Preliminary investigation of a novel breakwater combining coastal defence and energy generation for near shore environments

This paper presents the concept and initial tank testing of a novel low profile floating breakwater incorporating energy generation. The breakwater is intended to be anchored parallel to the coast with a beach at the front of the device to rotate the incoming waves towards collector tubes. The water hammer principle is used to harvest the high water particle velocities, charging a rear mounted high pressure reservoir which is then used to drive a conventional turbine for electrical energy production. The ability to provide breakwater benefits in smaller wave climates should open areas where combined protection and generation give competitive economic returns. Introduction The UK Government currently spend around £800 million per annum on flood and coastal defences with future forecasting predicting coastal erosion to increase by three to nine times by 2080 (Foresight, 2010). Coupled to this is the increasing requirement for sustainable energy using low pollution sources. Wave power devices fall into this category, and although many concept and prototype devices exist to convert the energy of sea waves into a useable form, as yet, there is no clear technology winner. To prove attractive, wave power technology devices must survive and provide a reliable source of power. Many have sights set on Atlantic wave climates where systems are remote and operate in vigorous 40 kW/m waves, however starting in smaller more sheltered coastal areas will provide appropriate lessons for further offshore expansion. The added advantage in this instance is that the device provides a robust sea defence. This breakwater is designed as a floating structure within the near-shore wave zone. As a semi submersible device (figure 1) it remains at wave trough level in larger waves to minimise loadings but fully intercepts smaller design range waves. It takes the waves into surge chambers which capitalise on the water hammer principle to provide a small flow at increased pressure. The surge pressure passes through a one way valve to a spinal collector pipe which gathers the incident energy from several locations along the breakwater length to feed a conventional turbine. The authors are not aware of other devices using this principle.