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Hydro electricity generation still has vast potential for expansion, HUGH DE LACY discovers.
But that’s simply not the case, according to Joseph Mayhew, senior advisor on renewable energy for the Energy Efficiency and Conservation Authority (EECA). Sure, there’s little public appetite for damming more of the country’s remaining big rivers, and even lesser ones like the Mokihinui north of Westport face a huge battle for resource consent. “But there are hundreds of megawatts of potential small-scale hydro projects around New Zealand waiting to be tapped,” Mayhew tells EnergyNZ. In the Waikato region alone, the home of the succession of big Mighty River Power hydro plants on the Waikato River, an EECA study has found the potential for more than 300MW of additional generation from plants of less than 20MW. Multiply that by the country’s dozen or so regions and the theoretical potential is there for a massive increase in hydro generation. Mayhew stresses the “theoretical” aspect of this estimate. “All that resource potential doesn’t mean the projects will actually be built, or even should be built, because you’ve got a lot of competing interests, including legitimate environmental concerns, or because there are other more economic opportunities. The key thing is that with a lot of these small hydro schemes you don’t need big rivers, and environmental impacts are generally less. “That’s why there’s so much potential ... we have so many small streams and rivers on which to build hydro plants whose effects are relatively benign environmentally, and quite often the impacts can be mitigated as well,” Mayhew says. Electricity Commission (EC) figures show that at present throughout the country there are 530MW of new generation actually under construction, a further 1448MW for which consent has been granted, 1999MW where the consent is under appeal, and 1317MW for which consent is being sought.
But EECA lists no fewer than 48 other hydro projects of up to 5MW already up and running, and generating a total of close to 80MW. They range from Northpower’s 5MW Wairua Falls plant near Whangarei, and King Country Energy’s 4.9MW Wairere Falls plant near Piopio, down to United Network’s Watercare Waitakere plant near Auckland and Counties Power’s Watercare Cossey’s dam plant a little further south that are less than 100kW each. And all these little plants, according to Mayhew, demonstrate just how great the potential for new small-scale hydro generation is. Many of them are owned by local interests, but no fewer than 25 are operated by Tauranga-based Trustpower, the publicly listed generator that is the country’s biggest aside from the ‘big four’ of Contact, Meridian, Mighty River Power and Genesis. Trustpower is expanding its small-hydro output to cover the gaps in its other renewable capacity when the wind doesn’t blow, and EECA’s keen to see more small and micro-hydro opportunities taken up. Mayhew says there are at least three main areas for the expansion of small-scale hydro generation; the re-commissioning of old and abandoned facilities, the integration of electricity generation with irrigation, and the use of for run-of-the-river schemes on streams or small rivers. “In the early 20th Century and up to the 1950s and 1960s there were lots of small-scale hydro projects providing electricity for regions and towns before the national grid was developed, and as things progressed a lot of them were abandoned or de-commissioned,” Mayhew says. “There’s still a lot of hydro infrastructure around with the potential to be re-developed or re-commissioned, and in some cases it can be cheaper than building a new plant.” Last year EECA conducted studies on two of these, the first of them an abandoned scheme on the Blackball Creek on the north side of the West Coast’s Grey River. Originally built as a water-race for gold-sluicing, its basic infrastructure still survives, and the Blackball Community Trust is conducting a campaign to get it operating again.
The other scheme EECA looked at is in Taihape in the central North Island, where the Hautapu River on the edge of the town was dammed three-quarters of a century ago to provide a megawatt of generation. The dam’s still there and a local group is hopeful of getting the plant going again, given that the project will have little additional environmental impacts on the river. The South Island’s rapidly growing irrigation capacity also offers great hydro generation potential, in addition to the 200 gigawatt hours Canterbury and Otago already produce. The most obvious potential lies in the rock-studded rip-rap walls whose only current use is to slow the rate of flow in the main irrigation channels. The rip-raps could be replaced relatively easily by generation plants that would power the irrigators, thereby reducing dependence on the national grid. They could also produce mechanical rotational energy powering pumps to drive the irrigators. “If you can use hydro energy to drive a pump, then you don’t need to purchase electricity from the grid, or you can reduce the amount you do buy to run the irrigation scheme,” says Mayhew. And then there’s the run-of-the-river concept. “You don’t need a dam – you don’t need to have any water storage. You temporarily divert a portion of the flow through a generator, then it goes back into the same stream.” Such smqall-scale systems could be a boon to farmers and those living in remote areas where the cost of reticulation by the national grid is often prohibitive. The average New Zealand household uses 8300 kilowatt hours of electricity a year, and even a small plant with an output of only 10 kilowatts could supply the equivalent of five households. “These really small schemes are actually one of the most cost-effective options for people to generate their own electricity,” Mayhew says. “If you’re a householder you have the option of putting up photo-voltaic panels on your roof, or even a small wind turbine, but if you have a small stream on your property it’s most likely to be the cheapest way of generating electricity on a very small household scale.” Be it on a household, farm or local regional scale, there’s still potential for hundreds more megawatts of electricity to be generated by hydro, he iterates.
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It’s become almost an article of faith that, with two-thirds of the nation’s electricity generation already coming from hydro, there’s little room for expansion of this most reliable of renewable energy sources.
That total of 5294MW includes no fewer than 12 hydro projects totalling between 493 and 618MW, and ranging in size from the North Bank irrigation tunnel in Canterbury (200-280MW) and the Mokihinui (80-100MW), to the 5MW Matiri project on the West Coast.
Given the Coast’s vast number of creeks and small rivers, and the fact that nearly all the region’s power has to be imported from Otago or Canterbury with a high level of accompanying loss, schemes such as Blackball could be of huge significance.