Wave power challenge

The main challenge in wave power is the large variation in size and energy content of waves. The peak power in a large wave is in the order of 30-40 times higher than in an average wave at the same site. Components in the system need to be sized for the peak power while revenue will be in proportion to the average power, the annual energy output.

The purpose of the power take-off in a wave energy converter (WEC) is to capture energy from the varying wave movements and convert it into electricity. Power is captured by applying a damping force against the movements of the buoy. The damping force that captures the most power depends to a large extent on the wave size. It is therefore essential that this force can be controlled and optimized for every wave.

The cost of components in the power take-off can be significantly reduced and the efficiency increased if the captured power is smoothed before the generator by an energy storage device. Such devices can however be very expensive and may also compromise the damping force control of the buoys, in which case the power capture performance is reduced.

WECs with hydraulic power take-offs often use a fixed displacement hydraulic cylinder in combination with hydraulic accumulators. The cost of hydraulic accumulators is however high, and the damping force cannot be controlled since it is dependant on the level of stored energy in the form of gas compression in the hydraulic accumulator. Hydraulic accumulators provide excellent power smoothing but increase the levelized cost of energy.

WECs with mechanical power take-offs can capture more than twice as much energy from the waves but often have limited energy storage capabilities to smooth the captured power before the generator.