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Feature

Harnessing The Wind

Using today's technology, wind power could satisfy most of the foreseen increases in electric power consumption.

Keith Dawber

New Zealand is blessed with a substantial wind energy resource. Studies over the last 15 years have attempted to quantify the magnitude of the resource and to identify the most important features of the wind flow patterns, such as diurnal and seasonal variations, extreme winds and typical lengths of calms. Only with very small wind energy conversion devices has any work been done on actually harnessing this energy in New Zealand.

The movement of air is one of the two main natural ways in which energy is transported across the Earth's surface. Ocean currents are the other. From an environmental viewpoint, the use of wind energy for electricity generation is an attractive proposition. The energy from the wind would be dissipated naturally anyway, and our interference with the flow pattern has a minimal global effect, unlike the burning of fossil fuels or the flooding of land for hydroelectric development. A similar argument applies to the conversion of wind energy into heat or water elevation.

Wind energy conversion has many other attractive features. The engineering technology is already available in a viable form. The size of any installation can be tailored easily to meet power demands. Very large amounts of energy do not suddenly become available, as with the commissioning of a large nuclear, coal or hydro station.

In many cases, the servicing of the equipment can be carried out by users with a minimum of specialist training. Very little land is required for supporting the actual conversion equipment and, if decommissioning is necessary, the land can be easily restored to its original state.

Practical Problems

The basic problems of wind energy conversion, however, are very challenging. Some of these stem from the nature of the medium itself. Wind energy density is comparatively low, thus requiring large turbines for appreciable energy conversion. Because the conversion equipment is large, it tends to be expensive, unsightly to some -- but beautiful to others -- and possibly noisy.

At any one site, the wind fluctuates over a very large range of wind velocities. As wind power is proportional to the cube of the wind velocity, this produces great stress on wind conversion equipment under fluctuating wind conditions.

Wind turbines have proven to be more financially viable in the 75kW to 300kW range than in smaller or larger sizes. Horizontal-axis machines with two or three-bladed propellers upwind of the support tower are quieter and have fewer vibration problems than other designs. In addition to mechanical braking, some form of air braking is usually necessary for safety shut-down in extremely high winds or for servicing.

Step-up gear boxes are necessary in most designs, due to the high revolution rate required for electric generators. Computer control of the turbine and generator is essential for electricity grid connection.

New Zealand Research

Up to now, most of the New Zealand work on wind energy has been in studying wind resources. A great deal of new wind data has had to be gathered, as existing data was mainly from inhabited sites, rather than from the often remote high-wind areas suitable for wind farm development.

Some records also exist from previously-manned lighthouses and sites with automatic weather stations. Radar tracking of regular balloon releases from Campbell Island and from some airports has provided additional data. Between 1974 and 1988, the Wind Energy Task Force produced a number of reports, published by the New Zealand Energy Research and Development Committee, relating to the wind energy resource.

Electricorp Production is at the moment undertaking a large-scale wind investigation at potential wind turbine sites in the North Island. It is expected that a pilot wind turbine in the 200 kW to 600kW range will soon be installed in the Wellington region.

Environmental restrictions limit development in most places outside those parts of New Zealand which are already developed for agricultural and pastoral farming. The proven total wind resources available from the regularly farmed areas are much larger than those required to support our present usage of electricity. Thus, these have the potential for provision of considerable future electrical supplies.

Powering The Future

As the costs of New Zealand's traditional forms of electricity generation go up, it is expected that those of wind energy generation will come down proportionally. The coupling of wind energy with existing hydro generation through the national electricity grid thus has great potential.

In Europe, the combined efforts of generating authorities, manufacturers, government and university research centres, and the European Community has lead to a strong effort in wind energy development. Very high reliability has been achieved at demonstration wind farms, such as the 4.1 MW Zeebrugge breakwater installation in Belgium. Denmark already generates 2% of its electricity from wind, with California and Hawaii having comparable wind generation figures.

New Zealand has the potential for much more than this. Large wind farms of at least 50 to 100 turbines are more likely to be financially viable than anything smaller. Routine servicing and maintenance costs can be kept down, and grid connection costs would be economical due to the scale of operation.

Environmental pressures will eventually force New Zealand to adopt a high profile in wind power application. It is very important that we gain experience in the 1990s, while some lead time is available to us. The installation of pilot wind turbines will establish the engineering viability of various designs under New Zealand conditions.

Electricorp has already made a start with the proposed Wellington installation, and it is to be hoped that many others will follow suit.

Keith Dawber is senior lecturer in physics at Otago University.