Comprehensive quantification of production costs for large-scale kelp aquaculture and cost reduction opportunities

A highly realistic techno-economic analysis (TEA) was developed to assess the cost of production (COP, US $ per fresh tonne kelp) for large-scale kelp aquaculture. The TEA resolves feedbacks across structural design and response, operational requirements and decisions, site properties, and biological response. We apply the TEA to a Saccharina latissima farming operation at a 100m deep, 405 hectare site located 20 km offshore in the Gulf of Maine. Our baseline scenario included a farm previously designed for minimal structure cost normalized by production capacity and operated according to procedures typical for contemporary US-based kelp farms. Assuming “line-of-sight” farm operations, i.e. those that could be implemented with existing technologies, the structure was redesigned for minimized COP (improved scenario). Leveraging the comprehensive nature of the TEA to balance operational and structural design choices, COP was reduced from $2,618 at baseline to $383 in the improved scenario. Primary cost reduction drivers included: (1) use of purpose-built, correctly sized vessels, (2) heavily mechanized operations, (3) at-sea processing of harvested kelp into a slurry (4) biomass storage in vessel holds, (5) structural design that minimizes loads, maximizes operational efficiency and spatial productivity, and (6) cultivation at maximal depths for site specific light penetration. Baseline results were most sensitive to workable wave height thresholds, vessel cruising speed, yield and distance from port. Improved scenario COP was most sensitive to yield, farm component lifespan, and structural costs. Results highlight that no single innovation in operations models or structural design will dictate potential COP minima for large-scale kelp farming.