policy is inconsistent and sensitive to external conditions.
Funding for macroalgae-based biofuels ebbs and flows and is often tied to conditions such as the cost of fossil fuels and political priorities. Absence of carbon pricing makes this a major challenge.(State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017, p. 111).
Lack of early-stage public funding deters private investment
Public investment is needed to “de-risk” early innovation and enable private financing, as seen with other technologies, including for existing competitive technologies.
Permitting seaweed farms is fragmented and slow.
Without streamlined, growth-supportive policies, scaling efforts will remain constrained. For example, burdensome and lengthy permitting can create unnecessary farming requirements and discourage investment, particularly in Europe and North America (Camarena Gómez and Lähteenmäki-Uutela, 2024).
Biofuels policy is inconsistent and sensitive to external conditions.
Funding for macroalgae-based biofuels ebbs and fows and is often tied to conditions such as the cost of fossil fuels and political priorities. Absence of carbon pricing makes this a major challenge.(State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017, p. 111)
Lack of early-stage public funding deters private investment.
Public investment is needed to “de-risk” early innovation and enable private financing, as seen with other technologies, including for existing competitive technologies.
Permitting seaweed farms is fragmented and slow.
Outside East and Southeast Asia, licensing frameworks are still emerging. Policy reforms are needed to reduce permitting burdens (without compromising environmental and social safeguards) and resolve space-use conflicts.
Biofuels policy is inconsistent and sensitive to external conditions.
Funding for macroalgae-based biofuels ebbs and fows and is often tied to conditions such as the cost of fossil fuels and political priorities. Absence of carbon pricing makes this a major challenge.(State of Technology Review-Algae Bioenergy: IEA Bioenergy, 2017, p. 111)
Lack of early-stage public funding deters private investment.
Public investment is needed to “de-risk” early innovation and enable private financing, as seen with other technologies, including for existing competitive technologies.
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