Contact Energy - CEN Chart

[Snoopy]

The interesting thing about the Clutha River that feeds Roxburgh, Clyde and maybe Onslow is that, unlike some of the northern hydro catchments, most of the water inflow happens in spring and summer. That is because most of the H2O inflow is a result of snowmelt and not rain. Now it is also true that the maximum power loads occur during the colder winter months. So to prepare for the winter, you would have to pump water up into Onslow in the previous summer and autumn to prepare for the upcoming winter. The Clyde dam is upstream of the Roxburgh dam. If water was taken from above the Roxburgh dam for Onslow, then the Clyde dam would have to supply that water. If the government 'ordered' Contact to release water to do this, then that means potentially less generation capability at Clyde for the winter, and more at Onslow. If Onslow becomes a 'Transpower battery', that in effect would transfer generation capability from Contact to Transpower. Not good for Contact shareholders :-(.

Of course not intimately knowing the seasonal river flow pattern, I may have painted out a pessimistic scenario. Maybe a summer or early autumn storm could push enough water flow into the Clutha river to keep both Clyde and Onslow topped up. I think Jantar has suggested in the past that Contact would be the natural operators of a proposed Onslow for all of these interrelated flow reasons, plus the fact they have maintenance staff on the ground locally..

This article has an opinion explaining why the Onslow project may turn out to be quite advantageous to Contact if it eventuates that Onslow pumps from Roxborough Lake

https://www.stuff.co.nz/business/129543702/lake-onslow-power-scheme-pioneer-criticises-idea-of-ugly-concrete-dam

From the Stuff Article:
"Waikato University associate professor Earl Bardsley, who came up with the idea of building the pumped hydro scheme, said it would be in Contact Energy’s interest to have water pumped from Lake Roxburgh during times of plentiful power supply and then released back to the lake when power generation from Lake Onslow was needed."

“With respect to a tunnel connecting to Lake Roxburgh, the point seems to be missed that the pumped water is later returned to Lake Roxburgh,” he said.

“Contact Energy would presumably be pleased that some of the water in Lake Roxburgh is shifted to be stored in Lake Onslow during times of low prices, then returned later to Lake Roxburgh at times of higher prices, thus increasing income from the Roxburgh power station.”

To clear up any naming and geographic confusion, Lake Dunstan feeds the Clyde dam. These are both upstream of Lake Roxburgh that feeds the Roxburgh dam. Both dams are owned and operated by Contact Energy.

I don't follow Prof. Earl Beardsly's argument.

a/ I get what he is saying about shifting water up to Onslow from Lake Roxburgh when prices are low. That means that water can be returned to Lake Roxburgh when prices are high (this bit makes sense as being positive for Contact).

But where did the water from Lake Roxburgh come from? It came upstream from the Clyde dam. And it would only benefit Contact to release extra water from the Clyde dam for Lake Roxburgh (and hence Onslow) when power prices are high.

b/ If the Clyde dam was forced to release water to fill Lake Roxburgh when prices were low (Prof Beardsly's scenario), then doesn't that mean that water will be running through the Clyde dam when prices are low? That surely is not what Contact Energy wants?

There is another problem with putting water supply into Lake Roxburgh for Onslow when the power from the Clyde dam is not needed. You are simply taking energy from one battery (Lake Dunstan) and putting it into another (Lake Onslow), with no net energy (or price?) gain.

SNOOPY