3 Meter Ocean Current Turbine >
Video Animation of 3m Turbine
The kinetic energy of the Gulf Stream has significant potential to supply Florida with much of its needed consumer electricity, provided that technically-feasible and environmentally-friendly harvesting technology can be developed. Although harnessing the energy of the Gulf Stream has been considered for over a century, no system has been installed for more that a few hours. Therefore, no technical or environmental knowledge-base exists for in-situ operation, from which to design turbines, or make decisions for policy and permitting. Thus, FAU’s Center of Excellence in Ocean Energy Technology intends to install a small-scale experimental ocean current turbine offshore south Florida.
The objective of the experiment is to develop, fabricate, and deploy a turbine to investigate and collect data about potential environmental impacts, as well as perform a technology assessment of the environment and equipment. The experiment is intended to be incremental in deployment times, beginning with an initial short term deployment (less than a day), and then progressing to deployment periods of up to, and exceeding, one month.
No turbine has been deployed offshore in the Gulf Stream for more than a few hours and thus, little, if any, knowledge exists about in-situ performance of technology. Although many laboratory tests, tow tank experiments, and numerical simulations have been performed, they are only approximations of the real operating environment. As well, these laboratory experiments cannot replicate the long term operating effects of real system deployment and operation. As a result, a strong level of confidence cannot be placed in existing analyses. Thus, this experiment is intended to assess the in-situ performance of existing technology and map out the technology areas of study.
Since no turbines have been deployed in the Gulf Stream for more than a few hours, no knowledge exists of the environmental impact. Although some statistical estimates can be made based on the species density, the actually interaction of the turbine and local biota cannot be assessed without deploying the system. Because of the macro level interaction of the biota, laboratory experiments cannot be used either. Thus, this experiment is an initial step at gather data and performing and quantifying the environmental impact which can be extrapolated to commercial scale.
The overall system consists of a main permanent mooring buoy connected to the ocean floor by a 5/8 inch diameter steel cable to a gravity anchor, a 20 kW turbine, and a twin-hull observation and control buoy.
The underwater turbine is a 20 kW open blade axial-flow horizontal turbine design, driven by a 3 m diameter 3-blade rotor. The turbine is connected to a flounder plate on the main mooring line by a synthetic rope. Using opposed buoyancy and weight modules mounted on its masts, it counters torque generated by the rotor blades. The underwater housing contains a generator, gearbox, and mechanical brake (to stop the rotor blades from turning) and is filled with bio-degradable oil. The turbine is connected to the observation and control buoy by: 1) a synthetic rope which is used to deploy and recover the turbine, 2) communications lines used to monitor and control the turbine, and 3) power cables used to transmit power to/from the turbine. Sensors on the turbine include, are but not limited to, an array of underwater cameras connected to video monitors and DVRs, vibration sensors, tachometers, temperature sensors, tilt sensors, and pressure sensors. The generator acts both as a generator and a motor (with brake redundancy via electric means).
The main buoy will be permanently moored at the experiment site, and will have an array of navigation and environmental sensors. The buoy will be powered by solar panels, and will have sufficient battery resources to independently supply power for one week to all onboard systems. The navigational instruments include safety and navigation lights, GPS, radar reflectors, and an Automatic Identification System (AIS) that notifies other vessels of the buoy’s name, location, and status. Environmental instruments include a buoy-mounted ADCP, and a bottom-mounted ADCP, that communicates with the buoy via an acoustic modem. The buoy has redundant buoy-to-shore communications that includes a cellular high baud-rate link, and a satellite modem. The main buoy will regularly communicate environmental and position data to shore via both communication means.
The twin hull observation and control buoy shall contain three winches to handle deck loading, mooring, and deploying/recovering the turbine, a turbine control system, a power dissipation block, cameras, lights, GPS, communications equipment, and survival gear. This buoy shall be moored directly to the main buoy by a synthetic mooring line.
A novel mooring system will be deployed that consists of 5/8 inch 1000 meter long steel cable with fairing along the upper 300 m of mooring line, and strum reducer over the lower portion. A 100 meter chain is used at the lower end of the cable, attached to a 25,000 lb gravity anchor. The mooring scope is 3.
The test site, 26° 11.00’ N 80° 50.00’ W, was chosen because it is outside of the Navy’s South Florida Testing Facility, and FAU has performed a preliminary environmental assessments of the area, that includes bathymetric mapping and 2 years of ocean current measurements from a bottom-mounted ADCP. This site is approximately 2 miles west of the mean location of the axis of the Gulf Stream, and lies on the outer end of the Miami Terrace. The water depth is 300 m, with directly adjacent waters exceeding 700 m in depth.
The main buoy and mooring system will be initially deployed for at least two weeks prior to the turbine and observation/control buoy. It will be checked daily (when weather permits) for drift and sea-keeping.
Once confidence is obtained in the performance of the main buoy and mooring system, the turbine and observation/control buoy will be deployed for short duration testing. The first deployment will be for less than 24 hours to evaluate system performance and immediate environmental impacts. The system will be continually monitored by personnel aboard the observation and control buoy, and aboard a 33 foot research vessel tied to the observation and control buoy. If adverse environmental impacts are observed, such as unacceptable fish or turtle kill, the turbine will be shut down immediately and retrieved.
Subsequent deployments will see the deployment periods increasing each time, with continual monitoring, until confidence can be obtained that the impact is acceptable. During all deployments, all video and sensor readings will be continually recorded.
