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The dirtiest electricity is on the rise again, with 62 per cent more coal burned to generate electricity in 2019, compared to the year before.

However, University of Auckland renewable energy researcher Kiti Suomalainen said coal provides a small fraction of the country’s power. “It had a significant-looking increase because it is low to begin with, luckily.”

Across 2019, 82 per cent of the country’s electricity came from renewable sources – a drop from the record high of 84 per cent in 2018.

Last year, the water stored in our hydro lakes decreased while our appetite for power rose slightly, according to the Energy in New Zealand 2020 report. Hydro power stations typically provide up to 60 per cent of the country’s power. Their output dropped by 3 per cent between 2018 and 2019, leaving a big gap.

“Overall, rainfall usually dictates quite strongly how much renewable electricity we have in the total,” Suomalainen said. “We’re still above 80 per cent total in renewables, so it’s not like we’re going in a bad direction. That’s just how hydro is.”

Wind turbines stepped up to fill some of the shortfall. However, fossil fuel generators such as Huntly’s coal and gas-fired units were also required to power up.

Natural gas generation is cleaner than coal, producing fewer greenhouse emissions for the same amount of power. However, natural gas was in short supply at the start of 2019, as a Taranaki gas field underwent maintenance. Consequently, electricity supplied from gas increased by just under 3 per cent last year – lower than it would have been without the shortages.

Easy-to-store coal filled most of the gap left by the hydro stations. “I think that’s a temporary solution to keep our lights on and keep the country going,” Suomalainen said.

Though coal-fired electricity has been sneaking up since 2016, this type of generation peaked in 2005. “That’s also when electricity emissions peaked,” she said.

Coal can be burned to generate electricity. However, this method of producing power is the most emissions intensive.
Coal can be burned to generate electricity. However, this method of producing power is the most emissions intensive.

Between 2018 and 2019, the country’s demand for power rose by 0.6 per cent. The dry weather was also a factor here – electricity use on farms went up, as irrigation systems switched on. Industrial users also increased their appetite by 1.5 per cent.

New Zealand had particularly low rainfall between January and July 2019, courtesy of the El Nino weather event. However, heavy storms in the South Island in December meant hydro lakes reached dangerously high levels. Rather than offering cheaper power and boosting the proportion of renewable electricity, generators chose to spill the excess water.

The report, produced by the Ministry of Business, Employment and Innovation, said our hydro lakes are relatively shallow compared to other countries and require regular rainfall to prevent levels dropping.

This means a back-up system is required for years when the lakes are low. Currently, coal and natural gas – when it’s available – fulfil this role.