The winds of change

Much of our electricity now comes from rain and wind, but, asks Greta Shirley, can they keep the lights on in a changing climate? 

Imagine, if you can, a life – or just a day – without electricity. For generation Y, it's right up there with air and water. Houses no longer have enough power sockets, and one look along the groaning shelves of small appliances in any homestore soon reveals why. Widescreen TVs, heat pumps, dehumidifiers, benchtop grills, juicers, cordless phones, electric blankets – they all need a constant diet of watts, and when the power goes out, it's like the world is on hold.

Consider then, when you flick the telly on, where that power comes from. It comes, in large part, from the weather we hate – rain and wind. More of New Zealand's power is generated by renewables – mostly hydro dams, geothermal bores and wind turbines – than in practically any other country. As of March this year, renewables powered 79 per cent of all electricity generated – the highest contribution since December 1996.

Hydro makes up around 60 per cent of our total generation, and while wind currently adds just under four per cent, that figure's set to increase. Another 5000 megawatts (MW) of renewable generation is either on the books or being built, edging us closer to a national target of 90 per cent renewable generation by 2025.

Electricity generation produces around 19 per cent of the country's greenhouse gases, but as more renewables come on stream, that figure falls. Latest Ministry of Economic Development (MED) figures show that electricity's CO2 emissions dropped by 24 per cent between 2008 and 2009.

But there's a down side: if you mean to make more and more power from wind and rain, you need a guaranteed supply, and Nature has yet to commit. Three of the last 10 years have been drier than average – a trend Dr James Renwick warns could become the new norm.

"The main message out of our climate change work," says NIWA's Principal Scientist, Climate Variability and Change, "is that the future isn't going to be all that much like the past. The shifts are going to be significant – we can't rely on what happened in the last 40 years to nail down how the future is going to look". That makes a weather-dependent generation network "very vulnerable" to climate change and variability, he says, and we need to start "paying attention". 

Natural climate cycles, such as the El Niño Southern  Oscillation (ENSO) and the Interdecadal Pacific Oscillation (IPO), have a huge bearing on our year-to-year weather, affecting westerly winds over the country which, in turn, determine the rainfall in the Southern Alps that feeds our hydro rivers and lakes. But there's another influence – still bigger, but less easy to predict, says Renwick. That's the greenhouse gases we keep pumping into the atmosphere. Ironically, our greenhouse gas emissions could hamper renewables' capacity to offset those very emissions.

Outlook changeable

Climate change will alter mean rainfall and wind patterns, and bring more extreme weather like droughts, flooding and storms. That's likely to hamper generation, and damage transmission infrastructure such as power lines. Temperatures are also tipped to continue rising. Depending on whether we curb, continue with, or increase our current greenhouse gas emissions, NIWA scientists predict that, by the end of the century, Auckland could get an additional 40 to 60 annual days above 25°C – well up on the 21 days it averages at the moment. Hamilton is tipped to get another 26 days a year over 25°C, and Christchurch 31. Wellington would get just three extra days.

That warming has interesting implications for electricity demand. All up, we currently use around 42,000 gigawatt hours a year, with about a third of that going to heat the water and homes of 1.7 million residential consumers. National consumption skyrockets on chilly winter nights, when heaters, heat pumps and electric blankets draw more than 6500MW (cold consumers set a new record during the big snow of mid-August: 7048MW at 6.00 pm on Monday 15). But as the mercury climbs, demand will start to shift to the summer, when we switch on more and more air conditioners, and farmers are forced to irrigate.

Together, that temporal shift, higher demand, greater fluctuations in our weather, and an increasing renewable generation portfolio conspire to make us "very dependent on what's happening with the climate," says Renwick. "We're vulnerable in a good way, I guess, because we're reducing our emissions, but ... we have to keep our eyes open".

Renwick says we should try to ease our dependence on rain "and look at other generation options like solar, marine and wind to help increase security of supply".

NIWA's National Centre for Energy Solutions conducts a range of research and consultancy work for the energy sector, including partnering new energy technologies like tide and wave energy. A growing appetite for renewables, says Chief Scientist for Energy, Dr Murray Poulter, means the Centre's work is increasingly about understanding how those energy resources will be impacted by weather and climate, over both short and long terms. That means producing resource assessments and models, national energy trends analyses and demand and resource forecasts.

Understanding the resources we have, and developing the right technologies to utilise them, will ensure our future electricity system has the optimum mix of sources, says Poulter. 

