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Topic

Offshore Wind-Powered Carbon Dioxide Removal – a Solid Carbon Initiative

Department of Mechanical Engineering

Date & location

• Friday, April 17, 2026

• 9:00 A.M.

• MacLaurin Building

• Room D202c

Reviewers

Supervisory Committee

• Dr. Curran Crawford, Department of Mechanical Engineering, ̽��ϵ�� (Supervisor)

• Dr. Brad Buckham, Department of Mechanical Engineering, UVic (Member)

• Dr. Richard Dewey, Ocean Networks Canada, UVic (Outside Member) 

External Examiner

• Dr. Claudio Alexis Rodríguez Castillo, Department of Naval Architecture, Ocean & Marine Engineering, University of Strathclyde 

Chair of Oral Examination

• Dr. Joseph Melton, School of Earth and Ocean Sciences, UVic

   

Abstract

If societies around the globe are to stabilise Earth’s surface temperature and prevent it from rising beyond levels compatible with human and non-human life, they must not only eliminate their current greenhouse gas (GHG) emissions but also remove accumulated emissions from the atmosphere. Of the different anthropogenic GHGs emitted, carbon dioxide (CO₂) has historically and is continuing to contribute the most to the warming of the atmosphere, ocean, and land. For this reason, it is the focus of this investigation.

This dissertation provides insights into and designs for two possible modular system solutions for offshore wind-powered carbon dioxide removal (CDR). The first one takes CO₂ directly from the air (known as direct air capture, or DAC), and the second one draws it out indirectly through the ocean (known as direct ocean capture, or DOC). Although not studied in this work, once captured, the CO₂ can be permanently sequestered via mineral trapping in mafic rocks, such as basalt formations. This is especially convenient as basalt covers most of the upper ocean crust and offers more than enough storage capacity to meet projected CDR needs. The feasibility of CO₂ mineralisation in subseafloor basalt is currently being investigated by the Solid Carbon project, to which this study contributes.

The prospect of storing CO₂ permanently in subseafloor basalt reservoirs motivated the idea to locate the capture of CO₂ offshore as well, where: the constraints on area use are more relaxed than onshore, the process can be powered by local renewable winds, and all required operating equipment can be housed on floating offshore wind turbine (FOWT) platforms. FOWT platforms are rapidly emerging technologies whose costs are less sensitive to water depth variations than more established fixed-bottom turbine platforms. As such, they are better suited for remote offshore applications, such as wind-powered DAC and wind-powered DOC. The integration of the CO₂ capture (whether DAC or DOC) and wind power systems on the same floating platform can reduce operational costs, since part of the maintenance of the two can be carried out together.

For the first proposed system solution, the FOWT-DAC platform, a dynamic analysis is conducted to modify as necessary and ensure that adding the DAC equipment to the moored wind platform disturbs its operation as little as possible. This is done by comparing the FOWT-DAC system’s floating stability and its fully coupled motion responses with those of the reference FOWT platform design. The research findings demonstrate good fit between the proposed system and the benchmark, suggesting that the hybrid FOWT-DAC platform behaves in a similar way to the reference system and can serve as a viable modular deployment approach.

For the second proposed system solution, the FOWT-DOC platform, four design scenarios are examined. Each draws seawater from increasingly greater depths – 20 m (Case 0), 100 m (Case 1), 200 m (Case 2), and 300 m (Case 3) - with incrementally higher dissolved inorganic carbon (DIC) concentrations. The energy intensity and cost of carbon capture in each case are then compared. The key finding is that, although Case 3 is the least energy intensive, it is not the most economical. This is explained by the rising linear costs associated with deeper withdrawal outweighing the benefits from seawater with correspondingly increased DIC concentration, which peaks between Cases 0 and 1, and diminishes progressively thereafter. As a result, the estimated cost is lowest for Case 2, which is almost 8% more cost-effective than Case 0.

Direct air capture and direct ocean capture are two emerging CDR methods with high potential to remove CO₂ from the atmosphere and could be coupled with offshore, permanent sequestration in subseafloor basalt. Although DOC is currently at an earlier stage of development than DAC, it could additionally help mitigate local ocean acidification, which together with climate change, is one of the seven planet boundaries currently transgressed. Both DAC and DOC are estimated to have similar costs of implementation, which are comparatively higher than those of many other CDR techniques. This may be an established but unfair comparison as not all CDR methods exhibit the same sequestration permanence (durability), among other key indicators. Future economic assessments should account for these differences and show the true societal cost of carbon removal across different residence times.