South Australia's giant Tesla battery has begun dispatching stored wind power into the electricity grid a day ahead of its scheduled switch-on.

Premier Jay Weatherill is visiting the battery site — alongside the Hornsdale windfarm near Jamestown in the state's mid north — on Friday, to mark its official opening on the first day of summer.

But with temperatures across South Australia and Victoria hitting the mid 30s, and output from the state's wind farms low, the battery was called upon early to help meet Thursday afternoon's peak demand.

The battery dispatched a maximum of 59 megawatts of power.

The 100MW/129MWh battery is capable of powering about 30,000 homes for a little over an hour.

The manufacturer, Tesla says the lithium-ion device — made up of PowerWall 2 batteries — is both the "largest" by storage and "most powerful" of its type in the world.

South Australian taxpayers will be subsidising its operation with up to $50 million over the next 10 years.

In return, the South Australian Government will have the right to use the battery to prevent load-shedding blackouts.

It will also be able to use a portion of the battery's output to provide system security services to the grid, in an effort to bring down prices.

Power voluntarily rationed in Victoria

The hot weather on the eve of summer prompted the Australian Energy Market Operator (AEMO) into taking the highly unusual step of paying power customers to reduce their electricity usage during the peak period.

The customer or customers involved have not been identified.

But they are likely to be heavy power users who volunteered to be directed to reduce their power usage under a "demand management" program.

That program is a key part of AEMO's plan to prevent unexpected blackouts this summer.

The plan was enacted after the closure of the Hazelwood coal-fired power station in Victoria.

It provides the market operator with about 1,000 megawatts of demand management and emergency generation to use to help balance supply and demand in the grid.