Wave energy converters (WECs) capture electricity from ocean surface waves, but the new industry requires fresh ideas to reduce the cost of energy.
National Renewable Energy Laboratory (NREL) researchers ook inspiration from the pitch control of wind turbine blades to develop a new design for WECs. When wind speed increases, turbine control systems adjust the pitch of their blades to account for the added load, which also ensures that the rotor speed does not exceed safe operating levels.
The high loads and harsh environment of open water—what researchers call “slamming events”—are inevitable hurdles for WEC developers. Designs have progressed over the past 20 years, but no one has yet provided a good solution for these slamming events.
The variable-geometry WEC can alter its shape to change how it interacts with waves. To develop the unique design, the team brainstormed on Venetian blinds, conceptualizing a series of horizontal flaps that span across the device. When opened, these flaps reduce the pressure on the WEC when the waves are particularly energetic—without sacrificing power output.
WECs with these flaps would use less steel, which reduces capital costs and lowers the levelized cost of energy.
Initially, the system would be controlled by a computer. Load and motion sensors would help the system decide when to open and close the flaps. Wave forecasting and radar could also be useful, for instance, if the system’s controller can see that a large wave will hit in 10 seconds, feedforward controls could reduce loading on the WEC structure and smooth power generation.
However a full levelized cost of energy analysis—will be necessary before the variable-geometry WEC concept is adopted by industry.