Revisiting Theoretical Limits for One-Degree-of-Freedom Wave Energy Converters
This work revisits the theoretical limits of one-degree-of-freedom wave energy converters. This paper considers the floating sphere used in the Ocean Energy Systems Task 10 Wave Energy Converter modeling and verification effort for analysis. Analytical equations are derived to determine bounds on the motion amplitude, time-averaged power, and power-take-off (PTO) force. A unique result was found that shows the time-averaged power absorbed by a wave energy converter can be defined solely by the inertial properties and radiation hydrodynamic coefficients. In addition, a unique expression for the PTO force amplitude was derived that has provided upper and lower bounds when resistive control is used to maximize power generation. For complex conjugate control, this same expression can only provide a lower bound, as there is theoretically no upper bound. These bounds are used to compare the performance of a floating sphere if it were to extract energy using surge or heave motion. The analysis shows that because of the differences in hydrodynamic coefficients of each oscillating mode, there will be different frequency ranges that provide better power capture efficiency. The influence of a motion constraint on power absorption while also utilizing a nonideal power take-off is examined and found to reduce the losses associated with bidirectional energy flow. The expression to calculate the time-averaged power with a nonideal PTO is modified by the mechanical-to-electrical efficiency and the ratio of the PTO spring and damping coefficients. The PTO spring and damping coefficients were separated in the expression, which allows for limits to be set on the possible values of PTO coefficients to ensure a net flow of power to the grid.
- Research Organization:
- National Renewable Energy Lab. (NREL), Golden, CO (United States)
- Sponsoring Organization:
- USDOE Office of Energy Efficiency and Renewable Energy (EERE), Water Power Technologies Office (EE-4W)
- DOE Contract Number:
- DE-AC36-08GO28308
- OSTI ID:
- 1669612
- Report Number(s):
- NREL/CP-5000-77934; MainId:31843; UUID:8837f1f1-04e3-41a8-83e3-97a0bcf90059; MainAdminID:18569
- Resource Relation:
- Conference: Presented at the ASME 2020 14th International Conference on Energy Sustainability, 17-18 June 2020; Related Information: 75701
- Country of Publication:
- United States
- Language:
- English
Similar Records
Revisiting Theoretical Limits for One Degree-of-Freedom Wave Energy Converters
Balancing Power Absorption and Structural Loading for an Assymmetric Heave Wave-Energy Converter in Regular Waves: Preprint