By Faith Jeremiah*
Wastewater ponds may seem an unlikely place to look for solutions to New Zealand’s electricity security crisis. But their underutilised surfaces could help tackle two problems at once – high power prices and algal growth.
Floating solar panels on wastewater ponds offer a multifaceted answer. They generate renewable energy, improve water quality in the treatment ponds and reduce costs.
Leading this approach is the 2020 installation of New Zealand’s first floating solar array at the Rosedale wastewater treatment plant in Auckland. This project demonstrates how New Zealand could double the country’s power supply without requiring additional land. It serves as a test for future deployments on other reservoirs and dams.
The project comprises 2,700 solar panels and 4,000 floating pontoons. It covers one hectare of the treatment pond, making excellent use of a marginal land asset in a dense urban environment.
The floating solar array generates 1,040 kilowatts of electricity and reduces 145 tonnes of carbon dioxide annually. It also saves NZ$4.5 million in electricity costs per year. The electricity it generates, alongside biogas co-generation, meets 25% of the plant’s energy needs.
The project represents the first use of floating solar and the first megawatt-sized solar project in the country. As energy prices soar and environmental pressures mount, it is time to start exploring innovative solutions with the resources we already have.
Wastewater ponds provide underused surface
New Zealand is currently grappling with an electricity crisis, marked by increasing demand, aging infrastructure and a challenging transition to renewable energy sources.
The country relies heavily on hydroelectric power. This makes it particularly vulnerable during periods of low water levels in hydro lakes, especially in winter. This in turn leads to frequent supply shortfalls and, combined with diminishing gas supplies, to rising electricity prices.
As New Zealand intensifies its efforts to integrate more renewable energy, we need innovative solutions to stabilise the grid and meet growing energy demands.
One underutilised resource lies in wastewater treatment ponds. New Zealand has more than 200 wastewater ponds, chosen for their simplicity and low operational costs. They remain the most common form of wastewater treatment because they are robust, require low energy, cope with high water and waste loads and provide buffer storage to avoid applying agricultural effluent to wet soils.
However, because of the high surface area and nutrient-rich environment, algal growth is one of the biggest issues with waste stabilisation ponds. This is exacerbated on days with high sunshine levels and warmer water temperatures. It complicates the treatment process and necessitates costly chemical interventions.
An opportunity for New Zealand
My background is in entrepreneurship and innovation and the idea of floating solar panels on New Zealand’s expansive wastewater ponds represents an untapped opportunity.
Apart from generating power and preventing algal growth, the solar panels provide shade that keeps the water cooler and reduces evaporation. This is critical for maintaining effective wastewater treatment.
Utility-scale solar panels are now recognised as the cheapest form of energy, with rapidly declining costs over the past five years.
While relatively new to New Zealand, floating solar panels have shown significant advantages in other parts of the world. New Zealand may be held back by a misconception that solar panels work best in hot and sunny climates. In fact, solar panels harness the sun’s energy – not its temperature – making New Zealand’s cooler climate an ideal environment for efficient solar energy generation.
Given New Zealand uses more energy per capita than 17 of our 30 OECD peers, floating solar panels on wastewater ponds could set an example for how we tackle energy and environmental challenges.
By turning underutilised spaces into power-generating assets, we not only address immediate needs but also pave the way for a more sustainable, resilient future.
*Faith Jeremiah, Lecturer in Business Management (Entrepreneurship and Innovation), Lincoln University, New Zealand.
This article is republished from The Conversation under a Creative Commons license. Read the original article.
41 Comments
Clever solution though. Only a test case at this stage, but easy enough to replicate across the country.
You're right though, I doubt it will double our electricity supply.
What a pity that Christchurch chose to build an stadium for the rugby boys instead of investing something like this.
Medium density housing = great for energy efficiency, but bad at having land spare for solar panels.
Also an issue in duplexes/townhouses where you largely just have a roof to work with but getting it wrong may also affect your neighbours and their building/insurances too.
What is the problem with putting solar panels in a sheep paddock? We have plenty of these fields and it doesn't make much difference to grass growth or stocking rates, so there is not much of a land-use cost.
Would the gains from having the panels in cooler water offset the higher installation and maintenance costs?
I work in that sector. The shading from. The PV tables actually increases grass growth . And lowers the demand for irrigation. The sheep keep the growth down so that the pv generation is not inhibited. Since most substations are out of town near existing farms there is no need for expensive transmission grid expansions. It's a win win win
This sort of proposal needs to turn itself into a 24/7 electricity supply solution if it wants to claim it solves the electricity security problem (which it calls a crisis) as I outlined in the weekend on my interest.co.nz article.
FYI, we've run articles recently on both rooftop solar and integrating solar panels with agricultural production;
The irony is that the idea uses a completely outmoded system to treat waste water: oxidation ponds! Anaerobic treatment, what mainly in Europe is used, required a far smaller land area, has even lesser energy inputs and creates biomethane and bio fertilizers. The author doesn't mention that oxidation ponds have to be dredged so now and then. There is a reason why those ponds have such a big surface.
The supposed electricity savings are undoubtedly incorrect. Somewhat surprisingly, the figure provided by the author is 30 times the figure for this Rosewater project supplied by Watercare. The author has muddled (as many do) the design capacity and the delivery capacity. The 1MW design capacity relates to what can be delivered at midday in summer. As a rule of thumb, divide the design capacity by 10 to get the delivered capacity for a solar design. And then factor in that this is largely delivered in summer daytime hours. Failure to understand the difference between design capacity and average delivery capacity makes the perspectives presented in the article incorrect.