When the IPO rouses in the northern Pacific, the effects, even on distant New Zealand, can be dramatic. The Southern Alps, for instance, might receive ten per cent less – or ten per cent more – rain. That may not sound like much, but it gives a hydro manager a headache; wet seasons are as awkward as dry ones. The next two decades will likely see more dry years, but long-term, in the South Island at least, that trend will flip, with warmer, more energetic air dumping more rain, more often. "Then management of flood flows is likely to become more of an issue for hydro generators," says Renwick.

Then there's snow melt, another major source of hydro supply. Recent NIWA models predict significant loss of seasonal snow cover, particularly in the South Island, as rainfall and temperatures change. Warming will probably boost the amount of glacial meltwater in the short term, but ultimately, glaciers might shrink drastically, or disappear altogether.

A weather eye

Meridian's Mike Roan keeps a sharp eye on the weather most days. "The accuracy of weather forecasts is...important to us," says the generator's Wholesale Markets Manager. Meridian is New Zealand's largest electricity generator, and manages about 70 per cent of total hydro storage through 

the Waitaki hydro scheme and the Manapouri power station. It also operates four wind farms around the country.

"We can't control the fuel we receive – we can only forecast when it might arrive. That forecast is very important for the decisions we have to make around how we use our storage".

That "fuel" is wind, rain and snow pack, so understanding what's going on with the climate, says Roan, is a preoccupation, both for day-to-day operational running and for long-term investment. NIWA helps out by monitoring Meridian's sites, providing information on inflows into the hydro system, automatically or manually, that is then used to operate the assets and manage consents.

It's also developing detailed forecasting tools to help generators calculate the generation they can offer the electricity market day-to-day.

Wind generation is a particularly tough one to pick, says Roan, but system operator Transpower demands accuracy. "Some days it starts off quite windy, and then dies away entirely. Transpower coordinates all of the energy sources across the country, whether it's us, Mighty River Power, or Genesis. They need to know our best forecasts of what wind might do, so they can bring on thermal-fired assets if the wind isn't producing much". 

Meridian is, understandably, very interested in how longerterm climate change will affect their "fuel". Last year, the generator looked hard at climate change and how it might impact future investment decisions. "When we're looking at refurbishing assets, or looking for places where we can build new ones that will last maybe 40 to 50 years, we have to look out over longer horizons," Roan says. "We need to be sure that the historical weather patterns for the catchments we operate in will remain reasonably the same".

Warmer temperatures this winter meant more rain, so hydro systems stood up well. But it's not always that way. Three dry years in the last decade showed us just how close black-outs can be.

Transpower knows this only too well. A temperamental grid has caused well-publicised power outages: the most serious, in 2006, left 700,000 customers in the dark. Transpower's Principal Strategy Investment Advisor, Mike Parker, says that's prompted the company to think harder about how future climate scenarios might impact on transmission. His job is to anticipate "all possible eventualities, however unlikely they seem today" – contingencies like more storms, high winds and snow. Or new technologies – or higher temperatures – pushing up demand. Parker says the lengthy lead-in time for new investment means that, more than most, Transpower has to think ahead. "If we have to build a new line somewhere because of new generation, we need seven to ten years to do it".

To best target investment, Transpower needs to know where new generation will come from. NIWA has helped out by developing a comprehensive map of electricity resources across the country. "We may not know exactly what new technologies will be developed," says Parker, "but we do know what the resources are, and where they are, so we can plan better for the future". But the wild card, he says, is Nature. "There's just so much uncertainty about climate change impacts. All we can do is keep monitoring what you guys (NIWA) are saying".

Running out of puff

So could renewables leave us in the lurch in a changing climate? MED's Energy Outlook to 2030 suggests that too much reliance on renewables, while helpful in reducing greenhouse gas emissions, would both "significantly raise" electricity prices, because of the high cost of building new infrastructure, and cause "electricity security issues" in the face of more climate variability. But Mike Roan disagrees: "The economics of renewable electricity resources are far superior to the alternatives – gas and/or coal-fired generation. Everyone is in the renewable generation space, with marginal investment in thermal peaking to offset some of the climate variability we might see".

The International Energy Agency recently commended New Zealand's "bold goal" of 90 per cent renewable electricity generation as "a large step in the right direction," a plaudit echoed by environmental groups. But a look through the Government's leaked draft energy strategy shows that direction has changed. Though it's still listed, the 90 per cent renewable target has slipped down the priority list, well behind development of more petroleum and mineral fuel sources.

Energy commentator and convenor of the Sustainable Energy Forum, Steve Goldthorpe, says renewables needn't be an Achilles heel: we just need to manage the climate risk by planning ahead, and maintaining some thermal back-up. "It's a bit like having an off-grid wind turbine or solar power on your own section. You still need to have a petrol generator in the shed that you bring out once in a while to cover emergencies".

