[AndrewDavis]

While I can't speak for other states (though I'd be surprised if they were different), power bills in Victoria are split into supply and usage. Eg each day costs 90c, then 30c per kw/h.

So you could eliminate the usage costs, but not the supply charge.

The whole reason for this is Australia's power grid is a market, where suppliers put in bids for how much they can produce, and at what price. And AEMO then selects the cheapest way to meet demand (paying the marginal price), but also expects residential rooftop solar a given.

As a result we often have an excess of power driving wholesale pricing into the negatives.

The free power is a way to increase usage at times when we're most likely to have negative pricing, and encourage use of high energy appliances like dishwashers etc to be run during that period to reduce demand the rest of the time.