28 Jul 2020

Lake Onslow hydro project: Pros and cons

From Nine To Noon, 9:25 am on 28 July 2020

A hydrologist says the proposed hydro project for Lake Onslow could be a centre for eco-tourism as well as a way to create power grid stability in dry seasons.

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Photo: Shellie Evans 2014/Wikipedia

Earl Bardsey says the benefits to the economy would be significant and would also present a chance to create a wildlife sanctuary, with a predator-proof fence around the Onslow basin and expanded reservoir.

Energy and Resources Minister Megan Woods this week said the government was looking into a recommendation by the Interim Climate Change Committee involving hydro schemes that pump water to manage peak demand, solve the problem of dry years for storage lakes and the irregular supply of renewable energy sources such as wind.

"It works like a battery because the stored energy in the water is released when it is used in the hydroelectric dam. This opens up huge possibilities for cheaper electricity and increased supply," she told media at the Hayward Substation in Wellington on Monday.

Woods predicted that if the recommendation proved viable, it would create thousands of jobs, make wholesale electricity cheaper and help to "green the grid" by doing away with the need to use coal and gas.

The minister added it would be a significant step towards 100 percent renewable power generation.

The analysis will mostly focus on a pumped hydro storage project at Lake Onslow in Central Otago, but will also include the assessment of smaller potential pumped storage options in the North Island, as well as other alternative technologies.

However, Bardsey says smaller schemes around North Island where most energy demand exists isn’t a solution, because the numbers don't add up.

“The little ponds and lakes in the North Island, there’s no way you can add those together to provide you with enough energy to take you through a dry year. In a way ideally, the Onslow geology and typography would be located in the North Island. But we have just make use of what nature gives us.”

He wrote a research paper in 2005 floating the Onslow idea as a viable project, which he subsequently fleshed out in a PhD thesis published last year.

“The idea is that during times of electricity high demand we will run water down from a high lake into the river and conversely when there is plenty of water available and the power is cheaper we’ll pump water up. When we have a dry year, there will be a reserve there available to be used.

“The actual amount that can be quite large, maybe being able to generate in excess of 1000 mega-watts and in terms of the actual energy storage we might be looking at doubling the existing energy-storing capacity, which is about 4000 giga-watts.”

The expense of the project is justified by the expense of not being able to meet future demand, he says.

 “If we’re going towards a green economy and we have our electric cars and our industrial heating from electricity and we generate green hydrogen. If we have a dry year and all that falls over, that’s going to be expensive as well."

An expanded Onslow Lake would have multiple uses and would offer grid flexibility, he adds.

“You have to keep in mind that Onslow will have multiple uses and it can also be used in the short-term, because you’re going to have 1000 mega-watts available to you to crank up and down at short notice to buffer further developments like wind energy for example.

"If you put too much wind energy into the grid you run the risk of grid instability. But if you have a large buffer like Onslow with 1000 mega-watts you can smooth out those short-term fluctuations. In addition to that it will operate all the time as part of the seasonal hydro storage."

Environmentally, Bardsey says his original motivation for proposing the scheme was to take storage away from existing hydro lakes which are set in soft glacial till, so the water levels going up and down each year have significant impacts on shorelines.

“My real hope is by taking some of the energy away from the hydro lakes and storing it an expanded Lake Onslow, which is surrounded by rock, we’d have a much better, environmentally suitable way of handling our seasonal water storages.”

Previous reservoir projects have been criticised for the impact on freshwater and terrestrial biodiversity.

Lake Onslow is a reservoir of approximately 8sq/km, with submerged wetlands. The project may see another 8sq/km submerged. However, he says for a business case to be successfully made, the environmental impact must be a “net-positive” and that efforts to protect surrounding waterways and habitats could achieve this.

“There are a number of possible options. One that I’d really like to see followed up – maybe we could actually extract those wetlands and put them onto a floating system. In other words, the wetlands are still there, but they’re converted to floating wetland that goes up-and-down with the water. And we can even have a bigger wetland that we have at present."

He says the endangered Teviot flathead galaxias fish, which reside in a tributary flowing into Lake Onslow, could be protected within a special reserve. In fact, the entire Onslow Basin could also be surrounded by a predator-proof fence so it could be managed as a wetland reserve, he says.

The government expects if the Lake Onslow project goes ahead it could create as many as 4500 jobs.

Bardsey hopes permanent jobs would also be created after the building project was completed.

“If we followed through with a protected wetland, I think that in itself would be a centre for eco-tourism, it would be well worth looking at.”

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