Thousands of Aussie farms could have on-site mini hydro plants

Tens of thousands of rural properties across Australia could potentially convert their dams into mini ‘Snowy hydro’ projects, a scientific assessment has found.

It could allow landholders to bolster energy independence and reduce carbon emissions via implementing a small-scale pumped hydro energy system (PHES).

The study by researchers at UNSW and Deakin University found more than 30,000 sites across Australia – mostly concentrated on the nation’s south and eastern seaboards – have suitable configurations for cost-effective dam-to-dam or dam-to-river systems.

Pumped hydro – whether at large commercial or small local scales – operates on a simple principle. Take two dams, separated by a slope. During periods of low energy use, excess electricity is used to pump water from the lower reserve to the uphill dam where it is effectively stored as potential energy. That potential is realised during peak energy use periods, where water from the upper reservoir is released down the steep gradient towards the downhill dam. As it descends through a channel, the water flows through a turbine to generate electricity.

The excess energy for up-slope pumping can be obtained from a connected power source. In the case of this assessment, an on-site solar array supplies surplus electricity to drive the pump.

In effect, the pumped hydro system works as a battery to store and discharge electricity with one estimate for a property in the Adelaide hills suggesting the operating costs are 30% less than operating a Tesla Powerwall.

“The physics is the same, but the service it’s providing is quite, quite different,” says the study’s lead researcher, Dr Nicholas Gilmore from the UNSW School of Mechanical and Manufacturing Engineering.

“Things like Snowy hydro are super-efficient, they benefit from economies of scale, [its] a mature technology that’s been around for decades, but that kind of hardware doesn’t exist on this scale… we’re retrofitting pumps from irrigation systems, so they’re nowhere near as efficient and don’t benefit from decades of optimisation.”

While Gilmore says improvements in micro-PHES technology could improve efficiency and further lower costs over time, the feasibility of potential farm dam conversions is mainly limited to single properties. Still, it’s a valuable consideration for a long-lived on-site battery.

To make the system economically viable, the researchers say a property needed a minimum potential capacity of 24kWH with a 17% minimum slope.

The intent was to determine properties that could have longer-lived backup power, considering the remoteness of many locations.

“We’re talking about backup power for more than a day, versus a battery, which is typically less than a day in a lot of situations – 8 hours or so,” Gilmore says.

“It gives the local residents a sense of security. Looking at battery attachment [to property] rates that are happening now, there have been some surveys done in the US around 1,500 homes that found someone who had experienced an outage was four times as likely to get battery and solar, rather than just solar by itself.”

“That security thesis is pretty persuasive. That would be one of the big benefits, and in certain applications, you save money on your electricity bill and reduce your emissions, basically by consuming more of your solar power than you generate with the storage.”

Gilmore’s team prepared a map of potential sites, charting the 30,000 micro-PHES locations capable of providing an average of 2 kW for 20 hours.

The majority of sites studied were dam-to-river systems, which outstrip the offer of dam-to-dam counterparts and, as Gilmore puts it “the advantage… is that you’ve got a steady supply of water”, though he acknowledges the potential environmental risks from continually extracting and inserting water to a river system.

“We’ve identified these promising sites based on theory, but we need to get out to the real world and then see how they actually perform,” Gilmore says.

“There are various approaches to managing irrigation on farmland, so if you had smart pumps and turbines for your energy storage, then there could be some synergies with the irrigation systems. Looking at how you would integrate that and then how you’d operate those operations would be interesting as well.”