South Australia's Essential Services Commission approved an application from Ergon to sell electricity to customers who used more than 160 megawatt hours a year - equating to a bill of around $20,000.

Ergon Energy said it would spend the next few months working to build its capacity before beginning its South Australian retail operations later this year.

The company already supplies electricity to large users in New South Wales, Victoria and the ACT.

Ergon claimed that competition in the business and corporate energy market in Queensland where Ergon Energy held the bilk of the competitive market, had produced substantial savings for some customers and had delivered improved services.

The company said it would be the only electricity retailer in South Australia offering customer partnering, or working with customers to add value to their businesses.