Levelized cost of energy for a Backward Bent Duct Buoy

https://doi.org/10.1016/j.ijome.2016.07.002Get rights and content

Highlights

  • Presentation of pneumatic and electric performance models for a floating oscillating water column and detailed technical analyses of the device design, anchor and mooring design, and power conversion chain components.

  • Presentation of the operations and maintenance, installation, and environmental permitting associated with the device in a Northern California USA climate.

  • Presentation of LCOE projections at multiple scales.

  • Each aspects uncertainty is discussed as it is presented. • Presentation of pneumatic and electric performance models for BBDB.

Abstract

The Reference Model Project, supported by the U.S. Department of Energy, was developed to provide publically available technical and economic benchmarks for a variety of marine energy converters. The methodology to achieve these benchmarks is to develop public domain designs that incorporate power performance estimates, structural models, anchor and mooring designs, power conversion chain designs, and estimates of the operations and maintenance, installation, and environmental permitting required. The reference model designs are intended to be conservative, robust, and experimentally verified. The Backward Bent Duct Buoy (BBDB) presented in this paper is one of three wave energy conversion devices studied within the Reference Model Project. Comprehensive modeling of the BBDB in a Northern California climate has enabled a full levelized cost of energy (LCOE) analysis to be completed on this device.

Introduction

The Reference Models serve as non-proprietary open-source study objects for technical and economic evaluation. The US Department of Energy has supported the creation of a total of 6 Reference Models, the first four are detailed in [1]. Three of these reference models are current energy converters (CECs): a horizontal axis tidal turbine, a vertical axis riverine turbine, and a horizontal axis open-ocean current turbine. Three of these reference models are wave energy converters (WECs): a floating 2-body point absorber, a pitching flap device, and a floating oscillating water column (OWC) device. The reference models are intended to provide a benchmark of technical and economic performance. The levelized cost of energy (LCOE), in dollars per kilowatt-hour ($/kW h), was estimated for each Reference Model, including LCOE for a single device and arrays of 10, 50, and 100 units in order to quantify cost reductions associated with economies of scale. The reference models also provide open-source designs with corresponding experimental data. The combination of these two intents has identified cost reduction pathways and research priorities for improving performance and reducing costs.

A Northern CA deployment climate, near Eureka, was selected as the reference wave energy resource [2]. The deployment climate in which this device was analyzed is the same for all of the WEC Reference Models. This site has an annual average incident wave power flux of 31.5 kWm.

A Backward Bent Duct Buoy (BBDB), shown in Fig. 1, is a floating OWC device composed of an L-shaped duct open to the ocean downstream from the wave propagation direction. The BBDB design was first proposed by Masuda [3] in the 1980’s and is one variety of floating OWC devices. The incident waves result in a fluctuating pressure within the air-chamber. Bidirectional air flow drives the turbine and produces an electrical power output. The BBDB benefits from the coupled surge, heave, and pitch rigid-body modes and the OWC’s resonance to expand the frequency range of efficient conversion [4].

This paper presents an overview of the detailed technical analyses that were completed on the BBDB. These detailed analyses included the development of:

  • pneumatic and electric performance models [4], [5] where a Wells Turbine was assumed,

  • an anchor and mooring layout designed to withstand a 100-year storm in the climate [6],

  • and a structural design [7].

The uncertainties associated with each of the technical analyses are highlighted as each is presented. Overviews of the operations and maintenance, installation, and environmental permitting are presented along with their uncertainties [2], [8].

These technical analyses facilitated the LCOE calculations assuming a 20-year operational life at multiple array scales [2]. This economic analysis is presented and the major cost drivers in this design are identified. Sensitivity analyses on key subsystems are presented to broaden the applicability of this work.

Due to the desire to have robust and conservative estimates, the LCOE should be viewed as a baseline. The modelling team has attempted to highlight areas of uncertainty associated with each of the analyses.

Section snippets

Mooring and foundation

The mooring system specifications are driven by the extreme sea states. In order to protect the Power Conversion Chain (PCC) of the device, the air chamber is assumed to be fully vented, thus the dynamics of the device are completely dictated by the structure’s response. During severe weather conditions, the devices diffraction parameter is approximately half of its wave height to characteristic length ratio which is a measure of the importance of the drag force [6]. Therefore, the hydrodynamic

Installation and infrastructure

The deployment strategy for the BBDB is similar to that prescribed for RM3 [1]. It accounted for the installation of the (1) mooring system, (2) subsea cable infrastructure, and (3) the devices themselves (including commissioning). This analysis assumed two of the DP-2 class vessels that ReVision specified for the RM3 installation to account for the significant mass of the BBDB and the mooring components. The BBDB is assumed to be mobilized from the Gulf of Mexico and the two DP-2 vessels would

Operations and maintenance

The requirements for the O&M vessel were: (1) sufficient deck space to handle mooring lines and cable repair; (2) dynamic positioning (DP-1) to allow for more effective operation; and (3) crane lifting capacity of 5 Mg at a 20-foot radius. A 10-person crew, approximately, was required to operate the vessel and carry out repair and maintenance activities. Operations were assumed to take place only during daylight hours (12 h per day) and the vessel would return to port at night.

