Political Cortex: Brain Food for the Body Politic

The answer to the world's energy needs may have been under our feet all this time, according to Jefferson Tester, professor of chemical engineering at the MIT Laboratory for Energy and the Environment. Tester says heat generated deep within the earth by the decay of naturally occurring isotopes has the potential to supply a tremendous amount of power -- thousands of times more than we now consume each year.

On the surface (no pun intended), Dr. Tester is clearly correct.   The core of the Earth is a compressed heart of iron and other heavy elements including a good dash of uranium, thorium, and their radioactive friends.  The result is that the core of the Earth is a heat engine kicking off around 37 terrawatts of power each year.  Not only that, but the planet's been at this heat production for a long time.  Heck, there is still energy stored in the ground from the impact that generated the moon.

It all sounds like a lot of juice, but then, it's a big planet.  The heat that actually reaches the surface does so mostly through unpredictable activities like sea floor spreading, volcanic activity, and earthquakes.  We should be glad that the big ball of molten metal is down there, because the core temp, along with the greenhouse effect, keeps the planet from being frozen over (Earth is actually a bit too far from the sun were it not for these compensating factors).  It also generates, by means not well understood, the magnetic field that helps shelter life on Earth from a lot of the nasty radiation zinging through space.  So we should all be very glad that it's hot in the basement.
But can that heat be our salvation?

We're all aware of geothermal energy.  In places like Iceland (situated on the Mid-Atlantic Ridge), the boiling water right at the surface provides local power.  In California, the Geysers Field has been producing power for decades.  But those locations are rarities.  

Still, though there may not be any geysers at the surface, it gets hot anywhere on Earth if you go deep enough.  Having once sweated my way through a mine that went down 1,700', I can tell you that the idea of hell being right next door does not seem that far fetched.

How much power is available if we could tap into it at any location?  Switching units (because I'm too lazy to work through all the conversions), the world currently consumes about 400 quadrillion BTUs per year (how many times do you get to use the word "quadrillion?").  According to Dr. Tester, we have about a hundred million quadrillion BTUs of "useable" heat hiding right under our feet.

Even if we don't get at it all, we still might get at enough to eliminate all existing sources of power.

How much of that massive resource base could we usefully extract? Imagine that only a fraction of a percent comes out. It's still big. A tenth of a percent is 100,000 quads. You have access to a tremendous amount of stored energy. And assessment studies have shown that this is thousands of times in excess of the amount of energy we consume per-year in the country. The trick is to get it out of the ground economically and efficiently and to do it in an environmentally sustainable manner. That's what a lot of the field efforts have focused on.

Geothermal energy works by exploiting the difference in temperature between one end of a heat exchange system and the other.  This works great with actual geysers, because the source of the water for the geyser includes a huge area of rock going down to great depth.  Previous attempts at extracting heat from normal "basement rock," haven't worked so well.  Rock down at the depths needed to reach working temperatures tends to be highly compacted and contain few pore spaces.  That means there's not much room for fluid pumped down there to spread out and bring back heat from a large area.

What Tester is proposing is a means of fracturing rock at depth, allowing water (or some other heat conducting fluid) to flow out from a well and gather up heat over a large area before being pumped back up.  If it can be done efficiently, we can in effect "mine heat" without removing material.

Like any new technology, there are technical issues. But I don't see any show-stoppers. I think that the evolution of the technology, with 30-plus years of field testing, has been very positive. The basic concept has been demonstrated. We know how to make large reservoirs. We need to connect them better, to stimulate them better than we have in the past using some of these hydraulic methods and diagnostics that are now available to us.
So it's the scale-up to a commercial-sized system that has to be done, making a heat mine that is large enough and productive enough to sustain the economic investment. But we believe that's possible to do based on where we are now with the technology.

It sounds good, but if commercial production is still somewhere in the future, and we can do wind or solar today, why should we bother with geothermal?  It's worth looking into because geothermal solves the biggest problems of other renewable sources: it's constant and you don't need auxiliary storage.

Geothermal has a couple of distinct differences. One, it is very scalable in baseload. Our coal-fired plants produce electricity 24 hours a day, 365 days a year. The nuclear power plants are the same way. Geothermal can meet that, without any need for auxiliary storage or a backup system. Solar would require some sort of storage if you wanted to run it when the sun's not out. And wind can't provide it without any backup at 100 percent reliability, because the typical availability factor of a wind system is about 30 percent or so, whereas the typical availability factor of a geothermal system is about 90 percent or better.

Tester believes that we can begin commercial production from his type of plant in around a decade.  As we all blister in the greenhouse-enhanced heat this summer, maybe we should look down for a solution.