Science Centres: Energy

New project to develop wave energy device

We are working with Industrial Research Ltd and Power Projects Ltd on a complex project to develop a prototype device to generate electricity from open water ocean waves.

It only takes a passing familiarity with New Zealand’s coasts to appreciate the immense power contained in ocean waves, but this is not an enterprise to be entered into lightly. The wave energy generator must survive in a harsh, corrosive, constantly moving environment.

There needs to be enough energy to make the device economic, but not too much so that it is destroyed. To assess this, NIWA has developed a satellite-based description of 20 years of wave history for the deep ocean around New Zealand, as well as a model of how waves evolve as they move into shallow, coastal water.

The data allow us to examine the variability in wave energy from an economic perspective. There is greater demand for electricity in winter, so we need to determine the size of the wave energy resource at these times.

Most people see waves coming into shore as nicely ordered crests, but out at sea it’s a different story. Waves can come from all directions and have a range of wave-lengths. Sitting in a small boat in a reasonable sea is like being in a tumble dryer – only wet. The simplest approach is to make sure your device is good at coping with the range of likely wave frequencies. But NIWA is working on a smarter approach – understanding and modelling the dynamics of individual waves, then designing the device to adapt to the conditions.

There’s no point having a smart device if it gets washed away and dashed to pieces on the shore. The challenge here is the interaction between the drag induced by the waves and currents and the elasticity of the mooring.

Recent collaboration between NIWA and the Ocean Engineering Laboratory at the University of New Hampshire has modelled such interactions for offshore mussel farms, and could apply the same approach to the wave energy device. If the device is going to remove energy from the wave then it changes the wave – even if only slightly. We need to understand these changes and their wider implications in order to determine how the wave energy device will affect the local environment.

This work is funded by the Foundation for Research, Science & Technology.

Average significant wave height around New Zealand for 1979-98.

The three essential ingredients for good wave power are: consistency, high energy, and a high wave period.

Wave period is the time it takes for successive waves to pass a fixed point. For example, the waves in the western reaches of Foveaux Strait are generated by winds over the whole south Tasman Sea and Southern Ocean extending to the Indian Ocean. The waves arrive as swell that has been generated hundreds or thousands of kilometres away. On average, the period of the waves is high; about 95% of the time, the most energetic parts of the waves are 11 seconds or more apart.

Waves in Foveaux Strait also meet the other two criteria, being consistently high, with the ‘significant wave height’ exceeding 2 m nearly 70% of the time. Significant wave height is the average of the highest one-third of waves in a fixed-length record.

NIWA has the database and expertise to advise on the best potential sites for marine energy generation.

Climate change & business - The Australia-New Zealand conference and Trade Expo 04

Key objectives

• To promote business opportunities and understanding of risks arising from climate change
• To showcase technologies and actions that reduce greenhouse gas emissions
• To identify how Government can link with business to address climate change

NIWA is a sponsor of this event which will be held at the Sky City Convention Centre, Auckland from 3 to 5 November.

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