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New Zealand’s first marine energy may first start generating electricity on the Chatham Islands taking energy from waves as they crash onto a rocky shoreline. By Lindsay Clark.
This Wave Energy Technology New Zealand project has been granted the first resource consent for a wave energy project wave energy converters at a relatively sheltered testing site four kilometres off the north Taranaki town of Waitara. Marine energy developments worldwide are mostly still in their early days, perhaps comparable to where wind power was at 20 years ago. Engineers around the world are still developing and testing a multitude of different concepts for both generation of electricity from both ocean waves and tidal flows. But one simle technology ideally adapted for small island communities is the British-developed Limpet wave energy plant which development company Chatham Islands Marine Energy plans to build into an exposed basalt rock shore on the main island. The wave power generator has the potential to have a favorable impact on the Chathams economy. The marine energy developer says the project is expected to halve the cost of diesel-fired electricity generation for the 700 islanders who currently pay over 80 cents per kilowatt hour compared with the average New Zealand cost of around 24 cents. Wave power will generate 220 kW which together with two 275 kW wind turbines recently erected on the island, would turn the costly diesel generators into back-up supply. Funding for the $5 million wave power construction will partly depend on some funds from the EECA Marine Energy Deployment Fund. The original Limpet plant installed on the Scottish island of Islay in 2000 was the world’s first commercial scale, grid connected wave energy plant. Just like the limpet shells which cling tightly to rocks in the surf, the box-like Wavegen Limpet wave energy plant is cemented into a channel cut in the rock. When waves enter the open gaps in the bottom of the box the water rises up inside the chamber pushing air up inside. The air is compressed upwards and forced through the air-driven Wells turbine which generates electricity. As the wave column falls air is sucked back through the turbine. The clever part about the turbine is that it spins the same direction regardless of whether the air is flowing in or out. The whole design is simple with no gearbox, no hydraulics or moving parts in the water. In fact nothing else except the turbine moves which means some of the devices now built in Europe have proven reliability as high as 95 percent. The proposed location is at a site just out of the main town of Waitangi, which is exposed to the prevailing southwesterly wave fronts. The solution may also become a model for other isolated communities. The other project to extract power from waves out in the sea, Wave Energy Technology New Zealand (or WET-NZ), is a joint venture between the Wellington-based Industrial Research Ltd and energy consultants Power Projects Ltd. Power Projects director John Huckerby says the Taranaki District Council has been granted a five year resource consent for the testing area offshore device in a relatively sheltered area where waves usually run from west to east along the coastline. WET-NZ is currently about to build a half-scale floating wave energy device which will be moored in the testing area next year. The 17-metre high, half-scale device will sit upright in the water with nearly all of the spar-type hull underwater. Only the top 1.5 metres of the two towers on top of the hull will sit out of the water. At water level an active float is mounted between the two towers. The float is designed to move around this axis with any wave movement. Power is generated from the motion between the relatively steady underwater spar hull and the moving float on top. Any motion between the float and the hull generates electricity through a hydraulic transmission. A power and communications cable will be laid out to the device from shore. Huckerby says the floating point absorber device, because it is still a research project, is only designed to generate a peak of 20kW of power. On current designs a full-scale version of the device would generate 200kW. Huckerby says this is about same as the amount of power generated by the first wind turbine built in Wellington in the early 1990s which was state of the art at the time. No efforts have been made yet by the project team to maximize the amount of power. He says more energy could be obtained by placing the devices in higher wave energy areas. For utility-scale generation the devices would likely to be developed in arrays of 10-100 units.
Energy NZ Vol.4 No.4 July-August 2010 |
Taking a different approach a consortium of New Zealand scientists are scaling up their experimental floating device to generate power from wave movements out in the ocean.