CORES (Components for Ocean Renewable Energy Systems)
The CORES (Components for Ocean Renewable Energy Systems) Project was a three year EU FP7 project bringing together 13 partners from research and development centres and small and medium enterprises from across the EU, coordinated by University College Cork. The project objective was to develop new concepts and components for power take off, control, moorings, risers, data acquisition and instrumentation for floating wave energy devices. Once developed, these components were tested on a floating oscillating water column (OWC) test platform at sea at the Galway Bay Intermediate Wave Energy Test Site.
Wave Energy Converters are at an early stage of development; in order for first generation devices and systems to progress towards full commercial realisation they must first develop into units suited to mass production.
The CORES project set out to address particular issues resulting from the development of Oscillating Water Column Wave Energy Converters (OWC WECs). Until recently these devices were primarily fixed shoreline devices, they have evolved into floating devices in deeper water and further offshore. Consequently new concepts and components need to be developed, and the CORES project addresses this need.
The concepts and components developed in this project covered aspects such as power take-off, control, moorings, risers, data acquisition and instrumentation. Once developed and tested through simulation and small scale tank tests in both 2D and 3D ocean wave basins, these elements were optimised and fitted onto a floating sea based platform for sea trials. This enabled the integration of the resulting real, validated and verified results into a holistic system model. This model provides a Toolbox for wave to wire simulations of complete WEC systems.
The primary objective of the CORES project was to create this wave to wire modelling “Toolbox”, which would allow developers to evaluate the effect of changes in device components on the performance and the economics of their devices. This Toolbox consists of a number of numerical models developed and validated at bench scale and through laboratory scale testing at sea.
Concepts for various components of floating OWCs were designed, modelled and developed; these components were subsequently integrated together on the Ocean Energy Buoy floating OWC platform for three months of sea trials for testing.
Some of the main achievements of the CORES project include the following:
• Successful deployment of a real wave energy device at sea for 3 months
• Demonstration of a robust electrical system over three months of sea trials
• Improved mooring design methods
• A validated turbine design methodology
• An improved air turbine design for OWCs
Traditionally, OWCs have used Wells air turbines for power take off. These turbines have been proven to operate effectively but are limited in their efficiency. Impulse turbines are less constrained by Mach number effects and centrifugal stresses than Wells turbines. Impulse turbines also have the advantage of a wider operating flow range than the Wells turbine. For the CORES project a new impulse turbine with moveable guide vanes was developed for testing on the OE Buoy. Moveable guide vanes were used so that for both directions of air flow through the turbine, the required swirl would be produced in the flow entering the rotor and blockage of the flow leaving the rotor would be minimised.
Barriers and Drivers
Renewable energy development has a direct relevance at the European level given the regions commitment to reducing the emissions levels imposed under the Kyoto Treaty and the committment to a target of 20% reduction in CO2 emissions by 2020. The resource available for wave power convertors in Europe is large and therefore not a barrier to potential development. It has been estimated that the total wave energy resource for all European coastlines is around 1000 TWh per annum. All EU members have developed National Renewable Energy Action Plans and these in most cases include firm commitments to ocean energy generation; For example, the Irish Government set a target of 500 MW by 2020 for Ocean energy systems.
The main barriers to this development are still related to the cost and reliability of wave energy convertors. Very few full scale devices have been tested at sea for any length of time and no commercial machines are available for grid based electricity production. A number of device concepts are under demonstration or development. However, there are a significant number of uncertainties associated with the assessment of performance of these systems. If they are to evolve into fully commercial products then they must be adapted to become capable of mass production and be site independent; the direct impact of this project will be in the area of lower costs and risk reduction.
The research and results from the CORES project have been disseminated to the wave energy industry and to academia. These results will contribute to overcoming some of the barriers that exist to the commercialisation of wave energy converters.
Sea trials of the CORES impulse turbine exceeded expectations. The turbine tested at sea was slightly more efficient than that predicted by model testing, especially for higher rotational speeds. In fact the CORES produced the most efficient air turbine to date with average cycle efficiencies up to 65%. The peak efficiency of the impulse turbine tested is similar to a Wells turbine but the efficiency improves in higher flow coefficients, resulting in the average power output being significantly higher.