Jan 12, 2015, graph from RenewEconomy article, http://reneweconomy.com.au/2015/day-rooftop-solar-met-one-third-south-australias-demand-66103
This graph is for a public holiday, but a similar evening peak would apply on business days too. Note how the electricity from Victorian brown coal generation balloons (the red part) as generation from SA’s rooftop solar PV declines at dusk. This is the time slot when a solar thermal plant with storage would come into its own.
If SA had a solar thermal plant with storage, it would capture heat all day and store it in its molten salt storage tank, then use that heat to generate electricity for several hours during that evening peak as output from rooftop solar declines. That way it would not compete with SA’s wind and solar PV generation, but would replace either imported electricity from Victoria or some of the SA-generated coal- or gas-fired electricity.
This illustrates the general principle behind CORENA’s Big Win project (possibly but not necessarily in SA) and is the reason for opting for solar thermal with storage rather than a solar PV farm or anything without storage. Storage capacity of some sort is the key.