Jun 142012

“… we have estimated the total EGS resource base to be more than 13 million exajoules (EJ). Using reasonable assumptions regarding how heat would be mined from stimulated EGS reservoirs, we also estimated the extractable portion to exceed 200,000 EJ or about 2,000 times the annual consumption of primary energy in the United States in 2005. With technology improvements, the economically extractable amount of useful energy could increase by a factor of 10 or more, thus making EGS sustainable for centuries.”      Read the entire MIT report:  The Future of Geothermal Energy (November 2006) here:

http://web.mit.edu/mitei/research/studies/geothermal-energy.shtml

Exajoules are actually a pretty useful energy measure.  1 Exajoule is about 278 TWh.  Earth always needs a steady flow of something between 12 and 18 TW of energy from all sources.  Estimates vary from source to source but are always within this range.  1 TW = 1 (24) (365) = 8760 TWh

So the planet needs something like 15 x 8760 = 130,000 TWh of energy from all sources annually or about 470 Exajoules.  Nice small numbers because EJ is a very big unit.

Does this  agree with 200,000 EJ being 2000 times the annual consumption of primary energy in the US in 2005?

Primary energy consumption was about 27,000 TWh for the US in 2005 which is about 97 EJ.

So, yes, 200,000 EJ is about 2000 times the annual consumption of primary energy in the US in 2005.

The US can access 200,000 EJ of geothermal energy using Enhanced Geothermal Systems and we need 100 EJ of energy from all sources per year.  EGS will last a while!