Solving power take-off issues in wave energy systems

Solving power take-off issues in wave energy systems

Wave energy research company

Limerick Wave Ltd is a wave energy research company, which uses mechanical motion rectification (MMR) to convert the reversing rotation of ocean wave energy converters to unidirectional rotation. The aim is to improve the efficiency of the conversion of wave energy into electricity, cope with the wide variations of power from the resource and resolve the so-called end-stop problem of inefficiency and even physical damage from instant reversals of rotation, which is a barrier to accessing wave energy. The Irish coast’s wave energy potential is estimated by the Irish Government at 12.5GW.

Prototype MMR devices

Limerick Wave’s ambition is to scale up its design by stages. To do so, demonstrations to potential investors are useful. IMaR, with Enterprise Ireland’s support, took delivery of prototype MMR devices and designed and constructed test apparatuses to demonstrate how reversing the direction of rotation of the input shaft of an MMR device does not appear to cause end-stop problems and continues to accelerate the rotation of a flywheel connected to the output side of the MMR device. IMaR connected the shaft of a motor to the input shaft of the MMR device with a universal joint to avoid having to perfectly align them. The motor included switches to enable instant reversal of rotation.

IMaR also introduced a 1:24 gearbox, to partially simulate the conversion that would occur in a real-world wave energy power station, from the period of an ocean wave (typically one cycle every 6-7 seconds) to 50Hz, the frequency of the electricity grid in Ireland.

“Ciaran Doyle and his IMaR team very successfully completed the testing on our device. The work completed involved moving a geared rack up and down due to the simulated movement of the sea-waves the geared rack moved through a mechanical motion rectifier (MMR) that turned the output shaft in one direction only. Attached to this output shaft was a dimensioned flywheel. The mechanical energy of the simulated sea-wave was known, and the rotational speed of the flywheel was measured to determine the energy transmitted to the flywheel. This enabled the IMaR team to determine the efficiency of our combined PTO + WEC technologies. Upon successful completion of the testing IMaR drafted a report for us.” Paddy Walsh- Limerick Wave Project