Session: 09-05-03 Wave Energy: Mooring and Control

Submission Number: 156384

An Updated Mooring Cost Modeling Tool Set With Application to a Reference Model Wave Energy Converter 

Technoeconomic analysis of marine hydrokinetic devices is a crucial step in bringing the technology from the design phase to operation. One important part of a successful technoeconomic analysis and design optimization is the material costs of the device components. The capital expenditures (CAPEX) for mooring systems of floating marine hydrokinetic devices are an understudied area without reliable published cost data. The goal of this work is twofold. First, we provide updated mooring cost metrics for floating marine energy devices. Second, we use these updated costs curves to analyze updated mooring designs for a reference model device. This work is part of a larger effort that will publish updated designs and CAPEX estimates for a range of reference devices and reference mooring systems.

The Department of Energy (DOE) sponsored reference model (RM) project created a set of six reference model designs of hydrokinetic devices with associated levelized cost of energy estimated for different reference sites and device array sizes. Five of these RMs, RM2-6, are floating designs. The reference model publications provide costs for the mooing systems of RM2-6, however these are based on a rough-estimate approach rather than grounded in robust technoeconomic analysis. The publications indicate that a more thorough mooring design and analysis process would be needed to get accurate mooring cost data. There is very limited other available cost data in the literature for floating marine hydrokinetic devices and wave energy devices. The Pelamis WEC deployment has published their mooring costs, however these costs are only representative of a single mooring design. Aside from these two sources, most literature refers to a few publications that are over a decade old that contain estimated costs for a limited set of mooring material types. This work aims to provide a set of cost modeling tools for all common mooring components and types, and then apply those tools to the RM3 device. 

Through outreach to industry suppliers and floating WEC deployers, we created a dataset of realistic mooring system component costs. By combining these costs with inflation adjusted open-source mooring costs from deployed projects, we developed a collection of cost curves that are widely applicable to many mooring system designs. These updated cost curves were implemented into two design tools: The System Advisor Model (SAM), and the quasi-static mooring design tool MoorPy. 

The second part of this work looks at an updated mooring design for the RM3 device and provides an example of how to apply these technoeconomic tools. We used the mooring dynamics modeling software MoorDyn coupled with WECSim to simulate RM3. Using MoorDyn, we were able to obtain design loads for all the components in the mooring systems operating in their respective design site conditions. Then, through an iterative design process we updated the mooring system materials and sizes to meet the design loads and reference model operational constraints. Finally, we used the updated costs to develop new mooring CAPEX estimates for the reference model.

The updated cost curves presented in this work will allow for more accurate technoeconomic modeling of floating hydrokinetic energy devices. This will address a gap in the literature for the cost of mooring system components. Additionally, the RM3 mooring system design and cost consideration will provide a template for the application of these new cost models. Future publications will present updated mooring designs and cost estimates for all the reference models, as well as examine a set of reference mooring designs to be implemented in SAM. 

Presenting Author: Ryan Davies National Renewable Energy Laboratory

Presenting Author Biography: Ryan Davies has been a mooring dynamics modeling engineer at the National Renewable Energy Laboratory for the past two years. He has been the primary developer of the mooring dynamics software MoorDyn, including updating the coupling of MoorDyn V2 and WECSim. He has also been involved in mooring optimization work for floating offshore wind farms as well as wave energy mooring design work. He received his bachelors in physics and environmental studies from Macalester College in St. Paul, Minnesota.