Upolu's supply was severely affected when two of the four generators at the main Fiaga power plant were damaged by lightning and thunderstorms on Monday.
The supply for the whole island was cut off for hours, and is running at only partial capacity.
The Electric Power Corporation chief executive, Tologata Tile Tuimaleali'ifano, said the design of the plant was supposed to withstand such storms.
"So now engineers are to look at protection [to see] if we have to install more protection systems to protect our generators and power equipment from future lightning and thunder storms."
The public should expect blackouts while the corporation was working to carry out repairs on the plant.
He told a news conference that the utility hoped to have Upolu's power supply back to normal next weekend.
Meanwhile, Tologata said the cost of the damage had not been finalised, but hundreds of power users on Upolu were affected including businesses.
He told reporters lightning and thunderstorms were an act of God, which was beyond their control.
Tologata said the corporation needed more rain to help small hydropower plants generating electricity to help feed the main power station.
Seven small hydropower plants, including one in Savaii, were commissioned last year as part of Samoa's renewable energy project.