Solar power plant "not for N.Z.’

Press, 8 July 1976, Page 1

Solar power plant "not for N.Z.’

The United States is building three prototype solar power stations, using a principle first developed by Archimedes in the Second Century 8.C.. according to a visiting American physicist. Professor A. Sievers.

The three solar plants—one of 5Mw and two of lOMw—w’ill each cost about ssom.

They are expensive—even uneconomic at present—and they require many more sunshine hours than are recorded anywhere in New Zealand. Professor Sievers, of Cornell Universitv. is a visiting Eriskine Fellow in the physics department at the Universitv of Canter-

bury. He was delivering the Chalklin Lecture yesterday to the Canterbury branch of the Royal Society of New Zealand at Lincoln College.

Discussing the proposed plants, he said that although the basic principles of solar energy use were well understood, there W’ere still many problems to be overcome.

About half the Slsom would be taken up by building banks of mirrors to reflect and focus the sun’s ravs. This was a manciple developed by Archimedes, who had found that several hundreds of soldiers reflecting and focusing sunlight from shore could

set fire to the sails of enemy ships lying off the coast'

The three prototype stations would use a tower, on top of which would be a water boiler and a solar heat collector. Mirrors about 5m square, in banks around the tower, reflected and focused sunlight on to the collector, which was made of material that absorbed about 95 per cent of the energy. The mirrors would be adjusted, through a sensor system or by computer, to follow the path of the sun across the skv. Heat absorbed by the collector in the tower would heat water in the adjacent boiler and the resultant steam would be fed into conventional steam

turbines to generate elec tricity.

He said that one of the problems of using solar energy was to find a suitable way to store sufficient energy for use at night and on overcast days. This was being overcome in the prototype stations by chanelling some of the steam into underground caverns, where the heat could be absorbed by suitable material. A cavern filled with natural rocks would do, he said. Professor Sievers said that 25 per cent of the United States’ energy requirements might be met bv solar energy by the year 2020. This included direct use of solar energy for domestic water and

space heating and fuels derived from crops. However, he said, solar power plants would not be feasible in New Zealand. New Zealand had an average of only 2000 sunshine hones annually, whereas suitable areas of the United States had about 4000 hours. But there was potential here for domestic solar heating. Apart from any other considerations, the plants being built in the United States would be uneconomic at present, compared with other power sources.

“But we have to start somewhere. By building it on a large scale like this, we will be able to see how it works and we will be able to define the problems more closely.”