New Zealand installs its biggest solar farm, floating on a wastewater pond

New Zealand has notched up two solar milestones in one project, with the completion of its first ever floating solar array and the country’s largest PV plant of any type – for now, at least – on top of a wastewater treatment pond on Auckland’s North Shore.

The landmark, megawatt-scale floating solar plant, made up of 2700 solar panels and 3000 floating pontoons, was installed by Vector Powersmart on the Rosedale wastewater treatment pond of Auckland council-owned utility Watercare.

The solar will be used to supply around 25% of the treatment plant’s electricity, used for the energy-intensive tasks of pumping and aeration that help natural bacteria break down the waste as part of the treatment process.

Watercare, which aims to cut its energy use by 8GWh by 2022 and to achieve energy self-sufficiency at its Mangere and Rosedale wastewater treatment plants by 2025, said the floating solar plant was a vital part of this plan.

“As a large user of energy, it’s important that we look at ways of reducing our environmental footprint and becoming more self-sufficient,” said Watercare chief executive Raveen Jaduram. “Innovative solutions like this on top of wastewater ponds are a smart way to reduce operational costs.”

Indeed, floating solar on top of waste treatment plants and reservoirs has been an obvious starting point for water utilities, not least of all in Australia, with one of the earliest examples being the 100kW system installed in early 2018 on the East Lismore sewage treatment plant in New South Wales.

“Vector PowerSmart’s capability to design and deliver this innovative system shows how new energy solutions are key to helping business reach their economic and environmental goals, and we’re proud to be working with Watercare to help it achieve both,” said Vector Group CEO Simon Mackenzie in a statement last month.

“[This is] the first time floating solar will be seen in New Zealand and the first megawatt-scale solar project to be confirmed. It can generate enough power over a year to run the equivalent of 200 average New Zealand homes for a year,” Mackenzie said.

“Even larger systems are already common overseas and with reports out of Australia of costs as low as 4-5c per kWh, when that scale arrives here we’ll see solar’s real potential to set a new cap on the wholesale market which over the past few days has been around double that.”

Watercare’s green energy specialist, Laurence Jenner, told Stuff.co.nz that the Rosedale array was expected to pay for itself well within its 25-30 year life expectancy, and that the utility was considering a similar plant at one of its water storage lakes in the Waitākere Ranges.

As RenewEconomy reported here in September 2019 when the project was announced, the Rosedale array is roughly double the country’s previously biggest solar installation, a 410kW facility at Yealands Estate Winery.

But Rosedale will not hold the title for long, with a 1.6MW rooftop array currently being installed on supermarket wholesaler Foodstuffs, near Auckland Airport. This would then be eclipsed by a 10MW solar farm proposed for unused land at Hawke’s Bay airport. And a 26MW project was also being considered to supply power to the NZ Oil Refinery at Marsden Point.