Abstract
The 1st generation Turbine Lander, a small-scale (1 m2 ) vertical-axis cross-flow turbine on a gravity foundation was deployed in Sequim Bay, Washington for 141 days from October 2023 to March 2024. In the 1st generation system, which represented a laboratory to field effort, a priority was placed on survivability over efficiency and, when possible, leveraged commercial off-the-shelf components instead of custom component development. Analysis of pre-deployment characterization data and performance data acquired in situ reveals a broad range of system inefficiencies and design modifications that could improve performance. At the same time, efforts to operationalize the concept following demonstration of feasibility required improvements to the system to enable autonomy. Specifically, the 1st generation system required 3-phase 480 Vac power input and included no integrated energy storage. The power electronics, designed for industrial automation, facilitated the acquisition of high-quality data, but at the cost of unsustainable high hotel loads for long-term deployments.
This project sought to address fundamental limitations of the 1st generation system design to advance the concept towards a hypothetical autonomous deployment in moderately energetic environments (i.e., maximum current speeds < 2.5 m/s). Based on lessons learned the following areas of focus emerged as design priorities for the 2nd generation system:
- Increase power capture of the rotor by modestly increasing its size, modifying its aspect ratio, and adjusting the preset angle of attack to enhance torque generation
- Decrease the potential for biofouling by minimizing protruding components (e.g., fasteners) and removing crevices in which floating flora could become lodged
- Minimize parasitic mechanical losses associated with seals and lubricants
- Leverage design modifications to enable the implementation of a broader range of control strategies, particularly those that can operate without inflow current measurements
- Identify and implement an alternative power electronics package to reduce hotel loads and generate direct current power to facilitate integration with energy storage
These objectives have been achieved and this report summarizes the design, fabrication, and characterization efforts involved with the development of the 2nd generation Turbine Lander system. First, we summarize the 1st generation system and previously recommended approaches for improving the system. The new power electronics, which were integrated in collaboration with researchers from the Monterey Bay Aquarium Research Institute (MBARI) are described. A new battery system, which is being developed in parallel to this project under a different contract, is introduced. Next, the new rotor design is introduced and supporting engineering design efforts, both analytical and numerical, are summarized. The report concludes with detailed performance characterization of the new rotor and power take-off with comparisons to the 1st generation unit and recommendations for future work.
These efforts have resulted in significant performance improvements. For example, the 1st generation system could not generate power until currents exceeded 1 m/s, and that value excluded the hotel loads of the power electronics. The new system achieves net power generation at inflow speeds less than 1 m/s after accounting for internal power consumption by the power electronics. As inflow speeds increase more significant gains in power generation have been achieved with the new design producing more than 2.3 kW at 2.5 m/s, over 800 W greater than the initial design. At inflow speeds between 1.25 and 1.75 m/s increased power outputs of greater than 200 W were achieved. These differences represent the integrated improvements achieved not by a single, significant modification to the system, but a large number of incremental changes and provide a pathway for achieving performance improvements in other small-scale systems where differences as small as a few 10’s of Watts determine concept feasibility.