South Africa’s power grid is expected to suffer from a supply crisis from 2011 up to the time new power stations are brought online to replace old plants, state utility Eskom warns.

Eskom customer network business chief officer Erica Johnson told Reuters that the country must generate an extra 20GW of power by 2020 and an additional 40GW by 2010 to meet domestic demand.

“From 2011, our maintenance window will start to be constrained. The adequacy of supply is a serious concern in 2011 and beyond,” Johnson told an Africa power conference in Johannesburg.

The utility is said to be confident in its ability to supply power during the World Cup in June, which is expected to create an additional demand of 275MW.