Renwick agrees: "The climate change scenarios NIWA puts out are designed to help energy companies think about risk to security of supply. They might say we don't have to think about it for 50 years. We say do it now".

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Emissions from the energy sector

Under the Kyoto Protocol, New Zealand is obliged to reduce its greenhouse gas emissions to 1990 levels (60.8 million tonnes per annum) before 2012, or pay a charge on any surplus. Since 1990, New Zealand's total energy emissions have increased by 35 per cent – around 1.6 per cent each year.

New Zealand's Greenhouse Gas Inventory 1990–2008, released last year, reported that our emissions were 74.7 million tonnes per annum, or 22.8 per cent higher than 1990 levels.

That was offset, however, by carbon sinks such as forests. In 2008, they soaked up around 26.2 million tonnes, bringing our net emissions down to around 48.5 million tonnes.

In an effort to meet our Kyoto obligations, the Government has implemented the Emissions Trading Scheme (ETS) which puts a price on greenhouse gases as an incentive to reduce emissions. The energy sector is subject to the ETS. 

Natural climate cycles

NIWA's research is looking at future climate scenarios, based on both natural cycles and long-term climate change, which is driven by greenhouse gas emissions. Two influential natural cycles affecting New Zealand's climate are the El Niño Southern Oscillation (ENSO) and the Interdecadal Pacific Oscillation (IPO). In certain phases, the various natural climate drivers combine – both with climate change and with each other – to produce highly variable weather. In other phases, they work against one another.

The ENSO cycle involves an exchange of heat in the upper layers of the ocean between the western and eastern equatorial Pacific, and associated changes to the trade winds in the tropical atmosphere. El Niño and La Niña refer to opposite phases of the cycle.

In El Niño years, New Zealand tends to get stronger or more frequent winds from the west in summer, leading to drought in east coast areas and more rain in the west. El Niño years tend to bring higher inflows to the key South Island hydrogeneration lakes, increasing security of electricity supply.

La Niñas have weaker impacts on New Zealand's climate: we tend to get more northeasterly winds, which bring moist, rainy conditions to the northeast parts of the North Island, and reduced rainfall in the South Island.

As a consequence, La Niña years tend to reduce flows to the main South Island hydro lakes, and a decreased security of supply.

The IPO is basically a longer version of the ENSO cycle, bringing 20- to 30-year periods of more frequent El Niño events, alternating with periods of stronger La Niña conditions.

Positive IPO phases bring South Island lake inflows around 10 per cent higher than the long-term average, and a decreased risk of dry years. 

In a negative IPO, westerly circulation slackens, and rainfall tends to ease in the west, bringing South Island lake inflows around 10 per cent lower than the long-term average, and an increased risk of dry years.

Climate patterns can affect the supply of electricity, but they also influence demand. In winter, El Niño phases are generally associated with cooler than normal conditions, triggering higher demand for heating.

In summer, La Niñas often mean warmer than normal conditions, prompting consumers to reach for the air conditioning remote. Climate change will likely boost electricity demand in summer for cooling, and ease demand in winter for heating.

The outlook

Out to 2040, the Ministry for the Environment expects annual mean rainfall to increase in Tasman, West Coast, Otago, Southland and the Chatham Islands. These areas are also likely to get more heavy downpours.

Northeastern districts – Northland, Auckland, Gisborne and Hawke's Bay – are predicted to get less rain.

A March 2011 NIWA study, Scenarios of Storminess and Regional Wind Extremes under Climate Change, found that extreme winds are likely to increase over this century in almost all regions in winter, but decrease in summer, especially around Wellington and across the South Island.

However, the increase in wind speeds isn't expected to be large; just a few per cent by the end of the century under a middle-of-the-range emissions scenario.

The study also predicted an increase in low-pressure activity over the Tasman Sea in summer, and a decrease in activity south of New Zealand. 

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Contact

Dr Murray Poulter
Chief Scientist, Atmosphere, Natural Hazards and Energy
murray.poulter@niwa.co.nz

Dr James Renwick
Principal Scientist, Climate Variability and Change
james.renwick@niwa.co.nz

Meridian Wholesale Markets Manager Mike Roan: “We have to look out over longer horizons". Credit: Dave Hansford
Seventy-nine per cent of our electricity comes from the climate: rain, snow, wind and sun. What happens when that climate changes? Credit: Dave Hansford
Meridian's Benmore Dam, in the Upper Waitaki Valley.