What is "pumped hydro"? 

Hydroelectricity is a method of generating electricity. Water from a dam upriver is released to flow through a channel to flow downhill, turning a turbine along the way. This produces electricity that is fed into the power grid. The water is not necessarily saved - it may, for example, be on a river and allowed to flow to the sea. Hydro electricity is clean and renewable energy, because there are no greenhouse gas emissions from its operation, and the dam is refilled by rain or runoff from its catchment.

Image: Dam and water storage from the Snowy Hydro scheme.

Image: Dam and water storage from the Snowy Hydro scheme.

Pumped hydro is actually a storage mechanism for electricity, and brings in an extra step. Two dams are connected by a pipeline. Electricity is generated elsewhere on the grid, and then used to pump water from the lower reservoir to the upper one. When the water is released, it produces hydroelectricity by turning the turbine, and is caught again in the lower reservoir to be used again when needed.

15-30% is lost in the process of storing and retrieving the energy.

Why bother? Because the linked reservoirs become a giant battery. If you produce more energy than you need at certain times, say, in the daytime from solar PV, or when there are strong winds but not much demand, you can use this excess energy to pump water from the lower to the upper reservoir. When you need more power, for example for the evening peak, you release the water and generate energy.

Unlike coal-fired generators, the turbines in pumped hydro systems can be started and stopped quickly - to meet temporary shortfalls from elsewhere in the grid.

Image: Pumped hydro storage and electricity generation (Australian Financial Review) 

Image: Pumped hydro storage and electricity generation (Australian Financial Review) 

What is planned for NSW?

Giant projects

The Snowy Hydro Scheme was built in the 1950s to provide hydroelectricity to the power grid of the eastern states.

In 2017, PM Malcolm Turnbull decided to rejig the scheme by linking two of its dams to become a pumped hydro project, Snowy 2.0. This means building 27 km of underground tunnels and an underground pumping station. Giant reversible turbines will both generate electricity when water falls, and pump water upwards when needed.

Snowy Hydro already uses pumped hydro at Tumut 3 Power Station. Snowy 2.0 is expected to generate new power from late 2024.

 Image: Snowy 2.0 Pumped Hydro Concept (Snowy Hydro)

Image: Snowy 2.0 Pumped Hydro Concept (Snowy Hydro)

The Federal Government bought the Snowy Hydro of both NSW and Victoria to advance the scheme. NSW received $4.1 billion from selling its share , and Premier Gladys Berejiklian announced it would be spent on regional infrastructure. 

The Snowy 2.0 system would be able to store up to 350GWh of electricity: enough -on average- to supply three million homes for a week, delivering power at a rate of 2,000MW, comparable to the ageing Liddell coal-fired station, and enough to ensure the stability and reliability of the system during prolonged weather events, such as wind or solar 'droughts'.

What's the downside?

Snowy 2.0 is an expensive investment (estimate $3.8 to $4.5 billion, plus modifications to transmission capacity). The market benefits could be between $4.2 and $6.8 billion, but this is over a period of more than 50 years. Alternative solutions could include battery storage, demand efficiency programs and carbon pricing.

By itself, Snowy 2 does not increase the amount of renewable energy generated. To be most effective, solar and wind capacity needs to be increased to match it. Most importantly, pumped hydro should never be used to absorb surplus power generated to keep coal-fired generators burning.

Environmental concerns about the project focus on the "spoil", the rock extracted from tunnelling, and the disturbance to Kosciusko National Park. The total amount of spoil has been estimated at 6.5 million cubic metres, and may contaminate the storage reservoirs if dumped in these as proposed.

In exploratory works, most of 750, 000 cubic metres of rock waste will be spread over 10 hectares near the Yarrangobilly River. Roads will be added or widened. In total, 114 hectares of national park will be disturbed. Several nationally threatened fauna species are found in this area, and a camping ground will be closed.

The Nature Conservation Council warns that splitting Snowy 2.0 into 5 stages means that the full environmental impact is hard to assess until work on the project is well underway.

Unfortunately, dams can produce a lot of methane from rotting vegetation. This can be largely avoided by clearing the land first. 

Big projects

Several other pumped hydro projects are happening in NSW. The Sydney Morning Herald reports (2018):

·       AGL has worked with Japanese firm Idemitsu to turn a former Hunter Valley coal mine into a pumped hydro storage plant to replace the energy that will be lost when AGL closes its coal-fired Liddell power station in 2022.

·       Origin is planning to double its existing Shoalhaven pumped hydro storage capability in the NSW Kangaroo Valley, near Wollongong.

Small to moderate projects, adding up to big

In 2017, an award-winning study by the Australian National University identified 22,000 sites across the country that could be suitable for pumped hydro energy storage (PHES). They were looking for pairs of dams with a drop of 250m between them, outside residential area, national parks "and other sensitive places'. These sites have not yet had geological, hydrological, environmental or other studies.

8,600 of these were in NSW/ACT. Their approximate energy storage capacity is 29,000 GWh.

In December 2018, the NSW Government launched a Pumped Hydro Road map, and plans for 24 hydro projects, most to provide electricity storage. The projects would be developed by the private sector on dams owned by WaterNSW.

WaterNSW has not publicly released the locations of the shortlisted proposals.