Bulwynkl makes a very interesting point. He observes that the area of the Yallourn power station's coal mine is about 25km^2:
Melbourne gets 4.34kWh/m^2/day solar energy. Thus, the land taken up by the yallourn coal mine collects 390TJ/day or equivalent to 4.52GW average power input. Assuming a 32% efficient solar thermal plant, this gives an average power output of 1.45GW. Yallourn B Coal power station generates 1.45GW peak power.
And you already have the turbine and distribution in place!