Techno-Economic Feasibility Analysis of Offshore Seaweed Farming for Bioenergy and Biobased Products

The purpose of this study is to provide an initial assessment of the technical and economic feasibility of cultivating seaweed offshore to produce biofuels. This report reviews the seaweed industry and the higher value products that could improve the economic attractiveness of seaweed biofuel production process. We review previous attempts at offshore seaweed culture for biofuels, the technical and economic challenges faced by those projects, and the lessons learned. Progress in offshore seaweed farming technology is also examined.

We propose a concept for offshore seaweed cultivation that positions large seaweed farms in natural nutrient upwelling areas. This concept greatly simplifies prior proposals based on artificial upwelling of deep ocean waters for nutrient supply. We conclude with a technology road map that recommends future activities to move offshore seaweed culture from the present concept and vision to a future commercial reality.

For the context of this report, “offshore” or “open ocean” growing conditions refers to growing seaweed in waters that are generally too deep for even giant kelp to survive on their own and that are free from the direct influence of land. Nearshore refers to habitats of sufficiently shallow depth to enable such seaweeds to attach and grow or which provide a sheltered environment for aquaculture operations. This report documents the long history of using seaweeds to meet human needs. The economic value of seaweeds worldwide is currently about $6 billion USD, primarily as food products, and also as hydrocolloids for the food and pharmaceutical industry, soil conditioners, animal feeds, and cosmetics. The total seaweed harvest is reported at 15.7 million metric ton wet weight (about one million ton dry weight) per year, of which almost 90% is produced by nearshore aquaculture production. Thus, seaweed farming is already a significant industry, with a sophisticated technological basis, ranging from the biotechnology to aquaculture, processing, and marketing of the many products derived from these plants.

As the need for renewable energy continues to grow, seaweed farming has the potential to help meet future energy needs. The oceans cover over 70% of the Earth’s surface. Use of just 1% of that along the ocean margins could supply about 3.5 billion dry ton of new biomass annually, if the production rates already achieved in coastal seaweed farms in countries like China could be projected for open ocean systems. This is three-times the maximum amount of terrestrial biomass that can be reasonably collected annually in the U.S. Such systems would not competewith the availability of fresh water, land, and nutrients needed to sustain terrestrial agriculture.

Large-scale open ocean seaweed farming for biofuels production was attempted in the 1970s and 1980s, but was not technically successful. However, the lessons learned from that earlier attempt, together with advances in open ocean engineering and the current energy economics, provide the basis and incentive to develop a novel approach to open ocean farming. Indeed, exploratory R&D activities in Japan, Korea, Denmark, Germany, and the United Kingdom, among others, are already pioneering new efforts in this area. Large-scale open ocean farming
could be used to produce the next generation biofuels, in particular butanol, for which historical precedence exists, and also to increase the supply of higher value animal feeds and bioproducts.

The technical and economic viability of seaweed biomass production for conversion into biofuels requires an understanding of the factors that limit their growth in nature and under managed aquaculture operations, the evaluation of processes for converting the biomass into biofuels, and a determination of the risk factors in a seaweed-to-energy pathway. As noted above, we propose a concept for offshore seaweed cultivation, which we call the “Offshore Seaweed Farm”. This would be based on one-km2 (100 hectare) dynamically positioned floating seaweed production platforms. A Marine Biorefinery would take the seaweed biomass and process it into biofuels and other products.