The air turbine driving an electrical generator is an essential component of the wave energy plant where the wave-induced pneumatic energy is converted into useful electrical energy. The turbine is subject to much more demanding conditions than more conventional turbines (water, gas, steam, wind): the air flow rate is largely random, varies widely with sea state, and its direction is reversed twice in each wave cycle. Besides, the damping provided by the turbine should match what is required by the hydrodynamic process of wave energy absorption.
Several types of self-rectifying air turbines have been proposed, and in some cases equipped OWC prototypes. The recently patented biradial air turbine has been found by numerical simulation and model testing to be the most efficient self-rectifying air turbine, apart from other advantages like its axial-compactness and capability to easily accommodate a fast acting air valve.
The OPERA novel turbine was designed to maximize the amount of energy absorbed from the waves, while taking into account its own rotation-speed-dependent aerodynamic efficiency and the efficiency of the electrical equipment under the widely varying sea states that characterize the local wave climate.
Before shipping the turbine to the Mutriku wave power plant this novel biradial turbine has undergone a testing programme at Instituto Superior Técnico (IST) Turbomachinery Laboratory under constant and varying unidirectional flow to assess performance of the turbine and the electrical generator.
Results from the turbine dry tests showed that the experimental values for the efficiency are fairly close to those predicted by the CFD calculations, thus validating the turbine design method.
More details about this testing of this Novel biradial turbine-generator set are available on the project deliverable “Turbine-generator set laboratory tests in variable unidirectional flow”.