Seaweed farming background and production cost estimates
-Global seaweed production reached 32.4 million dry tonnes in 2018
-At the high end, annual yield from ocean seaweed farms is on the order of 1 kg m−2 y−1 dry weight
-the energy content of seaweed can potentially support conversion of dry seaweed biomass to liquid biofuel at a rate of 4–5 kg l −1 (Das, Mondal, & Maiti, 2017).
- reduces global liquid fuel carbon emissions by one third may require on the order of 4 million km2 of seaweed farms
-area equivalent to all the agricultural land in use today in the United States
-we therefore model the production cost of large (10 km2 , or 1000 ha) farms of the future that are designed to survive in exposed, open ocean conditions.
-Early efforts to farm seaweeds for biofuel date back to the 1970s in the USA (Kim, Stekoll, & Yarish, 2019; Roesijadi, Copping, Huesemann, Forster, & Benemann, 2008; Sheehan et al., 1998);
-Mexico reflects farming structures that are unlikely to scale to deeper, exposed waters. Likewise, the $400 per dry tonne production cost estimated by Valderrama et al. (2015)
Seaweed farming concept for biofuel-scale production
The design and operating concept for the future farms we model in this paper, and many of the model input values and assumptions, were developed by teams funded by ARPA-E’s MARINER projects (US DoE, 2021)
The cost estimates for nursery systems to support both temperate and tropical largescale farming operations have been developed by the MARINER project team assuming a direct seeding approach for kelp (Stekoll et al., 2021) and a set of onshore nursery tanks to supply material for re-planting tropical seaweeds in the event of a farm shutdown or crop loss (Roberson et al., 2022).
The baseline farm operation for cool temperate kelp produces 32,800 dry tonnes of biomass per year on 10,900 km of grow ropes, and requires seven farm boats employing 42 crew members during the planting and harvest seasons. Capital investment is about $48 million, and annual operating cost about $4.7 million. The baseline tropical farm operation produces 41 700 dry tonnes per year on 10 200 km of grow ropes, and requires three farm boats and 24 crew members working year-round. Capital investment for the tropical farm is about $31 million, and annual operating cost about $5.2 million.
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