Submarine drones could grow a lot kelp in the open ocean

Marine BioEnergy is collaborating with a research team at the University of Southern California, Wrigley Institute for Environmental Studies. US Department of Energy, Advanced Research Projects Agency – Energy (ARPA-E) has provided $2.1 million in funding for a proof of concept.

Kelp grows best 100 and 300 meters beneath the surface, or where there are natural upwellings, typically along coasts. Can submarine drones hold nets and lines to suspend kelp crops in the open ocean ? Marine BioEnergy proposes to tether their kelp farms to drone submarines that will submerge the entire farm every night, bringing all of the kelp down to the nutrient rich water that it needs and then floating it back up again as the sun rises.

Kelp grows up to 2 feet per day and does not need weeding, pesticides, fertilizers, or any other kind of resource-intensive micromanagement.

The key test is: does a fast-growing kelp thrive when depth-cycled at night to absorb nutrients and surfaced during the day to absorb sunlight?

The first tests will depth-cycle kelps near-shore to measure resilience to pressure changes. The target kelp is Macrocystis. If Macrocystis does not thrive, an alternate native species will be tested.

Juvenile kelps will be attached to an anchored buoy system which will surface the kelps during the day and submerge them at night. Marine Biologist will monitor the kelps and the water nutrients regularly. The biomass will be weighed at the end of multiple experiments and compared to biomass from a group of controls.

The second set of tests will be anchored in deeper water where the conditions will closely replicate the open ocean environment. In the open ocean, the top layer is nutrient deplete and the kelp must absorb deep water nutrients to continue to produce biomass. The biomass will be weighed at the end of the 90-day growing/harvest cycle and compared to biomass from a group of controls.

As part of this effort, the Wrigley Institute will be developing a kelp nursery to grow sporeling on artificial substrate (long lines). The nursery long lines will be subjected to depth-cycling and are part of the preparation for commercial deployment.

They are trying to develop an open ocean cultivation system for macroalgae biomass using drone boats to hold long lines and nets. The kelp can be converted to biocrude. Giant kelp is one of the fastest growing sources of biomass, and the open ocean surface water is an immense, untapped region for growing kelp. However, kelp does not grow in the open ocean because it needs to attach to a hard surface, typically less than 40 meters deep. Kelp also needs nutrients that are only available in deep water or near shore but not on the surface of the open ocean. To overcome these obstacles, the team proposes to build inexpensive underwater drones that will tow large grids, to which the kelp is attached. These autonomous drones will be capable of towing the farms from sunlight-rich surface water during the day to nutrient-rich deep water during the night, and will submerge the farms to avoid storms and passing ships. A prerequisite for this vision will be successful demonstration of depth-cycling kelp plants from the surface to the deep ocean. Working with researchers at the University of Southern California, Wrigley Institute for Environmental Studies, Marine BioEnergy will develop and deploy first-of-kind technology to assess and apply this unique concept of kelp depth-cycling for deep water nutrient uptake to kelp production. Researchers at Pacific Northwest National Laboratory will convert this kelp to biocrude and document the quality. This technology could enable large-scale energy crop production in many regions of the open ocean, with an initial focus on the U.S. Exclusive Economic Zone off California.

Potential Impact:

If successful, Marine BioEnergy, Inc. would be able to grow giant kelp in open water to create an abundant and affordable feedstock for low-carbon biocrude.


Increasing the production of domestic biofuels would help diversify the resources we rely on for transportation, thus further reducing dependence upon imported crude oil.


The proposed technology would enable commercial biomass farming to be deployed in the open ocean, thereby reducing the demand for artificial fertilizer, land, and freshwater resources.

Marine BioEnergy estimates the open-ocean kelp farming method would result in “a cost per unit energy comparable to coal and natural gas: under $2.50/GJ.” You’d also end up with about 16 percent by mass of methane gas, which is useful, along with a solid waste byproduct that is very rich in nutrients and makes a great fertilizer

Marine BioEnergy, Inc. projects the cost of its biocrude to be competitive with conventional petroleum.