The United States
The Massachusetts Institute of Technology Report in 2006 for the Department of Energy that took into account the use of Enhanced Geothermal Systems (EGS) concluded that it would be affordable to generate 100 GWe (gigawatts of electricity) or more by 2050 in the US alone, for a maximum investment of US$1 billion in research and development over 15 years.
The MIT Report calculated the world's total EGS resources to be over 13,000 ZJ*. Of these, over 200 ZJ* would be extractable, with the potential to increase this to over 2,000 ZJ* with technology improvements - sufficient to provide all the world's present energy needs for several millennia.
The key characteristic of an EGS is that it reaches down into hard rock to extract the energy stored there. To extract this energy requires engineering a reservoir at depths between 2.5 and 10 kilometers. The MIT Report estimated that there was enough energy in hard rocks 10 km below the US to supply all the world's current needs for 30,000 years.
The MIT Report also found that EGS costs were found to be sensitive to four main factors, all of which could be government subsidised:
a. Temperature of the resource;
b. Fluid flow through the system measured in litres/second;
c. Drilling Costs; and
d. Power conversion efficiency.
*ZJ = zettajoule (1 zettajoule = 1021 or 1,000,000,000,000,000,000,000 Joules)