Under the term GeoThermal the University of Adelaide, Australia, in cooperation with the company Permatherm, does investigating an very inspiring combination of solar thermal power production with geothermal energy. The goals for the project are: “This project aims to reduce the cost of solar thermal energy by 40 per cent through the integration of renewable energy technologies, while also achieving up to 50% renewable energy and true base-load capability…”.
You fin more about this project at http://environmentinstitute.wordpress.com.
Thanks for the inspiration. We ought to look at similar combinations for solar heating.