Scheme gives supply security

Earl Bardsley, responding to an editorial in the Otago Daily Times, considers the advantages of a pumped storage scheme for South Island power generation.

Energy Minister Gerry Brownlee is quite correct to note that the Onslow scheme would be an expensive way to reduce occasional spill losses.

In fact, it is in the nature of pumped storage schemes to be net consumers of power rather than power producers.

As a long-term average, the new power gained from Waitaki and Clutha spill reduction would be mostly needed to offset the inevitable inefficiencies of the pumped storage operation.

Spill reduction is, therefore, simply a convenient means to avoid the scheme becoming a national power sink, with perhaps a little left over to give some net power gain.

However, the national advantage of the Onslow scheme is not spill reduction as an end in itself.

The real gains would be through observable security of electricity supply, environmental improvement, and provision of Waitaki irrigation water.

With respect to security of supply, our present hydro water-storage operation is strictly on a one-year cycle and we don't have storage capacity to avoid hydro scares when lake levels trend down significantly in autumn and winter.

As uncertainty increases when levels fall, there is fear of power blackouts, and the inevitable price spikes occur in the electricity spot market.

Such winter scares and price spikes have certainly been quite frequent since 2000, probably causing lost opportunities for overseas investment because we are perceived to have an insecure electricity supply.

With the pumped storage scheme in operation, the national hydro-energy storage would fluctuate around a much higher mean value, perhaps 6000GWh compared with the current low value of about 2700GWh.

With the extra energy buffer, the price spikes and insecurity would largely vanish from the spot market and would certainly give the nation a much better look to overseas investors.

Of course, the initial filling of the new lake will require considerable one-off energy expenditure in the pumping operation.

It would be ideal if the scheme had just been completed, because the extra Manapouri power available from reduced Comalco output would be available for pumping, rather than being lost as spill.

The simplest way to get the pumped storage scheme built would be to have legislative recognition of the environmental value of our existing hydro lakes.

That is, legislation would be passed so that after some given year in the future there would be a specified 1m normal seasonal operating range imposed for lakes Tekapo, Pukaki, Hawea, and Manapouri.

Contact Energy and Meridian would then quickly move to construct the scheme to keep the financial advantage of their capacity for significant winter generation, when electricity prices are highest.

The 1m range would serve to buffer flood events to prevent spill, with the water being released as soon as possible, ready for the next flood.

The excess power then generated from the downstream power stations would be sent to pumped storage.

This alternative mode of hydro-lake operation would certainly be an environmental improvement, with an end to unsightly winter drawdowns.

The new operation mode would be particularly favourable to increased irrigation development in the lower Waitaki River because there would be higher summer mean flows, coinciding with the growing season.

This increment of new water would occur every summer and not just in wet years, representing a real economic gain from the scheme.

The pumped storage scheme could also enable further developments.

In particular, new wind-power generation would not be compromised by increased spill losses.

There is the possibility, too, of controlling Lake Wakatipu at a slightly lower but more stable level so that some new power will be gained from water which would otherwise have spilled over the Roxburgh and Clyde stations.

This would have the dual effect of reducing the risk of Queenstown lake floods and reducing the Clutha flood risk at Balclutha.

As a further power source, the pumped storage scheme might itself be converted into a power scheme.

Pumping up water from Lake Roxburgh and then releasing it back through a second tunnel discharging far enough down the Clutha would give an elevation difference for new power generation.

Finally, there could even be advantage for the Dunedin city water supply.

The concept of Dunedin's water coming from the Clutha River may seem strange at first, but it would be quite possible to pump because the new pumped storage lake at Onslow would not be too far away from the intake point for the city supply and could be linked to it by a short tunnel.

-Associate Prof Earl Bardsley is from the Department of Earth and Ocean Sciences at the University of Waikato.

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