Rubbish dump methane to electricity is cheap and effective. The Canberra mugga lane tip has had a pilot plant~~, not sure if it's still running~~ generating 37 GWh a year

Hydro on the mainland is pretty much just Snowy Hydro. There was a project from a former government to make that pumped hydro. I don't think it has yet been finished. I don't know whether the project has been cancelled

37 GWh, now that's a "random" number

Solar thermal - yes, the leading technology is a field of heliostat mirrors focusing sunlight on a tower, melting and heating salt. That system can easily hold onto the heat in their salt for use at night

CSIRO in 2014 thought it was possible. I trust they did the maths right.