Your correspondent Cheryl Mahon does not fully understand how pumped hydro works.

In most regions, there is generally an excess of renewable energy at some time through the week when prices are low and water can be pumped uphill from a lower dam to an upper dam.

When electricity is scarce, or when prices are high, the water can be allowed to flow downhill through turbines to create the electricity needed.

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Yes, there is a loss of a bit over 20 per cent, but it is insignificant in the scheme of things.

As we add more and more solar and wind to the system, it is necessary to store it and that can be done by batteries or pumped hydro.

An increasing number of grid-scale batteries are now being added to the system and it may be that, in the future, pumped hydro won't be necessary, but in the meantime it is an excellent means of storing energy.