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.