"In summer, we will do more maintenance work... This will keep the system [at] risk," said Dames, while also urging the nation to save power.
Speaking at a briefing to the business community on energy efficiency in Pretoria, Dames said the power parastatal would continue to seek other supply options within and outside the country.
Eskom had this year conducted some maintenance work in winter so as to reduce the maintenance backlog.
"We want to meet demand and have spare capacity for maintenance," said Dames.
Public Enterprises Minister Malusi Gigaba said that most of the country's power stations were ageing, adding that the deferring of maintenance outages was now no longer feasible.
Maintenance backlogs, said Gigaba, began in 2010 due to South Africa hosting the Soccer World Cup.
"The point has been reached where meeting demand by deferring maintenance cannot be done any longer," said Gigaba.
Gigaba said a significant backlog remained, rendering the system vulnerable.
"A very tight balance between supply and demand remains," said the minister.
The department had been trying to ensure the elimination of backlogs by the end of December 2013.
Gigaba also highlighted the challenge of illegal power connections, as it tripped the system.
Dames said electricity theft was now seen as a serious crime and that to date, several prosecutions had happened.
"We have challenges of illegal connections, especially in townships, that overload the network," said the chief executive.
Gigaba added that a partnership between Eskom, residential customers and business was needed to address the challenge of a tight system.
"It is quite clear that the point for us is to address the challenges of a tight system until next year, and for the longer term we need a partnership... so that we use electricity efficiently.
"The old good times when we thought we had plenty of cheap electricity are gone and they're gone forever. Even when Medupi comes on board, we must change our behaviour towards electricity use," said Gigaba.
Challenging times for Eskom ranged between 5pm and 9pm, which according to Dames, at over 3 000 megawatts, was enough to power most neighbouring countries. Most of this power use was due to residential customers.
"We keep all power stations available during those hours; after 9pm, the stations come down to minimum power," said Dames.
When the first unit of the new coal fired Medupi power station comes on next year, it is expected to ease the pressure on the system.
Eskom has not had any load shedding since April 2008.
"We intend to keep the lights on," said Dames.