KeithW
Solardb, In broad terms I agree with you.
2000 sunshine hours per annum gives less than 6 hours per day.
Then there are all the winter hours plus the times of the day when the sun is at a low angle.
So getting 4 MWH per day from a 1 MW array would be quite some achievement.
And the price of daytime electricity at the site of the array is highly unlikely to exceed $800 per MWH (8c per kwh).
All it takes is back of the envelope calculations combined with an understanding of the basics of power versus energy to recognise that the basic premise of the article lacks credibility.
KeithW
i
Keith, a general rule of thumb is 4 hours per day average for the upper north island. Most decent brand panels are plus 5 or 10 % of their rating these days, with Mppt tracking I've seen over 600 Watts out of a 500 watt panel. Of course you don't design for any more than the rated power. I guess if you allow 10 % losses to the load , then your down to 3.6 hours.
Agree on the probable price , which ever way you slice it, the probable income they cite is out by a factor of at least4 or 5.Possibly 10.
In July, my 5kW install averaged 14kWh/day. So multiply panel capacity by 4 seems more reasonable as a daily production rate averaged over the year than divide by 10.
I still disagree any form of solar is useful as a dry year solution as you can't turn it up in a dry year, so it wont alter the shortfall.
Decentralise power generation and encourage/ incentivise residential solar installations...
Decentralising generation and storage would produce and consume power locally and reduce overall power transmission distances and volumes over distance, while also boosting maximum generation capacity
It would better utilise the infrastructure (generation and power line capacity) we already have at no additional cost, privatise the cost of the generation and localise demand and supply so that the risk of grid failures is also reduced
In principal we all see it, and may disagree on details... but people still believe that centralising is more efficient than decentralising which uber has proven can be equally effective if not more so, its pretty clear that local assets get used more efficiently... if you can pair demand and supply in a smaller area
Back that up with low-cost localised battery ballast farms comprised of upcycled or repurposed car batteries or other low cost energy storage units for peak period demand smoothing or nighttime use, and possibly include lower cost tech such as i.e. salt, sodium or other battery techs that are lower cost than lithium and under development worldwide
The cost for solar systems is still too high relative to AU and US markets even comparing with currency adjustments.. but increased demand would drop this cost and make the market far more competitive
Try Natron in North America... Sodium ion batteries are a thing.... and some BYD cars now have them...
I just said reuse car litium batteries at end of car life... most batteries are still 60kw+ and even after 10-15 years use in a car would still have 25-30kw capacities, that enough to power a normal household for 24hrs..!
Search 'just have a think' on YT, there is plenty of research and development happening in battery tech... some of these are simply not fully commercialised yet but ultimately will be...
Do some research.... downsides of sodium are they are heavier and 30% larger - but the material is much cheaper... and weight doesn't matter as much for stationary storage...
Seems like Natron is trying to secure funding to commercialise the product. So instead of doing something, we should do nothing because something better is coming along any day now?
BYD is more interesting thanks, i hadn't seen there was an actual product shipping already. Guess it will be a while before the sodium-ion is available for stationary applications.
You'd think BYD would start using it in their battery box given the lower energy density makes it more suitable than for mobile application. Are they hiding something?
- Sodium-ion battery charges faster than lithium-ion variants and have a three times higher lifecycle.
- Existing sodium-ion batteries have a cycle life of 5,000 times, significantly lower than the cycle life of commercial lithium iron phosphate batteries, which is 8,000-10,000 times.
seems a bit confused
https://www.gep.com/blog/strategy/lithium-ion-vs-sodium-ion-battery
So sodium batteries summary:
- Not yet manufactured at scale, only available if you buy one particular car in china
- Less dense than lithium-ion
- Wears out faster than lithium-ion
- Costs more than lithium-ion
As always, new battery tech shows allot of potential, but better to make you investment decisions based on actually available products.
I still remember watching a show on TV 30 years ago where they drove BMW 7 series powered by hydrogen. Shouldn't be long now.
Oh, and BYD the car manufacturer now has a Sodium ion electric car available which was featured on Driven...
So yes - they are commercialised and being put into cars now.... the car was called the BYD Seagull or Dolphin Mini but likely wont be introduced into NZ, but they are a ton cheaper than lithium batteries...
https://www.drivencarguide.co.nz/news/byd-breaks-ground-on-worlds-large…
https://www.stuff.co.nz/motoring/350206414/affordable-30k-ev-rumoured-a…
BYD Seagull.(I think USD) $11,300 car with 30kw or 38kw sodium ion battery
https://www.carscoops.com/2023/04/byds-seagull-starts-at-just-11300-and…
Quote " A key feature of the 30 kWh battery pack is that it is the first BYD model to use sodium-ion battery chemistry that is cheaper to manufacture."
Point made...
All EVs are cheap in china, not just ones made with sodium batteries.
"Here’s Why BYD Is Charging Twice The China Price For EVs Sold Abroad" https://insideevs.com/news/718036/byd-major-ev-markup-prices/
Natron Energy sodium Ion battery technology
https://natron.energy/our-technology/safety#:~:text=Our%20unique%20and%…
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