But before we can have a reliable national electricity supply based on renewables, the issue of  energy storage for later use must be addressed. Pumped hydro is regarded as part of the energy storage solution.

Pumped hydro is the simple process of using excess energy to pump water from one reservoir up a hill to another and hold it there until required. The potential energy represented by the stored water is like a huge battery.

This process already accounts for 97 per cent of energy storage worldwide.

Pumped hydro has been used in the United States since the 1920s. It is widespread in Europe, in the Scandinavian countries and in Japan.

It is important to note that pumped hydro operates on a closed system, so additional water is rarely required. Water use from pumped hydro is certainly far less than is use in existing coal-fired power stations.

Most pumped hydro sites are off river storage areas, involving the use of pairs of reservoirs, typically ranging from 10 to 100 hectares, in hilly terrain and joined by a pipe with a pump and a turbine. Water is circulated between the upper and lower reservoirs to store and generate power.

Water is stored in an upper reservoir and run through turbines to generate electricity when required, such as when the sun is not shining and the wind is not blowing. The water can then be pumped back uphill when electricity from renewables and other sources is abundant and cheaper, such as when the sun is shining and the wind is blowing.

Pumped hydro is great dispatch-able energy, as it can be fully operating within 60 seconds.

A recent study was conducted by the Australian National University and funded by the Australian Renewable Energy Agency (ARENA) looking into potential pumped hydro sites in Australia.

The results of the study concluded that nationwide there were at least 22,000 sites suitable for the establishment of pumped hydro facilities.

It has been estimated that only a small percentage of the identified sites would be necessary to provide storage to support a 100 per cent renewable energy system.

An example of a pumped hydro scheme is the recently ARENA-funded feasibility study into the building of a pumped hydro facility at a disused goldmine at Kidston, near Townsville. It is the first attempt anywhere in the world to employ disused mining pits as reservoirs for pumped storage.

Pumped hydro is yet another example of how much proven technology is available to provide a viable renewable energy generation and storage mix, and how possible it is for Australia to transition to a renewable energy system sooner rather than later.