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29 June, 2023 · 4 MIN READ

What is pumped hydro? We explain how it works.

Ever wondered how pumped hydro works? We explain what it is and how it fits in the wider energy landscape.

Solar, wind, hydro: renewable energy comes from a range of different sources, and each has an important role to play in our transition toward low emission electricity. However, while many people understand how solar and wind energy is generated, pumped hydro, and its place in the renewable energy playing field, is often misunderstood.

Today, we’re going to explain how pumped hydro works and how it fits in the wider energy landscape.

Is pumped hydro the same as conventional hydropower?

Firstly, let's tackle a common misconception: pumped hydro is different to conventional hydropower, but they can (and often do) work together.

Conventional hydropower uses flowing water to generate electricity. The water falls from the sky (as rain or snow), is collected within a reservoir which then runs down waterways through a power station to generate power. In conventional hydropower the water only ever goes in one direction.

Pumped hydro refers to the process of extracting power from the power system, storing it in water, then using that water to generate power when it is needed. This requires pumping water uphill to store it in a reservoir, then running the water back down again through the power station, putting energy back into the power system. The water goes in both directions.

When we talk about our projects, we’re referring to the construction of storage facilities – usually reservoirs – to hold large volumes of water, and the waterway tunnels and power station that connect them together. The energy needed to operate the system comes from excess renewable energy in power system, enabling excess renewable energy to be stored and then used at a when its needed.

How does pumped hydro work?

Pumped hydro is a closed water system that moves water between two (or more) large reservoirs to generate power.

The reservoirs are constructed at different heights: there is an upper reservoir, and a lower reservoir. The difference in height between the two reservoirs is called the scheme head. The head contributes to the amount of “energy” that is stored. The larger the head, the more energy that the power station can produce. Tunnels called power waterways are used to connect the reservoirs through to the power station cavern, which houses the pump turbines and other equipment required to generate electricity.

The horizontal distance between the two reservoirs is also an important factor in hydropower construction. The closer they are together, the more efficient the scheme.

When energy demand is high and there isn’t enough power coming into the system from renewable energy sources (mainly wind and solar), water is released from the upper reservoir through the pumped hydro scheme to the lower reservoir. The force of the water falling from the upper reservoir makes the turbines spin in the power station, which generates power. This power makes it way from the power station into the electricity network, which is used by business and households.

The water is then stored in lower reservoir until there is excess power in the system (renewable energy generation is greater than demand). The power station then goes into pump mode, moving the water from the lower reservoir back up to the upper reservoir.

Think of it as a large, rechargeable battery – using water, geography and the force of gravity.

Why do we need pumped hydro?

Energy storage technologies are an essential part of the future power system, and pumped hydro has an important role to play. Energy storage allows power generation to exactly match the needs of customers.

In fact, the CSIRO recently concluded that pumped hydro will become more significant in the future – especially as we move towards higher concentrations of wind and solar. This is because pumped hydro provides stable power for medium to long term durations, when the sun is not shining, and the wind is not blowing. Queensland Hydro’s projects will be able to provide large amounts of controllable power continuously for up to 24 hours.

When it comes to keeping the lights on for all customers, size really does matter. Our Borumba Pumped Hydro project is projected to generate 2,000 MW of power. Our proposed Pioneer-Burdekin Pumped Hydro project will be able to generate up to 5,000 MW of power, which would make it the largest pumped hydro storage facility in the world. When operating, both projects together would be able to service a significant portion of Queensland typical energy demand.

Read more about why we need pumped hydro here.

Is pumped hydro a new technology?

No, pumped hydro is a tried and tested technology that’s used globally. In fact, did you know that over 97% of the world’s stored energy comes from pumped hydro?

You may also be surprised to know that Queensland already has pumped hydro facilities in operation: Wivenhoe Dam has a pumped hydro storage facility, capable of producing 570 MW of power. Across Australia, there are also pumped hydro facilities in New South Wales.

Does it replace other renewable energy sources?

No. Pumped hydro is one part of the energy puzzle, and complements energy generation from renewable sources by providing the firming and stability required. Whether it’s solar, wind, chemical batteries or pumped hydro, all sources must work together to form a reliable, integrated, clean energy system.

At Queensland Hydro, we believe that pumped hydro is key to achieving the Queensland Government’s renewable energy target of 80% renewables by 2035.

You can find out more about the renewable energy targets in the Queensland Energy and Jobs Plan.

Published 29 June 2023. Updated 5 December 2023.