Australia's energy market has to prioritise South Australia after the state declared a period of emergency following two days of destructive storms.  The Australian Energy Market Operator will maintain control of the South Australian power supply for up to seven days, after the entire state lost power on Wednesday.  "His Excellency the Governor assented to the regulations which ensures the production, distribution and supply of electricity are declared to be essential services," Deputy Premier John Rau said on Thursday night.  Already battered, bruised and blacked out, South Australia copped another belting from the second destructive storm in two days.  The intense low-pressure system raged across Adelaide and parts of South Australia late on Thursday, 24 hours after supercell thunderstorms knocked out the state's entire power network.  It was packing winds of up to 140km/h, among the strongest the city has experienced, prompting an unprecedented warning from police for workers to head home early and stay home amid concerns emergency services might not be able to cope.  The winds brought down trees across a wide area, causing major damage, and ripped some mid-north buildings apart.  Heavy rain caused widespread flooding, from the Patawalonga River in Adelaide, to the Barossa and Clare Valleys, which copped 54mm of rain.  In Clare a caravan park was under threat and in the Barossa a dam burst, prompting an emergency flood warning for the town of Greenock.  Storm surges and huge waves also inundated some communities along the Spencer and St Vincent Gulf coasts, the worst centres affected including Port Pirie, Port Broughton and Moonta.  By late Thursday 30,000 properties remained without power, some because of Wednesday's statewide blackout and others as a result of new damage caused by the continued wild weather.  The State Emergency Service has responded to more than 660 calls for help, taking the tally to well over 1000 in the past 36 hours.  Police Commissioner Grant Stevens said extra police could be brought in from interstate to help cope with the crisis.  SES chief officer Chris Beattie warned the service was at risk of being stretched beyond capacity.  The latest emergency came after Wednesday's blackout when ferocious winds ripped up more than 20 transmission towers in the mid-north, taking out three of the state's four major transmission lines.  Premier Jay Weatherill described the storm as "catastrophic" and said it had involved weather events not seen before in SA, "such as twin tornadoes, which ripped through the northern parts of our state".  Transmission company ElectraNet said most services had been restored and it hoped to have one of the transmission lines repaired by Sunday, using temporary towers from interstate.  The company also backed assertions from the premier that no energy system in the world could have survived such an event without going down.  There's been no estimate of the economic cost of the blackout but major companies, including BHP Billiton and steel producer Arrium, have already warned of losses.  Arrium administrator Mark Mentha said the Whyalla steelworks was maintaining some critical operations with a generator but it did not have enough electricity for steelmaking operations, so production had halted.  Small businesses across the state were also expected to be hard hit as the state government announced $700 for individuals to cover immediate expenses.  On the bright side, police said there had been no issues with looting during the blackout and no serious storm-related injuries.
Emergency officials say South Australia is in for another day of wild weather on Thursday as an intense low moves across the state.