Thursday, July 28, 2005

Sizing geothermal energy availability

I don't know the underlying source for these figures but, from a New Scientist article on estimating nuclear decay's contribution:
Measurements of the temperature gradients across rocks in mines and boreholes have led geologists to estimate that the planet is internally generating between 30 and 44 terawatts of heat.
(N.B.: That's total, not just nuclear decay.) So, taking the middle value, Earth's total geothermal energy generation/release is about 3.7*10^13 watts. So, what can we compare this with? The CIA World Factbook's "World" entry tells us:
Electricity - production: 15.29 trillion kWh (2002)
2002 was not a leap year, so it had 365 days. That's 1.529*10^16 Wh/(365*24) h ~= 1.7*10^12 W or about 1/20 of the Earth's geothermal output.

Presumably much of that energy merely adds a couple of degrees to the temperature of the Earth's crust so I don't imagine that more than a tiny fraction of the total can be productively utilised and I therefore suspect that it'll never account for any signifigant fraction of electricity generation, much less total energy consumption (note that the above figures do not consider oil use in motor vehicles). This is not to say that it won't be useful for specific applications, particularly in areas with ready access to geothermal energy (volcanos, undersea vents, faultlines), just that it will only be a minor source, at least until fossil fuel becomes far less available than it is today. This has long been my intuition; now I have some rough numbers.