Lake Onslow drawbacks

Pumped storage schemes are used to control the electrical power demand in the grid system whereby energy is transferred to a storage dam at times when demand for power on the grid is low and then reused when demand is high.

This transfer of energy normally incurs losses of about 20%.

The proposed Lake Onslow scheme would take water from the Clutha River and pump it some 20 kilometres to the

lake. The abrasive silt in the Clutha river would require fine filters to prevent damage to the machinery. These filters, plus the long penstocks, would increase the losses overall to more like 30%.

The major drawback of the Lake Onslow scheme is its location.The biggest demand for electricity, apart from the Bluff smelter, in the country is the Auckland area. In order for a pump storage system to flatten the fluctuations in the grid power it needs to be of 300 to 500 Megawatt capacity.

To transmit this amount of energy some 1600 kilometres from Otago to Auckland, via the Cook Strait cables, would incur more losses making the scheme totally unrealistic.

Far better is to have a giant-sized chemical battery located in the Auckland area. The charging of the battery could be from the grid, wind generators, solar power or a combination of these. Pump storage schemes on the eastern side of Lake Taupō or at Turangi should be considered.

A scheme at Lake Onslow would take many years to build, during which time the number of electric cars, which have their batteries charged overnight, on the road would increase. This would negate the requirement for pump storage operation.

Ted Smith (retired power generation engineer), Makara