South Australian businesses are counting the costs of the ongoing blackout, as authorities work to restore remaining outages as quickly as possible.

Vincent Violante, who owns a seafood business in the north-eastern suburb of Newton, said he had lost around $20,000 worth of stock since the outage due to a severe storm on Saturday.

"That's hard, because we're trying to catch up now," he said.

The shop's power returned after 36 hours and Mr Violante said he had implemented contingency plans to store stock at other businesses in case of another blackout.

"We have to just keep going, we've got about 10 people employed here, so it's their livelihood as well," he said.

Opposition leader David Speirs said South Australians needed reassurance that there would not be another blackout leading up to the busy Christmas period.

Work has been underway to restore the state's only interconnector with Victoria, south of Tailem Bend, after it was damaged during Saturday's storms.

Without it, SA cannot export any of its surplus energy to the national grid.

"These storms happen and we're not pointing any fingers at anyone about that, but South Australia got islanded from the national grid and that really gives rise to a range of questions for us now," Mr Speirs said.

He said the "fragility of the grid here in South Australia can and may very well lead to blackouts in the future".

"The former Liberal government started work on building a second interstate connector, that'll add to resilience into the future, but that's obviously not up and running yet," he said.

The ABC has contacted the state government for comment. 

Around 4,500 properties remain without power this morning since damaging storms took down powerlines across the state.

SA Power Networks's Paul Roberts said major work was underway to restore the worst-hit areas, including 2 kilometres of powerlines in Upper Sturt.

"I would expect everyone to be back before the weekend definitely," he said.

While many shops have been forced to close their doors during the blackout, one cafe opened theirs to the wider community.

Joey Khoshnaw's cafe in the north-eastern suburb of Dernancourt did not lose power, but many in the area did.

So he opened his doors and offered a space for people to charge their devices and store goods in his fridge and freezer.

"It was just a little gesture to give back to the community," he said.

Sunny day ahead on Thursday

Meanwhile, uncertainty remains over whether household solar power will have to be switched off tomorrow, with authorities saying no decision has been made yet.

Authorities said Thursday would be the likeliest day for a request to switch off rooftop solar panels due to the sunny forecast.

Electranet chief executive Simon Emms said a request would come as a "last resort", but if a request was made, households may need to contact their solar panel providers to understand how to turn their panels off.

"This is not a normal situation, this is one abnormal day," he said.

"I hope South Australians will understand that and losing a few hours of solar production within a year won't be significant."