Failure rate

Environmental compliance

Responsible deployment of marine energy devices in estuaries, coastal areas, and major rivers requires that biological resources and ecosystems be protected through siting and permitting (consenting) processes. Scoping appropriate deployment locations, collecting pre-installation (baseline) and post-installation data all add to the cost of developing Marine Hydro-Kinetic (MHK) projects, and hence to the levelized cost of energy. The logic models that describe studies and processes for

Levelized cost of energy

The LCOE was calculated according to [30]. Specifically, the uniform financial parameters (such as tax, inflation, and project financial structure) were conformed to in the analysis. The fixed charge rate (FCR) (the annual return needed to meet investor revenue requirements) assumed in this analysis is 0.108. The standardized financial variables are detailed in Table 9. Two of these parameters, the depreciation tax shield (D) and FCR, are derived from the choice of the financial variables in

Conclusion

A full overview of the BBDB Reference Model was presented in this paper. The detailed technical analyses relating to the mooring, structure, performance, and PCC were highlighted. The analyses relating to installation, O&M, and environmental permitting for the BBDB off the Northern CA coast were also presented. This technical work was utilized in the full LCOE analysis presented at the end of the paper.

The LCOE presented is intended to be conservative. Both conservative and aggressive aspects

Acknowledgment

This work was funded by the U.S. Department of Energy’s Wind and Water Power Technologies Office. The research was in support of the Reference Model Project. The staff at HMRC were instrumental in obtaining the experimental data presented here. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract

References (31)

  • G. Copeland et al.

    Oscillating Water Column Structural Model

    (2014)
  • A. Copping et al.

    The Contribution of Environmental Siting and Permitting Requirements to the Cost of Energy for Oscillating Water Column Wave Energy Devices: Reference Model #6

    (2013)
  • S.K. Chakrabarti

    Hydrodynamics of Offshore Structures

    (1987)
  • Veritas, Det Norske, Offshore Standard DNV-OS-E301 Position Mooring...
  • J.C. Berg

    Extreme Ocean Wave Conditions for Northern California Wave Energy Conversion Device

    (2011)
  • Cited by (13)

    • Maximising the hydrodynamic performance of offshore oscillating water column wave energy converters

      2022, Applied Energy
      Citation Excerpt :

      The Spar-buoy OWC is a wave activated body as the hull is designed to become excited by the incoming wave and kinetic energy generated by the motions are converted into electricity [17]. Forward bent ducted [29,19] and backwards bent ducted [38,5] OWCs have a 90° bend in the chamber such that the submerged chamber opening is facing directly into or away from the waves. Asymmetrical OWCs [10,40] have a shallow forward wall and deep aft and side wall such that the submerged OWC chamber is completely open to the incoming waves.

    • Experimental study on a bottom corner of the floating WEC

      2022, Ocean Engineering
      Citation Excerpt :

      In Spain, the wave energy plant that generates grid electricity (with estimated electricity generation of 600 MWh annually) utilizes OWC wave energy converter (Sheng and Lewis, 2018). Moreover, a study was conducted on the levelized cost of energy (LCOE) that showed the development of big scale OWC that is able reduce the cost (Bull et al., 2016). This further emphasises that the OWC is a promising and developed wave energy converters.

    • Backward bent-duct buoy or frontward bent-duct buoy? Review, assessment and optimisation

      2019, Renewable and Sustainable Energy Reviews
      Citation Excerpt :

      However, since the interest of this work relies on the hydrodynamic performance comparison between both geometries, the same type of turbine and generator were adopted. The techno-economic methodology applied to assess three wave farms consisting of 1, 10 and 50 devices is similar to the one presented in Refs. [21,35]. The farms are made up of optimised geometry BBDBs with dimensions presented in Section 6.1.

    • Strategies to improve sustainability and offset the initial high capital expenditure of wave energy converters (WECs)

      2017, Renewable and Sustainable Energy Reviews
      Citation Excerpt :

      The LCOE for offshore wind energy varies from 100 €/MW h [19] to a maximum of ~300 €/MW h [132] for deep offshore wind farms, with the median market levelized cost being about 170 €/MW h [23]. For wave energy the LCOE varies greatly depending on technology [133], number of units and device structural mass [22,134], deployment depth [19], etc. Theoretically, the cost can be as little as 50 €/MW h [22], but practical it is much higher, usually ~1 K €/MW h or more [18] for a typical small wave farm (Table 6).

    View all citing articles on Scopus
    View full text