Lake Onslow proposal needs a reality check

AS a seasoned hydropower engineer, I’ve been following with interest the Lake Onslow proposal.

Much attention has been devoted to the benefits, but in the process some of the realities appear to have been overlooked.

First and foremost, such a scheme would be a net user of energy because, due to energy conversion efficiencies, it would take at least 30% more energy to pump the water from the Clutha to Lake Onslow than you’d get from the generating cycle, Lake Onslow to Clutha.

If such a scheme were to be used to make up generation on calm days and/ or in severe droughts, the economic justification would just not stack up against using the likes of Huntly thermal.

That said, it is recognised that the justification is more likely to be centred on carbon footprint terms. But even then, the carbon footprint of building such a scheme may be significant compared to the longerterm carbon footprint savings of the thermal generation that it supplants.

In this context, it is worth noting that cement manufacture accounts for about 8% of global carbon dioxide emissions — and the Onslow scheme would require huge quantities of concrete.

The Onslow scheme would be an atypical example of pumped storage which is normally only justifiable in a predominantly thermal generating system.

Thermal generation is applied to pump water to the upper reservoir at nighttime, and released during the day to match peak electricity demand. The underlying rationale is that whereas thermal generation cannot react quickly to variations in electricity demand, hydro can.

Given New Zealand’s abundance of hydro capacity, this conventional application of pumped storage is not applicable.

Murray Menzies

Mornington

Christchurch.

The exploiters of Queenstown can’t cope with the problems they create, so put it in Central Otago. Nice and quiet and peaceful there — just the place to handle all the nasty noise and hassle you want to throw at it, they say.

Don’t build an airport and they can’t come — now there’s a thought. And if it does go ahead, in spite of my curses on their heads, they can pay for their disruption. I suggest a tollgate at the start of the Kawarau Gorge, with eyewatering fees for buses and passenger vehicles.

Steve Moynihan

Cromwell

REGARDING the proposal to build an airport at Tarras (ODT, 23.7.20). There are already wellfunctioning airports in Dunedin, Invercargill and Queenstown which serve the lower half of the South Island. In this current era of critical climate change which we are facing, the proposal to build a further airport at Tarras can only be described as idiocy.

Bruce Lambie

Roslyn

Motoring cartoon

THE delightful cartoon circa the 1930s in the ‘‘Fast and Furious’’ article in the Weekend Mix(ODT, 25.7.20) shows an aggrieved motorist who, stopped by a policemen, asks, ‘‘Well, what law am I violating now?’’

To which the policeman replies, ‘‘I dunno yet, but you must be breaking some regulation . . . you’ve got a car, ‘aven’t you?’’

This response could well be the new 2020 Mission Statement of the Dunedin City Council which seems hellbent on making the lives of Dunedin’s motorists a continuing nightmare.

‘‘Plus ca change, plus c’est la meme chose’’!

Douglas Clark

Opoho ....................................

BIBLE READING: What I have vowed I will make good. Salvation comes from the Lord. — Jonah 2:9.

IN recognition of the importance of readers’ contributions to the letters page, the newspaper each week selects a Letter of the Week with a book prize courtesy of Penguin Random House. This week’s winner is T. Willis, of Dunedin, for a letter about the challenges and charms of cycling in Dunedin. The prize is a copy of Into the Unknown, by Ian Trafford. The winning letter was printed on Thursday and can be read on the ODT website.