Variable-Geometry Wave Energy Converter Design
NREL is exploring next-generation control strategies so wave energy converters can produce more power, handle extreme loads, and cost less.
Wave energy is not yet cost-competitive, in large part because of the high costs associated with building wave energy converters (WECs) robust enough to withstand large waves. NREL researchers are studying ways to reduce these structural costs and increase energy production to help wave energy achieve commercial success.
Benefits of Variable-Geometry
WECs traditionally have fixed-geometry hulls (that cannot change shape) and only one method to control their energy production: the generator, or power take-off (PTO). When a fixed-geometry WEC cannot avoid the full impact from extreme waves (a process known as load shedding), operators must place the device in survival mode, which halts power production in the moment and also limits production to specific wave conditions. Such limitations prevent the WEC from generating power over a wider range of sea states, leading to increased downtime, which could in turn dissuade developers, investors, and policymakers from accepting wave energy as renewable technology capable of providing consistent power.
NREL researchers are exploring new WEC designs to learn whether they could help optimize power production and costs. One such design is called variable geometry. Variable-geometry WECs can change shape in more energetic sea states to allow potentially destructive waves to pass by. A design using variable geometry could have several benefits, such as:
- Adding a second way to control a WEC, similar to blade pitch control in a wind turbine
- Allowing WEC operators to adjust a device’s geometry to shed potentially destructive loads in large-to-extreme sea states or increase power absorption in low-to-moderate sea states
- Enabling WECs to capture more energy, operate more efficiently, and generate more cost-competitive wave energy.
Don't just take NREL’s word on the exciting opportunities that are available with
the variable-geometry concept. Find out what other external collaborators are saying
about their work on the project.
"The NREL team's work in redesigning traditional oscillating surge wave energy converters has paved the way for effectively reducing the levelized cost of energy. It’s been a privilege to contribute to this project, as it has broadened my perspective on innovative design strategies to transition toward a sustainable and economically feasible future in marine energy." —Tania Demonte Gonzalez, doctoral candidate at Michigan Technological University
“Working on this project has been an exciting chapter in my development as a renewable energy engineer. It has allowed me to broaden my direct involvement in the advancement of offshore wave energy and increased my experience in potent STEM tools. It has afforded me amazing opportunities to meet inspirational researchers and the ability to travel abroad to participate in the International Network on Offshore Renewable Energy conference as well as connecting with other incredibly knowledgeable and passionate engineers, expanding my network, and sharing ideas. This has been a great investment in developing my network and experience that I will be drawing from in years to come.” —Murphy Gay, master’s student at the University of Michigan, and National Consortium for Graduate Degrees for Minorities in Engineering and Science Fellow
“It is a great opportunity for the Ocean Resources and Renewable Energy Group at the University of Massachusetts Amherst to be working on this project with NREL. The novelty of the idea and the outcomes of our earlier Technology Commercialization Fund project have enabled us to secure more funds to continue development and improve on the performance of the variable-geometry oscillating surge wave energy converter. At the end of the day, our goal is to develop a reliable wave energy converter that can survive in the ocean environment.” —Krish Sharman, professor, University of Massachusetts Amherst
Controlling Peak Power and Fatigue Damage Accumulation
Because waves fluctuate, WEC developers must design components to handle loads many times greater than the average. That means devices need a PTO capacity that far exceeds its average power output, a need that can significantly increase the PTO cost. Operators can potentially reduce their peak-to-average power ratio and maximize or maintain their WEC’s power output through variable-geometry designs or energy storage. These design upgrades could help developers:
- Deliver more stable voltage and frequency to the grid
- Reduce the size, weight, and peak power of the PTO
- Balance energy production against structural costs as well as generator size and cost (variable-geometry control parameters can be designed for a specific site’s wave conditions)
- Greatly reduce the cyclic fatigue loads on all system components.
A utility-scale wave energy converter will likely be designed to last for 25 years. Lowering peak loads could help reduce fatigue damage, which could extend a device’s life span and reduce its levelized cost of energy by reducing operational and maintenance costs.
A Window Into the Future of Wave Energy, NREL (2022)
Harnessing the Waves, The American Society of Mechanical Engineers (2022)
Design of a Two-Body Wave Energy Converter Featuring Controllable Geometry, 42nd International Conference on Ocean, Offshore, and Arctic Engineering (2023)
Fatigue and Structural Load Analysis and Control for Variable-Geometry Wave Energy Converters, U.S Department of Energy Water Power Technologies Office Peer Review (2022)
Significant Cost Reduction Potential for Wave Energy Conversion Devices With Variable-Geometry Modules, U.S. Department of Energy Water Power Technologies Office Peer Review (2022)
Influence on Structural Loading of a Wave Energy Converter by Controlling Variable-Geometry Components and the Power Take-Off, 41st International Conference on Ocean, Offshore, and Arctic Engineering (2022)
Numerical Model Development of a Variable-Geometry Attenuator Wave Energy Converter, 39th International Conference on Ocean, Offshore, and Arctic Engineering (2020)
Submerged Pressure Differential Plate Wave Energy Converter With Variable Geometry, European Wave and Tidal Energy Conference (2019)