Decisions on South Africa's future energy supply should be made early to cope with rising demand, Eskom CEO Brian Dames said on Tuesday.

"We must decide now to build the next power plant. We must not make the mistake to build when it is too late," he told the African Utility Week exhibition in Johannesburg.

With urbanisation and technology pushing up electricity demand world-wide, investing in infrastructure was important.

Dames said South Africa's concerns about energy supply would subside as capacity to generate power increased, but other countries in Africa were not so fortunate. It was in the country's interest to facilitate increased power capacity on the continent.

Turning to tariffs, Dames said South Africa's electricity prices were not yet cost-effective. Increases over a longer period of time, matching the rise in inflation, was where tariff increases should eventually settle.

He said if increased capacity was created, it had to be paid for.

The growth in energy supply needed to be more efficient and address climate change while keeping the lights on, Dames said.