Power waste

There is an aspect to the spilling of water from Otago's hydro lakes that those who embrace the concept of wind energy ought to ponder.

The "wasted" water represents lost generating potential, especially that which will be needed in the coming winter when demand is at its peak.

Since the lakes are "full" because of the spring snow melt and the unseasonable summer rains in the high country, the excess cannot be stored, so must be passed through the dams without realising its energy capacity.

But if all the wind farms planned for Otago were capable of operating right now, and the electricity generated given the required priority (since it cannot be stored), even more water would be being spilled from the hydro lakes.

The point has been made by a Waikato University academic, Associate Prof Earl Bardsley, that it is possible the wind power schemes in the South Island will generate no net power when there are summer spill losses.

Dr Bardsley is an advocate of a concept that has long been argued in the South, that of a large pumped storage scheme which would provide much of the winter electricity needs while keeping the hydro lakes from being emptied and to allow room for storage when the summer flows come.

"There is no way of forecasting these high summer flows, but extra storage would allow for that and avoid these situations," he says.

Dr Bardsley has written and studied extensively about using the so-called Onslow-Manorburn depression in Otago as the upper reservoir of what would be the world's largest pumped storage scheme, with an energy storage capacity of 10,200 GWh of realisable potential energy, more than triple the total national hydro-power energy storage capacity.

He has suggested that the scheme could either operate on a seasonal cycle or act as a passive energy reserve to buffer existing hydro-power capacity against the effect of dry years.

In a paper discussing the idea published in the Journal of Hydrology in 2005, Dr Bardsley made a point even more valid today: " . . . it is left an open question as to whether it would be viable within the current grid system . . ."

It is perhaps unfortunately ironic that the power savings urged upon everyone last winter, and which led to reasonable levels being maintained in the hydro lakes, mean in effect that the savings are being represented by the spilled water today because there is insufficient storage capacity in the lakes - and insufficient capacity in the national grid to make better use of the potential, but lost, generation.

We are certainly reaching a point where line capacity is getting out of kilter with generating capacity, and concerns about this have been raised many times at recent hearings into the various wind farm projects.

If the Government is really serious about major infrastructure projects, building more lines capacity would seem to be in urgent need of priority.

Pumping "surplus" water from the Clutha River into a storage lake such as that proposed would seem, on the face of it, to be a project well worth investigating properly, but it is very unlikely any of the power generators would touch it today since their function is to seek the earliest possible return on their investment.

The Minister of Energy, Gerry Brownlee, is reported to have been rather cool on the idea, too, concerned about the potential cost (at least $1 billion) and intermittent need.

But is the need likely to be so intermittent in a future where energy shortages and high cost are expected to become routine? Such a scheme would seem to be an ideal long-term state project, possibly deriving its capital cost from the Cullen fund, now that it should be investing 40% of its income in New Zealand.

It is said that the extent of the spilling of water in the South's hydro lakes is rare, and has not occurred at the present level for a decade.

Even if this is the case, and is due to an unpredictable combination of circumstances, it should not preclude the duty of the Electricity Commission and indeed the Government to examine all possible sources of efficiency in power generation and distribution, along with security of supply.

The pumped storage scheme is surely worth a closer look in these circumstances.


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