Optimizing an Ocean Current Energy Conversion Device for Powering Marine Sensors

Ocean sensors are critical for monitoring marine conditions and understanding ocean ecosystems. However, the deployment duration of these sensors is presently limited by their battery lives, resulting in costly and time-consuming maintenance. Previously, the Water and Energy Research Laboratory (WERL), with input from the Commonwealth Scientific and Industrial Research Organisation (CSIRO), sought to overcome this limitation by harvesting energy from ocean currents to power these sensors. They developed an ocean current energy conversion (CEC) device and tested a prototype in a tow tank, the results of which demonstrated the ability to generate at least 1 W of power from currents as slow as 0.27 m/s. These results strongly indicated feasibility of the concept and the value of continued development. Major present goals include reducing its minimum water speed to 0.2 m/s and performing in-ocean testing. The target of 0.2 m/s was identified in the initial feasibility study for the concept and would significantly increase the range of locations in which the CEC device could be deployed. To move towards this slower water speed, WERL is optimizing the device's turbine using computational fluid dynamics (CFD) and CSIRO is improving the device's alternator, electronics, and subsystem integration. For turbine optimization, we used CFD simulations in multiple design-of-experiment studies to identify key turbine blade geometry parameters that influence turbine output at different operating points. This work was used to generate optimized blades, which we manufactured and installed on the CEC device prototype for retesting in the tow tank. The test results showed that we achieved our target minimum water speed of 0.2 m/s. We also developed and validated a predictive mathematical model of the alternator. This, together with a previously-developed predictive model of the overall device, allowed us to study how alternator design parameters affect the device efficiency. We found that a new alternator could improve the device efficiency by 15–20 percentage points compared to the first prototype. We plan to implement improved blades, alternator, and onboard electronics on a new CEC device prototype. This new prototype will then undergo in-ocean testing to demonstrate full field functionality of the concept.