Paired Rural Dams & Super Pits As Alternative Batteries

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Australia still has a large agricultural industry (in between the mines, that is), and all of these properties have dams, for irrigation of crops and for watering livestock. Around the various dams, there is a lot of space. What if these dams could be used to generate and store electricity? Floating solar panels to reduce evaporation and paired dams could provide the power to run the homestead, or even be supplied to rural towns. They could be alternative batteries. (Related: Is Pumped Hydro The Answer?)

Using the energy from falling water is an ancient concept. It is what powered the woolen mills of Yorkshire where my Grandmother worked from the age of 12 in the early 1900s. The mill ponds and the giant water wheels are still there, though no longer working. In this age of rapid climate change, the good news is that we are finding new uses for old technology.

Dr Nicholas Gilmore, lecturer in Mechanical and Manufacturing Engineering at the University of New South Wales, decided to research the possibilities of using paired rural dams. You can read the technical paper here. It goes by the catchy title: “Continental-scale assessment of micro-pumped hydro energy storage using agricultural reservoirs.” Dr Gilmore is an engineer who investigates future energy systems.

Although relative cost will be the final decider, the ideal site would be paired dams, not too far apart (500 metres was judged the most practical), with a relative height difference creating a slope of at least 17%. Pairing with a river would also be advantageous, but most Australian inland rivers do not have a constant flow. The water would need the opportunity to flow downstream to drive a turbine, then excess power would need to be available (likely from solar during the day) to pump the water back up for storage.

The research team determined that the dams would need to be large enough to store 24 kWh when 70% full. Satellite imagery located about 30,000 suitable pairs with an average of 30 kWh of energy storage. That’s a lot of possibilities — many of which should prove viable. Some of these pairs may cross property boundaries requiring some negotiation, but still might prove cheaper than building new dams, installing large batteries, or trucking diesel in for generators.

Based on figures produced by a Belgian research team, Dr Gilmore and his colleagues generated their cost estimates and found that a single-pump generator system is competitive with batteries.

The bespoke design used by the Belgians uses a single pipe that runs between the two water bodies, and also uses a pump to move the water uphill. The same pump acts as a generator when run in reverse. It can deliver about 17 kilowatt-hours of electricity from its 625-cubic-metre water capacity. This single pump-generator is estimated to cost less than lithium batteries on a per-kWh basis.

“Like any new technology, it’s sort of inefficient, so it has scope to get better in the future. We’re sort of jury-rigging pumps from other applications and running them in reverse to generate power,” Dr Gilmore says. Innovative Australian farmers have been solving problems by jury rigging and making do for a long time. It will be great to see them run their own on farm experimentation and research with this idea.

“While household batteries are better for delivering immediate or dispatchable power, and they can deliver higher loads, micro-PHEV systems have their own strengths,” Dr Gilmore said. “The advantage it has is you can store lots and lots of energy [compared with batteries]. It allows you to extend the use of your solar power for longer periods.”

For on-farm security in drought-prone Australia, farmers may wish to keep their diesels as backup nonetheless.

The Australian National University in Canberra is also investigating pumped hydro as an alternative battery, but they are concentrating on “Super Pits.” Emeritus Professor Andrew Blakers of the ANU College of Engineering, Computing and Cybernetics lists electrical energy generation and storage as one of his areas of expertise. In a recent paper, he tells us: “The ANU is now working on expanding this work to a brownfield survey. The aim is to survey the vicinity of existing reservoirs and mining pits to find out whether there is a possible matching reservoir site that could be used to form a good pumped hydro pair.”

The ANU team is mapping potential sites for building paired reservoirs around Australia (and globally), with a minimum of 2 gigawatt-hours storage. See the interactive map here. Some of the sites can store more than 500 GWh. That’s bigger than Snowy 2.0, which was touted as being able to supply enough energy for 3 million homes. At this rate, there would be enough storage to meet Australia’s need 300 times over. This many options means that the best sites can be chosen: “Which is really good because you can be extremely choosy,” Professor Blakers said.

Old mine pits can be converted to reservoirs for pumped hydro. Australia has plenty of those. A good example is the 250MW Kidston Pumped Storage Hydro Project located in far north Queensland. Watch the video here. 

According to the Australian Financial Review, “the fact the Kidston project has taken a decade to reach near completion and require significant taxpayer funding is also a cautionary tale for other pumped hydro projects in the pipeline.”

Genex Power’s chief executive, James Harding, tells AFR: “This project ticks all the boxes. Beautiful rock structure [granodiorite] which the tunnellers love. And the reservoirs are so close. It’s a very compact site. We have shown it can be done. That’s one of the benefits of making projects happen is you can learn from it and people can believe it can be done.”

Professor Blakers has his eye on another goldmine: “There’s a twinkle-in-the-eye proposal to use the Kalgoorlie Super Pit [in Western Australia] when they stop looking for gold in it. That would be a fantastic site because it’s a free pit with enormous volume. [And] there are a few really good sites up in the Pilbara.”

As Australia transitions from fossil fuels to renewables, energy storage has been identified by the Australian Energy Market Operator (AEMO) as the most pressing need. We may only have a decade to get it right. The UN and the daily news are telling us that climate change is progressing rapidly and becoming kore and more deadly, with floods in Libya and wildfires on the Greek islands as examples.

AEMO tells us that in Australian alone, energy storage capacity needs to be increased by 17 times in the next 27 years. It has identified large-scale pumped hydro as a necessary strategy to help stabilise the grid. Micro-pumped-hydro energy storage as proposed by Dr Gilmore’s team will help rural Australians reduce emissions and provide green power to their properties, but it won’t play a role in grid storage. Every little bit helps. “… I think security is a big one. People want to feel like they’ve got a reliable power supply,” Dr Gilmore adds.

Even suburban households are looking for security by installing not just solar panels but also battery backup systems. I have one — it is charging my Tesla from the solar on the roof as I type.

The cost of diesel and its transport to rural properties is continuing to rise despite the government subsidy (about 10%). This could drive rural property owners to seek alternative batteries to power their businesses. The use of super pits for pumped hydro will power industry and feed the grid. Big or small, we need all options on the table as we transition from fossil fuels to renewables.