New drilling technologies
The study of Massachusetts Institute of Technology "The Future of Geothermal Energy – Impact of Enhanced Geothermal Systems (EGS) on the United States in the 21st Century" (2006) points out the essential importance of developing an economical deep geothermal boring technology. With old boring technologies, bore price rises exponentially with depth.
Source: Wikipedia — New drilling technologies (CC BY-SA 4.0)