New Zealand has excellent renewable electricity resources. We’ve got hydro, wind and geothermal up the wazoo. In a typical year, more than 70% of our electricity comes from renewable sources, and the government wants this to increase to 90% by 2025 (for non-dry years).
Source: Energy in New Zealand 2013, MBIE
Researchers at the University of Canterbury have been investigating whether NZ could generate 100% of our electricity from renewable sources. Dr Ian Mason, part of the research team, gave a presentation on this topic at the NERI Energy Conference last year.
The researchers are all from UC’s College of Engineering, and they have focussed on whether it is technically feasible for NZ to go fully renewable.
Since I’ve lost my notes (!) from the conference last year, I’m going to quote from a paper published by the researchers (Ian Mason, Shannon Page & Arthur Williamson – referred to as “Mason et al” below). If video is more your thing, though, here is a video of Dr Mason giving a similar presentation at a conference in California. There’s also a good newspaper article on their research here.
Do renewables have enough growth capacity?
If renewables are going to grow their share of generation, we’ll obviously need to build new plants. So the first question is, can we build enough capacity to match current demand, and allow for future growth?
According to Mason et al:
Recent resource estimates published by… EECA indicate near-term potential for 6600 MW of new wind generation, 4680 MW of new hydro generation, 635 MW of new geothermal generation and 3090 GWh/ year of electricity from woody biomass
That compares to current capacities of 622 MW of wind, 5,254 MW of hydro, and 731 MW of geothermal. Theoretically, we could develop twice as much hydro and geothermal as we have now, or ten times as much wind. In practise, we’d run into issues with the wind, since it can’t be relied on to blow when you need it – but Mason et al refer to several studies which suggest that “penetration levels well above 20%” are possible. That’s still three or four times what we have now.
Even the woody biomass contribution could be fairly substantial. New Zealand currently uses around 43,000 GWh/ year, so biomass could account for up to 7% of that.
Overall, growth in capacity isn’t an issue – there’s plenty of room for growth, although some of those plants will cost more to build than others. The other question is:
Can an all-renewable system meet demand in peak periods, or in “dry years”?
This is the tricky part. Electricity demand fluctuates quite a lot during the day, and during the year. We use more electricity in the evening, as people get home from work, shower, flick on the TV, and start cooking dinner. We also use more power in winter, mainly for extra heating. An all-renewable system would need to cope with both these patterns, as well as any unexpected demand surges.
The other issue is that hydro generation forms the backbone of our power system. For those plants to operate at full blast, we need good rainfall, running into the rivers which fill up the hydro lakes. Every now and again, we get a “dry year” with rainfall that is well below average. This means that we can’t generate as much hydro electricity.
“Dry years” aren’t that dry – the difference between our best year for hydro generation (2004) and our worst recent year (2001) was around 20%, or 5,000 GWh – but that’s still quite a bit of slack which other plants need to take up. And the crunch comes during winter, when demand is high and supply is struggling to match it.
So, how do you design an all-renewable system? You let the wind turbines turn whenever they can, as that’s essentially free electricity. Most of the geothermal plants will also run constantly. These are your “base load” plants. Hydro is also part of the base load, but the aim is to use as little of it as possible, since that’s the easiest form of energy to store for when you might need it later.
You also need “peaker” plants, which only run during higher demand periods. Hydro plants can actually gear up and down their production pretty quickly, so they’re a good option. To do this, they need to have “stored energy” ready to go – water reservoirs or lakes.
From Mason et al: “A significant characteristic of New Zealand’s hydro generation system is the relatively low energy storage capacity. When all lakes are full this amounts to approximately 34 days reserve at peak winter demand (approximately 130 GWh/d in 2007), assuming zero inflow”.
For an all-renewable system, you’d need to build a bit more storage. You might consider a “pumped-hydro energy storage” (PHES) system for some plants. That means that when there’s plenty of electricity available – the wind is blowing, and it’s a beautiful summer day – you use some of the excess hydro energy to pump water uphill, into another reservoir. During high-demand periods, you let it flow down again, delivering more energy to the power plant.
Ian Mason’s presentation assumes that we build PHES equivalent to 8% of the current hydro storage. As far as I can tell, there aren’t any other increases in storage – although I seem to remember him mentioning that current lakes would need to be dipped into more heavily. At present, the lakes have “minimum storage levels”, and need consent from the regulator to go below those levels. The minimum levels are perhaps on the conservative side at the moment,
It’s also possible to use biomass on a seasonal basis: burning it during the winter to match the greater demand. However, Mason et al don’t think it’s necessary, and this energy source isn’t developed further in their model.
From Mason et al:
The proportion of dispatchable generation in the final mixes was 75–78%, as wind was the only non-dispatchable source. Load shifting, pumped storage hydro generation, biomass-derived gas- fired generation and additional conventional hydro were considered the most likely peaking generation options for New Zealand. These are in addition to the response capabilities of the existing hydro system. Hydro turbine response times of 6–15 s (spinning reserve) can be assumed; implying that full power can be readily achieved within a half-hour period (the resolution of the modelling). Gas turbine response times of seconds (hot reserve) to minutes (cold reserve) can be assumed, again implying that full power could be achieved within a half- hour period.
One of the conclusions from Ian Mason’s presentation is that NZ can indeed develop a 100% renewable system. Whether this would be economically feasible, or likely under the current market structure, are different questions – the presentation does consider them as well, and finds that we’re unlikely to get there given current policy settings. I’ll look at this another day.
Second, third and fourth opinions?
The Herald also published an article in their Element magazine a couple of years ago, written by Dr. Eric Martinot (“senior research director at the Institute for Sustainable Energy Policies in Tokyo and a teaching fellow at Victoria University of Wellington”). He began his article with:
New Zealand could easily reach the goal of nearly 100% of its electricity from renewable energy in the coming two decades. And it would be folly not to.
Benjamin K. Sovacool and Charmaine Watts wrote a paper called “Going Completely Renewable: Is It Possible (Let Alone Desirable)?”, published in The Electricity Journal, vol. 22 issue 4.
According to them, New Zealand has “the resource base necessary to transition to a renewable electricity sector”, and “a completely renewable power sector is technically feasible. There are no sound technical reasons why existing renewable power plants could not replace all conventional units. To quote just one of a plethora of recent studies, ‘‘it is clearly feasible to replace the present fossil fuel energy infrastructure . . . with renewables.’’.
Greenpeace commissioned a study from the Institute of Technical Thermodynamics of the German Aerospace Centre, which found that “New Zealand can have 100% renewable electricity by 2025”.