Geothermal
Geothermal power is competitive with coal and less expensive than wind when the resource is very near to the surface; for example in the ‘pacific rim of fire’ countries. Many plants already exist around the world in volcanic areas. Unlike wind or solar geothermal power is continuous and ‘base load’. But the easily exploited resource is geographically limited and its contribution to total energy consumed worldwide is negligible compared to that of hydro and wind.
Deep geothermal is more widely distributed and is being explored in several locations in Australia but at the present time substantial technical issues have not been fully resolved and the capital cost of extraction is likely to be very high (leading to a high carbon footprint and very high cost per kWh).
Nevertheless it is hoped that geothermal power could compliment wind or solar as the REC value climbs and/or an ETS comes into effect.