Ocean-power installation up and running
By Paul Evans
March 2, 2009
March 3, 2009 Renewable Energy Company Oceanlinx has re-deployed its full-scale wave energy conversion unit at Port Kembla in Australia. First deployed in 2005, the unit has been undergoing planned refurbishment and modifications for the past several months. The Oceanlinx wave generator, which is an Oscillating Water Column (OWC) device, is one of six installations around the world currently being trialed.
Ocean waves contain enormous amounts of energy. As this energy passes the Oceanlinx device, the water inside the OWC (a chamber which is open underneath the waterline) rises and falls, compressing and displacing the air inside, driving it past a turbine which is housed at the narrowest point in the chamber.
Since the OWC chamber narrows, the air is accelerated to its highest velocity as it passes the turbine, allowing for maximal extraction of the energy. The oscillatory wave motion causes a similar oscillatory airflow through the chamber, and the turbine converts energy on both the up and down stroke.
This turbine converts the energy in the airflow into mechanical energy that drives an electrical generator. The chamber and turbine are the essence of the Oceanlinx Wave Energy System.
The Denniss-Auld Turbine
The turbine used in an OWC is a key element in the device’s economic performance, and is considered by wave energy experts as a significant barrier to commercializing OWCs.
Most turbines are designed to function for gas or liquid flowing in one direction and at constant velocity with the blades designed to take advantage of the optimal “angle of attack”. However, when the flow is not always from the same direction or a constant velocity, traditional turbines become ineffective.
Previous attempts to address this difficulty have mostly resulted in turbines with varying degrees of efficiency. The Oceanlinx turbine, however, uses a different method - variable pitch blades - which, with the slower rotational speed and higher torque of the turbine, improves efficiency and reliability and reduces the need for maintenance.
The turbine uses a sensor system with a pressure transducer which measures the pressure exerted on the ocean floor by each wave as it approaches the capture chamber, or as it enters the chamber. The transducer sends a voltage signal proportional to the pressure that identifies the height, duration and shape of each wave. The system is calibrated to prevent small-scale “noise” from activating it.
The signal from the transducer is sent to a Programmable Logic Controller (PLC) which adjusts various parameters in real time, such as the blade angle and turbine speed. These are calibrated in the algorithm based upon the particular conditions and energy content of the site at any particular point in time.
The generator, which is coupled to the Oceanlinx turbine, is designed so that the electrical control will vary the speed and torque characteristic of the generator load real-time to maximize the power transfer.
A 450 Kw induction motor is used as the generator at the Port Kembla installation, with coupling to the electricity grid provided by a fully regenerative electronic control system. The grid interconnection point and the control system are located in a weatherproof building external to the air duct. The voltage of the three-phase connection at this point is 415 V at 50 Hz. The electrical interface between the generator and the mains supply comprises two bi-directional DC/AC 3-phase inverters to smooth power from the turbine to match grid power requirements.
A single Oceanlinx power unit can generate peak power outputs of 100 Kw up to 1.5 MW, depending on the wave climate and specific power requirements of the local population. Where peak capacities of greater than 1.5 MW are required, multiple units can be deployed in the same general area, all connected back to shore by the one electrical cable, thus constituting a wave farm. There is no theoretical limit to the number of units that can be deployed in any one location. Units can be spaced close together to reduce the impact of waves on the shore (acting as a quasi-breakwater), or spaced further apart to negate any impact on the inter-tidal zone.
The company started work on the Port Kembla project a decade ago backed by a government grant and has since has raised $50 Million in investment funding. The Port Kembla wave power generator supplies 450kw to the grid under a Power Purchase Agreement (“PPA”) signed with Australian utility Integral Energy.
The wave energy device developed and installed by Oceanlinx can be viewed in high resolution on Google Earth. The MK 1 device can be viewed at 34° 27’ 07.6” S, 150° 54’ 06.8” E. Simply type these coordinates into the Fly To section, in the upper left hand corner of the Google Earth page.
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