As solar and wind renewable technologies continue to disrupt the energy market, a new renewable player has snuck into town and is starting to make waves, literally. Carnegie Wave Energy’s Perth Wave Energy Project (PWEP) uses pump-powered technology to generate power from the ocean’s waves and is the world’s first commercial-scale wave energy array to be connected to the grid and produce desalinated water.
In September 2015, the Perth based Carnegie Wave Energy Project broke a world record by completing 14,000 cumulative operating hours – the highest number of hours ever recorded for the global wave energy industry.
Carnegie Wave Energy is now gearing up to deploy the next set of wave energy units, CETO 6, in 2018.
The project, created by Carnegie Wave Energy and funded by the Australian Renewable Energy Agency (ARENA), was a pilot program involving CETO 5 units, which are fully-submerged buoys that use waves to drive pumps and generators and deliver power back to shore through subsea cables.
Craig Wale, Hydraulics Engineer at Carnegie Wave Energy, said CETO 5 uses the hydraulic energy generated to turn an electric generator onshore and export to the local power grid.
The hydraulic energy also assists with a reverse-osmosis desalination process – significantly reducing the electrical power required to produce potable water.
“CETO is a unique, fully-submerged, pump-based technology whereby a buoy heaves with the ocean’s waves, one to two metres below the surface of the ocean, driving a hydraulic cylinder,” said Mr Wale.
“Hydraulic pressure from the cylinder is accumulated and used to propel a hydraulic motors coupled to electric generators. The PWEP used CETO 5 technology which had the pressurised fluid (hydraulic energy) travel onshore for conversion to electrical energy.”
The CETO 5 units that were used in the project each had a rated capacity of 240 kW, and Mr Wale said pumps played a significant role in the CETO systems.
“The PWEP used two Parker bent-axis fixed displacement hydraulic motors and these hydraulic motors are integral to our power-take-off. That is, the way we convert the hydraulic power generated through the actuation of the hydraulic cylinder into grid-exportable electric power.
“By spinning a hydraulic motor with high pressure fluid, we can spin a coupled electric motor and generate electricity.”
When the buoy heaves upwards, the single acting hydraulic cylinder generates high-pressure flow which travels to the onshore plant.
The pressure surge is smoothed by a bank of accumulators before the flow is split to the two hydraulic motors which sit in parallel.
The high-pressure flow then spins the hydraulic motors which are each coupled to a squirrel-cage induction generator.
When the buoy heaves downwards, the hydraulic cylinder draws in low pressure fluid from a bank of accumulators that sit downstream of the hydraulic motor’s outlet, ready to re-pressurise the fluid with the next upwards heave.
Waves versus solar and wind
As with any system, the pumps themselves require some maintenance, and Carnegie Wave Energy has constantly monitored and recorded the hydraulic motor case drain flow rate, which was a good indicator of the health of the motor.
“High or accelerating case drain flows indicate increasing internal clearances, and hence wear, which needs attention. By continuously recording this data, we could capture the entire history of a hydraulic motor’s health and take preventative maintenance actions when necessary,” Mr Wale said.
“From an engineer’s perspective, the technology presents a multitude of challenges, which calls for innovative solutions and a marrying of many disciplines – mechanical, civil, electrical and electronic – making it a very interesting technology to develop.”
While solar and wind energy are the most well known forms of renewable power generation, Mr Wale said that wave energy can be more advantageous than these methods.
“One of the advantages is that wave energy is much more predictable than wind energy. Wind energy tends to vary in seconds and minutes, whereas waves can be predicted accurately hours and sometimes days in advance,” said Mr Wale.
“Furthermore, the energy density in the ocean means that for an equivalent power extraction, wave farms consume much smaller areas than solar farms, and are also completely out of sight.”
So far there have been five CETO wave energy systems created as part of pilot programs to continually improve the technology.
The project is now finished with all units pulled out of the water and de-commissioned but the next set of units, CETO 6, is set to be deployed in early 2018 approximately 10km west of Australia’s largest naval base, Garden Island, in Western Australia.
Mr Wale said the next generation CETO 6 units differ as they incorporate the power-take-off and hydraulic-to-electric conversion within the buoy, and deliver high voltage electricity to shore via a subsea cable.
“Carnegie is also preparing to begin construction, subject to approvals, of its Garden Island microgrid project which will see the installation of a 2MW photovoltaic array and battery storage, with provision to later incorporate wind and wave generation.”