Researchers seek power from wind

Press, 6 August 1976, Page 12

Researchers seek power from wind

By

E. T. BEARDSLEY.

Information Officer,

University of Canterbury

Windmills, one of man’s most basic machines, may reappear in selected parts of Canterbury, and elsewhere in New Zealand within a few years to produce power for the national grid. But they will differ vastly from the wmd machines used in Persia hundreds of years before Christ and from the Dutch windmills which dotted the countryside in eight-eenth-century Europe. Even the name, “wees;” for wind energy conversion systems, will be different.

One of the wees under consideration for New Zealand is the vertical axis Darrieus machine shown in the accompanying photograph. Visitors to the School of Engineering conversazione at the University of Canterbury todav and tomorrow will be able to see one of them in action.

But many nor’-westers will thunder over the Main Divide before these windmills are installed and producing power. Wind speeds averaging seven metres a second (about 15.7 miles an houri are necessary for wees to be economically competitive at the present time and the first task is to find sites where the average wind speed is of this order. The New Zealanded Energy Research and Development Committee established a task force, drawn from the Universities of Canterbury and Otago, Lincoln College, and several Government departments, to determine possible .sites, first by analysing meteorological records and then by tak’ng detailed records in the most likely places. Preliminary results suggest that the Rakaia Gorge, the Makara hills, west of Wellington, and the Rocklands area inland from Dunedm. are possible candidates and more than 50 anemometers and gust recorders are taking detailed records

at some of these and other sites.

Wind speed increases with height above the ground and reches its maximum about 300 metres up. The output of a machine can therefore be increased by mounting it high, but this means larger, stronger and more expensive towers.

The tunnelling effect of South Island river valleys, in which the wind can reach twice its usual speed, is also being considered. Work is being undertaken in the Department of Mechanical Engineering’s wind tunnel to investigate the way in which hills and escarpments, valleys and gorges, accelerate and modify the approaching wind. A well-chosen hilltop site that doubles the approach wind speed would increase the available wind energy eight times. At a wind speed of seven metres a second, the energy flowing through an area one metre square is equivalent -to about 220 watts. Wind energy is proportional to the cube of wind velocity so that a doubling in wind speed would yield 1760 watts. But even with a 100 per cent efficient machine, only 59.3 of the available energy could be converted. In fact the most efficient wees converts about 75 per cent of the theoretical maximum so that at a wind speed of seven metres a second it would extract 97.85 watts a square metre and at 14 metres a second, 782.2 watts

The site investigation work is fundamental. Wind speeds, hourly, daily, seasonally and annually, cannot be predicted. Measurement i's essential. But even when these tests are completed, there are other important factors to be taken into account. The proximity of roads, transmission lines and existing load centres will have a bearing on the choice of sites. So will the availa-

bility of land and environmental and legal considerations. And when these questions have been resolved there will still be two major problems; what sort of wees should be used and how the power they produce will be used. It is estimated that wind pow’er potential is at least 10 times greater than total hydro-electric power. “But,” says Dr. David Lindley, a senior lecturer in the Mechanical Engineering Department, “while there appears to be an abundance of ‘free’ energy, there is no such thing as a free lunch. The challenge is to convert this free resource to economically viable (in both the energy and economic sense) energy and power.” Dr Lindley is the member of the task force responsible for preparing a “state of the art” report on w'ind energy conveision to determine which wees should be used and at Auckland University anoth-ir group is investigating ways of getting wind-generated electricity into the grid.

Dr Lindley has been impressed by research in the United States and Canada. Thirty-five years ago a Pennsylvania company built a vast machine, known as the Smith-Putnam windmill, with a 33.53 metre tower and a two-bladed propeller 53.34 metres in diameter with each blade weighing 8136 kilogrammes. It produced 1250 kilowatts in winds of 30 miles an hour and ran on and off for five years before metal fatigue caused a break in a blade.

Dr Lindley says studies precipitated by the energy crisis have shown that modern versions of the SmithPutnam could be built in 2000 kilowatt versions where there was a mean annual wind speed of seven metres a second for a capital cost of about $650 per

installed peak kilowatt. They could generate electricity for about 2.2 cents per kilowatt hour. A 100 kilowatt machine has been built in the United States and four others, ranging from 40 metres to 60 metres in diameter, are planned over the next two years. In Canada six Darrieus machines will be field tested soon. The Canadian Government is constructing a 30-metre. diameter version of this machine which will stand over 40 metres high and have an output of 200 kW in 24 mph wind. It is to be located on Magdalen Island in the Gulf of St Lawrence and is to feed power to the local grid.

The version of the machine on display at Ham is 5 metres in diameter and has a rating of about 4kW in a 20 mph wind. It is to be used for field tests to determine how closely windmills can be spaced without lowering the power output of individual machines as well as to measure stresses in the blades under a range of operating conditions. The blades presently drive a d.c. generator, though other methods of extracting power will be investigated at a later stage. New Zealand is in a particularly advantageous position to exploit wind energy, said Dr Lindley. Its hydrobased electricity system provides desirable inherent storage so there would be no need to store wind power in batteries, flywheels, compressed air and so on. Windderived electricity could be fed into the grid and treated as a water and fuel saver.

“The studies being undertaken may well show that between 5 and 10 per cent of the electricity generated annually could come from wind power and be interfaced with the grid,” he said. “By 1989 we could envisage between 300 MW to 600 MW supplied from 1000 to 2000 MW of installed peak wees capacity. More peak capacity is re-

quired because wind cannot be relied upon to supply the peak installed power all year round. These machines could be arranged in from 10 to 20 ‘farms’ of 100 units, each of one megawatt rating.” Smaller machines to supply electricity in the Chatham Islands and Stewart Island, perhaps supplementing

existing diesel electric pwoer were also envisaged. “We may have to wait five years or more for the United States to produce the technology and for a large enough market to be generated for wees unless some effort is made to establish a New Zealand capability to manufacture these machines,” Dr Lindley said.