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• Solar-thermal seaweed biorefinery with offshore intensively grown biomass was analysed. • Co-production of protein, hydrochar, ethanol, distilled water and electricity was analysed. • The overall First Law efficiency is 32% and can reach 40% with energy recovery from aqueous phase. • Seaweed, electricity and protein prices are key for the profitability of the biorefinery. • The lowest environmental impacts are achieved with HDPV cage, PV electricity, and rail transport. Combing solar energy with biomass processing facilities are emerging systems for efficient use of solar energy for electricity generation, energy storage, and production of renewable materials. In this work, we propose a novel combination of solar thermal energy systems with marine macroalgae biorefinery, which requires energy inputs for biomass cultivation and processing. In this work, we analyze a 10-ton dry weight per hour capacity pilot-scale hybrid solar seaweed biorefinery, located at the Mishor Rotem near Dimona, the current location for solar-thermal projects in Israel, where seaweed biomass supply comes from a hypothetical offshore farm located 15 km offshore. Our energy and mass balance analysis show that the overall First Law efficiency of the hybrid solar seaweed biorefinery system for the co-production of protein, hydrochar, ethanol, distilled water, and electricity is 32% and can exceed 40% with additional waste stream recycling. Our cost-benefit analysis of the proposed solar-seaweed biorefinery shows that the prices of seaweed, electricity, and protein are the key drivers of the profitability of the production process. The environmental impacts of the hybrid solar-seaweed biorefinery with intensified offshore cultivated biomass were quantified under various seaweed cultivation, transportation, and processing strategies. [ABSTRACT FROM AUTHOR]

Offshore grown macroalgae biomass could provide a sustainable feedstock for biorefineries. However, tools to assess its potential for producing biofuels, food and chemicals are limited. In this work, we determined the net annual primary productivity (NPP) for Ulva sp. (Chlorophyta), using a single layer cultivation in a shallow, coastal site in Israel. We also evaluated the implied potential bioethanol production under literature based conversion rates. Overall, the daily growth rate of Ulva sp. was 4.5 ± 1.1%, corresponding to an annual average productivity of 5.8 ± 1.5 g DW m −2 day −1 . In comparison, laboratory experiments showed that under nutrients saturation conditions Ulva sp. daily growth rate achieved 33 ± 6%. The average NPP of Ulva sp . offshore was 838 ± 201 g C m −2 year −1 , which is higher than the global average of 290 g C m −2 year −1 NPP estimated for terrestrial biomass in the Middle East. These results position Ulva sp. at the high end of potential crops for bioenergy under the prevailing conditions of the Eastern Mediterranean Sea. We found that with 90% confidence, with the respect to the conversion distribution, the annual ethanol production from Ulva sp. biomass, grown in a layer reactor is 229.5 g ethanol m −2 year −1 .This translates to an energy density of 5.74 MJ m −2 year −1 and power density of 0.18 W m −2 . Growth intensification, to the rates observed at the laboratory conditions, with currently reported conversion yields, could increase, with 90% confidence, the annual ethanol production density of Ulva sp. to 1735 g ethanol m −2 year −1 , which translates to an energy density of 43.5 MJ m −2 year −1 and a power density 1.36 W m −2 . Based on the measured NPP, we estimated the size of offshore area allocation required to provide biomass for bioethanol sufficient to replace 5–100% of oil used in transportation in Israel. We also performed a sensitivity analysis on the biomass productivity, national CO 2 emissions reduction, ethanol potential, feedstock costs and sizes of the required allocated areas. [ABSTRACT FROM AUTHOR]