Transmission network already threatened by climate hazards, data shows

Source: Radio New Zealand

Thousands of high-voltage pylons and other national grid sites are exposed to flooding, along with hundreds of kilometres of transmission lines, data provided to RNZ shows.

Network owners say increasingly frequent severe weather driven by climate change is heightening the flooding risk to distribution infrastructure too, along with damage caused by high winds and treefall.

Transpower is already pursuing plans to raise the height of some transmission sites, or even move them, while lines companies are pushing for increased powers to deal with ‘out of zone’ trees they currently cannot trim.

But together with sustainable energy advocates, they say having more distributed energy sources, such as solar panels and batteries, could also help to keep the lights on during weather emergencies.

Hundreds of people in the lower North Island went all of last week without power, after a storm brought down hundreds of lines in Wellington, the Wairarapa and Whanganui-Rangitīkei areas.

That followed prolonged power outages in Southland and Otago after a severe storm in late October.

Clutha Valley farmer Richard Hunter was among those affected, after the storm brought hundreds of trees down across his property, including onto power lines.

Hunter said the clean-up had been lengthy and expensive.

“We’ve employed an extra person to help with fencing, we’ve had a digger come through to lift a lot of trees off fences and clear fencelines, and that work’s still ongoing.”

Since the storm, he has increased generator capacity on the farm and would “possibly” be better prepared for another long outage.

“But you just don’t know how widespread the next event might be.”

Data published by Earth Sciences New Zealand (ESNZ) last year showed that 46 transmission sites such as substations are exposed to a flood hazard – more than 20 percent of the 216 sites around the country.

Additional data, released exclusively to RNZ, shows that more than 3800 pylons, towers, and other national grid structures are also exposed (10 percent), along with 1235km of the country’s transmission lines (11 percent).

The proportion of transmission infrastructure exposed is projected to rise with every additional degree of warming.

Some regions are more vulnerable than others.

The largest number of affected transmission sites and structures are in Canterbury, while the proportion of both lines and structures exposed in Bay of Plenty is among the highest of any region.

Of the 470km of lines in Bay of Plenty, 16.8 percent are exposed, while 17.5 percent of the region’s more than 1800 structures are at risk.

ESNZ principal scientist Emily Lane said the exposure was high, even before taking the effects of future warming into account.

“We’ve got quite a lot of our infrastructure in these vulnerable areas.”

Just because an asset was exposed to flooding did not mean it would fail, though.

“Oftentimes there will be a flood and the power poles might be just sticking out of the water and that’s actually not a problem,” Lane said.

“But if you’ve got high velocity [water] you might get scour. If you’ve got debris, the debris might pile up against the pylon and that could increase the scour or increase the loading on it and that’s when you start getting problems.”

There were also indirect threats.

“If a structure gets damaged by another hazard and that’s in a flood-affected area, you can’t get to it because of the flooding – you can get these cascading impacts.”

The modelling was unable to take into account any mitigation or other protective features, such as elevated floor heights at substations, she said.

“What our hope is, is that Transpower is using this and going, ok, these are the places we need to check out.

“It might be that they go, we actually already knew about this and we’ve built the floor height to this level and so we’re comfortable that that’s ok.”

Building a more resilient network

Transpower’s strategy, performance and risk manager Julian Morton said climate resilience had been part of Transpower’s asset management approach for more than a decade.

The transmission network ran through “some pretty rugged country” and flooding, land stability and access were all risks.

“We know climate change is increasing the threat to some of our sites,” he said.

The state-owned enterprise had a list of 12 substations that were high-priority for being adapted or moved to better protect them from future flooding.

First off the blocks would be Redclyffe substation in Hawke’s Bay, which failed during Cyclone Gabrielle when it was flooded.

The Commerce Commission granted approval late last year for Transpower to go ahead with plans to redevelop the substation on the existing site, but with raised floor heights to keep it above future floodwaters.

Transpower considered, but rejected, a plan to move the entire substation to higher ground, at an estimated cost of $280 million.

The approved plan is expected to cost $44m.

Other locations might require more drastic measures as time went by, Morton said.

“We’re looking at … what are our future options at those sites like South Dunedin where we know that we’re going to run out of runway where just elevating may not tick the box.”

The ESNZ data, produced as part of a wider project to map inland flooding risk across the country, only included national grid infrastructure.

It did not take into account local distribution networks.

However, Electricity Networks Aotearoa (ENA) chief executive Tracey Kai, whose organisation represents the 29 lines companies in New Zealand, said climate change was starting to test them too.

“We build infrastructure for 100-year events, but those 100-year events are not only happening more frequently, but they’re more severe than when we forecasted them initially,” Kai said.

After Cyclone Gabrielle, her organisation analysed the causes of local network outages to 240,000 people and found a fairly even split between tree damage, older infrastructure failing, and flooding.

A “bugbear” for ENA’s members was not being able to manage trees that were outside minimum clearance zones but still posed a threat to lines, Kai said.

Legislation had been drafted that would restrict new planting around lines, and that would help, she said.

However, lines companies were pushing for further changes that would shift the onus of trimming and managing trees onto commercial and public owners of trees, such as forestry companies and councils.

“Network companies are fine looking after what we call mum and dad trees, so trees outside my house, outside your house,” Kai said.

“But those that derive a return from that tree planting should be bearing that cost really.”

The role of ‘distributed energy’

Sustainable Energy Aotearoa innovation pathways manager Gareth Williams said frequent severe weather events were showing up “just how vulnerable the networks are”.

Improving the resilience of that infrastructure where possible was important, but some of the options were “horrendously expensive”, he said.

“There are definitely fixes, but at what cost?”

The country should also be rolling out distributed energy, where generation and storage happened locally through technologies like solar panels, batteries, and electric vehicles.

That could play “a critical role” in making households and communities more resilient, he said.

“If there’s an upstream [outage] and there’s enough solar and batteries, essentially you can create the network as a whole series of little microgrids so each microgrid can operate independently.”

It was unlikely to provide enough electricity for people to run their power as usual, but it would keep the essentials going, Williams said.

“You could have a microgrid providing a basic electricity supply for lights, televisions, refrigeration, phone-charging, internet – for quite an extended period.”

Tracey Kai said as more renewables were rolled out, it made sense to have “everything, everywhere, all at once”.

“If you have distributed energy, whether it’s your electric vehicle or solar or batteries, if you can afford the upfront cost of those things, not only will it bring your power bill down in the long run, but also it provides resilience.”

She would go “one step further” than just individual installations.

“Solar on marae, solar on schools, they’re all options because it means that it’s not just a household that benefits or a neighborhood, it means that anyone who’s affected, they can kind of stand that up as a place of refuge and safety while services are being restored.”

Six reviews since Cyclone Gabrielle had talked about the importance of community hubs, Kai said.

“That is something that would make a real difference.”

A resilient network would still be needed, though.

“You will still need supply from the grid. And if you are exporting back in and selling your excess power, you’re still going to need a network to transport your electrons on.”

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– Published by EveningReport.nz and AsiaPacificReport.nz, see: MIL OSI in partnership with Radio New Zealand