Powering towards a low-carbon future

Trustpower's Mahinerangi wind farm and hydro storage lake. Photo by Stephen Jaquiery.
Trustpower's Mahinerangi wind farm and hydro storage lake. Photo by Stephen Jaquiery.
New Zealand is in the enviable position of generating a large part of its energy from renewable sources, but it could do much better yet, says a University of Canterbury researcher. Tom McKinlay reports.

The Antarctic's visit this week saw electricity consumption in Otago peaking, as heaters were switched on and electric blankets dialled up to toasty.

Much of the power for such appliances in New Zealand is supplied by renewable generation - hydro, wind and geothermal.

But a sizeable chunk continues to come from burning fossil fuels, making its own small contribution towards pushing atmospheric carbon dioxide past 400ppm and into new and risky territory.

It does not have to be that way, according to Dr Ian Mason, a research fellow in environmental and energy engineering and carbon management at Canterbury University.

In fact, Dr Mason says, New Zealand's electricity system could be 100% renewable tomorrow (metaphorically speaking) by increasing wind and geothermal generation, and switching between them depending on conditions.

New Zealand's electricity generation mix includes about 56% hydro and 25% fossil fuels (21% gas), at present. Wind makes only a small contribution, but could be generating almost 20%, Dr Mason says.

A 100% renewable system would have something like hydro 56%, geothermal 23.5%, wind 19.3% and biomass 1%.

To achieve this, Dr Mason says, we need to install 700 3MW turbines and 10 geothermal plants of 60MW each. To get around not-in-my-backyard opposition, some wind farms could be built offshore, he says.

The switch to 100% renewables would also probably require some pumped-storage hydro or gas turbines on standby, the former using surplus energy when both the wind was blowing and the rain was falling to pump water to a storage lake for use in times of peak demand.

Using a gas turbine occasionally would make for a 99.8% renewable system - near enough to 100% and ''a good transitional strategy''.

Dr Mason's figures are based on research looking at recent electricity use in New Zealand, including times when the weather was not kind.

''It was modelled at half-hourly periods (the time interval of the electricity market) over six years, including 2008 - the driest year on record,'' Dr Mason says.

Even in testing years such as 2008, Dr Mason's modelling found few periods of deficit in the system, so the requirement for something like pumped-storage hydro would not be large, he says.

Dr Mason also hints at a bigger prize.

The country's total energy use is 40% renewable primary energy and 60% fossil fuels, and a bigger investment in electricity generation could make serious inroads into the CO2-producing chunk of that.

''In order to electrify the light vehicle fleet, an estimated 464 3MW turbines in addition to those specified above would be needed according to research at the University of Waikato,'' Dr Mason says.

Demand-side measures would also be needed, with greater emphasis on walking or cycling and public transport, and demand-management technology such as smart meters would come into play to shift electricity use away from peak times.

''So, could we 'do it all' if large-scale electrification of transport is added? I would say that it makes sense from an energy point of view, could be done using a relatively small increase in the size of the 100% renewable electricity system modelled, and is definitely worth pursuing - but it does require some further research for New Zealand,'' Dr Mason says.

Offshore wind farms aside, all this will probably require more turbines somewhere near you. Dr Mason has no problem with objections to placing them in areas of outstanding natural beauty, but says those who do object, must also turn their minds to where they might be happy to see them.

He offers a quote from the UK, which he says addresses the urgency climate change presents:

''... this is about a forced march to that place, rather than an evolutionary stroll. It is about pursuing vision, or anticipating events, rather than responding to them.''

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