Ocean-energy electric generators like wave- and tidal-power systems hold lots of potential for the future of renewable, carbon-free energy. Among the advantages, waves have a much greater energy density than does wind. Power plants can be relatively small and located near coastal cities, limiting transmission distances. And wave energy is much more predictable than wind or solar.
On the downside, however, the systems face some serious roadblocks on the path to widespread adoption, including concerns about reliability. Corrosive seawater and turbulent and heaving seas can quickly wreck a wave generator.
That’s why a wave-energy system called CETO, deployed by Carnegie Clean Energy, is a breakthrough of sorts. The company last year completed a trial off the coast of Western Australia that ran for more than 12 months.
The Perth Wave Energy Project (PWEP) was the first demonstration of a complete grid-connected CETO system anywhere in the world, according to company officials, with three units operating together in an array to produce electrical power.
Three CETO 5 units operated for over 13,000 cumulative hours and supplied power to a nearby naval base.
The CETO system converts ocean wave energy into zero-emission electricity. It can also be designed to make desalinated water through a reverse-osmosis process. In this so-called point-absorber wave generator, the up-and-down oscillating movement of a large buoy produces reciprocating motion in a hydraulic cylinder tethered to the sea floor. The cylinder acts as a linear pump that sends high-pressure, variable-flow fluid to accumulators which, in turn, supply a steady flow to hydraulic motors. The motors then drive electric generators that produce electricity. Low-pressure fluid exits the motors and returns to the cylinder to complete the hydraulic circuit.
The units differ from other wave-energy devices as they operate underwater and are not noticeable from shore. By keeping the buoys fully submerged in deep water, and not at the surface, the Carnegie devices overcome a problem that has long plagued the wave-energy sector: machines readily get damaged or destroyed by impacts from breaking waves and severe storms such as hurricanes.
PWEP was a pilot project. Key objectives mainly focused on demonstrating the viability of CETO technology and learning how to deploy multiple units as a complete system. The company successfully operated the largest CETO units to date, confirmed long-term survivability, and generated and transmitted utility-compliant electricity to the grid for a sustained period.
The project also validated the accuracy of Carnegie’s mathematical models in predicting system performance, and verified the system has minimal environmental impact.
The next step will be to deploy larger CETO 6 wave generators in a commercial venture. The CETO 6 design builds on previous experience and incorporates some important improvements, said company officials. For one, the size of the buoyant actuator has a significant influence on power output and diameter will increase to approximately 20 m from 11 m. Power output will increase to 1 MW from 240 kW in the CETO 5 units.
CETO 6 will also generate power inside the buoy, rather than with pumps, accumulators and other hydraulic components mounted to the seabed and generating electricity on-shore, as with the PWEP CETO 5 system. Locating power generation within the buoy reduces offshore installation time and maintenance costs. The successful demonstration of CETO for generation and transmission of electrical power will let Carnegie take advantage of wave resources in deeper waters, farther from shore—and significantly increase the size of the potential commercial market.
Carnegie Clean Energy
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