Photovoltaics and wind combined now constitute 50 per cent and 100 per cent of new-build generation capacity worldwide and in Australia respectively. However, when the wind doesn't blow, and the sun doesn't shine, how do you generate reliable power? This is a standard objection to solar and wind generation, but there are straightforward solutions.

One is the distributed nature of generation. When it's cloudy in Canberra, it's probably windy. Or if not, it'll be windy and sunny in Adelaide or north Queensland. Australia is a large country with excellent sun and wind resources. This means that solar and wind electricity is always being generated somewhere. In this way, the grid is like a giant battery, with many sources feeding in at any given time.

This is backed up by a modern, efficient grid, so that power transmission losses even over long distances are small (generally a few per cent).

Renewable generation from millions of grid-connected photovoltaic and wind generators using a network with many nodes and pathways is highly resilient. If part of the system fails then another takes its place. A parallel is the internet, which was designed by US Defence to be able to operate even after extensive damage.

Renewable generation of this sort is actually more robust than the current system, which relies on a small number of large power stations. If only one of those goes down, the impact can be large.

Another part of the solution is pumped hydro energy storage. It's not a new idea, going back to the 1890s in Italy and Switzerland. Today, 99 per cent of storage around the world uses it because it's cheap compared with alternatives such as batteries.

Pumped hydro is simple, and already used in Australia at sites such as Talbingo Dam and Kangaroo Valley. Generators run when demand is high, and water flows into a pond below. When demand is low and power is cheap, operators buy it from the grid, and use it to pump water back into the upper reservoir.

Closed-cycle pumped hydro doesn't flood a river in a national park. Off-river schemes can be anywhere there's a pair of reservoirs – essentially large farm dams of a few hectares located in hilly farmland. Water flows between the upper and lower dams.

The only loss is evaporation (which is small), and since there are no rivers the heavy costs of flood mitigation are avoided.

Response by: Professor Andrew Blakers

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