Revisiting Theoretical Limits for One Degree-of-Freedom Wave Energy Converters

Tom, Nathan M.

doi:10.1115/1.4049287

Revisiting Theoretical Limits for One Degree-of-Freedom Wave Energy Converters

Journal Article · Fri Jan 22 00:00:00 EST 2021 · Journal of Energy Resources Technology

DOI:https://doi.org/10.1115/1.4049287· OSTI ID:1768267

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National Renewable Energy Lab. (NREL), Golden, CO (United States)

This work revisits the theoretical limits of one degree-of-freedom wave energy converters (WECs). This work considers the floating sphere used in the OES Task 10 WEC modeling and verification effort for analysis. Analytical equations are derived to determine bounds on displacement amplitude, time-averaged power (TAP), and power-take-off (PTO) force. A unique result found shows that the TAP absorbed by a WEC can be defined solely by the inertial properties and radiation hydrodynamic coefficients. In addition, a unique expression for the PTO force was derived that provides lower and upper bounds when resistive control is used to maximize power generation. For complex conjugate control, this same expression only provides a lower bound, as there is theoretically no upper bound. These bounds assist in comparing the performance of the floating sphere if it were to extract energy using surge or heave motion. The analysis shows because of differences in hydrodynamic coefficients for each oscillating mode, there are different frequency ranges that provide better power capture efficiency. The influence of a motion constraint on TAP while utilizing a nonideal power take-off is examined and found to reduce the losses associated with bidirectional energy flow. The expression to calculate TAP with a nonideal PTO is modified by the electrical conversion efficiency and the ratio of the PTO spring and damping coefficients. Furthermore, the PTO spring and damping coefficients were separated in the expression, allowing for limits to be set on the PTO coefficients to ensure net power generation.

View Accepted Manuscript (DOE)

Research Organization:: National Renewable Energy Laboratory (NREL), Golden, CO (United States)

Sponsoring Organization:: USDOE Office of Energy Efficiency and Renewable Energy (EERE), Water Power Technologies Office

Grant/Contract Number:: AC36-08GO28308

OSTI ID:: 1768267

Report Number(s):: NREL/JA--5700-77709; MainId:30624; UUID:04c0bd80-6b46-4e57-8a98-0cef7357fd47; MainAdminID:18521

Journal Information:: Journal of Energy Resources Technology, Journal Name: Journal of Energy Resources Technology Journal Issue: 9 Vol. 143; ISSN 0195-0738

Publisher:: ASMECopyright Statement

Country of Publication:: United States

Language:: English

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