This report is an addendum to SAND2013-9040: Methodology for Design and Economic Analysis of Marine Energy Conversion (MEC) Technologies. This report describes an Oscillating Water Column Wave Energy Converter reference model design in a complementary manner to Reference Models 1-4 contained in the above report. In this report, a conceptual design for an Oscillating Water Column Wave Energy Converter (WEC) device appropriate for the modeled reference resource site was identified, and a detailed backward bent duct buoy (BBDB) device design was developed using a combination of numerical modeling tools and scaled physical models. Our team used the methodology in SAND2013-9040 for the economic analysis that included costs for designing, manufacturing, deploying, and operating commercial-scale MEC arrays, up to 100 devices. The methodology was applied to identify key cost drivers and to estimate levelized cost of energy (LCOE) for this RM6 Oscillating Water Column device in dollars per kilowatt-hour ($/kWh). Although many costs were difficult to estimate at this time due to the lack of operational experience, the main contribution of this work was to disseminate a detailed set of methodologies and models that allow for an initial cost analysis of this emerging technology. This project is sponsored by the U.S. Department of Energy's (DOE) Wind and Water Power Technologies Program Office (WWPTO), within the Office of Energy Efficiency & Renewable Energy (EERE). Sandia National Laboratories, the lead in this effort, collaborated with partners from National Laboratories, industry, and universities to design and test this reference model.
Experiments were conducted with a Backward Bent Duct Buoy (BBDB) oscillating water column wave energy conversion device with a scaling factor of 50 at HMRC at University College Cork, Ireland. Results were compared to numerical performance models. This work experimentally verified the migration of the natural resonance location of the water column due to hydrodynamic coupling for a floating non- axisymmetric device without a power conversion chain PCC present. In addition, the experimental results verified the performance model with a PCC of the same non- axisymmetric device when both floating and grounded.
To reduce the price of the reference Backward Bent Duct Buoy (BBDB), a study was done analyzing the effects of reducing the mooring line length, and a new mooring design was developed. It was found that the overall length of the mooring lines could be reduced by 1290 meters, allowing a significant price reduction of the system. In this paper, we will first give a description of the model and the storm environment it will be subject to. We will then give a recommendation for the new mooring system, followed by a discussion of the severe weather simulation results, and an analysis of the conservative and aggressive aspects of the design.
An oscillating water column (OWC) wave energy converter is a structure with an opening to the ocean below the free surface, i.e. a structure with a moonpool. Two structural models for a non-axisymmetric terminator design OWC, the Backward Bent Duct Buoy (BBDB) are discussed in this report. The results of this structural model design study are intended to inform experiments and modeling underway in support of the U.S. Department of Energy (DOE) initiated Reference Model Project (RMP). A detailed design developed by Re Vision Consulting used stiffeners and girders to stabilize the structure against the hydrostatic loads experienced by a BBDB device. Additional support plates were added to this structure to account for loads arising from the mooring line attachment points. A simplified structure was designed in a modular fashion. This simplified design allows easy alterations to the buoyancy chambers and uncomplicated analysis of resulting changes in buoyancy.
This analysis utilizes a 5 - MW VAWT topside design envelope created by Sandia National Laboratories to compare floating platform options for each turbine in the design space. The platform designs are based on two existing designs, the OC3 Hywind spar - buoy and Principal Power's WindFloat semi - submersible. These designs are scaled using Froude - scaling relationships to determine an appropriately sized spar - buoy and semi - submersible design for each topside. Both the physical size of the required platform as well as mooring configurations are considered. Results are compared with a comparable 5 - MW HAWT in order to identify potential differences in the platform and mooring sizing between the VAWT and HAWT. The study shows that there is potential for cost savings due to reduced platform size requirements for the VAWT.
Smith, Christopher S.; Bull, Diana L.; Willits, Steven M.; Fontaine, Arnold A.
This Technical Report presents work completed by The Applied Research Laboratory at The Pennsylvania State University, in conjunction with Sandia National Labs, on the optimization of the power conversion chain (PCC) design to maximize the Average Annual Electric Power (AAEP) output of an Oscillating Water Column (OWC) device. The design consists of two independent stages. First, the design of a floating OWC, a Backward Bent Duct Buoy (BBDB), and second the design of the PCC. The pneumatic power output of the BBDB in random waves is optimized through the use of a hydrodynamically coupled, linear, frequency-domain, performance model that links the oscillating structure to internal air-pressure fluctuations. The PCC optimization is centered on the selection and sizing of a Wells Turbine and electric power generation equipment. The optimization of the PCC involves the following variables: the type of Wells Turbine (fixed or variable pitched, with and without guide vanes), the radius of the turbine, the optimal vent pressure, the sizing of the power electronics, and number of turbines. Also included in this Technical Report are further details on how rotor thrust and torque are estimated, along with further details on the type of variable frequency drive selected.
When considering the future of offshore wind energy, developing cost effective methods of harnessing the offshore wind resource represents a significant challenge which must be overcome to make offshore wind a viable option. As the majority of the capital investment in offshore wind is in the form of infrastructure and operation and maintenance costs, reducing these expenditures could greatly reduce the cost of energy (COE) for an offshore wind project. Sandia National Laboratory and its partners (TU Delft, University of Maine, Iowa State, and TPI Composites) believe that vertical axis wind turbines (VAWTs) offer multiple advantages over other rotor configurations considering this new COE breakdown. The unique arrangement of a VAWT allows the heavy generator and related components to be located at the base of the tower as opposed to the top, as is typical of a horizontal axis wind turbine (HAWT). This configuration lowers the topside CG which reduces the platform stability requirements, leading to smaller and cheaper platforms. Additionally this locates high maintenance systems close to the ocean surface thus increasing maintainability. To support this project and the general wind research community, the Offshore Wind ENergy Simulation (OWENS) toolkit is being developed in conjunction with Texas A&M as an open source, modular aero-elastic analysis code with the capability to analyze floating VAWTS. The OWENS toolkit aims to establish a robust and flexible finite element framework and VAWT mesh generation utility, coupled with a modular interface that allows users to integrate easily with existing codes, such as aerodynamic and hydrodynamic codes.
This report considers and prioritizes the primary potential technical costreduction pathways for offshore wave activated body attenuators designed for ocean resources. This report focuses on technical research and development costreduction pathways related to the device technology rather than environmental monitoring or permitting opportunities. Three sources of information were used to understand current cost drivers and develop a prioritized list of potential costreduction pathways: a literature review of technical work related to attenuators, a reference device compiled from literature sources, and a webinar with each of three industry device developers. Data from these information sources were aggregated and prioritized with respect to the potential impact on the lifetime levelized cost of energy, the potential for progress, the potential for success, and the confidence in success. Results indicate the five most promising costreduction pathways include advanced controls, an optimized structural design, improved power conversion, planned maintenance scheduling, and an optimized device profile.
